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  • 1.
    Abiodun, B. and Enger, L.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
    The role of advection of fluxes on modelling dispersion in convective boundary2002In: Quart. J. Roy. Met. Soc., Vol. 128, 1589-1607 p.Article in journal (Refereed)
  • 2. Achberger, C
    et al.
    Chen, D L
    Alexandersson, Hans
    SMHI.
    The surface winds of Sweden during 1999-20002006In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 26, no 2, 159-178 p.Article in journal (Refereed)
    Abstract [en]

    This study aims at increasing our understanding of the regional wind climate in Sweden. Spatial and temporal patterns of the surface winds are presented for the years 1999-2000. Annual mean wind speeds range between 2 and 5 m/s with high values at exposed mountainous sites and on islands off the coast. Combining wind speed and direction into mean wind velocities shows that flow conditions are stronger and more coherent in space in southern Sweden than in central and northern Sweden. The spatial scale, defined as the distance between stations when the correlation for wind speed drops to similar to 0.37, was determined by pairwise correlations between all possible station pairs. Scales range from 38 to 530 km for wind speed and from 40 to 830 km for wind direction depending on the region. They tend to be smaller in central and northern Sweden, where the more pronounced relief has a larger influence on the local wind conditions. The strength and the timing of the annual and diurnal wind speed cycle have been estimated for each station. Amplitudes of the annual cycle are greater at exposed sites and correlate generally well with annual mean wind speeds. Monthly mean wind speeds peak in winter in southern Sweden, but peak in other seasons in the remaining regions. In winter, weaker pressure gradients over northern Sweden and surface-near temperature inversions contribute to weaker surface winds. Diurnal cycles vary in strength between summer and winter. Compared to the last normal climate period (1961-1990), 1999-2000 is characterized by the increased occurrence of westerly and southerly geostrophic flow. Copyright (C) 2005 Royal Meteorological Society.

  • 3. Achtert, P.
    et al.
    Brooks, I. M.
    Brooks, B. J.
    Moat, B. I.
    Prytherch, J.
    Persson, P. O. G.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Measurement of wind profiles by motion-stabilised ship-borne Doppler lidar2015In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 8, no 11, 4993-5007 p.Article in journal (Refereed)
    Abstract [en]

    Three months of Doppler lidar wind measurements were obtained during the Arctic Cloud Summer Experiment on the icebreakerOden during the summer of 2014. Such ship-borne Doppler measurements require active stabilisation to remove the effects of ship motion. We demonstrate that the combination of a commercial Doppler lidar with a custom-made motion-stabilisation platform enables the retrieval of wind profiles in the Arctic atmospheric boundary layer during both cruising and ice-breaking with statistical uncertainties comparable to land-based measurements. This held true particularly within the atmospheric boundary layer even though the overall aerosol load was very low. Motion stabilisation was successful for high wind speeds in open water and the resulting wave conditions. It allows for the retrieval of vertical winds with a random error below 0.2 m s−1. The comparison of lidar-measured wind and radio soundings gives a mean bias of 0.3 m s−1 (2°) and a mean standard deviation of 1.1 m s−1 (12°) for wind speed (wind direction). The agreement for wind direction degrades with height. The combination of a motion-stabilised platform with a low-maintenance autonomous Doppler lidar has the potential to enable continuous long-term high-resolution ship-based wind profile measurements over the oceans.

  • 4.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Birmili, W.
    Nowak, A.
    Wehner, B.
    Wiedensohler, A.
    Takegawa, N.
    Kondo, Y.
    Miyazaki, Y.
    Hu, M.
    Zhu, T.
    Hygroscopic growth of tropospheric particle number size distributions over the North China Plain2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, D00G07- p.Article in journal (Refereed)
    Abstract [en]

    The hygroscopic growth of atmospheric submicrometer particle size distributions (diameter D-p ranging from 22 to 900 nm) was studied at a rural/suburban site in the North China Plain within the framework of the international Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) research project. The goal was to characterize the regional aerosol in the polluted northeastern plain in China. Size descriptive hygroscopic growth factors (DHGFs) were determined as a function of relative humidity (RH) by relating the particle number size distribution at a dry condition ( 100 nm), the DHGF are substantially higher than in the Aitken particle mode (D-p < 100 nm) as a result of different chemical composition. The size-dependent behavior of the DHGF highlights the relevance of particulate sulfate production over the North China Plain, accomplished by secondary formation from the gas phase and, potentially, liquid phase processes in convective clouds. Furthermore, all results concerning the DHGF show a significant dependency on meteorological air masses. The hygroscopic growth of accumulation mode particles correlates significantly with the PM1-mass fraction of sulfate ions determined by chemical analysis. Finally, this investigation provides a parameterization of the hygroscopic growth of 250-nm particles, which might be useful when predicting visibility and radiative forcing and performing atmospheric aerosol model validations.

  • 5.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Karlsson Andersson, M.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Khosrawi, Farahnaz
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    On the linkage between tropospheric and Polar Stratospheric clouds in the Arctic as observed by space-borne lidar2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 8, 3791-3798 p.Article in journal (Refereed)
    Abstract [en]

    The type of Polar stratospheric clouds (PSCs) as well as their temporal and spatial extent are important for the occurrence of heterogeneous reactions in the polar stratosphere. The formation of PSCs depends strongly on temperature. However, the mechanisms of the formation of solid PSCs are still poorly understood. Recent satellite studies of Antarctic PSCs have shown that their formation can be associated with deep-tropospheric clouds which have the ability to cool the lower stratosphere radiatively and/or adiabatically. In the present study, lidar measurements aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite were used to investigate whether the formation of Arctic PSCs can be associated with deep-tropospheric clouds as well. Deep-tropospheric cloud systems have a vertical extent of more than 6.5 km with a cloud top height above 7 km altitude. PSCs observed by CALIPSO during the Arctic winter 2007/2008 were classified according to their type (STS, NAT, or ice) and to the kind of underlying tropospheric clouds. Our analysis reveals that 172 out of 211 observed PSCs occurred in connection with tropospheric clouds. 72% of these 172 observed PSCs occurred above deep-tropospheric clouds. We also find that the type of PSC seems to be connected to the characteristics of the underlying tropospheric cloud system. During the Arctic winter 2007/2008 PSCs consisting of ice were mainly observed in connection with deep-tropospheric cloud systems while no ice PSC was detected above cirrus. Furthermore, we find no correlation between the occurrence of PSCs and the top temperature of tropospheric clouds. Thus, our findings suggest that Arctic PSC formation is connected to adiabatice cooling, i.e. dynamic effects rather than radiative cooling.

  • 6.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Khaplanov, Mikhail
    Stockholm University, Faculty of Science, Department of Meteorology .
    Khosrawi, Farahnaz
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Pure rotational-Raman channels of the Esrange lidar for temperature and particle extinction measurements in the troposphere and lower stratosphere2013In: Atmospheric Measurement Techniques, ISSN 1867-8548, Vol. 6, no 1, 91-98 p.Article in journal (Refereed)
    Abstract [en]

    The Department of Meteorology at Stockholm University operates the Esrange Rayleigh/Raman lidar at Esrange(68° N, 21° E) near the Swedish city of Kiruna. This paper describes the design and first measurements of the newpure rotational-Raman channel of the Esrange lidar. The Esrange lidar uses a pulsed Nd:YAG solid-state laser operating at 532 nm as light source with a repetition rate of 20 Hz and a pulse energy of 350 mJ. The minimum vertical resolution is 150m and the integration time for one profile is 5000 shots. The newly implemented channel allows for measurements of atmospheric temperature at altitudes below 35 km and is currently optimized for temperature measurements between 180 and 200 K. This corresponds to conditions in the lower Arctic stratosphere during winter. In addition to the temperature measurements, the aerosol extinction coefficientand the aerosol backscatter coefficient at 532 nm can be measured in dependently. Our filter-based design minimizes the systematic error in the obtained temperature profile to less than 0.51 K. By combining rotational-Raman measurements (5–35 km height) and the integration technique (30–80 kmheight), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the upper troposphere up to the mesosphere. With the improved setup, the system can be used to validate current lidar-based polar stratospheric cloud classification schemes. The new capability of the instrument measuring temperature and aerosol extinction furthermore enables studies of the thermal structure and variability of the upper troposphere/lower stratosphere. Although several lidars are operated at polar latitudes, there are few instruments that are capable of measuring temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratospherewith daylight capability.

