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  • 1.
    Acosta Navarro, J. C.
    et al.
    Stockholm University, Sweden .
    Smolander, S.
    University of Helsinki, Finland .
    Struthers, Hamish
    Linköping University, National Supercomputer Centre (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 millennium2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 11, 6867-6885 p.Article in journal (Refereed)
    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.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Smolander, S.
    Struthers, H.
    Zorita, E.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kaplan, J. O.
    Guenther, A.
    Arneth, A.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Global emissions of terpenoid VOCs from terrestrial vegetation in the last millennium2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 11, 6867-6885 p.Article in journal (Refereed)
    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 University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Zurich, Dept Geog, Zurich, Switzerland..
    Propagation of biases in climate models from the synoptic to the regional scale: Implications for bias adjustment2016In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, no 5, 2075-2089 p.Article in journal (Refereed)
    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 University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    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 case2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 21, 11334-11351 p.Article in journal (Refereed)
    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.
    Andersson, Camilla
    et al.
    SMHI, Research Department, Air quality.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    European ozone in a future climate: Importance of changes in dry deposition and isoprene emissions2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, D02303Article in journal (Refereed)
    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.

  • 6. Bigg, E K
    et al.
    Leck, C
    Cloud-active particles over the central Arctic Ocean2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, 32155-32166 p.Article in journal (Refereed)
    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.

  • 7. Bigg, E K
    et al.
    Leck, C
    Properties of the aerosol over the central Arctic Ocean2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, 32101-32109 p.Article in journal (Refereed)
    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.

  • 8. 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 consequences2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, 32167-32185 p.Article in journal (Refereed)
    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.

  • 9. Bigg, E. Keith
    et al.
    Leck, Caroline
    The composition of fragments of bubbles bursting at the ocean surface2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D11Article in journal (Refereed)
    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.

  • 10.
    Bikkina, Srinivas
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ram, Kirpa
    Sarin, M. M.
    Sheesley, Rebecca J.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kirillova, Elena N.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rengarajan, R.
    Sudheer, A. K.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Carbon isotope-constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo-Gangetic Plain2017In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, no 9, 4903-4923 p.Article in journal (Refereed)
    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.

  • 11.
    Bikkina, Srinivas
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Sarin, M. M.
    Sheesley, R. J.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kirillova, E.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rengarajan, R.
    Sudheer, A. K.
    Ram, K.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Banaras Hindu University, India.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India2016In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, no 9, 4797-4809 p.Article in journal (Refereed)
    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.

  • 12. 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 summer2009In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114Article in journal (Refereed)
    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.

  • 13. Björkman, Mats P.
    et al.
    Vega, Carmen P.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    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 snow2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 22, 12953-12976 p.Article in journal (Refereed)
    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.

  • 14.
    Bosch, Carme
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, August
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kirillova, Elena N.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Budhavant, Krishnakant
    Tiwari, Suresh
    Praveen, P. S.
    Russell, Lynn M.
    Beres, Nicholas D.
    Ramanathan, Veerabhadran
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (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 Ocean2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 20, 11743-11759 p.Article in journal (Refereed)
    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.

  • 15.
    Bourgeois, Quentin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 16, 8411-8425 p.Article in journal (Refereed)
    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.

  • 16. Chen, Bing
    et al.
    Zhu, Zhejing
    Wang, Xinfeng
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Chen, Jianmin
    Zhang, Qingzhu
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Reconciling modeling with observations of radiative absorption of black carbon aerosols2017In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, no 11, 5932-5942 p.Article in journal (Refereed)
    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.

  • 17. Cheymol, Anne
    et al.
    De Backer, Hugo
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Stuebi, Rene
    Comparison and validation of the aerosol optical depth obtained with the Langley plot method in the UV-B from Brewer Ozone Spectrophotometer measurements2006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D16, D16202Article in journal (Refereed)
    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.

  • 18.
    Chiacchio, Marc
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Pausata, Francesco S. R.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Messori, Gabriele
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Chin, Mian
    Onskog, Thomas
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Barrie, Leonard
    Stockholm University, Faculty of Science, Department of Meteorology .
    On the links between meteorological variables, aerosols, and tropical cyclone frequency in individual ocean basins2017In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, no 2, 802-822 p.Article in journal (Refereed)
    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.

  • 19.
    Chiacchio, Marc
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . 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 brightening2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 5, 1951-1971 p.Article in journal (Refereed)
    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.

