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  • 1.
    Acosta Navarro, J. C.
    et al.
    Stockholm University, Sweden .
    Smolander, S.
    University of Helsinki, Finland .
    Struthers, Hamish
    Linköpings universitet, Nationellt superdatorcentrum (NSC).
    Zorita, E.
    Institute for Coastal Research, Geesthacht, Germany.
    Ekman, A. M. L.
    Stockholm University, Sweden .
    Kaplan, J. O.
    Ecole Polytechnique Federal de Lausanne, Switzerland.
    Guenther, A.
    PNNL, Richland, WA USA .
    Arneth, A.
    Karlsruhe Institute of Technology, Garmisch-Partenkirchen, Germany.
    Riipinen, I.
    Stockholm University, Sweden .
    Global emissions of terpenoid VOCs from terrestrial vegetation in the last millennium2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 11, s. 6867-6885Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated the millennial variability (1000 A.D.-2000 A.D.) of global biogenic volatile organic compound (BVOC) emissions by using two independent numerical models: The Model of Emissions of Gases and Aerosols from Nature (MEGAN), for isoprene, monoterpene, and sesquiterpene, and Lund-Potsdam-Jena-General Ecosystem Simulator (LPJ-GUESS), for isoprene and monoterpenes. We found the millennial trends of global isoprene emissions to be mostly affected by land cover and atmospheric carbon dioxide changes, whereas monoterpene and sesquiterpene emission trends were dominated by temperature change. Isoprene emissions declined substantially in regions with large and rapid land cover change. In addition, isoprene emission sensitivity to drought proved to have significant short-term global effects. By the end of the past millennium MEGAN isoprene emissions were 634 TgC yr-1 (13% and 19% less than during 1750-1850 and 1000-1200, respectively), and LPJ-GUESS emissions were 323 TgC yr-1(15% and 20% less than during 1750-1850 and 1000-1200, respectively). Monoterpene emissions were 89 TgC yr-1(10% and 6% higher than during 1750-1850 and 1000-1200, respectively) in MEGAN, and 24 TgC yr-1 (2% higher and 5% less than during 1750-1850 and 1000-1200, respectively) in LPJ-GUESS. MEGAN sesquiterpene emissions were 36 TgC yr-1(10% and 4% higher than during 1750-1850 and 1000-1200, respectively). Although both models capture similar emission trends, the magnitude of the emissions are different. This highlights the importance of building better constraints on VOC emissions from terrestrial vegetation.

  • 2.
    Acosta Navarro, Juan Camilo
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Smolander, S.
    Struthers, H.
    Zorita, E.
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Kaplan, J. O.
    Guenther, A.
    Arneth, A.
    Riipinen, Ilona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Global emissions of terpenoid VOCs from terrestrial vegetation in the last millennium2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 11, s. 6867-6885Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigated the millennial variability (1000 A.D.-2000 A.D.) of global biogenic volatile organic compound (BVOC) emissions by using two independent numerical models: The Model of Emissions of Gases and Aerosols from Nature (MEGAN), for isoprene, monoterpene, and sesquiterpene, and Lund-Potsdam-Jena-General Ecosystem Simulator (LPJ-GUESS), for isoprene and monoterpenes. We found the millennial trends of global isoprene emissions to be mostly affected by land cover and atmospheric carbon dioxide changes, whereas monoterpene and sesquiterpene emission trends were dominated by temperature change. Isoprene emissions declined substantially in regions with large and rapid land cover change. In addition, isoprene emission sensitivity to drought proved to have significant short-term global effects. By the end of the past millennium MEGAN isoprene emissions were 634 TgC yr-1 (13% and 19% less than during 1750-1850 and 1000-1200, respectively), and LPJ-GUESS emissions were 323 TgC yr-1(15% and 20% less than during 1750-1850 and 1000-1200, respectively). Monoterpene emissions were 89 TgC yr-1(10% and 6% higher than during 1750-1850 and 1000-1200, respectively) in MEGAN, and 24 TgC yr-1 (2% higher and 5% less than during 1750-1850 and 1000-1200, respectively) in LPJ-GUESS. MEGAN sesquiterpene emissions were 36 TgC yr-1(10% and 4% higher than during 1750-1850 and 1000-1200, respectively). Although both models capture similar emission trends, the magnitude of the emissions are different. This highlights the importance of building better constraints on VOC emissions from terrestrial vegetation.

  • 3.
    Addor, Nans
    et al.
    Univ Zurich, Dept Geog, Zurich, Switzerland.;Natl Ctr Atmospher Res, Appl Res Lab, POB 3000, Boulder, CO 80307 USA..
    Rohrer, Marco
    Univ Bern, Oeschger Ctr Climate Change Res, Bern, Switzerland.;Univ Bern, Inst Geog, Bern, Switzerland..
    Furrer, Reinhard
    Univ Zurich, Dept Math, Zurich, Switzerland..
    Seibert, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära. Univ Zurich, Dept Geog, Zurich, Switzerland..
    Propagation of biases in climate models from the synoptic to the regional scale: Implications for bias adjustment2016Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, nr 5, s. 2075-2089Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bias adjustment methods usually do not account for the origins of biases in climate models and instead perform empirical adjustments. Biases in the synoptic circulation are for instance often overlooked when postprocessing regional climate model (RCM) simulations driven by general circulation models (GCMs). Yet considering atmospheric circulation helps to establish links between the synoptic and the regional scale, and thereby provides insights into the physical processes leading to RCM biases. Here we investigate how synoptic circulation biases impact regional climate simulations and influence our ability to mitigate biases in precipitation and temperature using quantile mapping. We considered 20 GCM-RCM combinations from the ENSEMBLES project and characterized the dominant atmospheric flow over the Alpine domain using circulation types. We report in particular a systematic overestimation of the frequency of westerly flow in winter. We show that it contributes to the generalized overestimation of winter precipitation over Switzerland, and this wet regional bias can be reduced by improving the simulation of synoptic circulation. We also demonstrate that statistical bias adjustment relying on quantile mapping is sensitive to circulation biases, which leads to residual errors in the postprocessed time series. Overall, decomposing GCM-RCM time series using circulation types reveals connections missed by analyses relying on monthly or seasonal values. Our results underscore the necessity to better diagnose process misrepresentation in climate models to progress with bias adjustment and impact modeling.

  • 4.
    Aires, Filipe
    et al.
    Estellus, Paris.
    Prigent, Catherine
    Estellus, Paris.
    Orlandi, Emiliano
    Cologne university.
    Milz, Mathias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Eriksson, Patrick
    Chalmers University of Technology.
    Crewell, Susanne
    Cologne university.
    Lin, Chung-Chi
    ESA, ESTEC.
    Kangas, Ville
    ESA, ESTEC.
    Microwave hyperspectral measurements for temperature and humidity atmospheric profiling from satellite: The clear-sky case2015Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 21, s. 11334-11351Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study investigates the benefits of a satellite HYper-spectral Microwave Sensor (HYMS) for the retrieval of atmospheric temperature and humidity profiles, in the context of Numerical Weather Prediction (NWP). In the infrared, hyper-spectral instruments have already improved the accuracy of NWP forecasts. Microwave instruments so far only provide observations for a limited number of carefully selected channels. An information content analysis is conducted here to assess the impact of hyper-spectral microwave measurements on the retrieval of temperature and water vapor profiles under clear-sky conditions. It uses radiative transfer simulations over a large variety of atmospheric situations. It accounts for realistic observation (instrument and radiative transfer) noise and for a priori information assumptions compatible with NWP practices. The estimated retrieval performance of the HYMS instrument is compared to those of the microwave instruments to be deployed on board the future generation of European operational meteorological satellites (MetOp-SG). The results confirm the positive impact of a HYMS instrument on the atmospheric profiling capabilities compared to MetOp-SG. Temperature retrieval uncertainty, compared to a priori information, is reduced by 2 to 10%, depending on the atmospheric height, and improvement rates are much higher than what will be obtained with MetOp-SG. For humidity sounding these improvements can reach 30%, a significant benefit as compared to MetOp-SG results especially below 250 hPa. The results are not very sensitive to the instrument noise, under our assumptions. The main impact provided by the hyper-spectral information originates from the higher resolution in the O2 band around 60 GHz. The results are presented over ocean at nadir but similar conclusions are obtained for other incidence angles and over land

  • 5. Akperov, Mirseid
    et al.
    Rinke, Annette
    Mokhov, Igor I.
    Matthes, Heidrun
    Semenov, Vladimir A.
    Adakudlu, Muralidhar
    Cassano, John
    Christensen, Jens H.
    Dembitskaya, Mariya A.
    Dethloff, Klaus
    Fettweis, Xavier
    Glisan, Justin
    Gutjahr, Oliver
    Heinemann, Guenther
    Koenigk, Torben
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Koldunov, Nikolay V.
    Laprise, Rene
    Mottram, Ruth
    Nikiema, Oumarou
    Scinocca, John F.
    Sein, Dmitry
    Sobolowski, Stefan
    Winger, Katja
    Zhang, Wenxin
    Cyclone Activity in the Arctic From an Ensemble of Regional Climate Models (Arctic CORDEX)2018Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, nr 5, s. 2537-2554Artikel i tidskrift (Refereegranskat)
  • 6. Akperov, Mirseid
    et al.
    Rinke, Annette
    Mokhov, Igor I.
    Matthes, Heidrun
    Semenov, Vladimir A.
    Adakudlu, Muralidhar
    Cassano, John
    Christensen, Jens H.
    Dembitskaya, Mariya A.
    Dethloff, Klaus
    Fettweis, Xavier
    Glisan, Justin
    Gutjahr, Oliver
    Heinemann, Günther
    Koenigk, Torben
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Koldunov, Nikolay V.
    Laprise, René
    Mottram, Ruth
    Nikiéma, Oumarou
    Scinocca, John F.
    Sein, Dmitry
    Sobolowski, Stefan
    Winger, Katja
    Zhang, Wenxin
    Cyclone Activity in the Arctic From an Ensemble of Regional Climate Models (Arctic CORDEX)2018Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, nr 5, s. 2537-2554Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ability of state-of-the-art regional climate models to simulate cyclone activity in the Arctic is assessed based on an ensemble of 13 simulations from 11 models from the Arctic-CORDEX initiative. Some models employ large-scale spectral nudging techniques. Cyclone characteristics simulated by the ensemble are compared with the results forced by four reanalyses (ERA-Interim, National Centers for Environmental Prediction-Climate Forecast System Reanalysis, National Aeronautics and Space Administration-Modern-Era Retrospective analysis for Research and Applications Version 2, and Japan Meteorological Agency-Japanese 55-year reanalysis) in winter and summer for 1981-2010 period. In addition, we compare cyclone statistics between ERA-Interim and the Arctic System Reanalysis reanalyses for 2000-2010. Biases in cyclone frequency, intensity, and size over the Arctic are also quantified. Variations in cyclone frequency across the models are partly attributed to the differences in cyclone frequency over land. The variations across the models are largest for small and shallow cyclones for both seasons. A connection between biases in the zonal wind at 200hPa and cyclone characteristics is found for both seasons. Most models underestimate zonal wind speed in both seasons, which likely leads to underestimation of cyclone mean depth and deep cyclone frequency in the Arctic. In general, the regional climate models are able to represent the spatial distribution of cyclone characteristics in the Arctic but models that employ large-scale spectral nudging show a better agreement with ERA-Interim reanalysis than the rest of the models. Trends also exhibit the benefits of nudging. Models with spectral nudging are able to reproduce the cyclone trends, whereas most of the nonnudged models fail to do so. However, the cyclone characteristics and trends are sensitive to the choice of nudged variables.