  • 7.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Khosrawi, Farahnaz
    Stockholm University, Faculty of Science, Department of Meteorology .
    Blum, U.
    Fricke, K. H.
    Investigation of polar stratospheric clouds in January 2008 by means of ground-based and spaceborne lidar measurements and microphysical box model simulations2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, D07201- p.Article in journal (Refereed)
    Abstract [en]

    Polar stratospheric clouds (PSCs) play a key role in heterogeneous chemistry and ozone depletion in the lower stratosphere. The type of PSC as well as their temporal and spatial extent are important for the occurrence of heterogeneous reactions and, thus, ozone depletion. In this study a combination of ground-based and spaceborne lidar measurements were used together with microphysical box model simulations along back trajectories to investigate the formation and alteration of Arctic PSCs. The measurements were made by the Rayleigh/Mie/Raman lidar system at Esrange and by the Cloud-Aerosol Lidar with Orthogonal Polarization aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Between 20 and 23 January 2008 PSCs composed of liquid particles were observed by CALIPSO between Greenland and the western side of the Scandinavian Mountains. Between 21 and 23 January 2008 the Esrange lidar observed a PSC composed of distinct layers of liquid and solid particles on the eastern side of the mountain range. Microphysical box model simulations along air parcel back trajectories indicate that liquid particles had formed at least 40 h before the observation at Esrange. Furthermore, the model indicates a high HNO(3) uptake into the liquid layer between 10 and 20 h before the observation. The PSC was formed when the air mass was over Greenland. On two occasions during these 20 h, CALIPSO observed PSCs when its measurement tracks crossed the air parcel back trajectory ending at the location of the Esrange lidar. Backscatter ratios calculated from the output of the box model simulation indicate good agreement with the values observed with the Esrange lidar and by CALIPSO. The box model simulations along the back trajectories from Esrange to the CALIPSO ground track and beyond provide us with the unique opportunity to relate ground-based and spaceborne lidar measurements that were not performed at the same spatial location and time. Furthermore, possible differences in the observations from ground and space can be traced to temporal and/or geographically induced changes in particle microphysics within the measured PSCs.

  • 8.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tesche, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Assessing lidar-based classification schemes for polar stratospheric clouds based on 16 years of measurements at Esrange, Sweden2014In: Journal of Geophysical Research: Atmospheres, ISSN 2169-8996, Vol. 119, no 3, 1386-1405 p.Article in journal (Refereed)
    Abstract [en]

    Lidar measurements of polar stratospheric clouds (PSCs) are commonly analyzed in classification schemes that apply the backscatter ratio and the particle depolarization ratio. This similarity of input data suggests comparable results of different classification schemes—despite measurements being performed with a variety of mostly custom-made instruments. Based on a time series of 16 years of lidar measurements at Esrange (68°N, 21°E), Sweden, we show that PSC classification differs substantially depending on the applied scheme. The discrepancies result from varying threshold values of lidar-derived parameters used to define certain PSC types. The resulting inconsistencies could impact the understanding of long-term PSC observations documented in the literature. We identify two out of seven considered classification schemes that are most likely to give reliable results and should be used in future lidar-based studies. Using polarized backscatter ratios gives the advantage of increased contrast for observations of weakly backscattering and weakly depolarizing particles. Improved confidence in PSC classification can be achieved by a more comprehensive consideration of the effect of measurement uncertainties. The particle depolarization ratio is the key to a reliable identification of different PSC types. Hence, detailed information on the calibration of the polarization-sensitive measurement channels should be provided to assess the findings of a study. Presently, most PSC measurements with lidar are performed at 532 nm only. The information from additional polarization-sensitive measurements in the near infrared could lead to an improved PSC classification. Coincident lidar-based temperature measurements at PSC level might provide useful information for an assessment of PSC classification.

  • 9.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Anthropogenic influence on climate through changes in aerosol emissions from air pollution and land use change2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Particulate matter suspended in air (i.e. aerosol particles) exerts a substantial influence on the climate of our planet and is responsible for causing severe public health problems in many regions across the globe. Human activities have altered the natural and anthropogenic emissions of aerosol particles through direct emissions or indirectly by modifying natural sources. The climate effects of the latter have been largely overlooked. Humans have dramatically altered the land surface of the planet causing changes in natural aerosol emissions from vegetated areas. Regulation on anthropogenic and natural aerosol emissions have the potential to affect the climate on regional to global scales. Furthermore, the regional climate effects of aerosol particles could potentially be very different than the ones caused by other climate forcers (e.g. well mixed greenhouse gases). The main objective of this work was to investigate the climatic effects of land use and air pollution via aerosol changes.

    Using numerical model simulations it was found that land use changes in the past millennium have likely caused a positive radiative forcing via aerosol climate interactions. The forcing is an order of magnitude smaller and has an opposite sign than the radiative forcing caused by direct aerosol emissions changes from other human activities. The results also indicate that future reductions of fossil fuel aerosols via air quality regulations may lead to an additional warming of the planet by mid-21st century and could also cause an important Arctic amplification of the warming. In addition, the mean position of the intertropical convergence zone and the Asian monsoon appear to be sensitive to aerosol emission reductions from air quality regulations. For these reasons, climate mitigation policies should take into consideration aerosol air pollution, which has not received sufficient attention in the past.

  • 10.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Historical anthropogenic radiative forcing of changes in biogenic secondary organic aerosol2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Human activities have lead to changes in the energy balance of the Earth and the global climate. Changes in atmospheric aerosols are the second largest contributor to climate change after greenhouse gases since 1750 A.D. Land-use practices and other environmental drivers have caused changes in the emission of biogenic volatile organic compounds (BVOCs) and secondary organic aerosol (SOA) well before 1750 A.D, possibly causing climate effects through aerosol-radiation and aerosol-cloud interactions. Two numerical emission models LPJ-GUESS and MEGAN were used to quantify the changes in aerosol forming BVOC emissions in the past millennium. A chemical transport model of the atmosphere (GEOS-Chem-TOMAS) was driven with those BVOC emissions to quantify the effects on radiation caused by millennial changes in SOA.

    The specific objectives of this licentiate thesis are: 1) to understand what drove the changes in aerosol-forming BVOC emissions (i.e. isoprene, monoterpenes and sesquiterpenes) and to quantify these changes; 2) to calculate for the first time the combined historical aerosol direct and aerosol-cloud albedo effects on radiation from changing BVOC emissions through SOA formation; 3) to investigate how important the biological climate feedback associated to BVOC emissions and SOA formation is from a global climate perspective.

    We find that global isoprene emissions decreased after 1800 A.D. by about 12% - 15%. This decrease was dominated by losses of natural vegetation, whereas monoterpene and sesquiterpene emissions increased by about 2% - 10%, driven mostly by rising surface air temperatures. From 1000 A.D. to 1800 A.D, isoprene, monoterpene and sesquiterpene emissions decline by 3% - 8% driven by both, natural vegetation losses, and the moderate global cooling between the medieval climate anomaly and the little ice age. The millennial reduction in BVOC emissions lead to a 0.5% to 2% reduction in climatically relevant aerosol particles (> 80 nm) and cause a direct radiative forcing between +0.02 W/m² and +0.07 W/m², and an indirect radiative forcing between -0.02 W/m² and +0.02 W/m². The suggested biological climate feedback seems to be too small to have observable consequences on the global climate in the recent past.

  • 11.
    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.