  • 20.
    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 spectrometry2003In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 108, no D23Article in journal (Refereed)
    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.

  • 21. 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, Core Services.
    Reconstructing of erythemal ultraviolet radiation levels in Europe for the past 4 decades2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, D10102Article in journal (Refereed)
    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.

  • 22.
    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 cap2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D19, D19104Article in journal (Refereed)
    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.

  • 23. Dwyer, J. R.
    et al.
    Saleh, Z.
    Rassoul, H. K.
    Concha, D.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Jerauld, J.
    Uman, M. A.
    Rakov, V. A.
    A study of X-ray emission from laboratory sparks in air at atmospheric pressure2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, D23207- p.Article in journal (Refereed)
  • 24.
    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 packs2013In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 118, no 24, 13614-13627 p.Article in journal (Refereed)
  • 25.
    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 snow2009In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114, D19112Article in journal (Refereed)
    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.

  • 26. Garstang, M
    et al.
    Tyson, P D
    Swap, R
    Edwards, M
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Lindesay, J A
    Horizontal and vertical transport of air over southern Africa1996In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, no D19, 23721-23736 p.Article in journal (Refereed)
    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.

  • 27. Giamarelou, Maria
    et al.
    Eleftheriadis, Konstantinos
    Nyeki, Stephan
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Torseth, Kjetil
    Biskos, George
    Indirect evidence of the composition of nucleation mode atmospheric particles in the high Arctic2016In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, no 2, 965-975 p.Article in journal (Refereed)
    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.

  • 28.
    Glantz, Paul
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bourassa, Adam
    Herber, Andreas
    Iversen, Trond
    Karlsson, Johannes
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kirkevag, Alf
    Maturilli, Marion
    Seland, Oyvind
    Stebel, Kerstin
    Struthers, Hamish
    Tesche, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Thomason, Larry
    Remote sensing of aerosols in the Arctic for an evaluation of global climate model simulations2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 13, 8169-8188 p.Article in journal (Refereed)
    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.

  • 29.
    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 simulations2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 13, 8169-8188 p.Article in journal (Refereed)
    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.

  • 30. 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 core2006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D7, D07110Article in journal (Refereed)
    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.

  • 31. Grisogono, Branko
    et al.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Thermal mesoscale circulations on the Baltic coast 2. Perturbation of surface parameters1996In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, 18999-19012 p.Article in journal (Refereed)
  • 32. 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 system2009In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114, D04202Article in journal (Refereed)
    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.

  • 33. Groot Zwaaftink, C. D.
    et al.
    Grythe, Henrik
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. 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 Arctic2016In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, no 22, 13678-13697 p.Article in journal (Refereed)
    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.

  • 34. Haapanala, Paivi
    et al.
    Raisanen, Petri
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Nousiainen, Timo
    Sensitivity of the shortwave radiative effect of dust on particle shape: Comparison of spheres and spheroids2012In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 117, D08201Article in journal (Refereed)
    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.

  • 35. Hedfors, J
    et al.
    Aldahan, A
    Kulan, A
    Possnert, G
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Vintersved, I
    Clouds and Be-7: Perusing connections between cosmic rays and climate2006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D2, D02208Article in journal (Refereed)
    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.

  • 36. 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 aerosol2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D21, 27555-27571 p.Article in journal (Refereed)
    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.

  • 37. Holl, G.
    et al.
    Eliasson, Salomon
    SMHI, Research Department, Atmospheric remote sensing.
    Mendrok, J.
    Buehler, S. A.
    SPARE-ICE: Synergistic ice water path from passive operational sensors2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 3, 1504-1523 p.Article in journal (Refereed)
    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.

  • 38.
    Hultgren, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jorg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tomographic and spectral views on the lifecycle of polar mesospheric clouds from Odin/OSIRIS2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 24, 14129-14143 p.Article in journal (Refereed)
    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.

  • 39.
    Hultgren, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tomographic and spectral views on the lifecycle of Polar Mesospheric Clouds from Odin/OSIRISIn: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996Article in journal (Refereed)
  • 40.
    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 Ocean2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, D06201Article in journal (Refereed)
    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.