  • 7. An, Wenling
    et al.
    Hou, Shugui
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Zhang, Wangbin
    Wu, Shuangye
    Xu, Hao
    Pang, Hongxi
    Wang, Yetang
    Liu, Yaping
    Enhanced Recent Local Moisture Recycling on the Northwestern Tibetan Plateau Deduced From Ice Core Deuterium Excess Records2017Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, nr 23, s. 12541-12556Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local moisture recycling plays an essential role in maintaining an active hydrological cycle of the Tibetan Plateau (TP). Previous studies were largely limited to the seasonal time scale due to short and sparse observations, especially for the northwestern TP. In this study, we used a two-component mixing model to estimate local moisture recycling over the past decades from the deuterium excess records of two ice cores (i.e., Chongce and Zangser Kangri) from the northwestern TP. The results show that on average almost half of the precipitation on the northwestern TP is provided by local moisture recycling. In addition, the local moisture recycling ratio has increased evidently on the northwestern TP, suggesting an enhanced hydrological cycle. This recent increase could be due to the climatic and environmental changes on the TP in the past decades. Rapid increases in temperature and precipitation have enhanced evaporation. Changes of land surface of plateau have significantly increased evapotranspiration. All of these have intensified local moisture recycling. However, the mixing model used in this study only includes a limited number of climate factors. Some of the extreme values of moisture recycling ratio could be caused by large-scale atmospheric circulation and other climatic and weather events. Moreover, the potential mechanisms for the increase in local recycling need to be further examined, since the numeric simulations from climate models did not reproduce the increased contribution of local moisture recycling in precipitation.

  • 8.
    Andersson, Camilla
    et al.
    SMHI, Forskningsavdelningen, Luftmiljö.
    Engardt, Magnuz
    SMHI, Forskningsavdelningen, Luftmiljö.
    European ozone in a future climate: Importance of changes in dry deposition and isoprene emissions2010Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, artikel-id D02303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Projections of future surface ozone over Europe conducted utilizing chemistry transport models (CTMs) coupled to climate models differ greatly, even in sign. CTM sensitivity studies were conducted in order to investigate the importance of changes in natural isoprene emissions and dry deposition to vegetation, both coupled to meteorology. This knowledge can be used to improve surface ozone projections. Our simulations suggest climate change over Europe would cause changes in surface ozone between -4.0 to +13 ppb(v) on average (April-September) and -3.5 to +25 ppb(v) on average (April-September) daily maximum from 1961 - 1990 to 2071 - 2100. The change is positive in the southwest and negative in the north. The isoprene emissions increased by a factor of about 1.8 from 1961 - 1990 to 2071 - 2100. A rescaling of isoprene emissions shows that the large increase in isoprene emission is of importance (0 - 30% of the change in surface ozone) in central, southern, and western Europe. The use of a formulation for ozone dry deposition to vegetation, dependent on meteorology, and changes in snow cover, affecting the dry deposition, are more important processes. The changes in dry deposition to vegetation (not including changes in aerodynamic resistance) explain up to 80% of the surface ozone change in Spain. Therefore it is vital to include meteorological dependence for dry deposition of ozone to vegetation in surface ozone projections. Isoprene emissions are of less importance, but they are nonnegligible and should definitely be emitted online in climate ozone projection studies.

  • 9. Bigg, E K
    et al.
    Leck, C
    Cloud-active particles over the central Arctic Ocean2001Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, nr D23, s. 32155-32166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Concentrations of cloud condensation (CCN) and ice forming nuclei (IFN) were measured throughout an expedition by icebreaker around the central Arctic Ocean including the North Pole from July 15 to September 23, 1996. Daily median CCN concentrations at 0.25% supersaturation were typically in the range 15 to 50 cm(-3), but concentrations varied by 3 orders of magnitude over the expedition and commonly by an order of magnitude within a day. They were highest near the ice edge and fell by almost an order of magnitude in the first 36 hours of transport from the open sea into the pack ice region. For longer transport times they increased again indicating a local source, suggested to be drops injected into the air by bubbles bursting on open leads. Median concentrations of IFN ranged from 18 M 3 just inside the pack ice at the beginning of the expedition to 1 m(-3) at the end. The differences with transport time from the ice edge were less marked than for CCN. Comparison of CCN measurements with simultaneously measured number size distributions showed that the median concentration active at a given supersaturation was only 71% of the number expected if at I the particles had been composed of pure ammonium sulfate. Transmission electron microscope observations of individual particles suggested an evolution of many CCN from nonvolatile, nonhygroscopic particles <50 nm by acquisition of the oxidation products of dimethyl sulfide. Cloud processing added further mass. The largest primary source within the pack ice region was deduced to be film drops from bursting bubbles yielding liquid particles with a high organic content and surfactant properties. A relationship between CCN number and sulfur mass is derived which extends previous results to lower CCN numbers and indicates a greater sensitivity to change in sulfate mass than at lower latitudes. Bacteria and probable submicron fragments of marine organisms were identified in the samples and suggested to be the source of IFN.

  • 10. Bigg, E K
    et al.
    Leck, C
    Properties of the aerosol over the central Arctic Ocean2001Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, nr D23, s. 32101-32109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transmission electron microscopy was used to examine the morphology and some physical and chemical properties of individual particles collected north of latitude 80degreesN by impaction or electrostatic precipitation during the period July 21 to September 18, 1996. Particles smaller than 50 nm in diameter showed no evidence of the presence of sulfuric acid, previously believed responsible for new particle formation. Many were crystalline or semicrystalline often with pentagonal or hexagonal habit and more heat resistant than ammonium salts. Most were unaffected by decane or xylene vapor, but some were wholly or partly dissolved, indicating that they were chemically different. Sulfuric acid, ammonia, and probably methane sulfonic acid appeared to be mainly responsible for growth of these particles to the sizes that could become involved in cloud drop formation, about 80-100 nm in diameter. Much greater diversity was present in larger particles, the most numerous class of which usually appeared to be very variable mixtures of sulfuric acid, methane sulfonic acid, and their ammonium salts. All contained significant organic material. Particles containing sea salt were generally larger than 250 nm in diameter and contained an amazing variety of other material, much of it organic. On days with sunshine unusual numbers of particles <5 nm and in the range 10-50 nm in diameter occurred. At the same time, concentrations of three different types of particle with diameters of the order of 100 nm were enhanced. One group was liquid when collected, had a large organic content, and wet the collecting surface. The other two were bacteria and flat insoluble plates some of which contained fragments of diatoms. It is proposed that they were ejected into the air by bubbles bursting on the open leads.

  • 11. Bigg, E K
    et al.
    Leck, C
    Nilsson, E D
    Sudden changes in aerosol and gas concentrations in the central Arctic marine boundary layer: Causes and consequences2001Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, nr D23, s. 32167-32185Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurements of aerosol number size distributions and concentrations of the precursor gases dimethyl sulfide, sulfur dioxide and ammonia were made within the pack ice region of the central Arctic Ocean during July and August 1996 from the icebreaker Oden. Changes in concentration, sometimes exceeding the entire seasonal variation, often occurred within an hour and attempts to find the reasons for them are described. Vertical profiles of aerosol concentration in Aitken and accumulation mode particles obtained on helicopter flights revealed intense concentration gradients in the lowest 1000 m. Those below 100 m were common. Concentrations of accumulation mode particles were usually greater near the surface than at 100 m. Four representative case studies for which vertical aerosol profiles were obtained are presented. Observations of rapid large changes in near-surface concentration of aerosols in different size ranges are compared with the vertical profiles, meteorological information, and acoustic or optical remote sensing to infer processes causing the changes. Comparison of simultaneous variations in aerosols and precursor gas concentrations are used to define the vertical profiles of the gases. It was found that dimethyl sulfide and ammonia concentrations usually must have been strongly depleted near the surface relative to concentrations at about 100 m. Sulfur dioxide profiles appeared to be more complex. Turbulence or vertical air motions initiated by atmospheric wave motions trapped within the stable boundary layer appeared to be directly responsible for many of the sudden concentration changes, through interaction with concentration gradients close to the surface. The presence of low-level jets also had direct or indirect influences on mixing in the lowest few hundred meters. The extent to which aerosols measured near the surface can determine the microphysics of central Arctic marine boundary layer clouds is examined.

  • 12. Bigg, E. Keith
    et al.
    Leck, Caroline
    The composition of fragments of bubbles bursting at the ocean surface2008Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, nr D11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Air bubbles bursting on artificial seawater in laboratory experiments have been found to inject numerous particles <200 nm diameter into the atmosphere, some experiments showing copious production of particles as small as 10 nm. Some observations of the real marine aerosol support the presence of a large proportion of sea salt <200 nm diameter, while others suggest that it is absent, or nearly so. It is argued here that the observations showing its presence may be misinterpretations. If this is so, modification of currently accepted theories of particle injection into the atmosphere by bursting bubbles would be required. Highly surface active exopolymers produced by bacteria and algae, the microgels formed by them, and large concentrations of submicrometer particulates are known to be present in the ocean. Their possible influence on bubble formation, bubble bursting and particle injection into the atmosphere are discussed. Electron microscopy of individual particles at a number of sites supports the proposal that the exopolymers are involved in these processes. Ultraviolet light and acidification cause structural and chemical changes to exopolymers and their gels exposed to the atmosphere so that marine aerosol will have properties that change with atmospheric residence time.