  • 12. Agarwal, Sahil
    et al.
    Wettlaufer, John S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Yale University, United States; University of Oxford, United Kingdom.
    The Statistical Properties of Sea Ice Velocity Fields2017In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 30, no 13, 4873-4881 p.Article in journal (Refereed)
    Abstract [en]

    By arguing that the surface pressure field over the Arctic Ocean can be treated as an isotropic, stationary, homogeneous, Gaussian random field, Thorndike estimated a number of covariance functions from two years of data (1979 and 1980). Given the active interest in changes of general circulation quantities and indices in the polar regions during the recent few decades, the spatial correlations in sea ice velocity fields are of particular interest. It is thus natural to ask, "How persistent are these correlations?'' To this end, a multifractal stochastic treatment is developed to analyze observed Arctic sea ice velocity fields from satellites and buoys for the period 1978-2015. Since it was previously found that the Arctic equivalent ice extent (EIE) has a white noise structure on annual to biannual time scales, the connection between EIE and ice motion is assessed. The long-term stationarity of the spatial correlation structure of the velocity fields and the robustness of their white noise structure on multiple time scales is demonstrated; these factors (i) combine to explain the white noise characteristics of the EIE on annual to biannual time scales and (ii) explain why the fluctuations in the ice velocity are proportional to fluctuations in the geostrophic winds on time scales of days to months. Moreover, it is shown that the statistical structure of these two quantities is commensurate from days to years, which may be related to the increasing prevalence of free drift in the ice pack.

  • 13.
    Ahlm, L.
    et al.
    Stockholm University.
    Krejci, R.
    Stockholm University.
    Nilsson, E. D.
    Stockholm University.
    Martensson, E. M.
    Stockholm University.
    Vogt, M.
    Stockholm University.
    Artaxo, P.
    Emission and dry deposition of accumulation mode particles in the Amazon Basin2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 21, 10237-10253 p.Article in journal (Refereed)
    Abstract [en]

    Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25-2.5 mu m were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25-0.45 mu m in diameter, were in general dominated by deposition in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. Transfer velocities within this particle size range were observed to increase linearly with increasing friction velocity and increasing particle diameter. In the diameter range 0.5-2.5 mu m, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net upward fluxes were observed. However, in wind sectors associated with higher anthropogenic influence, deposition fluxes dominated. The net upward fluxes were interpreted as a result of primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The net emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and were best correlated with horizontal wind speed according to the equation log(10)F = 0.48.U + 2.21 where F is the net emission number flux of 0.5-2.5 mu m particles [m(-2) s(-1)] and U is the horizontal wind speed [ms(-1)] at the top of the tower.

  • 14.
    Ahlm, L.
    et al.
    Stockholm University.
    Nilsson, E. D.
    Stockholm University.
    Krejci, R.
    Stockholm University.
    Martensson, E. M.
    Stockholm University.
    Vogt, M.
    Stockholm University.
    Artaxo, P.
    A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 6, 3063-3079 p.Article in journal (Refereed)
    Abstract [en]

    Vertical number fluxes of aerosol particles and vertical fluxes of CO(2) were measured with the eddy covariance method at the top of a 53 m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO(2) fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO(2), and being released from the canopy when conditions become more turbulent in the morning.

  • 15.
    Ahlm, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Julin, Jan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fountoukis, C.
    Pandis, S. N.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Particle number concentrations over Europe in 2030: the role of emissions and new particle formation2013In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, E-ISSN 1680-7375, Vol. 13, no 20, 10271-10283 p.Article in journal (Refereed)
    Abstract [en]

    The aerosol particle number concentration is a key parameter when estimating impacts of aerosol particles on climate and human health. We use a three-dimensional chemical transport model with detailed microphysics, PMCAMx-UF, to simulate particle number concentrations over Europe in the year 2030, by applying emission scenarios for trace gases and primary aerosols. The scenarios are based on expected changes in anthropogenic emissions of sulfur dioxide, ammonia, nitrogen oxides, and primary aerosol particles with a diameter less than 2.5 mu m (PM2.5) focusing on a photochemically active period, and the implications for other seasons are discussed. For the baseline scenario, which represents a best estimate of the evolution of anthropogenic emissions in Europe, PMCAMx-UF predicts that the total particle number concentration (N-tot) will decrease by 30-70% between 2008 and 2030. The number concentration of particles larger than 100 nm (N-100), a proxy for cloud condensation nuclei (CCN) concentration, is predicted to decrease by 40-70% during the same period. The predicted decrease in N-tot is mainly a result of reduced new particle formation due to the expected reduction in SO2 emissions, whereas the predicted decrease in N-100 is a result of both decreasing condensational growth and reduced primary aerosol emissions. For larger emission reductions, PMCAMx-UF predicts reductions of 60-80% in both N-tot and N-100 over Europe. Sensitivity tests reveal that a reduction in SO2 emissions is far more efficient than any other emission reduction investigated, in reducing N-tot. For N-100, emission reductions of both SO2 and PM2.5 contribute significantly to the reduced concentration, even though SO2 plays the dominant role once more. The impact of SO2 for both new particle formation and growth over Europe may be expected to be somewhat higher during the simulated period with high photochemical activity than during times of the year with less incoming solar radiation. The predicted reductions in both N-tot and N-100 between 2008 and 2030 in this study will likely reduce both the aerosol direct and indirect effects, and limit the damaging effects of aerosol particles on human health in Europe

  • 16. Ahmad, M R
    et al.
    Esa, M R M
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Measurement of bit error rate at 2,4 GHz due to lightning interference2012In: Proceeding of the 31st International Conference on Lightning Protection ICLP 2012, 2012Conference paper (Refereed)
    Abstract [en]

    This paper analyzes the interference of lightning flashes with wireless communication systems operating in the microwave band at 2.4 GHz. A bit error rate (BER) measurement method was used to evaluate BER during 3 heavy thunderstorms on January 25, March 17 and March 20, all in year 2011. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW) conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-of-sight (LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higher recorded BER. The maximum recorded BER was 9.9·101 and the average recorded BER was 9.95·10 -3 during the thunderstorms with the average fair weather BER values under the influence of adjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10 -6 respectively. We conclude that wireless communication systems operating at 2.4 GHz microwave frequency can be significantly interfered by lightning.

  • 17.
    Ahmad, Mohd Riduan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universiti Teknikal Malaysia Melaka.
    Interaction of Lightning Flashes with Wireless Communication Networks: Special Attention to Narrow Bipolar Pulses2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, the features of electric field signatures of narrow bipolar pulses (NBPs) generated by cloud flashes are investigated and their effects on wireless communication systems are studied. A handful amount of NBPs (14.5%) have been observed to occur as part of cloud-to-ground flashes in South Malaysia. Occurrence of NBPs in Sweden has been reported for the first time in this thesis. The electric field waveform characteristics of NBPs as part of cloud-to-ground flashes were similar to isolated NBPs found in Sweden and South Malaysia and also to those isolated NBPs reported by previous studies from various geographical areas. This is a strong indication that their breakdown mechanisms are similar at any latitudes regardless of geographical areas.

    A comparative study on the occurrence of NBPs and other forms of lightning flashes across various geographical areas ranging from northern regions to the tropics is presented. As the latitude decreased from Uppsala, Sweden (59.8°N) to South Malaysia (1.5°N), the percentage of NBP emissions relative to the total number of lightning flashes increased significantly from 0.13% to 12%. Occurrences of positive NBPs were more common than negative NBPs at all observed latitudes. However, as latitudes decreased, the negative NBP emissions increased significantly from 20% (Sweden) to 45% (South Malaysia). Factors involving mixed-phase region elevations and vertical extents of thundercloud tops are invoked to explain the observed results. These factors are fundamentally latitude dependent.

    In this thesis, the interaction between microwave radiations emitted by cloud-to-ground and cloud flashes events and bits transmission in wireless communication networks are also presented. To the best of our knowledge, this is the first time such effects are investigated in the literature. Narrow bipolar pulses were found to be the strongest source of interference that interfered with the bits transmission.

  • 18.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Esa, Mona Riza Binti Mohd
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dutkiewicz, E.
    Wireless Communications and Networking Lab, Macquarie University, Sydney, Australien.
    Lightning interference in multiple antennas wireless communication systems2012In: Journal of Lightning Research, ISSN 1652-8034, Vol. 4, 155-165 p.Article in journal (Refereed)
    Abstract [en]

    This paper analyzes the interference of lightning flashes with multiple antennas wireless communicationsystems operating in the microwave band at 2.4 GHz and 5.2 GHz. A bit error rate (BER) measurement method was usedto evaluate BER and packet error rate (PER) during 5 heavy thunderstorms on January 25 and March 17 to 20, 2011,respectively. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW)conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-ofsight(LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higherrecorded BER. The maximum recorded BER was 9.9·10-1 and the average recorded BER and PER were 2.07·10-2 and2.44·10-2 respectively during the thunderstorms with the average fair weather BER and PER values under the influence ofadjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10-6 respectively. Weconclude that multiple antennas wireless communication systems operating at the microwave frequency can besignificantly interfered by lightning.