  • 41.
    Isoz, Oscar
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Eriksson, Per
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Intercalibration of microwave temperature sounders using radio occultation measurements2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 9, 3758-3773 p.Article in journal (Refereed)
    Abstract [en]

    This is a study of the usefulness of radio occultation (RO) data for intercomparing different microwave temperature (MWT) sounding instruments. The RO data used are from the Global Navigational Satellite System Receiver for Atmospheric Sounding on the Metop-A and B satellites. The MWT sounders investigated are the Advanced Microwave Sounding Unit-A instruments on the satellites NOAA 15, 16, and 18 and Metop-A. We collocate RO and MWT data and then use these collocations to study various aspects of the MWT instruments. In addition, two different versions of the MWT data are compared: standard operational data (OPR) and the NOAA Integrated Microwave Intercalibration Approach data (IMICA). The time series of monthly mean differences shows that there are robust patterns for each satellite and data version, which mostly drift only slowly over time. The intersatellite spread, measured by the standard deviation of the yearly mean values by all satellites, is between 0.1 and 0.4 K, depending on channel, with no significant differences between OPR and IMICA data. The only notable exception is Channel 8 of NOAA 16, which appears to have a time-varying offset of 0.5–1 K relative to the other instruments. At this point it is not clear whether this deviation is real or a sampling artifact, so further study is needed. Due to the large number of collocations used, it is possible to also investigate the scene brightness and scan angle dependence of the MWT bias (relative to RO). First results of such an analysis are presented and discussed. Particularly, the investigation of the scan angle dependence is novel, since this bias pattern is difficult to assess without RO data. Further work is needed on these angular dependences, before conclusions are robust enough to include in data recalibration efforts, but our overall conclusion is that RO collocations are a powerful tool for intercomparing MWT sounders.

  • 42. Jiang, Xianan
    et al.
    Waliser, Duane E.
    Xavier, Prince K.
    Petch, Jon
    Klingaman, Nicholas P.
    Woolnough, Steven J.
    Guan, Bin
    Bellon, Gilles
    Crueger, Traute
    DeMott, Charlotte
    Hannay, Cecile
    Lin, Hai
    Hu, Wenting
    Kim, Daehyun
    Lappen, Cara-Lyn
    Lu, Mong-Ming
    Ma, Hsi-Yen
    Miyakawa, Tomoki
    Ridout, James A.
    Schubert, Siegfried D.
    Scinocca, John
    Seo, Kyong-Hwan
    Shindo, Eiki
    Song, Xiaoliang
    Stan, Cristiana
    Tseng, Wan-Ling
    Wang, Wanqiu
    Wu, Tongwen
    Wu, Xiaoqing
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Zhang, Guang J.
    Zhu, Hongyan
    Vertical structure and physical processes of the Madden-Julian oscillation: Exploring key model physics in climate simulations2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 10, 4718-4748 p.Article in journal (Refereed)
    Abstract [en]

    Aimed at reducing deficiencies in representing the Madden-Julian oscillation (MJO) in general circulation models (GCMs), a global model evaluation project on vertical structure and physical processes of the MJO was coordinated. In this paper, results from the climate simulation component of this project are reported. It is shown that the MJO remains a great challenge in these latest generation GCMs. The systematic eastward propagation of the MJO is only well simulated in about one fourth of the total participating models. The observed vertical westward tilt with altitude of the MJO is well simulated in good MJO models but not in the poor ones. Damped Kelvin wave responses to the east of convection in the lower troposphere could be responsible for the missing MJO preconditioning process in these poor MJO models. Several process-oriented diagnostics were conducted to discriminate key processes for realistic MJO simulations. While large-scale rainfall partition and low-level mean zonal winds over the Indo-Pacific in a model are not found to be closely associated with its MJO skill, two metrics, including the low-level relative humidity difference between high- and low-rain events and seasonal mean gross moist stability, exhibit statistically significant correlations with the MJO performance. It is further indicated that increased cloud-radiative feedback tends to be associated with reduced amplitude of intraseasonal variability, which is incompatible with the radiative instability theory previously proposed for the MJO. Results in this study confirm that inclusion of air-sea interaction can lead to significant improvement in simulating the MJO.