  • 13.
    Bikkina, Srinivas
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Ram, Kirpa
    Sarin, M. M.
    Sheesley, Rebecca J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Kirillova, Elena N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Rengarajan, R.
    Sudheer, A. K.
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Carbon isotope-constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo-Gangetic Plain2017Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, nr 9, s. 4903-4923Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Indo-Gangetic Plain (IGP) in northern India, Pakistan, and Bangladesh is a major source of carbonaceous aerosols in South Asia. However, poorly constrained seasonality of their sources over the IGP leads to large uncertainty in climate and health effects. Here we present a first data set for year-round radiocarbon (C-14) and stable carbon (C-13)-based source apportionment of total carbon (TC) in ambient PM10 (n = 17) collected from an urban site (Kanpur: 26.5 degrees N, 80.3 degrees E) in the IGP during January 2007 to January 2008. The year-round C-14-based fraction biomass (f(bio-TC)) estimate at Kanpur averages 777% and emphasizes an impact of biomass burning emissions (BBEs). The highest f(bio-TC) (%) is observed in fall season (October-November, 856%) followed by winter (December-February, 804%) and spring (March-May, 758%), while lowest values are found in summer (June-September, 69 +/- 2%). Since biomass/coal combustion and vehicular emissions mostly contribute to carbonaceous aerosols over the IGP, we predict C-13(TC) (C-13(pred)) over Kanpur using known C-13 source signatures and the measured C-14 value of each sample. The seasonal variability of C-13(obs)-C-13(pred) versus C-14(TC) together with air mass back trajectories and Moderate Resolution Imaging Spectroradiometer fire count data reveal that carbonaceous aerosols in winter/fall are significantly influenced by atmospheric aging (downwind transport of crop residue burning/wood combustion emissions in the northern IGP), while local sources (wheat residue combustion/vehicular emissions) dominate in spring/summer. Given the large temporal and seasonal variability in sources and emission strength of TC over the IGP, C-14-based constraints are, thus, crucial for reducing their uncertainties in carbonaceous aerosol budgets in climate models.

  • 14.
    Bikkina, Srinivas
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Sarin, M. M.
    Sheesley, R. J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Kirillova, E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Rengarajan, R.
    Sudheer, A. K.
    Ram, K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. Banaras Hindu University, India.
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India2016Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, nr 9, s. 4797-4809Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large-scale emissions of carbonaceous aerosols (CA) from South Asia impact both regional climate and air quality, yet their sources are not well constrained. Here we use source-diagnostic stable and radiocarbon isotopes (delta C-13 and Delta C-14) to characterize CA sources at a semiurban site (Hisar: 29.2 degrees N, 75.2 degrees E) in the NW Indo-Gangetic Plain (IGP) and a remote high-altitude location in the Himalayan foothills (Manora Peak: 29.4 degrees N, 79.5 degrees E, 1950 m above sea level) in northern India during winter. The Delta C-14 of total aerosol organic carbon (TOC) varied from -178% to -63% at Hisar and from -198% to -1% at Manora Peak. The absence of significant differences in the C-14-based fraction biomass of TOC between Hisar (0.81 +/- 0.03) and Manora Peak (0.82 +/- 0.07) reveals that biomass burning/biogenic emissions (BBEs) are the dominant sources of CA at both sites. Combining this information with d13C, other chemical tracers (K+/OC and SO42-/EC) and air mass back trajectory analyses indicate similar source regions in the IGP (e.g., Punjab and Haryana). These results highlight that CA from BBEs in the IGP are not only confined to the atmospheric boundary layer but also extend to higher elevations of the troposphere, where the synoptic-scale circulations could substantially influence their abundances both to the Himalayas and over the downwind oceanic regions such as the Indian Ocean. Given the vast emissions of CA from postharvest crop residue combustion practices in the IGP during early Northeast Monsoon, this information is important for both improved process and model understanding of climate and health effects, as well as in guiding policy decision aiming at reducing emissions.

  • 15. Birch, C. E.
    et al.
    Brooks, I. M.
    Tjernstrom, M.
    Milton, S. F.
    Earnshaw, P.
    Soderberg, S.
    Persson, P. Ola G.
    The performance of a global and mesoscale model over the central Arctic Ocean during late summer2009Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurements of turbulent fluxes, clouds, radiation, and profiles of mean meteorological parameters, obtained over an ice floe in the central Arctic Ocean during the Arctic Ocean Experiment 2001, are used to evaluate the performance of U. K. Met Office Unified Model (MetUM) and Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) in the lower atmosphere during late summer. Both the latest version of the MetUM and the version operational in 2001 are used in the comparison to gain an insight as to whether updates to the model have improved its performance over the Arctic region. As with previous model evaluations over the Arctic, the pressure, humidity, and wind fields are satisfactorily represented in all three models. The older version of the MetUM underpredicts the occurrence of low-level Arctic clouds, and the liquid and ice cloud water partitioning is inaccurate compared to observations made during SHEBA. In the newer version, simulated ice and liquid water paths are improved, but the occurrence of low-level clouds are overpredicted. Both versions overestimate the amount of radiative heat absorbed at the surface, leading to a significant feedback of errors involving the surface albedo, which causes a large positive bias the surface temperature. Cloud forcing in COAMPS produces similar biases in the downwelling shortwave and longwave radiation fluxes to those produced by UM(G25). The surface albedo parameterization is, however, more realistic, and thus, the total heat flux and surface temperature are more accurate for the majority of the observation period.

  • 16. Björkman, Mats P.
    et al.
    Vega, Carmen P.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten och landskapslära.
    Kühnel, Rafael
    Spataro, Francesca
    Ianniello, Antonietta
    Esposito, Giulio
    Kaiser, Jan
    Marca, Alina
    Hodson, Andy
    Isaksson, Elisabeth
    Roberts, Tjarda J.
    Nitrate post-depositional processes in Svalbard surface snow2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 22, s. 12953-12976Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The snowpack acts as a sink for atmospheric reactive nitrogen, but several postdeposition pathways have been reported to alter the concentration and isotopic composition of snow nitrate with implications for atmospheric boundary layer chemistry, ice core records, and terrestrial ecology following snow melt. Careful daily sampling of surface snow during winter (11–15 February 2010) and springtime (9 April to 5 May 2010) near Ny-Ålesund, Svalbard reveals a complex pattern of processes within the snowpack. Dry deposition was found to dominate over postdeposition losses, with a net nitrate deposition rate of (0.6 ± 0.2) µmol m−2 d−1 to homogeneous surface snow. At Ny-Ålesund, such surface dry deposition can either solely result from long-range atmospheric transport of oxidized nitrogen or include the redeposition of photolytic/bacterial emission originating from deeper snow layers. Our data further confirm that polar basin air masses bring 15N-depleted nitrate to Svalbard, while high nitrate δ(18O) values only occur in connection with ozone-depleted air, and show that these signatures are reflected in the deposited nitrate. Such ozone-depleted air is attributed to active halogen chemistry in the air masses advected to the site. However, here the Ny-Ålesund surface snow was shown to have an active role in the halogen dynamics for this region, as indicated by declining bromide concentrations and increasing nitrate δ(18O), during high BrO (low-ozone) events. The data also indicate that the snowpack BrO-NOx cycling continued in postevent periods, when ambient ozone and BrO levels recovered.

  • 17.
    Bosch, Carme
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Kirillova, Elena N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Budhavant, Krishnakant
    Tiwari, Suresh
    Praveen, P. S.
    Russell, Lynn M.
    Beres, Nicholas D.
    Ramanathan, Veerabhadran
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Source-diagnostic dual-isotope composition and optical properties of water-soluble organic carbon and elemental carbon in the South Asian outflow intercepted over the Indian Ocean2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 20, s. 11743-11759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dual carbon isotope signatures and optical properties of carbonaceous aerosols have been investigated simultaneously for the first time in the South Asian outflow during an intensive campaign at the Maldives Climate Observatory on Hanimaadhoo (MCOH) (February and March 2012). As one component of the Cloud Aerosol Radiative Forcing Dynamics Experiment, this paper reports on the sources and the atmospheric processing of elemental carbon (EC) and water-soluble organic carbon (WSOC) as examined by a dual carbon isotope approach. The radiocarbon (C-14) data show that WSOC has a significantly higher biomass/biogenic contribution (865%) compared to EC (594%). The more C-13-enriched signature of MCOH-WSOC (-20.80.7) compared to MCOH-EC (-25.8 +/- 0.3 parts per thousand) and megacity Delhi WSOC (-24.1 +/- 0.9 parts per thousand) suggests that WSOC is significantly more affected by aging during long-range transport than EC. The C-13-C-14 signal suggests that the wintertime WSOC intercepted over the Indian Ocean largely represents aged primary biomass burning aerosols. Since light-absorbing organic carbon aerosols (Brown Carbon (BrC)) have recently been identified as potential contributors to positive radiative forcing, optical properties of WSOC were also investigated. The mass absorption cross section of WSOC (MAC(365)) was 0.5 +/- 0.2 m(2)g(-1) which is lower than what has been observed at near-source sites, indicating a net decrease of WSOC light-absorption character during long-range transport. Near-surface WSOC at MCOH accounted for similar to 1% of the total direct solar absorbance relative to EC, which is lower than the BrC absorption inferred from solar spectral observations of ambient aerosols, suggesting that a significant portion of BrC might be included in the water-insoluble portion of organic aerosols.

  • 18.
    Bourgeois, Quentin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Krejci, Radovan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment2015Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 16, s. 8411-8425Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Six years (200702012) of data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument were used to investigate the vertical distribution and transport of aerosols over the tropical South American continent and the southeast Pacific Ocean. The multiyear aerosol extinction assessment indicates that aerosols, mainly biomass burning particles emitted during the dry season in the Amazon Basin, are lifted in significant amounts over the Andes. The aerosols are mainly transported in the planetary boundary layer between the surface and 2 km altitude with an aerosol extinction maximum near the surface. During the transport toward the Andes, the aerosol extinction decreases at a rate of 0.02 km(-1) per kilometer of altitude likely due to dilution and deposition processes. Aerosols reaching the top of the Andes, at altitudes typically between 4 and 5 km, are entrained into the free troposphere (FT) over the southeast Pacific Ocean. A comparison between CALIOP observations and ERA-Interim reanalysis data indicates that during their long-range transport over the tropical Pacific Ocean, these aerosols are slowly transported toward the marine boundary layer by the large-scale subsidence at a rate of 0.4 cm s(-1). The observed vertical/horizontal transport ratio is 0.700.8 m km(-1) Continental aerosols linked to transport over the Andes can be traced on average over 4000 km away from the continent indicating an aerosol residence time of 809 days in the FT over the Pacific Ocean. The FT aerosol optical depth (AOD) above the Pacific Ocean near South American coast accounts on average for 6% and 25% of the total AOD during the season of low and high biomass burning, respectively. This result shows that, during the biomass burning season, continental aerosols largely influence the AOD over the remote southeast Pacific Ocean. Overall, FT AOD decrease exponentially with the distance to continental sources at a rate of about 10% per degree of longitude over the Pacific Ocean.