  • 19.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Occurrence of Narrow Bipolar Event as Part of Cloud-to-Ground Flash in Tropical Thunderstorms2014Conference paper (Refereed)
  • 20.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, 810-813 p.Conference paper (Refereed)
    Abstract [en]

    In this paper, temporal characteristics of several initial electric field pulses of preliminary breakdown process (PBP) from very close negative cloud-to-ground (CG) flashes are compared to close narrow bipolar pulses (NBPs) to observe any similarity that may exists. Interestingly, we found that the initial PBP pulses are similar to close NBP with zero crossing time less than 5 mu s, do not preceded by any slow field change and followed by pronounce static component. As NBPs are believed to be a result of relativistic runaway electron avalanches discharge, this finding is an indication that the initial electric field pulses of PBP are perhaps the result of the same discharge mechanism.

  • 21.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri Abadi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universiti Teknikal Malaysia Melaka.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Latitude Dependence of Narrow Bipolar Pulse Emissions2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, Vol. 128, 40-45 p.Article in journal (Refereed)
  • 22.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri Abadi
    Universiti Teknikal Malaysia Melaka.
    Electric Field Signature of Narrow Bipolar Pulse Observed in Sweden2014In: Atmospheric research, ISSN 0169-8095Article in journal (Refereed)
  • 23.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Johari, Dalina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ismail, Mohd Muzafar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chaotic Pulse Train in Cloud-to-Ground and Cloud Flashes of Tropical Thunderstorms2014Conference paper (Refereed)
    Abstract [en]

    In this paper, we report for the first time the observation of chaotic pulse train (CPT) preceding natural subsequent negative return strokes and also CPT occurrence in IC flashes from tropical thunderstorms in South Malaysia. In CG flashes, all CPTs were occurred in between return strokes with 41.1% have occurred between the first and second return strokes. The maximum number of CPT in one sequence is 3, which can be observed between the first and third return strokes only. In IC flashes, all CPTs were observed to occur in between IC flash pulses.

  • 24.
    Ahmad, M.R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rashid, M.
    Aziz, M.H.A.
    Esa, M.R.M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dutkiewicz, E.
    Analysis of Lightning-induced Transient in 2.4 GHz Wireless Communication System2011In: Proceeding of IEEE International Conference on Space Science and Communication (IconSpace), Penang, Malaysia, pp225-230, 2011Conference paper (Refereed)
  • 25. Ahmad, Noor Azlinda
    et al.
    Baharudin, Zikri A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Radiation field spectra of long-duration cloud flashes2015In: Atmospheric Science Letters, ISSN 1530-261X, Vol. 16, no 2, 91-95 p.Article in journal (Refereed)
    Abstract [en]

    The preliminary results of radiation electric fields produced by long-duration cloud flashes have been Fourier analyzed to determine the frequency spectrum in the range of 10kHz-10MHz. The flashes were recorded within a distance of less than 20km. The spectrum was normalized to 50km distance and it shows a f(-1) dependence within the entire frequency range.

  • 26.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Baharudin, Z. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saleh, Ziad
    Dwyer, Joseph R.
    Rassoul, Hamid K.
    The first electric field pulse of cloud and cloud-to-ground lightning discharges2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 2-3, 143-150 p.Article in journal (Refereed)
    Abstract [en]

    In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as [`]small', [`]medium' and [`]large', depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.

  • 27.
    Akinde, Michael
    et al.
    SMHI.
    Bohlen, M H
    Johnson, T
    Lakshmanan, L V S
    Srivastava, D
    Efficient OLAP query processing in distributed data warehouses2003In: Information Systems, ISSN 0306-4379, Vol. 28, no 1-2, 111-135 p.Article in journal (Refereed)
    Abstract [en]

    The success of Internet applications has led to an explosive growth in the demand for bandwidth from. Internet Service Providers. Managing an Internet protocol network requires collecting and analyzing network data, such as flow-level traffic statistics. Such analyses can typically be expressed as OLAP queries, e.g., correlated aggregate queries and data cubes. Current day OLAP tools for this task assume the availability of the data in a centralized data warehouse. However, the inherently distributed nature of data collection and the huge amount of data extracted at each collection point make it impractical to gather all data at a centralized site. One solution is to maintain a distributed data warehouse, consisting of local data warehouses at-each collection point and a coordinator site, with most of the processing being performed at the local sites. In this paper, we consider the problem of efficient evaluation of OLAP queries over a distributed data warehouse. We have developed the Skalla system for this task. Skalla translates OLAP queries, specified as certain algebraic expressions, into distributed evaluation plans which are shipped to individual sites. A salient property of our approach is that only partial results are shipped - never parts of the detail data. We propose a variety of optimizations to minimize both the synchronization traffic and the local processing done at each site. We finally present an experimental study based on TPC-R data. Our results demonstrate the scalability of our techniques and quantify the performance benefits of the optimization techniques that have gone into the Skalla system. (C) 2002 Elsevier Science Ltd. All rights reserved.

  • 28.
    Akyuz, Mose
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Larsson, Anders
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Franke, Axel
    Characteristics of Laser-triggered Electric Discharges in Air2005In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 12, no 5, 1060-1070 p.Article in journal (Refereed)
  • 29. Alberoni, P P
    et al.
    Andersson, T
    SMHI.
    Mezzasalma, P
    Michelson, Daniel
    SMHI, Core Services.
    Nanni, S
    Use of the vertical reflectivity profile for identification of anomalous propagation2001In: Meteorological Applications, ISSN 1350-4827, E-ISSN 1469-8080, Vol. 8, no 3, 257-266 p.Article in journal (Refereed)
    Abstract [en]

    Anomalous propagation (anaprop), analogous to the upper mirage in the visual wavelengths, is still a major problem in radar meteorology. This phenomenon assumes particular importance in automatic recognition and estimation of rainfall. Anaprop echoes from terrain features such as hills and coasts Often give echoes up to 50-60 dBZ equivalent to heavy rain or hail in severe thunderstorms. Anaprop echoes from sea waves may be comparable in strength to those from moderate precipitation and also form similar patterns. Based on the evidence that the vertical reflectivity profile of precipitation is quite different from the anaprop profile, two methods for anaprop identification are presented. The method proposed by the Servizio Meteorologico Regionale (SMR, Italy) simply uses the operational scan procedure to discriminate between precipitation and anaprop. At the Swedish Meteorological and Hydrological Institute an 'ad hoc' scan strategy has been developed in order to obtain much more detail of the lowest reflectivity profile. A number of statistical parameters have been used to achieve a better discrimination between precipitation, land and sea clutter. A number of case studies, representing different echo intensities and patterns, and including a case of anaprop with embedded precipitation, are presented to assess the impact of these methods.

  • 30.
    Alexandersson, Hans
    SMHI.
    Temperatur och nederbörd i Sverige 1860 -20012002Report (Other academic)
    Abstract [en]

    Swedish temperature and precipitation series from 1860-2001 are analysed  in this report. Sweden  is divided into four regions. These are defined according to the drainage basins: Gulf of Bothnia (Bv), Bothnian Sea (Bh), Proper Baltic Sea (EÖ) and Kattegatt and Skagerrak (Vh). Annual series of  temperature and precipitation as well as series for the traditional  seasons  winter (December  previous year, January, February), spring (March, April, May), summer (June, July, August) and autumn (Sep­ tember, October, November) are presented. All series have been homgenised and all missing values for incomplete series have been filled out by    interpolation.

     

    Generally the analyses show that Sweden has become warmer  and wetter  in this centennial  perspective.  As a rule changes and trends are larger in the two northerly regions (Bv and Bh). The increase of annual temperature amounts to 0.9° (Bv), 0.8° (Bh), 0.5° (EÖ) and 0.5° (Vh) when data from the colder period 1860-1925 is compared with the warmer period 1926-2001. Annual precipitation <luring the drier period 1860-1920  is compared  with the wetter  period  1921-2001. The  relative changes  are 23% (Bv), 15% (Bh), 7% (EÖ) and 7% (Vh). Spring temperature  and winter precipitation  show especially !arge    mcreases.