  • 43.
    Josefsson, Weine
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Effect of clouds on UV irradiance: As estimated from cloud amount, cloud type, precipitation, global radiation and sunshine duration2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D4, 4927-4935 p.Article in journal (Refereed)
    Abstract [en]

    Ten years of measurements of UV irradiance, monitored by the Robertson-Berger (RB) meter in Norrkoping, 58.58 degrees N, 16.15 degrees E, Sweden, have been combined with concurrent synoptic cloud observations, measurements of sunshine duration, and global radiation to establish the relative influence of clouds on UV irradiance. It is shown that the cloud effect for UV wavelengths is less than for the whole solar spectrum (global radiation). Relations retrieved for global radiation may be used by correcting for the differences. High-level clouds are more transparent than low- and medium-level clouds. As expected, it was found that precipitating clouds in general are more opaque than nonprecipitating clouds. If there is any solar elevation dependency in the effect of clouds, it is small. Using only total cloud amount as parameter to model, the cloud effect on UV irradiance will give a substantial uncertainty, which can be decreased considerably using cloud type and/or information on precipitation conditions. It has also been shown that sunshine duration can be used in a similar way as cloud covet.

  • 44.
    Kahnert, Michael
    et al.
    SMHI, Research Department, Air quality.
    Nousiainen, T
    Veihelmann, B
    Spherical and spheroidal model particles as an error source in aerosol climate forcing and radiance computations: A case study for feldspar aerosols2005In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 110, no D18, D18S13Article in journal (Refereed)
    Abstract [en]

    A case study for feldspar aerosols is conducted to assess the errors introduced by simple model particles in radiance and flux simulations. The spectral radiance field and net flux are computed for a realistic phase function of feldspar aerosols measured in the laboratory at 633 nm. Results are compared to computations with spherical and spheroidal model particles. It is found that the use of spherical model particles introduces large spectral radiance errors at top of atmosphere (TOA) between -6 and 31%. Using a new shape parameterization of spheroids reduces the error range to -1 to 6%. Spherical model particles yield an absolute TOA spectral net flux error of -6.1 mW m(-2) nm(-1). An equiprobable shape distribution of spheroids results in only minor improvements, but the new shape parameterization yields an error of only -0.8 mW m(-2) nm(-1). A variation of the refractive index m reveals that the resulting changes in the TOA spectral net flux are slightly smaller than the error caused by assuming the particles to be spherical. However, the uncertainty of m is commonly considered the major error source in aerosol radiative forcing simulations, whereas the use of spherical model particles is often not seriously questioned. This study implies that this notion needs to be reconsidered. Should the relative spectral net flux errors be representative for the entire spectrum, then the use of spherical model particles may be among the major error sources in broadband flux simulations. The new spheroidal shape parameterization can, however, substantially improve the results.

  • 45.
    Karlsson, Karl-Göran
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Evaluation of regional cloud climate simulations over Scandinavia using a 10-year NOAA advanced very high resolution radiometer cloud climatology2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D1, D01203Article in journal (Refereed)
    Abstract [en]

    A satellite-derived (NOAA Advanced Very High Resolution Radiometer) cloud climatology over the Scandinavian region covering the period 1991 - 2001 has been used to evaluate the performance of cloud simulations of the Swedish Meteorological and Hydrological Institute Rossby Centre regional climate model (RCA3). Several methods of adapting the satellite and model data sets to allow a meaningful comparison were applied. RCA3-simulated total cloud cover was shown to agree within a few percent of the satellite-retrieved cloud amounts on seasonal and annual timescales. However, a substantial imbalance between the respective RCA3 contributions from low-, medium- and high-level clouds was seen. The differences from satellite-derived contributions were +2.4% for high-level clouds, -5.2% for medium-level clouds and +4.0% for low- level clouds. In addition, an overrepresentation of cloud categories with high optical thicknesses was seen for all vertical cloud groups, particularly during the summer season. Some specific features of the geographical distribution of cloudiness were also noticed. Most pronounced were the excess of cloud amounts over the Scandinavian mountain range and a deficit leeward of the mountains. The overall results imply problems with the RCA3-modeled surface radiation budget components by causing reduced incoming solar radiation and increased downwelling longwave radiation.