  • 19. Brooks, Ian M.
    et al.
    Tjernstrom, Michael
    Persson, P. Ola G.
    Shupe, Matthew D.
    Atkinson, Rebecca A.
    Canut, Guylaine
    Birch, Cathryn E.
    Mauritsen, Thorsten
    Sedlar, Joseph
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Brooks, Barbara J.
    The Turbulent Structure of the Arctic Summer Boundary Layer During The Arctic Summer Cloud-Ocean Study2017Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, nr 18, s. 9685-9704Artikel i tidskrift (Refereegranskat)
  • 20. Brooks, Ian M.
    et al.
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Persson, P. Ola G.
    Shupe, Matthew D.
    Atkinson, Rebecca A.
    Canut, Guylaine
    Birch, Cathryn E.
    Mauritsen, Thorsten
    Sedlar, Joseph
    Brooks, Barbara J.
    The Turbulent Structure of the Arctic Summer Boundary Layer During The Arctic Summer Cloud-Ocean Study2017Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, nr 18, s. 9685-9704Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mostly ice covered Arctic Ocean is dominated by low-level liquid-or mixed-phase clouds. Turbulence within stratocumulus is primarily driven by cloud top cooling that induces convective instability. Using a suite of in situ and remote sensing instruments we characterize turbulent mixing in Arctic stratocumulus, and for the first time we estimate profiles of the gradient Richardson number at relatively high resolution in both time (10 min) and altitude (10 m). It is found that the mixing occurs both within the cloud, as expected, and by wind shear instability near the surface. About 75% of the time these two layers are separated by a stably stratified inversion at 100-200 m altitude. Exceptions are associated with low cloud bases that allow the cloud-driven turbulence to reach the surface. The results imply that turbulent coupling between the surface and the cloud is sporadic or intermittent.

    Plain Language Summary: The lower atmosphere over the summertime Arctic Ocean often consists of two well-mixed layers-a surface mixed layer and a cloud mixed layer-that are separated by a weak decoupling layer at about 100 to 300 m above the surface. In these cases, the cloud cannot interact directly with the surface. Large-scale forecast and climate models consistently fail to reproduce this observed structure and may thus fail to correctly reproduce the cloud properties and the amount of energy absorbed by or emitted from the surface as solar and infrared radiation. This contributes to errors in reproducing changes in sea ice concentration over time. Here we use measurements made in the central Arctic to study the processes controlling whether or not the cloud is coupled to the surface. The effect of wind at the surface is found not to be a controlling factor. The depth of the cloud mixed layer is critical, but the multiple processes influencing it cannot be separated using the data available here. However, cooling at cloud top by infrared radiation is key, as is the extension of cloud into the temperature inversion-a unique feature of Arctic clouds.

  • 21. Chen, Bing
    et al.
    Zhu, Zhejing
    Wang, Xinfeng
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Chen, Jianmin
    Zhang, Qingzhu
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Reconciling modeling with observations of radiative absorption of black carbon aerosols2017Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, nr 11, s. 5932-5942Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The physical treatment of internal mixing and aging of black carbon (BC) aerosols that allow for enhanced solar absorption of the BC is an important parameterization in climate models. Many climate models predict a factor of 2-3 lower aerosol absorption optical depth (AAOD) than the atmospheric columnar absorption observed from ground-based networks such as AERONET, likely because these models do not parameterize properly the BC absorption enhancement (E-MAC). Models that are configured with an internal mixing have predicted large variations of E-MAC, which are poorly constrained from ambient measurements. We determined the BC E-MAC from aerosol coatings with a two-step solvent experiment to remove both organic and inorganic coatings in ambient fine particulate matter (PM2.5). Observations in a rural North China site showed that the E-MAC varied from 1.4 to 3. The E-MAC increases simultaneously with SO42-/EC ratios, suggesting the photochemical production of sulfate coatings enhanced BC absorption. A global climate model, parameterized to account for these observational constraints, verifies that sulfates are primary drivers of the BC absorption enhancement in severely polluted area in China. This magnification of the radiative forcing of coated BC is stronger by a factor of similar to 2 than predicted by the standard parameterization (external mixing) in the climate model and is in better agreement with AERONET observations of AAOD. This result would be useful for testing the representation of solar absorption by BC-containing particles in the newer generation of climate models. Plain Language Summary Atmospheric black carbon (BC) or soot in fine particulate matter (PM2.5) is emitted from incomplete combustion of fossil fuel or biomass/biofuel. The BC is an important pollutant for both air quality and Earth's energy balance, and the BC radiative forcing maybe second only to that of CO2. The photochemical production of nonabsorbing secondary aerosols may create a coating on BC and may thereby act as a lens which may enhance the light absorption. However, this absorption enhancement is poorly constrained by ambient measurements, and thus the estimates of BC climate forcing remain highly uncertain. To this end, an aerosol filter dissolution-filtration (AFD) with two-step solvent dissolution protocol was employed to remove both organic and inorganic coatings and then investigate their effects on BC light absorption. The observations and model simulation showed that the BC warming effect likely doubled due to lens effect from secondary aerosols.

  • 22. Cheymol, Anne
    et al.
    De Backer, Hugo
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Stuebi, Rene
    Comparison and validation of the aerosol optical depth obtained with the Langley plot method in the UV-B from Brewer Ozone Spectrophotometer measurements2006Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, nr D16, artikel-id D16202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [ 1] The Aerosol Optical Depths (AODs) retrieved from Brewer Ozone Spectrophotometer measurements with a method previously developed (Cheymol and De Backer, 2003) are now validated by comparisons between AODs from six Brewer spectrophotometers and two CSEM SPM2000 sunphotometers: two Brewer spectrophotometers 016 and 178 at Uccle in Belgium; one Brewer spectrophotometer 128 and one sunphotometer CSEM SPM2000 at Norrkoping in Sweden; and three Brewer instruments 040, 072, 156 at Arosa and one CSEM SPM2000 sunphotometer at Davos in Switzerland. The comparison between AODs from Brewer spectrophotometer 128 at 320.1 nm and sunphotometer SPM2000 at 368 nm at Norrkoping shows that the AODs obtained from the Brewer measurements with the Langley Plot Method (LPM) are very accurate if the neutral density filter spectral transmittances are well known: with the measured values of these filters, the correlation coefficient, the slope, and the intercept of the regression line are 0.98, 0.85 +/- 0.004, and 0.02 +/- 0.0014, respectively. The bias observed is mainly owing to the wavelength difference between the two instruments. The comparison between AODs from different Brewer spectrophotometers confirm that AODs will be in very good agreement if they are measured with several Brewer instruments at the same place: At Uccle, the correlation coefficient, slope, and intercept of the regression line are 0.98, 1.02 +/- 0.003, and 0.06 +/- 0.001, respectively; at Arosa, the comparisons between the AODs from three Brewer spectrophotometers 040, 072, and 156 give a correlation coefficient, a slope, and an intercept of the regression line above 0.94, 0.98 and below 0.04, respectively.

  • 23.
    Chiacchio, Marc
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Pausata, Francesco S. R.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Messori, Gabriele
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Hannachi, Abdel
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Chin, Mian
    Onskog, Thomas
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Barrie, Leonard
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    On the links between meteorological variables, aerosols, and tropical cyclone frequency in individual ocean basins2017Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, nr 2, s. 802-822Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A generalized linear model based on Poisson regression has been used to assess the impact of environmental variables modulating tropical cyclone frequency in six main cyclone development areas: the East Pacific, West Pacific, North Atlantic, North Indian, South Indian, and South Pacific. The analysis covers the period 1980-2009 and focuses on widely used meteorological parameters including wind shear, sea surface temperature, and relative humidity from different reanalyses as well as aerosol optical depth for different compounds simulated by the Goddard Chemistry Aerosol Radiation and Transport model. Circulation indices are also included. Cyclone frequency is obtained from the International Best Track Archive for Climate Stewardship. A strong link is found between cyclone frequency and the relative sea surface temperature, Atlantic Meridional Mode, and wind shear with significant explained log likelihoods in the North Atlantic of 37%, 27%, and 28%, respectively. A significant impact of black carbon and organic aerosols on cyclone frequency is found over the North Indian Ocean, with explained log likelihoods of 27%. A weaker but still significant impact is found for observed dust aerosols in the North Atlantic with an explained log likelihood of 11%. Changes in lower stratospheric temperatures explain 28% of the log likelihood in the North Atlantic. Lower stratospheric temperatures from a subset of Coupled Model Intercomparison Project Phase 5 models properly simulate the warming and subsequent cooling of the lower stratosphere that follows a volcanic eruption but underestimates the cooling by about 0.5 degrees C.

  • 24.
    Chiacchio, Marc
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Abdus Salam International Centre for Theoretical Physics, Italy.
    Solmon, Fabien
    Giorgi, Filippo
    Stackhouse, Paul, Jr.
    Wild, Martin
    Evaluation of the radiation budget with a regional climate model over Europe and inspection of dimming and brightening2015Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 5, s. 1951-1971Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shortwave (SW) and longwave (LW) components of the radiation budget at the surface and top of atmosphere (TOA) are evaluated in the regional climate model RegCM version 4 driven by European Centre for Medium-Range Weather Forecasts Reanalysis over Europe. The simulated radiative components were evaluated with those from satellite-based products and reanalysis. At the surface the model overestimated the absorbed solar radiation but was compensated by a greater loss of thermal energy while both SW and LW TOA net fluxes were underestimated representing too little solar energy absorbed and too little outgoing thermal energy. Averaged biases in radiative parameters were generally within 25 Wm(-2), were dependent on differences by as much as 0.2 in cloud fraction, surface, and planetary albedo and less dependent on surface temperature associated with the surface longwave parameters, and are in line with other studies. Clear-sky fluxes showed better results when cloud cover differences had no influence. We also found a clear distinction between land versus water with smaller biases over land at the surface and over water at the TOA due to differences in cloud fraction and albedo. Finally, we inspected dimming and brightening for the period 1979-2010 with an indication for dimming early in the time series (i.e., 1979-1987) and brightening after, which agrees with surface-based observations. After 2000, however, a decrease in the brightening by more than 1 order of magnitude was evident which is in contrast to the continued brightening found in surface records and satellite-derived estimates.