     

    Comparisons with runoff data indicate that evapotranspiration has become much larger. It is argued that the substantial increase of forest biomass could be one explanation and higher temperatures could be another. The increase of forest biomass leads to larger interception and then larger evaporation and as a rule also larger transpiration. The warming in spring and autumn leads to a longer active season for the vegetation.

  • 31. Allen, G.
    et al.
    Coe, H.
    Clarke, A.
    Bretherton, C.
    Wood, R.
    Abel, S. J.
    Barrett, P.
    Brown, P.
    George, R.
    Freitag, S.
    McNaughton, C.
    Howell, S.
    Shank, L.
    Kapustin, V.
    Brekhovskikh, V.
    Kleinman, L.
    Lee, Y-N
    Springston, S.
    Toniazzo, T.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fochesatto, J.
    Shaw, G.
    Krecl, P.
    Brooks, B.
    McMeeking, G.
    Bower, K. N.
    Williams, P. I.
    Crosier, J.
    Crawford, I.
    Connolly, P.
    Allan, J. D.
    Covert, D.
    Bandy, A. R.
    Russell, L. M.
    Trembath, J.
    Bart, M.
    McQuaid, J. B.
    Wang, J.
    Chand, D.
    South East Pacific atmospheric composition and variability sampled = ong 20 degrees S during VOCALS-REx2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, Vol. 11, no 11, 5237-5262 p.Article in journal (Refereed)
    Abstract [en]

    The VAMOS Ocean-Cloud-Atmosphere-Land Regional Experiment (VOCALS-REx) was conducted from 15 October to 15 November 2008 in the South East Pacific (SEP) region to investigate interactions between land, sea and atmosphere in this unique tropical eastern ocean environment and to improve the skill of global and regional models in = presenting the region. This study synthesises selected aircraft, ship = d surface site observations from VOCALS-REx to statistically summarise = d characterise the atmospheric composition and variability of the = rine Boundary Layer (MBL) and Free Troposphere (FT) along the 20 = grees S parallel between 70 degrees W and 85 degrees W. Significant = nal gradients in mean MBL sub-micron aerosol particle size and = mposition, carbon monoxide, sulphur dioxide and ozone were seen over = e campaign, with a generally more variable and polluted coastal = vironment and a less variable, more pristine remote maritime regime. = adients in aerosol and trace gas concentrations were observed to be = sociated with strong gradients in cloud droplet number. The FT was = ten more polluted in terms of trace gases than the MBL in the mean; = wever increased variability in the FT composition suggests an episodic = ture to elevated concentrations. This is consistent with a complex = rtical interleaving of airmasses with diverse sources and hence = llutant concentrations as seen by generalised back trajectory = alysis, which suggests contributions from both local and long-range = urces. Furthermore, back trajectory analysis demonstrates that the = served zonal gradients both in the boundary layer and the free = oposphere are characteristic of marked changes in airmass history with = stance offshore - coastal boundary layer airmasses having been in = cent contact with the local land surface and remote maritime airmasses = ving resided over ocean for in excess of ten days. Boundary layer = mposition to the east of 75 degrees W was observed to be dominated by = astal emissions from sources to the west of the Andes, with evidence = r diurnal pumping of the Andean boundary layer above the height of the = rine capping inversion. Analysis of intra-campaign variability in = mospheric composition was not found to be significantly correlated = th observed low-frequency variability in the large scale flow pattern; = mpaign-average interquartile ranges of CO, SO(2) and O(3) = ncentrations at all longitudes were observed to dominate over much = aller differences in median concentrations calculated between periods = different flow regimes. The campaign climatology presented here aims = provide a valuable dataset to inform model simulation and future = ocess studies, particularly in the context of aerosol-cloud = teraction and further evaluation of dynamical processes in the SEP = gion for conditions analogous to those during VOCALS-REx. To this end, = r results are discussed in terms of coastal, transitional and remote = atial regimes in the MBL and FT and a gridded dataset are provided as = resource.

  • 32. Almeida, Joao
    et al.
    Schobesberger, Siegfried
    Kuerten, Andreas
    Ortega, Ismael K.
    Kupiainen-Maatta, Oona
    Praplan, Arnaud P.
    Adamov, Alexey
    Amorim, Antonio
    Bianchi, Federico
    Breitenlechner, Martin
    David, Andre
    Dommen, Josef
    Donahue, Neil M.
    Downard, Andrew
    Dunne, Eimear
    Duplissy, Jonathan
    Ehrhart, Sebastian
    Flagan, Richard C.
    Franchin, Alessandro
    Guida, Roberto
    Hakala, Jani
    Hansel, Armin
    Heinritzi, Martin
    Henschel, Henning
    Jokinen, Tuija
    Junninen, Heikki
    Kajos, Maija
    Kangasluoma, Juha
    Keskinen, Helmi
    Kupc, Agnieszka
    Kurten, Theo
    Kvashin, Alexander N.
    Laaksonen, Ari
    Lehtipalo, Katrianne
    Leiminger, Markus
    Leppa, Johannes
    Loukonen, Ville
    Makhmutov, Vladimir
    Mathot, Serge
    McGrath, Matthew J.
    Nieminen, Tuomo
    Olenius, Tinja
    Onnela, Antti
    Petaja, Tuukka
    Riccobono, Francesco
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rissanen, Matti
    Rondo, Linda
    Ruuskanen, Taina
    Santos, Filipe D.
    Sarnela, Nina
    Schallhart, Simon
    Schnitzhofer, Ralf
    Seinfeld, John H.
    Simon, Mario
    Sipila, Mikko
    Stozhkov, Yuri
    Stratmann, Frank
    Tome, Antonio
    Troestl, Jasmin
    Tsagkogeorgas, Georgios
    Vaattovaara, Petri
    Viisanen, Yrjo
    Virtanen, Annele
    Vrtala, Aron
    Wagner, Paul E.
    Weingartner, Ernest
    Wex, Heike
    Williamson, Christina
    Wimmer, Daniela
    Ye, Penglin
    Yli-Juuti, Taina
    Carslaw, Kenneth S.
    Kulmala, Markku
    Curtius, Joachim
    Baltensperger, Urs
    Worsnop, Douglas R.
    Vehkamaki, Hanna
    Kirkby, Jasper
    Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere2013In: Nature, ISSN 0028-0836, Vol. 502, no 7471, 359-+ p.Article in journal (Refereed)
    Abstract [en]

    Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei(1). Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes(2). Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases(2). However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere(3). It is thought that amines may enhance nucleation(4-16), but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.

  • 33.
    Andersson, Ambjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Utvärdering av svavel- och kvävedepositioner från sjöfart: en modellstudie2010Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The shipping sector is a significant source of sulfur- and nitrogen-emissions. Depositions of oxidized sulfur and nitrogen i.e. sulfate and nitrate, in the form of wet and dry deposition contribute to acidification and deterioration of air quality. Political instruments to reduce sulfur emissions during the last years have contributed to the reduction of sulfur emissions, i.e. new instruments have been implemented in form of restrictions in sulfur content in ships fuel.

    The shipping sector’s emissions of sulfur and nitrogen have been studied by using “the Unified EMEP Model”, a chemical atmospheric transport model, with data collected during the year 2005. The deposition of sulfur and nitrogen from shipping in different countries has been compared to the total deposition from all sources in Europe. Deposition of sulfur and nitrogen in the Baltic Sea and the countries in the in the draining basin from individual sea has also been studied.

    The results have shown that deposition of sulfur and nitrogen is intense near the source. But it also spread far away from the source, however with decreasing concentrations in relation with distance to the source. Depositions in the north of Europe from shipping are highest near big ports and   Clear tracks from shipping in the depositions field are obtained near big ports and also in the Atlantic and the Mediterranean Sea. Countries with longer coastline have higher concentrations than those with less or none sea traffic in the near region.

    To study how roughness length over sea impacts the spread of sulfur the Charnock-parameter has been varied from 0,00072 to 0,085. The study doesn’t provide any clear findings of influence of the parameter in spread of sulfur. A theory to this result is the low resolution in the model. It is probably too small differences in the depositions field due to the roughness length.

    Monthly variations of sulfur and nitrogen deposits in the Baltic Sea have been made in order to study how variations in such precipitation affect the distribution of sulfur and nitrogen.