  • 46. Kaurola, J.
    et al.
    Lindfors, A.
    Lakkala, K.
    Hansen, G.
    Josefsson, Weine
    SMHI, Core Services.
    Vuilleumier, L.
    Feister, U.
    Slaper, H.
    On the usability of the ERA-40 reanalysis in the estimation of past surface UV radiation over Europe2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, D24107Article in journal (Refereed)
    Abstract [en]

    Erythemal daily UV doses have been calculated using input data from the ERA-40 reanalysis for years 1958-2002. The quality of input parameters for UV calculations has been validated with available ground based total ozone data and estimates of Cloud Modification Factor (CMF), and the results have been compared with existing UV data. Owing to limited availability of validation data especially during 1960s and 1970s the analysis focused on sites located in central and northern Europe. The current work is the first step in deriving reliable long-term UV time series from the ERA-40 reanalysis. Total ozone from the ERA-40 reanalysis is affected by significant biases, especially before satellite ozone measurements were available for assimilation. Estimations of the effect of clouds on surface UV were made using global radiation (300-3000 nm) budgets at the surface because available ERA-40 cloud data do not allow good estimates of surface daily UV doses. There are some problems with ERA-40 solar radiation budgets which cause systematic biases in calculated daily UV doses. Comparison of calculated daily erythemal UV doses against ground-based UV data indicate that ERA-40 UV doses are typically overestimated by 6-18% in central and northern Europe and underestimated by 9-17% at Davos, Switzerland. Root-mean-square errors of the calculated daily UV doses are usually in the range of 30-40%. Trends of UV doses were calculated for the concurrent period of the TOMS satellite UV data (1979-2002). The trends of zonally averaged ERA-40 and TOMS UV agree well and are mostly of the same sign and magnitude.

  • 47. Kaurola, J
    et al.
    Taalas, P
    Koskela, T
    Borkowski, J
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Long-term variations of UV-B doses at three stations in northern Europe2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D16, 20813-20820 p.Article in journal (Refereed)
    Abstract [en]

    Recent analysis of the total ozone observations indicate a negative trend of about 4%/decade in the Northern Hemisphere midlatitudes during the last two decades [WMO, 1999]. The effect of this decline on surface UV levels is of interest to a variety of applications. In this work the long-term variation of UV radiation at three stations located in northern Europe (Belsk, Norrkoping, and Jokioinen) has been studied using data from (1) ground-based observations, (2) surface UV doses determined using TOMS satellite measurements, and (3) reconstructed UV doses using observations of global radiation, total ozone, and radiative transfer modeling. For each station the estimates of daily UV doses from various sources have been intercompared, and a trend analysis has been performed to reveal long-term changes in the UV radiation. Data sets, which start in the late 1970s or early 1980s, show a general positive trend in annual doses of UV radiation. Some of these upward trends are statistically significant. For Belsk the increases are in the range of 5-15% per decade during spring and summer. The largest increases, about 20%/decade, has been observed in Norrkoping during spring. At Jokioinen there has been a slight upward trend in UV throughout the year. The analysis of reconstructed Belsk data from 1966 onward shows that the positive trend since late 1970s was preceeded by a negative trend. The reason for such changes is probably not only related to the changes in the total ozone but also to changes in aerosol content and cloudiness. The agreement of the UV series based on different data sources is good. This was studied using a subset of data in which it was required that data from all possible sources were available. The different trend estimates were in very close agreement with each other. However, there were often differences in absolute values, which is probably related to problems in calibration and limitations of the models.

  • 48. Kekonen, T
    et al.
    Moore, J
    Peramaki, P
    Mulvaney, R
    Isaksson, E
    Pohjola, V
    van de Wal, R S W
    The 800 year long ion record from the Lomonosovfonna (Svalbard) ice core2005In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 110, no D7, D07304Article in journal (Refereed)
    Abstract [en]

    We present a high-resolution record of water-soluble ion chemistry from a 121 m ice core spanning about 800 years. The core is well dated to 2/3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1/3 of the core. This core suffers from modest seasonal melt, and so we present concentration data in decadal running means to minimize percolation effects. Sea-salt ions (Na+, Cl-, Mg2+, and K+) account for more than 70% of all ions. In general, sea-salt ion concentrations are rather variable and have no clear association with climatic variations. Sulfate, with 74% being from non-sea-salt sources, has higher concentrations than seen on Vestfonna ice cap but lower than in Ny-angstrom lesund aerosols, suggesting central Spitsbergen receives more marine (westerly) air masses than Ny-angstrom lesund but more sulfate enriched (easterly) air masses than Nordaustlandet. Clear anthropogenic impacts are found for sulfate, nitrate, and ammonium (and probably excess chloride) after the mid twentieth century, with sulfate showing a significant rise by the end of the nineteenth century. Sulfate and methanesulfonate concentrations correlate well during the twentieth century, and it is clear that most of the preindustrial sulfate is of biogenic origin. Terrestrial component (Ca2+) has the highest concentrations in the coldest part of the Little Ice Age, suggesting more windy conditions, transporting local terrestrial dust to the ice cap. All ion concentrations decrease at the end of the twentieth century, which reflects loss of ions by runoff, with non-sea-salt magnesium being particularly sensitive to melting.