  • 25.
    Clarmann, T. Von
    et al.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Ceccherini, S.
    Istituto di Fisica Applicata “Nello Carrara,”, Florence.
    Doicu, A.
    Deutsches Zentrum für Luft-und Raumfahrt (DLR).
    Dudhia, A.
    Atmospheric, Oceanic, and Planetary Physics, Oxford University.
    Funke, B.
    Instituto de Astrofísica de Andalucía CSIC, Granada.
    Grabowski, U.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Hilgers, S.
    Deutsches Zentrum für Luft-und Raumfahrt (DLR).
    Jay, V.
    Rutherford Appleton Laboratory, Oxfordshire.
    Linden, A.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    López-Puertas, M.
    Instituto de Astrofísica de Andalucía CSIC, Granada.
    Martin-Torres, Javier
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe, Analytical Services and Materials Inc., Hampton.
    Payne, V.
    Atmospheric, Oceanic, and Planetary Physics, Oxford University.
    Reburn, J.
    Rutherford Appleton Laboratory, Oxfordshire.
    Ridolfi, M.
    Dipertemento di Chimica Fisica e Inorganica, Universitá di Bologna.
    Schreier, F.
    Deutsches Zentrum für Luft-und Raumfahrt (DLR).
    Schwarz, G.
    Deutsches Zentrum für Luft-und Raumfahrt (DLR).
    Siddans, R.
    Rutherford Appleton Laboratory, Oxfordshire.
    Steck, T.
    Institut für Meteorologie und Klimaforschung, Universität Karlsruhe.
    A blind test retrieval experiment for infrared limb emission spectrometry2003Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 108, nr D23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The functionality and characteristics of six different data processors (i.e., retrieval codes in their actual software and hardware environment) for analysis of high-resolution limb emission infrared spectra recorded by the space-borne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have been validated by means of a blind test retrieval experiment based on synthetic spectra. For this purpose a self-consistent set of atmospheric state parameters, including pressure, temperature, vibrational temperatures, and abundances of trace gases and aerosols, has been generated and used as input for radiative transfer calculations for MIPAS measurement geometry and configuration. These spectra were convolved with the MIPAS field of view, spectrally degraded by the MIPAS instrument line shape, and, finally, superimposed with synthetic measurement noise. These synthetic MIPAS measurements were distributed among the participants of the project “Advanced MIPAS level-2 data analysis” (AMIL2DA), who performed temperature and species abundance profile retrievals by inverse radiative transfer calculations. While the retrieved profiles of atmospheric state parameters reflect some characteristics of the individual data processors, it was shown that all the data processors under investigation are capable of producing reliable results in the sense that deviations of retrieved results from the reference profiles are within the margin that is consistent with analytical error estimation.

  • 26. den Outer, P. N.
    et al.
    Slaper, H.
    Kaurola, J.
    Lindfors, A.
    Kazantzidis, A.
    Bais, A. F.
    Feister, U.
    Junk, J.
    Janouch, M.
    Josefsson, Weine
    SMHI, Samhälle och säkerhet.
    Reconstructing of erythemal ultraviolet radiation levels in Europe for the past 4 decades2010Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, artikel-id D10102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper is based on a comparative study on ultraviolet radiation (UV) measurements and UV reconstruction models for eight sites in Europe. Reconstruction models include neural network techniques and radiative transfer modeling combined with empirical relationships. The models have been validated against quality-controlled ground-based measurements, 8 to 20 years, on time scales ranging from daily to yearly UV sums. The standard deviations in the ratios of modeled to measured daily sums vary between 10 and 15%. The yearly sums agree within a 5% range. Depending on the availability of ancillary measurements, reconstructions have been carried out to the early 1960s. A method has been set up to educe one best estimate of the historical UV levels that takes into account the long-term stability and underlying agreement of the models, and the agreement with actual UV measurements. Using this best estimate, the yearly sums of erythemally weighted UV irradiance showed a range of 300 kJ/m(2) at 67 degrees N to 750 kJ/m(2) at 40 degrees N. The year-to-year variability was lowest at 40 degrees N with a relative variation of 4.3%; for central and northern European latitudes this year-to-year variation was 5.2 to 6.5%. With regard to the period 1980 to 2006, first-order trend lines range from 0.3 +/- 0.1 to 0.6 +/- 0.2% per year, approximately two thirds of which can be attributed to the diminishing of cloudiness and one third to ozone decline.

  • 27.
    Divine, D. V.
    et al.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Pohjola, V.
    Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden..
    Meijer, H.
    Univ Groningen, Ctr Isotope Res, NL-9714 AG Groningen, Netherlands..
    de Wal, R. S. W. van
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, NL-3508 TA Utrecht, Netherlands..
    Martma, T.
    Tallinn Univ Technol, Inst Geol, EE-19086 Tallinn, Estonia..
    Moore, J.
    Univ Lapland, Arctic Ctr, FIN-96101 Rovaniemi, Finland..
    Sjogren, B.
    Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden..
    Godtliebsen, F.
    Univ Tromso, Dept Math & Stat, N-9037 Tromso, Norway..
    Deuterium excess record from a small Arctic ice cap2008Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, nr D19, artikel-id D19104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we present a deuterium excess (d) record from an ice core drilled on a small ice cap in Svalbard in 1997. The core site is located at Lomonosovfonna at 1255 m asl, and the analyzed time series spans the period 1400-1990 A. D. The record shows pronounced multidecadal to centennial-scale variations coherent with sea surface temperature changes registered in the subtropical to southern middle-latitude North Atlantic during the instrumental period. We interpret the negative trend in the deuterium excess during the 1400s and 1500s as an indication of cooling in the North Atlantic associated with the onset of the Little Ice Age. Consistently positive anomalies of d after 1900, peaking at about 1950, correspond with well-documented contemporary warming. Yet the maximum values of deuterium excess during 1900-1990 are not as high as in the early part of the record (pre-1550). This suggests that the sea surface temperatures during this earlier period of time in the North Atlantic to the south of approximately 45 degrees N were at least comparable with those registered in the 20th century before the end of the 1980s. We examine the potential for a cold bias to exist in the deuterium excess record due to increased evaporation from the local colder sources of moisture having isotopically cold signature. It is argued that despite a recent oceanic warming, the contribution from this local moisture to the Lomonosovfonna precipitation budget is still insufficient to interfere with the isotopic signal from the primary moisture region in the midlatitude North Atlantic.

  • 28. Dwyer, J. R.
    et al.
    Saleh, Z.
    Rassoul, H. K.
    Concha, D.
    Rahman, Mahbubur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
    Jerauld, J.
    Uman, M. A.
    Rakov, V. A.
    A study of X-ray emission from laboratory sparks in air at atmospheric pressure2008Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, s. D23207-Artikel i tidskrift (Refereegranskat)
  • 29.
    Fang, Wenzheng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. East China Normal University, China.
    Du, Ke
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Xing, Zhenyu
    Cho, Chaeyoon
    Kim, Sang-Woo
    Deng, Junjun
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Dual-Isotope Constraints on Seasonally Resolved Source Fingerprinting of Black Carbon Aerosols in Sites of the Four Emission Hot Spot Regions of China2018Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, nr 20, s. 11735-11747Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite much recent efforts, the emission sources of black carbon (BC) aerosols. central input to understanding and predicting environmental and climate impact. remain highly uncertain. Here we present observational delta C-13/Delta C-14-based constraints on the sources of BC aerosols over the four seasons in each of the four key hot spot emission regions of China: Beijing-Tianjin-Hebei (BTH-Wuqing; where Wuqing is the sampling location), Yangtze River Delta (YRD-Haining), Pearl River Delta (PRD-Zhongshan), and Sichuan Basin (SC-Deyang). Overall, BC loadings were highest in winter, yet elevated loadings were also observed in other seasons, for example, spring at SC-Deyang and fall at PRD-Zhongshan. Annually, the dominant BC sources were coal (50 +/- 20%) for BTH-Wuqing, liquid fossil for YRD-Haining (46 +/- 8%) and PRD-Zhongshan (48 +/- 18%), whereas liquid fossil (42 +/- 17%) and biomass burning (41 +/- 14%) equally affected SC-Deyang. There is also different but distinct seasonalities in BC sources for the different sites. As an example, for BTH-Wuqing coal burning increased from summer to winter, while summer and spring BTH-Wuqing were more influenced by liquid fossil. In contrast, for YRD-Haining, the relative importance of emission sources was more constant over the year. These quantitative observational constraints on source-seasonality of BC aerosols in receptor sites located in China's four key economic zones highlight that regulatory control on BC aerosol emissions from different fuels should consider both seasonal and regional variations. Our results also suggest that models on estimates of BC-induced climate and air quality should consider variations over both regional and seasonal scales.

  • 30.
    Forsstrom, S.
    et al.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Skeie, R. B.
    CICERO, Oslo, Norway..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Pedersen, C. A.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Hudson, S. R.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Berntsen, T. K.
    CICERO, Oslo, Norway.;Univ Oslo, Fac Math & Nat Sci, Oslo, Norway..
    Lihavainen, H.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Godtliebsen, F.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway.;Univ Tromso, Fac Sci & Technol, Tromso, Norway..
    Gerland, S.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Elemental carbon measurements in European Arctic snow packs2013Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 118, nr 24, s. 13614-13627Artikel i tidskrift (Refereegranskat)
  • 31.
    Forsstrom, S.
    et al.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Ström, J.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway.;Stockholm Univ, Dept Appl Environm Sci ITM, SE-10691 Stockholm, Sweden..
    Pedersen, C. A.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Gerland, S.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Elemental carbon distribution in Svalbard snow2009Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114, artikel-id D19112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The concentration of apparent elemental carbon (ECa, based on a thermal-optical method) in the snow was investigated in Svalbard (European Arctic) during spring 2007. The median ECa concentration of 81 samples was 4.1 mu g l(-1) and the values ranged from 0 to 80.8 mu g l(-1) of melt water. The median concentration is nearly an order of magnitude lower than the previously published data of equivalent black carbon (BCe, based on an optical method), obtained from Svalbard snow in the 1980s. A systematic regional difference was evident: ECa concentrations were higher in east Svalbard compared to west Svalbard. The observations of snow ECa cover spatial scales up to several hundred kilometers, which is comparable to the resolution of many climate models. Measurements of atmospheric carbonaceous aerosol (2002-2008) at Zeppelin station in Ny-Alesund, Svalbard, were divided to air mass sectors based on calculated back trajectories. The results show that air originating from the eastern sector contains more than two and half times higher levels of soot than air arriving from south to west. The observed east-west gradient of ECa concentrations in snow may be because of a combination of the atmospheric concentration gradient, the orographic effect of the archipelago, and the efficient scavenging of the carbonaceous particles through precipitation.