     

  • 34.
    Andersson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Air-sea exchange of O2 and CO2: Processes controlling the transfer efficiency2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    World oceans cover more than 70% of the earth surface and constitutes a major sink of atmospheric CO2. Two of the most important gases in the marine carbon cycling are O2 and CO2 and hence accurate descriptions of the air-sea gas exchange of these gases are crucial. Still there is a lack of knowledge of the relative importance of processes controlling the efficiency of the air-sea gas transfer. This is especially true for Arctic and high latitude seas were studies on air-sea gas exchange are few. By studying processes causing water-side turbulence, using gases of different solubility and various measurement techniques, more knowledge on the governing processes can be obtained.

    Here we present the very first air-sea fluxes of O2 using atmospheric eddy covariance measurements and investigate the dependence between the gas transfer velocity of O2 and turbulence generated by the mean wind. The instrument was found to suffer from the limited precision and time response, causing significant corrections on the O2 flux. After correcting for this, the O2 fluxes displays an anti-correlation with the air-sea fluxes of CO2 in agreement with the measured air-sea gradient of O2. The transfer velocities for O2 indicates a stronger wind dependence than other commonly used parameterizations of the transfer velocity for CO2 and O2, this especially for wind speeds > 5 m s-1 where the typical onset of wave breaking occur.

    During two winter months eddy covariance measurements were taken over a high Arctic fjord. The data revealed a significant enhancement of the gas transfer velocity for CO2 from water-side convection, generated by cooling of surface waters. The dependence between water-side convection and gas transfer velocity were found for winds as high as 9 m s-1, but were strongest for wind speeds< 7  m s-1.  The data also showed on enhanced air-sea gas transfer of CO2 when conditions were unstable very close to neutral. This enhanced transfer were associated to increased contribution to the CO2 flux from downdraft of air with higher concentrations of CO2.  The combined effect of water-side convection and turbulence generated by wind results in a very effective transfer, thus the air-sea gas exchange at these latitudes may be significantly underestimated.

  • 35.
    Andersson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    En statistisk kartläggning av dimma för Arlanda flygplats2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Since the beginning of weather forecasting fog has caused many meteorologists severe problems, and in aviation it has been one of the main reasons for several crashes. Even today with the latest numerical models, predicting fog is a difficult task. New studies have shown that to predict fog the model must be able to resolve inversion layers down to 10 m. Even then the precision in determination of the visibility inside the fog is down to 50 % (Gultepe, 2007). In those cases a statistical mapping of fog at a certain place could be a good complement to the numerical models in determining time of formation and visibility. In this study I have used METAR observations made at Arlanda airport from 1993-07-01 to 2009-11-03, which are made every half an hour. In the mapping Radiation fog, Advection fog, Precipitation fog and fog caused by lowering of clouds (cbl. fog) was sorted out. I also looked into the behavior of ice fog vs. water fog.The results showed that radiation fog was the most common fog type (43,6 %) and had the lowest rate of visibility followed by cbl. fog. Radiation fog also had its highest frequency on summer and autumn, while advection fog and precipitation fog was concentrated into wintertime. Additionally the study showed that the frequency of the times when radiation fog covers the whole airport started to decrease at the beginning of the 21st century. Coinciding with when the expansion of the airport was finished including a new runway. In the comparison between water fog and ice fog it was clear that the distribution of visibility was similar. The lowest visibilities in water fog was found at the highest temperatures and highest specific liquid water content while in ice fog the lowest visibilities where found for temperatures in the neighborhood of - 20 °C. For temperatures below - 20 °C there were no observations of fog.

  • 36.
    Andersson, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sahlee, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Using eddy covariance to estimate air-sea gas transfer velocity for oxygen2016In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 159, 67-75 p.Article in journal (Refereed)
    Abstract [en]

    Air-sea gas transfer velocity for O2 is calculated using directly measured fluxes with the eddy covariance technique. It is a direct method and is frequently used to determine fluxes of heat, humidity, and CO2, but has not previously been used to estimate transfer velocities for O2, using atmospheric eddy covariance data. The measured O2 fluxes are upward directed, in agreement with the measured air-sea gradient of the O-2 concentration, and opposite to the direction of the simultaneously measured CO2 fluxes. The transfer velocities estimated from measurements are compared with prominent wind speed parameterizations of the transfer velocity for CO2 and O2, previously established from various measurement techniques. Our result indicates stronger wind speed dependence for the transfer velocity of O2 compared to CO2 starting at intermediate wind speeds. This stronger wind speed dependence appears to coincide with the onset of whitecap formation in the flux footprint and the strong curvature of a cubic wind -dependent function for the transfer velocity provides the best fit to the data. Additional data using the measured O2 flux and an indirect method (based on the Photosynthetic Quotient) to estimate oxygen concentration in water, support the stronger wind dependence for the transfer velocity of O2 O-2 to CO2.

  • 37.
    Andersson, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Sahlée, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Using a High-Frequency Fluorescent Oxygen Probe in Atmospheric Eddy Covariance Applications2014In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 31, no 11, 2498-2511 p.Article in journal (Refereed)
    Abstract [en]

    During the years 2010-13, atmospheric eddy covariance measurement of oxygen was performed at the marine site Ostergarnsholm in the Baltic Sea. The fast response optode Microx TX3 was used with two different types of tapered sensors. In spite of the increased lifetime, the optical isolated sensor is limited by the slower response time and is unsuitable for ground-based eddy covariance measurements. The sensor without optical isolation shows a -2/3 slope within the inertial subrange and attains sufficient response time and precision to be used in air-sea applications during continuous periods of 1-4 days. Spectral and cospectral analysis shows oxygen measured with the nonoptical isolated sensor to follow the same shape as for CO2 and water vapor when normalized. The sampling rate of the Microx TX3 is 2Hz; however, the sensor was found to have a limited response and resolution, yielding a flux loss in the frequency range f > 0.3Hz. This can be corrected for by applying cospectral similarity simultaneously using measurements of latent heat as the reference signal. On average the magnitude of the cospectral correction added 20% to the uncorrected oxygen flux during neutral atmospheric stratification.

  • 38.
    Andersson, August
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sheesley, Rebecca J.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krusa, Martin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Johansson, Christer
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    (14)C-Based source assessment of soot aerosols in Stockholm and the Swedish EMEP-Aspvreten regional background site2011In: Atmospheric Environment, ISSN 1352-2310, Vol. 45, no 1, 215-222 p.Article in journal (Refereed)
    Abstract [en]

    Combustion-derived soot or black carbon (BC) in the atmosphere has a strong influence on both climate and human health. In order to propose effective mitigation strategies for BC emissions it is of importance to investigate geographical distributions and seasonal variations of BC emission sources. Here, a radiocarbon methodology is used to distinguish between fossil fuel and biomass burning sources of soot carbon (SC). SC is isolated for subsequent off-line (14)C quantification with the chemothermal oxidation method at 375 degrees C (CTO-375 method), which reflects a recalcitrant portion of the BC continuum known to minimize inadvertent inclusion of any non-pyrogenic organic matter. Monitored wind directions largely excluded impact from the Stockholm metropolitan region at the EMEP-Aspvreten rural station 70 km to the south-west. Nevertheless, the Stockholm city and the rural stations yielded similar relative source contributions with fraction biomass (f(biomass)) for fall and winter periods in the range of one-third to half. Large temporal variations in (14)C-based source apportionment was noted for both the 6 week fall and the 4 month winter observations. The f(biomass) appeared to be related to the SC concentration suggesting that periods of elevated BC levels may be caused by increased wood fuel combustion. These results for the largest metropolitan area in Scandinavia combine with other recent (14)C-based studies of combustion-derived aerosol fractions to suggest that biofuel combustion is contributing a large portion of the BC load to the northern European atmosphere.

  • 39.
    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.