  • 49. Kerminen, V M
    et al.
    Leck, C
    Sulfur chemistry over the central Arctic Ocean during the summer: Gas-to-particle transformation2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, 32087-32099 p.Article in journal (Refereed)
    Abstract [en]

    Atmospheric gas-to-particle transformation of the oxidation products of dimethyl sulfide (DMS) was investigated over the central Arctic Ocean by using observational data and a coupled gas phase chemistry-aerosol dynamics model. Chemical compounds investigated were sulfuric acid (H2SO4(g)), methasulfonic acid (MSA(g)), and sulfur dioxide (SO2(g)) in the gas phase, and non-sea-salt sulfate (nss-SO42-) and MSA in the particulate phase. During the advection from the open ocean to over the pack ice region, the particulate phase was found to be influenced significantly by three processes: (1) rapid removal of particulate matter during the first 1-2 days of advection, (2) continual formation of particulate nss-SO42- and MSA, and (3) local production of particles consisting mostly of matter other than nss-SO42- and MSA over the pack ice. In the absence of clouds and fogs, the principal sink for the vapors H2SO4(g) and MSA(g) were their condensational transport to submicron particles. SO2(g) was influenced significantly by both dry deposition and gas phase oxidation. Although there is a local source of coarse sea-salt particles within the pack ice region, the role of these particles in the budgets of nss-SO42- and SO2(g), and probably also in the budget of MSA, is only minor, especially when compared with marine regions at lower latitudes. The performance of the DMS gas-phase chemistry scheme was tested against field data using a measurement case influenced minimally by clouds/fogs and the free troposphere. The predicted concentration of nss-SO42- was within the uncertainties of the analysis, whereas that of MSA was high by a factor of 3-6. This demonstrates that not only heterogeneous reactions involved in atmospheric DMS chemistry but also certain gas-phase reactions require further investigation.

  • 50. Klingaman, Nicholas P.
    et al.
    Woolnough, Steven J.
    Jiang, Xianan
    Waliser, Duane
    Xavier, Prince K.
    Petch, Jon
    Caian, Mihaela
    SMHI, Research Department, Climate research - Rossby Centre.
    Hannay, Cecile
    Kim, Daehyun
    Ma, Hsi-Yen
    Merryfield, William J.
    Miyakawa, Tomoki
    Pritchard, Mike
    Ridout, James A.
    Roehrig, Romain
    Shindo, Eiki
    Vitart, Frederic
    Wang, Hailan
    Cavanaugh, Nicholas R.
    Mapes, Brian E.
    Shelly, Ann
    Zhang, Guang J.
    Vertical structure and physical processes of the Madden-Julian oscillation: Linking hindcast fidelity to simulated diabatic heating and moistening2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 10, 4690-4717 p.Article in journal (Refereed)
    Abstract [en]

    Many theories for the Madden-Julian oscillation (MJO) focus on diabatic processes, particularly the evolution of vertical heating and moistening. Poor MJO performance in weather and climate models is often blamed on biases in these processes and their interactions with the large-scale circulation. We introduce one of the three components of a model evaluation project, which aims to connect MJO fidelity in models to their representations of several physical processes, focusing on diabatic heating and moistening. This component consists of 20day hindcasts, initialized daily during two MJO events in winter 2009-2010. The 13 models exhibit a range of skill: several have accurate forecasts to 20days lead, while others perform similarly to statistical models (8-11days). Models that maintain the observed MJO amplitude accurately predict propagation, but not vice versa. We find no link between hindcast fidelity and the precipitation-moisture relationship, in contrast to other recent studies. There is also no relationship between models' performance and the evolution of their diabatic heating profiles with rain rate. A more robust association emerges between models' fidelity and net moistening: the highest-skill models show a clear transition from low-level moistening for light rainfall to midlevel moistening at moderate rainfall and upper level moistening for heavy rainfall. The midlevel moistening, arising from both dynamics and physics, may be most important. Accurately representing many processes may be necessary but not sufficient for capturing the MJO, which suggests that models fail to predict the MJO for a broad range of reasons and limits the possibility of finding a panacea.

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