  • 32. Garstang, M
    et al.
    Tyson, P D
    Swap, R
    Edwards, M
    Kållberg, Per
    SMHI, Forskningsavdelningen, Meteorologi.
    Lindesay, J A
    Horizontal and vertical transport of air over southern Africa1996Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, nr D19, s. 23721-23736Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tropospheric air trajectories that occurred during the Southern African Fire-Atmosphere Research Initiative (SAFARI) in August-October 1992 are described in terms of a circulation classification scheme and the vertical stability of the atmosphere. Three major and frequently occurring stable discontinuities are found to control vertical transport of aerosols in the subtropical atmosphere at the end of the dry season. Of these, the main subsidence-induced feature is a spatially ubiquitous and temporally persistent absolutely stable layer at an altitude of about 5 km (3.5 km above the interior plateau elevation). This effective obstacle to vertical mixing is observed to persist without break for up to 40 days. Below this feature an absolutely stable layer at 3 km (1.5 km above the surface) prevails on and off at the top of the surface mixing layer for up to 7 days at a time, being broken by the passage of regularly occurring westerly wave disturbances. Above the middle-level discontinuity a further absolutely stable layer is frequently discerned at an altitude of about 8 km. It is shown that five basic modes can be used to describe horizontal aerosol transportation fields over southern Africa. Dominating these is the anticyclone mode which results in frequent recirculation at spatial scales varying from hundreds to thousands of kilometers. In exiting the anticyclonic circulation, transport on the northern periphery of the system is to the west over the Atlantic Ocean via a semistationary easterly wave over the western part of the subcontinent. On the southern periphery, wave perturbations in the westerly enhance transports which exit the subcontinent to the east into the Indian Ocean. Independently derived data suggest that during SAFARI only 4% of the total transport of air from three locations south of 18 degrees 8 was into the Atlantic Ocean. Over 90% of the transport was into the Indian Ocean across 35 degrees E. This result reflects circulation fields typical of the extremely dry conditions prevailing in 1992. The integrated effect of the control exerted by atmospheric stability on vertical mixing, on the one hand, and the nature of the horizontal circulation fields, on the other, is to produce a distinctive suite of transport patterns that go a long way to explain the observed high concentrations of tropospheric aerosols and trace gases observed over the subcontinent in winter and spring, as well as over the tropical South Atlantic and southwestern Indian Oceans.

  • 33. Giamarelou, Maria
    et al.
    Eleftheriadis, Konstantinos
    Nyeki, Stephan
    Tunved, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Torseth, Kjetil
    Biskos, George
    Indirect evidence of the composition of nucleation mode atmospheric particles in the high Arctic2016Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, nr 2, s. 965-975Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previous long-term observations have shown that nanoparticle formation events are common in the summer-time high Arctic and linked to local photochemical activity. However, current knowledge is limited with respect to the chemical precursors of resulting nanoparticles and the compounds involved in their subsequent growth. Here we report case-study measurements during new particle formation (NPF) events of the particle size distribution (diameter>7nm) and for the first time the volatility of monodisperse particles having diameter 40nm, providing indirect information about their composition. Volatility measurements provide indirect evidence that a predominant fraction of the 12nm particle population is ammoniated sulfates in the summertime high Arctic. Our observations further suggest that the majority of the sub-40nm particle population during NPF events does not exist in the form of sulfuric acid but rather as partly or fully neutralized ammoniated sulfates.

  • 34.
    Glantz, Paul
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Bourassa, Adam
    Herber, Andreas
    Iversen, Trond
    Karlsson, Johannes
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Kirkevag, Alf
    Maturilli, Marion
    Seland, Oyvind
    Stebel, Kerstin
    Struthers, Hamish
    Tesche, Matthias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Thomason, Larry
    Remote sensing of aerosols in the Arctic for an evaluation of global climate model simulations2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 13, s. 8169-8188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua retrievals of aerosol optical thickness (AOT) at 555 nm are compared to Sun photometer measurements from Svalbard for a period of 9 years. For the 642 daily coincident measurements that were obtained, MODIS AOT generally varies within the predicted uncertainty of the retrieval over ocean (Delta AOT = +/- 0.03 +/- 0.05 . AOT). The results from the remote sensing have been used to examine the accuracy in estimates of aerosol optical properties in the Arctic, generated by global climate models and from in situ measurements at the Zeppelin station, Svalbard. AOT simulated with the Norwegian Earth System Model/Community Atmosphere Model version 4 Oslo global climate model does not reproduce the observed seasonal variability of the Arctic aerosol. The model overestimates clear-sky AOT by nearly a factor of 2 for the background summer season, while tending to underestimate the values in the spring season. Furthermore, large differences in all-sky AOT of up to 1 order of magnitude are found for the Coupled Model Intercomparison Project phase 5 model ensemble for the spring and summer seasons. Large differences between satellite/ground-based remote sensing of AOT and AOT estimated from dry and humidified scattering coefficients are found for the subarctic marine boundary layer in summer.

  • 35.
    Glantz, Paul
    et al.
    Stockholm University, Sweden .
    Bourassa, Adam
    University of Saskatchewan, Canada .
    Herber, Andreas
    Alfred Wegener Institute Polar and Marine Research, Bremerhaven, Germany.
    Iversen, Trond
    ECMWF, Reading, UK; Norwegian Meteorological Institute, Oslo, Norway.
    Karlsson, Johannes
    Stockholm University, Sweden .
    Kirkevåg, Alf
    Norwegian Meteorological Institute, Oslo, Norway.
    Maturilli, Marion
    Alfred Wegener Institute Polar and Marine Research, Bremerhaven, Germany.
    Seland, Øyvind
    Norwegian Meteorological Institute, Oslo, Norway.
    Stebel, Kerstin
    Norwegian Institute for Air Research, Oslo, Norway.
    Struthers, Hamish
    Tesche, Matthias
    Stockholm University, Sweden .
    Thomason, Larry
    NASA Langley Research Center, Hampton, Virginia, USA.
    Remote sensing of aerosols in the Arctic for an evaluation of global climate model simulations2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 13, s. 8169-8188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua retrievals of aerosol optical thickness (AOT) at 555 nm are compared to Sun photometer measurements from Svalbard for a period of 9 years. For the 642 daily coincident measurements that were obtained, MODIS AOT generally varies within the predicted uncertainty of the retrieval over ocean (Delta AOT = +/- 0.03 +/- 0.05 . AOT). The results from the remote sensing have been used to examine the accuracy in estimates of aerosol optical properties in the Arctic, generated by global climate models and from in situ measurements at the Zeppelin station, Svalbard. AOT simulated with the Norwegian Earth System Model/Community Atmosphere Model version 4 Oslo global climate model does not reproduce the observed seasonal variability of the Arctic aerosol. The model overestimates clear-sky AOT by nearly a factor of 2 for the background summer season, while tending to underestimate the values in the spring season. Furthermore, large differences in all-sky AOT of up to 1 order of magnitude are found for the Coupled Model Intercomparison Project phase 5 model ensemble for the spring and summer seasons. Large differences between satellite/ground-based remote sensing of AOT and AOT estimated from dry and humidified scattering coefficients are found for the subarctic marine boundary layer in summer.

  • 36. Grinsted, A
    et al.
    Moore, J C
    Pohjola, V
    Martma, T
    Isaksson, E
    Svalbard summer melting, continentality, and sea ice extent from the Lomonosovfonna ice core2006Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, nr D7, artikel-id D07110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We develop a continentality proxy (1600-1930) based on amplitudes of the annual signal in oxygen isotopes in an ice core. We show via modeling that by using 5 and 15 year average amplitudes the effects of diffusion and varying layer thickness can be minimized, such that amplitudes then reflect real seasonal changes in delta O-18 under the influence of melt. A model of chemical fractionation in ice based on differing elution rates for pairs of ions is developed as a proxy for summer melt (1130-1990). The best pairs are sodium with magnesium and potassium with chloride. The continentality and melt proxies are validated against twentieth-century instrumental records and longer historical climate proxies. In addition to summer temperature, the melt proxy also appears to reflect sea ice extent, likely as a result of sodium chloride fractionation in the oceanic sea ice margin source area that is dependent on winter temperatures. We show that the climate history they depict is consistent with what we see from isotopic paleothermometry. Continentality was greatest during the Little Ice Age but decreased around 1870, 20-30 years before the rise in temperatures indicated by the delta O-18 profile. The degree of summer melt was significantly larger during the period 1130-1300 than in the 1990s.

  • 37. Grisogono, Branko
    et al.
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Thermal mesoscale circulations on the Baltic coast 2. Perturbation of surface parameters1996Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, s. 18999-19012Artikel i tidskrift (Refereegranskat)
  • 38. Groenholm, T.
    et al.
    Launiainen, S.
    Ahlm, L.
    Stockholm University.
    Martensson, E. M.
    Stockholm University.
    Kulmala, M.
    Vesala, T.
    Nilsson, E. D.
    Stockholm University.
    Aerosol particle dry deposition to canopy and forest floor measured by two-layer eddy covariance system2009Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114, artikel-id D04202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present, to our knowledge for the first time, results from subcanopy (forest trunk space) aerosol flux measurements with the eddy covariance (EC) technique. The measurements were performed at the SMEAR II measurement station located in a Scots pine forest in southern Finland during spring 2003 when the ground was snow covered and in situ biogenic particle formation took place almost every day. Spectral analysis showed that the EC method can be applied to estimate subcanopy aerosol fluxes and thereby ground deposition in a forest. By using the two-layer EC measurements we were able to investigate the fraction of the total aerosol deposition taking place in the canopy and on the forest floor. We found that the ratio of subcanopy to above- canopy flux is dependent on the strength of turbulence. When the friction velocity was low (u(*) < 0.25 m s(-1)), approximately 35% of the depositing particles penetrated the canopy and deposited on the ground. When u* increased, the fractional deposition on the forest floor decreased almost linearly, and in strongly turbulent conditions (u(*)> 1.0 m s(-1)) the ground deposition contributed only around 10% to the total deposition. Thus, it seems that increased turbulence enhances the importance of the canopy for aerosol deposition and the relative importance of the forest floor to the total deposition diminishes.