  • 40.
    Andersson, Camilla
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Langner, Joakim
    Inter-annual variations of ozone and nitrogen dioxide over Europe during 1958-2003 simulated with a regional CTM2007In: Water, Air and Soil Pollution, ISSN 0049-6979, Vol. 7, 15-23 p.Article in journal (Refereed)
    Abstract [en]

    Abstract Inter-annual variability of surface ozone(O3) and nitrogen dioxide (NO2) over Europe hasbeen studied over the period 1958-2003 using athree-dimensional Chemistry-Transport Model coupledto meteorological data from the ERA40 data setproduced at the European Centre of Medium-rangeWeather Forecasts (ECMWF). Emissions and boundaryconditions were kept at present levels throughoutthe simulation period. It was found that the annualmean NO2 concentration varies between ±50% andthe summer mean O3 concentration varies between-10 and +20 percent (%) compared to the 46-yearaverage over the model domain. There is alsovariation in ozone and NO2 over longer time scales.The last 22 years display high concentrations ofozone in central and south-western Europe and lowconcentrations in north-eastern Europe. The first22 years display very high concentrations of NO2over the North Sea. There is indication of trends inozone and nitrogen dioxide but this has to beinvestigated further. Such information is one factorthat should be taken into account when consideringfuture control strategies.

  • 41.
    Andersson, Camilla
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Langner, Joakim
    Bergström, Robert
    Interannual variation and trends in air pollution over Europe due to climate variability during 1958–2001 simulated with a regional CTM coupled to the ERA40 reanalysis2007In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, Vol. 59, 77-98 p.Article in journal (Refereed)
    Abstract [en]

    A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of surface ozone (O3), nitrogen dioxide (NO2) and particulate matter (PM) and its constituents over Europe during 1958–2001. The model was coupled to the meteorological reanalysis ERA40, produced at the European Centre for Medium-range Weather Forecasts. Emissions and boundary conditions of chemical compounds and PM were kept constant at present levels.

    The average European interannual variation, due to meteorological variability, ranges from 3% for O3, 5%for NO2, 9% for PM, 6–9% for dry deposition, to about 20% for wet deposition of sulphur and nitrogen. For the period 1979–2001 the trend in ozone, due to climate variability is increasing in central and southwestern Europe and decreasing in northeastern Europe, the trend in NO2 is approximately opposite. The trend in PM is positive in eastern Europe. There are negative trends in wet deposition in southwestern and central Europe and positive trends in dry deposition overall. A bias in ERA40 precipitation could be partly responsible for the trends. The variation and trends need to be considered when interpreting measurements and designing measurement campaigns.

  • 42.
    Andersson, Camilla
    et al.
    SMHI, Research Department, Air quality.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Bergström, Robert
    SMHI, Research Department, Air quality.
    Interannual variation and trends in air pollution over Europe due to climate variability during 1958-2001 simulated with a regional CTM coupled to the ERA40 reanalysis2007In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 59, no 1, 77-98 p.Article in journal (Refereed)
    Abstract [en]

    A three-dimensional Chemistry Transport Model was used to study the meteorologically induced interannual variability and trends in deposition of sulphur and nitrogen as well as concentrations of surface ozone (O(3)), nitrogen dioxide (NO(2)) and particulate matter (PM) and its constituents over Europe during 1958-2001. The model was coupled to the meteorological reanalysis ERA40, produced at the European Centre for Medium-range Weather Forecasts. Emissions and boundary conditions of chemical compounds and PM were kept constant at present levels. The average European interannual variation, due to meteorological variability, ranges from 3% for O(3), 5% for NO(2), 9% for PM, 6-9% for dry deposition, to about 20% for wet deposition of sulphur and nitrogen. For the period 1979-2001 the trend in ozone, due to climate variability is increasing in central and southwestern Europe and decreasing in northeastern Europe, the trend in NO(2) is approximately opposite. The trend in PM is positive in eastern Europe. There are negative trends in wet deposition in southwestern and central Europe and positive trends in dry deposition overall. A bias in ERA40 precipitation could be partly responsible for the trends. The variation and trends need to be considered when interpreting measurements and designing measurement campaigns.

  • 43. Andersson, E.
    et al.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Methodology for evaluating lateral boundary conditions in the regional chemical transport model MATCH (v5.5.0) using combined satellite and ground-based observations2015In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 8, no 11, 3747-3763 p.Article in journal (Refereed)
    Abstract [en]

    Hemispheric transport of air pollutants can have a significant impact on regional air quality, as well as on the effect of air pollutants on regional climate. An accurate representation of hemispheric transport in regional chemical transport models (CTMs) depends on the specification of the lateral boundary conditions (LBCs). This study focuses on the methodology for evaluating LBCs of two moderately long-lived trace gases, carbon monoxide (CO) and ozone (O-3), for the European model domain and over a 7-year period, 2006-2012. The method is based on combining the use of satellite observations at the lateral boundary with the use of both satellite and in situ ground observations within the model domain. The LBCs are generated by the global European Monitoring and Evaluation Programme Meteorological Synthesizing Centre - West (EMEP MSC-W) model; they are evaluated at the lateral boundaries by comparison with satellite observations of the Terra-MOPITT (Measurements Of Pollution In The Troposphere) sensor (CO) and the Aura-OMI (Ozone Monitoring Instrument) sensor (O-3). The LBCs from the global model lie well within the satellite uncertainties for both CO and O-3. The biases increase below 700 hPa for both species. However, the satellite retrievals below this height are strongly influenced by the a priori data; hence, they are less reliable than at, e.g. 500 hPa. CO is, on average, underestimated by the global model, while O-3 tends to be overestimated during winter, and underestimated during summer. A regional CTM is run with (a) the validated monthly climatological LBCs from the global model; (b) dynamical LBCs from the global model; and (c) constant LBCs based on in situ ground observations near the domain boundary. The results are validated against independent satellite retrievals from the Aqua-AIRS (Atmospheric InfraRed Sounder) sensor at 500 hPa, and against in situ ground observations from the Global Atmospheric Watch (GAW) network. It is found that (i) the use of LBCs from the global model gives reliable in-domain results for O-3 and CO at 500 hPa. Taking AIRS retrievals as a reference, the use of these LBCs substantially improves spatial pattern correlations in the free troposphere as compared to results obtained with fixed LBCs based on ground observations. Also, the magnitude of the bias is reduced by the new LBCs for both trace gases. This demonstrates that the validation methodology based on using satellite observations at the domain boundary is sufficiently robust in the free troposphere. (ii) The impact of the LBCs on ground concentrations is significant only at locations in close proximity to the domain boundary. As the satellite data near the ground mainly reflect the a priori estimate used in the retrieval procedure, they are of little use for evaluating the effect of LBCs on ground concentrations. Rather, the evaluation of ground-level concentrations needs to rely on in situ ground observations. (iii) The improvements of dynamic over climatological LBCs become most apparent when using accumulated ozone over threshold 40 ppb (AOT40) as a metric. Also, when focusing on ground observations taken near the inflow boundary of the model domain, one finds that the use of dynamical LBCs yields a more accurate representation of the seasonal variation, as well as of the variability of the trace gas concentrations on shorter timescales.

  • 44.
    Andersson, Erik
    Stockholm University, Faculty of Science, Department of Meteorology .
    A Variational data assimilation scheme and its use of meteorological observations1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Meteorological data assimilation is the process by which a model simulation of the atmosphere is corrected by observations. In operational weather forecasting, this is done in near real-time, to provide accurate initial conditions for numerical forecasts. The accuracy of the forecasts depends crucially on the accuracy of the data assimilation.

    The increase in available computing power and the theoretical advances in data assimilation methods have recently enabled the European Centre for Medium-Range Weather Forecasts (ECMWF) to develop and introduce operationally a new data assimilation scheme (4D-Var), based on variational methods. The four papers of this thesis present recent developments that have exploited some of the most promising possibilities of 4D-Var with respect to observation usage. They have all been incorporated in operational practice at ECMWF.

    Variational data assimilation schemes have several advantages that make the new scheme more flexible than earlier schemes with respect to the use of observations. The introduction of 4D-Var has enabled the effective use of a wider range of meteorological observations than previously possible. This includes, as will be demonstrated in this thesis, both conventional observations and satellite measurements.

    In the first paper we develop a method for the use of satellite radiance observations, and investigate the aspects of 4D-Var that make the scheme particularly well suited for the assimilation of data from a growing variety of space based observing systems. In the second paper we develop a variational quality control method. The third paper investigates the flow-dependence of the 4D-Var response to time series of surface pressure observations in the vicinity of a rapidly developing storm. The final paper presents a diagnostic method for tuning of the 4D-Var system.