  • 39. Groot Zwaaftink, C. D.
    et al.
    Grythe, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. Norwegian Institute for Air Research, Norway; Finnish Meteorological Institute, Finland.
    Skov, H.
    Stohl, A.
    Substantial contribution of northern high-latitude sources to mineral dust in the Arctic2016Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, nr 22, s. 13678-13697Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the Arctic, impurities in the atmosphere and cryosphere can strongly affect the atmospheric radiation and surface energy balance. While black carbon has hence received much attention, mineral dust has been in the background. Mineral dust is not only transported into the Arctic from remote regions but also, possibly increasingly, generated in the region itself. Here we study mineral dust in the Arctic based on global transport model simulations. For this, we have developed a dust mobilization scheme in combination with the Lagrangian particle dispersion model FLEXPART. A model evaluation, based on measurements of surface concentrations and annual deposition at a number of stations and aircraft vertical profiles, shows the suitability of this model to study global dust transport. Simulations indicate that about 3% of global dust emission originates from high-latitude dust sources in the Arctic. Due to limited convection and enhanced efficiency of removal, dust emitted in these source regions is mostly deposited closer to the source than dust from for instance Asia or Africa. This leads to dominant contributions of local dust sources to total surface dust concentrations (similar to 85%) and dust deposition (similar to 90%) in the Arctic region. Dust deposition from local sources peaks in autumn, while dust deposition from remote sources occurs mainly in spring in the Arctic. With increasing altitude, remote sources become more important for dust concentrations as well as deposition. Therefore, total atmospheric dust loads in the Arctic are strongly influenced by Asian (similar to 38%) and African (similar to 32%) dust, whereas local dust contributes only 27%. Dust loads are thus largest in spring when remote dust is efficiently transported into the Arctic. Overall, our study shows that contributions of local dust sources are more important in the Arctic than previously thought, particularly with respect to surface concentrations and dust deposition.

  • 40. Haapanala, Paivi
    et al.
    Raisanen, Petri
    Kahnert, Michael
    SMHI, Forskningsavdelningen, Luftmiljö.
    Nousiainen, Timo
    Sensitivity of the shortwave radiative effect of dust on particle shape: Comparison of spheres and spheroids2012Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 117, artikel-id D08201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The sensitivity of direct shortwave radiative effects of dust (DRE) to assumed particle shape is investigated. Radiative transfer simulations are conducted using optical properties of either spheres, mass-equivalent spheroids (mass-conserving case), or (mass-equivalent) spheroids whose number concentration is modified so that they have the same midvisible optical thickness (tau(545 nm)) as spheres (tau-conserving case). The impact of particle shape on DRE is investigated for different dust particle effective radii, optical thickness of the dust cloud, solar zenith angle, and spectral surface albedo (ocean, grass, and desert). It is found that the influence of particle shape on the DRE is strongest over ocean. It also depends very strongly on the shape distribution of spheroids used, to a degree that the results for two distributions of spheroids may deviate more from each other than from those for spheres. Finally, the effects of nonsphericity largely depend on whether the mass- or tau-conserving case is considered. For example, when using a shape distribution of spheroids recommended in a recent study for approximating the single-scattering properties of dust, the DRE at the surface differs at most 5% from that from spherical particles in the mass-conserving case. This stems from compensating nonsphericity effects on optical thickness, asymmetry parameter, and single-scattering albedo. However, in the tau-conserving case, the negative DRE at the surface can be up to 15% weaker for spheroids than spheres.

  • 41.
    Hare, B. M.
    et al.
    Univ Groningen, Netherlands.
    Scholten, O.
    Univ Groningen, Netherlands;Vrije Univ Brussel, Belgium.
    Bonardi, A.
    Radboud Univ Nijmegen, Netherlands.
    Buitink, S.
    Vrije Univ Brussel, Belgium.
    Corstanje, A.
    Radboud Univ Nijmegen, Netherlands.
    Ebert, U.
    Ctr Math & Comp Sci, Netherlands;Eindhoven Univ Technol, Netherlands.
    Falcke, H.
    Vrije Univ Brussel, Belgium;NIKHEF, Netherlands;Netherlands Inst Radio Astron ASTRON, Netherlands;Max Planck Inst Radioastron, Germany.
    Horandel, J. R.
    Radboud Univ Nijmegen, Netherlands;NIKHEF, Netherlands.
    Leijnse, H.
    Royal Netherlands Meteorol Inst, Netherlands.
    Mitra, P.
    Vrije Univ Brussel, Belgium.
    Mulrey, K.
    Vrije Univ Brussel, Belgium.
    Nelles, A.
    Radboud Univ Nijmegen, Netherlands;Univ Calif Irvine, USA.
    Rachen, J. P.
    Radboud Univ Nijmegen, Netherlands.
    Rossetto, L.
    Radboud Univ Nijmegen, Netherlands.
    Rutjes, C.
    Ctr Math & Comp Sci, Netherlands.
    Schellart, P.
    Radboud Univ Nijmegen, Netherlands;Princeton Univ, USA.
    Thoudam, Satyendra
    Linnéuniversitetet, Fakulteten för teknik (FTK), Institutionen för fysik och elektroteknik (IFE).
    Trinh, T. N. G.
    Univ Groningen, Netherlands..
    ter Veen, S.
    Radboud Univ Nijmegen, Netherlands;Netherlands Inst Radio Astron ASTRON, Netherlands.
    Winchen, T.
    Vrije Univ Brussel, Belgium.
    LOFAR Lightning Imaging: Mapping Lightning With Nanosecond Precision2018Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, nr 5, s. 2861-2876Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lightning mapping technology has proven instrumental in understanding lightning. In this work we present a pipeline that can use lightning observed by the LOw-Frequency ARray (LOFAR) radio telescope to construct a 3-D map of the flash. We show that LOFAR has unparalleled precision, on the order of meters, even for lightning flashes that are over 20km outside the area enclosed by LOFAR antennas (approximate to 3,200km(2)), and can potentially locate over 10,000 sources per lightning flash. We also show that LOFAR is the first lightning mapping system that is sensitive to the spatial structure of the electrical current during individual lightning leader steps.

  • 42.
    He, Lixia
    et al.
    Nanjing Univ Informat Sci & Technol, Minist Educ KLME, Key Lab Meteorol Disaster, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, CIC FEMD, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, Nanjing, Jiangsu, Peoples R China;Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Azadifar, Mohammad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland;Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rachidi, Farhad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Rubinstein, Marcos
    Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rakov, Vladimir A.
    Univ Florida, Dept Elect & Comp Engn, Gainesville, FL USA;Russian Acad Sci, Inst Appl Phys, Nizhnii Novgorod, Russia.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Pavanello, Davide
    Univ Appl Sci Western Switzerland, Inst Syst Engn, Sion, Switzerland.
    Xing, Hongyan
    Nanjing Univ Informat Sci & Technol, Minist Educ KLME, Key Lab Meteorol Disaster, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, CIC FEMD, Nanjing, Jiangsu, Peoples R China;Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, Nanjing, Jiangsu, Peoples R China.
    An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Santis Tower2018Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, nr 8, s. 4045-4059Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a study on the characteristics of current and electric field pulses associated with upward lightning flashes initiated from the instrumented Santis Tower in Switzerland. The electric field was measured 15km from the tower. Upward flashes always begin with the initial stage composed of the upward-leader phase and the initial-continuous-current (ICC) phase. Four types of current pulses are identified and analyzed in the paper: (1) return-stroke pulses, which occur after the extinction of the ICC and are preceded by essentially no-current time intervals; (2) mixed-mode ICC pulses, defined as fast pulses superimposed on the ICC, which have characteristics very similar to those of return strokes and are believed to be associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC-carrying channel at relatively small junction heights; (3) classical M-component pulses superimposed on the continuing current following some return strokes; and (4) M-component-type ICC pulses, presumably associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC-carrying channel at relatively large junction heights. We consider a data set consisting of 9 return-stroke pulses, 70 mixed-mode ICC pulses, 11 classical M-component pulses, and 19 M-component-type ICC pulses (a total of 109 pulses). The salient characteristics of the current and field waveforms are analyzed. A new criterion is proposed to distinguish between mixed-mode and M-component-type pulses, which is based on the current waveform features. The characteristics of M-component-type pulses during the initial stage are found to be similar to those of classical M-component pulses occurring during the continuing current after some return strokes. It is also found that about 41% of mixed-mode ICC pulses were preceded by microsecond-scale pulses occurring in electric field records some hundreds of microseconds prior to the onset of the current, very similar to microsecond-scale electric field pulses observed for M-component-type ICC pulses and which can be attributed to the junction of an in-cloud leader channel to the current-carrying channel to ground. Classical M-component pulses and M-component-type ICC pulses tend to have larger risetimes ranging from 6.3 to 430s. On the other hand, return-stroke pulses and mixed-mode ICC pulses have current risetimes ranging from 0.5 to 28s. Finally, our data suggest that the 8-s criterion for the current risetime proposed by Flache et al. is a reasonable tool to distinguish between return strokes and classical M-components. However, mixed-mode ICC pulses superimposed on the ICC can sometimes have considerably longer risetimes, up to about 28s, as observed in this study.