  • 45.
    Andersson, Lovisa
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Studie av MIUU-modellen och implementering av urbana parametrar i modellens energibalansrutin2009Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This is a study of the MIUU-model with its existing parameterization of the lower boundary. In this model the lower boundary conditions are determined by an energy balance routine presented by Deardorff (1978), which has a prognostic equation for the surface temperature. Prior to this study there were no urban parameters presented in the MIUU-model. The different ground properties were all, with the sole exception for water, described by the values for clay loam. This study investigates if the urban impacts on the meteorological parameters can be modeled by the MIUU-model. The values of the parameters in the energy balance equation are changed to values more representative of urban areas. The parameters altered in the energy equation are the albedot, emissivity, roughness length, soil moisture and the temperature in the ground. The effects of changing the geostrophic wind and the cloudiness have also been studied.

     

    Implementing the urban parameters in the MIUU-model results in an increased surface temperature over the urban areas during the day. It also leads to a higher turbulent kinetic energy due to the urban areas roughness. The MIUU-model can however, with its present parameterisation of the energy balance routine and the used urban parameters, not model an urban heat island after sundown. In spite of that, this should be when the differences between urban and rural areas are most prominent. Possibly this could depend on the changes made to the soil moisture parameters, or on the models definitions of the ground heat flux. Therefore, consistent with the fact that implementation of the urban parameters results in decreased ground heat flux over the urban areas at both day and night. A reduced ground heat flux is also found even though the shielding factor of vegetation decreases and the shortwave radiation to the ground increases.

  • 46.
    Andersson, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Uppsala Centre for Sustainable Development, CSD Uppsala, The Baltic University Programme.
    Tol, Richard S.J.
    Max Planck Institute for Meteorology in Hamburg.
    Graham, L. Phil
    Swedish Meteorological and Hydrological Institute.
    Bergström, Sten
    Swedish Meteorological and Hydrological Institute.
    Rydén, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Uppsala Centre for Sustainable Development, CSD Uppsala, The Baltic University Programme.
    Azar, Christian
    University of Gothenburg.
    10. Impacts on the Global Atmosphere: Climate Change and Ozone Depletion2003In: Environmental Science: Understanding, protecting and managing the environment in the Baltic Sea Region / [ed] Lars Rydén, Pawel Migula and Magnus Andersson, Uppsala: Baltic University Press , 2003, 1, 294-323 p.Chapter in book (Other (popular science, discussion, etc.))
  • 47.
    Andersson, Stefan
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
    Undersökning av luftkvaliteten vid småskalig biobränsleförbränning i två kommuner med modellsystemet VEDAIR2007Independent thesis Basic level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An Internet application, VEDAIR, for estimation of air quality in regions with small-scale combustion of bio fuel has been developed by Swedish Meteorological and Hydrological Institute with financing from Swedish Energy Agency and Swedish Environmental Protection Agency. The model contains user interface and a coupled model concept where concentrations of atmospheric pollutions are calculated for regional, urban and local contributions. In this report the model is described and a first study of air quality considering PM10 (particles with a diameter less than 10 µm) in two Swedish municipalities, Vänersborg and Gnosjö, is introduced.

    According to the result, there are areas with poor air quality even in smaller Swedish municipalities, mostly due to high emission from buildings with older wood heating furnace without hydraulic accumulator.

    In Vänersborg three areas were analysed in VEDAIR for the year 2003: Vargön, Mariedal and the downtown district. In the whole municipality the upper evaluation threshold for PM10, which is defined as 14 µg/m3 for annual average, was exceeded due to background contribution of particles. In all areas, however, the concentrations of PM10 were less than the environmental quality norms. In Vargön, where wood heating furnaces are commonly used, in some areas the concentration of particles was as big as or bigger than the downtown district (annual average of 20 µg/m3). However, in downtown the pollutants were more spread. Biggest concentrations of PM10 were estimated in Mariedal, due to emissions from older wood heating furnaces and streets, mostly in areas with unfavourable meteorological conditions. Measurements of PM10 in the area are therefore suggested. Biggest concentrations of PM10 were prevailed during winter, due to great heating need in combination with cooler air temperature and more stable stratification. The local contribution of PM10 was negative correlated with temperature. In the downtown district, however, the biggest concentrations of PM10 were obtained during spring due to usage of studded tyres.

    In Gnosjö the air quality considering PM10 was analysed in the areas Götarp, downtown and Gårö. Calculations in VEDAIR showed that the emissions from traffic were much less than wood heating furnace. The background annual average of PM10 in Gnosjö was 1 µg/m3 higher than Vänersborg. The air quality was quite equal as in Vänersborg, but there was an area in Gårö where the environmental quality norms considering PM10 almost were exceeded, this mostly due to emission from one building with high heating need.

    In this study a comparison between calculated concentrations of PM10 with measured concentrations in Gnosjö for the period 3 November to 31 December 2003 was also made. The validation showed that VEDAIR underestimated the concentrations, but the result was anyway reasonable. Before, validations have only been performed for the northern part of Sweden, and this study indicates that VEDAIR also estimates concentrations of PM10 sufficiently well in southern part of Sweden.

    The study also showed that if a house owner would replace an old wood heating furnace by a modern furnace with hydraulic accumulator, the annual average of the concentration of PM10 could decrease by 4 µg/m3 which is a reduction of 25%.

  • 48.
    Andersson, Tage
    SMHI, Research Department, Atmospheric remote sensing.
    A HEAVY MESOSCALE SNOWFALL EVENT IN NORTHERN GERMANY1991In: METEOROLOGICAL MAGAZINE, ISSN 0026-1149, Vol. 120, no 1425, 67-68 p.Article in journal (Refereed)
  • 49.
    Andersson, Tage
    SMHI, Research Department.
    VAD winds from C band Ericsson Doppler Weather Radars1998In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 7, no 6, 309-319 p.Article in journal (Refereed)
    Abstract [en]

    The VAD (Velocity Azimuth Display) technique for retrieving winds from a single Doppler weather radar is well known as a robust and simple one, though still not used on its merits. Precipitation generally gives VAD winds, but it is less known that even in high latitudes during the warmer seasons the Doppler weather radars of today record enough clear air echos to give wind profiles in the planetary boundary layer. There are, however, few verifications of VAD winds in general, and hardly any concerning clear air. In this paper mainly VAD winds from one Ericsson Doppler Weather Radar in Jonsered, Gothenburg (57.723 degrees N, 12.172 degrees E, 164 m above MSL) are compared to Radiosonde Winds (RAWINDs) from Landwetter (57.668 degrees N, 12.296 degrees E, 155 m above MSL). The sites are about 10 km apart, and the radiosonde is within the range used for the VAD (30 km). The VAD soundings were made each hour, and the radiosoundings every 6th (00, 06, 12 and 18 UTC). About seven months of data were available (9 Dec. 1994 to 14 Feb. 1995 and 28 Jun. to 30 Nov. 1995). The LORAN C system was used to retrieve the RAWINDs during the first period (Dec. 1994 to Feb. 1995), and the OMEGA system was used during the second period. The comparisons are made using the five standard pressure levels, 925, 850, 700, 500 and 400 hPa, corresponding to heights above MSL of about 750, 1450, 3000, 5600 and 7200 m. As overall results, the average differences, in m/s, between the VAD and RAWIND were largest at the lowest (geometrically) levels, and higher up more or less constant with height. This is remarkable, since the wind speed increases with height, and the relative differences thus decrease with height. As an example, the average of the magnitude of the wind vector differences was 3.2 m/s at 925 hPa, but about 2.8 m/s at the higher levels. The differences also tend to be somewhat larger for winds retrieved from clear air echos. In the planetary boundary layer during summer, that is up to about 800 hPa, the availability of VAD winds was about 90 %. The availability decreases with height, and at 400 hPa it was 15 % for the whole period. Comparisons are also performed between VAD winds and winds from a limited area model, HIRLAM.

  • 50.
    Andersson, Tage
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Andersson, M
    SMHI.
    Jacobsson, Caje
    SMHI.
    Nilsson, Stefan
    SMHI.
    THERMODYNAMIC INDEXES FOR FORECASTING THUNDERSTORMS IN SOUTHERN SWEDEN1989In: METEOROLOGICAL MAGAZINE, ISSN 0026-1149, Vol. 118, no 1404, 141-146 p.Article in journal (Refereed)
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