  • 43.
    He, Lixia
    et al.
    Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, CIC FEMD, Nanjing, Jiangsu, Peoples R China;Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Rachidi, Farhad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland.
    Azadifar, Mohammad
    Swiss Fed Inst Technol EPFL, Electromagnet Compatibil Lab, Lausanne, Switzerland;Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rubinstein, Marcos
    Univ Appl Sci Western Switzerland, Inst Informat & Commun Technol, Yverdon, Switzerland.
    Rakov, Vladimir A.
    Univ Florida, Dept Elect & Comp Engn, Gainseville, FL USA;Natl Res Univ Higher Sch Econ, Moscow Inst Elect & Math, Moscow, Russia.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Pavanello, Davide
    Univ Appl Sci Western Switzerland HES SO, Inst Sustainable Energy, Sion, Switzerland.
    Xing, Hongyan
    Nanjing Univ Informat Sci & Technol, Jiangsu Key Lab Meteorol Observat & Informat Proc, CIC FEMD, Nanjing, Jiangsu, Peoples R China.
    Electromagnetic Fields Associated With the M-Component Mode of Charge Transfer2019Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 124, nr 13, s. 6791-6809Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-component or leader/return-stroke-like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC-carrying channel at relatively short distance from the tower top, resulting in the so-called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M-component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Santis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with the M-component charge transfer mode (including classical M-component pulses and M-component-type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2-Dimentional Finite-Difference Time Domain method, in which the M-component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Santis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M-component and M-component-type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of the M-component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M-component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M-component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch-to-channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E-field and 1.9 for the H-field. For a junction height greater than 6 km, the E-field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, ) in which an electric field propagation factor of 1. 8 was inferred for return strokes and mixed-mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return-stroke-like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 mu s or so) for which the tendency reverses. Finally, model-predicted fields associated with different charge transfer modes, namely, return stroke, mixed-mode, classical M-component, and M-component-type ICC pulse are compared with experimental observations at the Santis Tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed-mode models (1.0 km for the return stroke and 0.8 km for the mixed-mode pulse) are lower than the value of 2.0 km typically used in the literature.

  • 44. Hedfors, J
    et al.
    Aldahan, A
    Kulan, A
    Possnert, G
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Vintersved, I
    Clouds and Be-7: Perusing connections between cosmic rays and climate2006Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, nr D2, artikel-id D02208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    [1] Time series data on Be-7, precipitation, temperature, and satellite imagery of cloud cover over Scandinavia, together with cosmic ray and sunspot activity, were used to elucidate the relationship between cosmic rays and clouds, and ultimately climate change. The results indicate a coherent negative correlation between total cloud cover and Be-7 on intraseasonal, seasonal, and decadal scales. Although the reasons behind this correlation are unclear, a full-scale implication of this feature is in the possible use of Be-7 and Be-10 records for proxy paleo-reconstruction of total cloud cover. This is a strongly needed, but generally difficult to quantify parameter in climate models.

  • 45. Hillamo, R
    et al.
    Kerminen, V M
    Aurela, M
    Makela, T
    Maenhaut, W
    Leck, C
    Modal structure of chemical mass size distribution in the high Arctic aerosol2001Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, nr D21, s. 27555-27571Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chemical mass size distributions of aerosol particles were measured in the remote marine boundary layer over the central Arctic Ocean as part of the Atmospheric Research Program on the Arctic Ocean Expedition 1996 (AOE-96). An inertial impaction method was used to classify aerosol particles into different size classes for subsequent chemical analysis. The particle chemical composition was determined by ion chromatography and by the particle-induced X-ray emission technique. Continuous particle size spectra were extracted from the raw data using a data inversion method. Clear and varying modal structures for aerosols consisting of primary sea-salt particles or of secondary particles related to dimethyl sulfide emissions were found. Concentration levels of all modes decreased rapidly when the distance from open sea increased. In the submicrometer size range the major ions found by ion chromatography were sulfate, methane sulfonate, and ammonium. They had most of the time a clear Aitken mode and one or two accumulation modes, with aerodynamic mass median diameters around 0.1 mum, 0.3 mum, and between 0.5-1.0 mum, respectively. The overall submicron size distributions of these three ions were quite similar, suggesting that they were internally mixed over most of this size range. The corresponding modal structure was consistent with the mass size distributions derived from the particle number size distributions measured with a differential mobility particle sizer. The Aitken to accumulation mode mass ratio for nss-sulfate and MSA was substantially higher during clear skies than during cloudy periods. Primary sea-salt particles formed a mode with an aerodynamic mass median diameter around 2 mum. In general, the resulting continuous mass size distributions displayed a clear modal structure consistent with our understanding of the two known major source mechanisms. One is the sea-salt aerosol emerging from seawater by bubble bursting. The other is related to dimethylsulfide (DMS) emissions from biogenic processes in seawater, followed by gas-to-particle conversion, formation of particulate sulfate and methane sulfonate (MSA) and neutralization by ammonia.

  • 46. Holl, G.
    et al.
    Eliasson, Salomon
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Mendrok, J.
    Buehler, S. A.
    SPARE-ICE: Synergistic ice water path from passive operational sensors2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 3, s. 1504-1523Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article presents SPARE-ICE, the Synergistic Passive Atmospheric Retrieval Experiment-ICE. SPARE-ICE is the first Ice Water Path (IWP) product combining infrared and microwave radiances. By using only passive operational sensors, the SPARE-ICE retrieval can be used to process data from at least the NOAA 15 to 19 and MetOp satellites, obtaining time series from 1998 onward. The retrieval is developed using collocations between passive operational sensors (solar, terrestrial infrared, microwave), the CloudSat radar, and the CALIPSO lidar. The collocations form a retrieval database matching measurements from passive sensors against the existing active combined radar-lidar product 2C-ICE. With this retrieval database, we train a pair of artificial neural networks to detect clouds and retrieve IWP. When considering solar, terrestrial infrared, and microwave-based measurements, we show that any combination of two techniques performs better than either single-technique retrieval. We choose not to include solar reflectances in SPARE-ICE, because the improvement is small, and so that SPARE-ICE can be retrieved both daytime and nighttime. The median fractional error between SPARE-ICE and 2C-ICE is around a factor 2, a figure similar to the random error between 2C-ICE ice water content (IWC) and in situ measurements. A comparison of SPARE-ICE with Moderate Resolution Imaging Spectroradiometer (MODIS), Pathfinder Atmospheric Extended (PATMOS-X), and Microwave Surface and Precipitation Products System (MSPPS) indicates that SPARE-ICE appears to perform well even in difficult conditions. SPARE-ICE is available for public use.

  • 47.
    Hultgren, Kristoffer
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jorg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tomographic and spectral views on the lifecycle of polar mesospheric clouds from Odin/OSIRIS2014Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 24, s. 14129-14143Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vertical and horizontal structures of Polar Mesospheric Clouds (PMC) have been recovered by tomographic retrieval from the OSIRIS instrument aboard the Odin satellite. The tomographic algorithm has been used to return local scattering coefficients at seven wavelengths in the ultraviolet. This spectral information is used to retrieve PMC particle sizes, number density, and ice mass density. While substantial horizontal variations are found, local vertical structures are overall consistent with the idea of a growth-sedimentation process leading to a visible cloud. Large numbers of small particles are present near the top of the observed cloud layer. Toward lower altitudes, particle sizes increase while particle number densities decrease. A close relationship is found between the distribution of local PMC scattering coefficient and ice mass density. The bottom of the cloud often features large particles with mode radii exceeding 70 nm that rain out of the cloud before sublimating. The number density of these large particles is small, and they do not contribute significantly to the overall cloud brightness. As a consequence, the presence of these large particles can be difficult to identify for remote sensing techniques that integrate over the entire cloud column. When it comes to deriving absolute values of particle mode radius and number density, there is a strong sensitivity to assumptions on the mathematical form of the particle size distribution. We see a continued strong need to resolve this issue by co-analysis of various remote sensing techniques and observation geometries.

  • 48.
    Hultgren, Kristoffer
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jörg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tomographic and spectral views on the lifecycle of Polar Mesospheric Clouds from Odin/OSIRISIngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996Artikel i tidskrift (Refereegranskat)
  • 49.
    Hultin, Kim A. H.
    et al.
    Stockholm University.
    Nilsson, E. Douglas
    Stockholm University.
    Krejci, Radovan
    Stockholm University.
    Martensson, E. Monica
    Stockholm University.
    Ehn, Mikael
    Hagstrom, Ake
    de Leeuw, Gerrit
    In situ laboratory sea spray production during the Marine Aerosol Production 2006 cruise on the northeastern Atlantic Ocean2010Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, artikel-id D06201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bubbles bursting from whitecaps are considered to be the most effective mechanism for particulate matter to be ejected into the atmosphere from the Earth's oceans. To realistically predict the climate effect of marine aerosols, global climate models require process-based understanding of particle formation from bubble bursting. During a cruise on the highly biologically active waters of the northeastern Atlantic Ocean in the summer of 2006, the submicrometer primary marine aerosol produced by a jet of seawater impinging on a seawater surface was investigated. The produced aerosol size spectra were centered on 200 nm in dry diameter and were conservative in shape throughout the cruise. The aerosol number production was negatively correlated with dissolved oxygen (DO) in the water (r < -0.6 for particles of dry diameter D-p > 200 nm). An increased surfactant concentration as a result of biological activity affecting the oxygen saturation is thought to diminish the particle production. The lack of influence of chlorophyll on aerosol production indicates that hydrocarbons produced directly by the photosynthesis are not essential for sea spray production. The upward mixing of deeper ocean water as a result of higher wind speed appears to affect the aerosol particle production, making wind speed influence aerosol production in more ways than by increasing the amount of whitecaps. The bubble spectra produced by the jet of seawater was representative of breaking waves at open sea, and the particle number production was positively correlated with increasing bubble number concentration with a peak production of 40-50 particles per bubble.

  • 50.
    Höpner, Friederike
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Bender, Frida A.-M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Leck, Caroline
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Investigation of Two Optical Methods for Aerosol‐Type Classification Extended to a Northern Indian Ocean Site2019Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 124, nr 15, s. 8743-8763Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Methods for determining aerosol types in cases where chemical composition measurements are not available are useful for improved aerosol radiative forcing estimates. In this study, two aerosol characterization methods by Cazorla et al. (2013, https://doi.org/10.5194/acp-13-9337-2013; CA13) and Costabile et al. (2013, https://doi.org/10.5194/acp-13-2455-2013; CO13) using wavelength‐dependent particle absorption and scattering are used, to assess their applicability and examine their limitations. Long‐term ambient particle optical property and chemical composition (major inorganic ions and bulk carbon) measurements from the Maldives Climate Observatory Hanimaadhoo as well as concurrent air mass trajectories are utilized to test the classifications based on the determined absorption Ångström exponent, scattering Ångström exponent, and single scattering albedo. The resulting aerosol types from the CA13 method show a good qualitative agreement with the particle chemical composition and air mass origin. In general, the size differentiation using the scattering Ångström exponent works very well for both methods, while the composition identification depending mainly on the absorption Ångström exponent can result in aerosol misclassifications at Maldives Climate Observatory Hanimaadhoo. To broaden the applicability of the CA13 method, we suggest to include an underlying marine aerosol group in the classification scheme. The classification of the CO13 method is less clear, and its applicability is limited when it is extended to aerosols in this environment at ambient humidity.

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