| 1. |
- Achtert, Peggy, 1982-, et al.
(författare)
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Hygroscopic growth of tropospheric particle number size distributions over the North China Plain
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114, s. D00G07-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Achtert, Peggy, 1982-, et al.
(författare)
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Investigation of polar stratospheric clouds in January 2008 by means of ground-based and spaceborne lidar measurements and microphysical box model simulations
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. D07201-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Andersson, Camilla, 1979-, et al.
(författare)
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European ozone in a future climate : The importance of changes in dry deposition and isoprene emissions
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. D02303-
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Tidskriftsartikel (refereegranskat)abstract
- [1] Using a regional chemistry transport model (CTM) driven with meteorological data from a regional climate model (A2 emission scenario) we have investigated important processes for determining surface ozone concentration across Europe in a future climate. Anthropogenic ozone precursor emissions were kept constant (year 2000) to isolate the effect of climate change from 1961-1990 to 2021-2050 and 2071-2100. Biogenic isoprene emissions were calculated on-line. The results point to substantial increase in daily mean and daily maximum surface ozone over central and southern Europe. The importance of changes in natural isoprene emissions and dry deposition were investigated especially.[2] The isoprene emissions increased by a factor of about 1.8 from the current to the second future period. However, a sensitivity study using a sophisticated rescaling of isoprene emissions shows that the large increase in isoprene emission is of moderate importance in southern Europe for the strong increase in surface ozone (it can explain up to 30% of the change in central, southern and western Europe).[3] The soil-moisture dependent ozone dry deposition formulation and changes in snow cover, affecting the dry deposition, are more important processes: soil moisture dependence explains up to 80% of the change in Spain. Therefore it is vital to include soil moisture dependence in a model study of this type. Isoprene emissions are of less importance (0-30% in central and southern Europe), but not dismissible and should definitely be emitted on-line in climate-ozone projection studies.
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| 4. |
- Asokan, Shilpa M., 1979-, et al.
(författare)
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Vapor flux by evapotranspiration : effects of changes in climate, land-use and water-use
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:D24
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced evapotranspiration (ET) over irrigated land and associated latent heat flux change can modify the climate. Model studies of such climate change effects of irrigation are commonly based on land use parameterizations, in terms of irrigated land area, or land area equipped for irrigation. Actual ET change, however, may also be driven by water use change in addition to land use change. This study quantifies and compares ET changes due to changes in climate, land use, and water use from the preirrigation period 1901–1955 to the recent period 1990–2000 (with irrigation) for the example case of Mahanadi River Basin (MRB) in India. The results show that actual water use per unit area of irrigated land may vary greatly over a hydrological drainage basin. In MRB, much higher water use per irrigated land unit in the downstream humid basin parts leads to higher vapor flux by ET, and irrigation‐induced ET flux change, than in the upstream, water‐stressed basin parts. This is consistent with water supply limitations in water‐stressed basins. In contrast, the assumption in land use−based models that irrigation maintains high soil moisture contents can imply higher modeled water use and therefore also higher modeled ET fluxes under dry conditions than under humid conditions. The present results indicate water use as an important driver of regional climate change, in addition to land use and greenhouse gas‐driven changes.
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| 5. |
- Austin, John, et al.
(författare)
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Chemistry-climate model simulations of spring Antarctic ozone
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. D00M11-
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Tidskriftsartikel (refereegranskat)abstract
- Coupled chemistry-climate model simulations covering the recent past and continuing throughout the 21st century have been completed with a range of different models. Common forcings are used for the halogen amounts and greenhouse gas concentrations, as expected under the Montreal Protocol (with amendments) and Intergovernmental Panel on Climate Change A1b Scenario. The simulations of the Antarctic ozone hole are compared using commonly used diagnostics: the minimum ozone, the maximum area of ozone below 220 DU, and the ozone mass deficit below 220 DU. Despite the fact that the processes responsible for ozone depletion are reasonably well understood, a wide range of results is obtained. Comparisons with observations indicate that one of the reasons for the model underprediction in ozone hole area is the tendency for models to underpredict, by up to 35%, the area of low temperatures responsible for polar stratospheric cloud formation. Models also typically have species gradients that are too weak at the edge of the polar vortex, suggesting that there is too much mixing of air across the vortex edge. Other models show a high bias in total column ozone which restricts the size of the ozone hole (defined by a 220 DU threshold). The results of those models which agree best with observations are examined in more detail. For several models the ozone hole does not disappear this century but a small ozone hole of up to three million square kilometers continues to occur in most springs even after 2070.
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| 6. |
- Backstrand, K., et al.
(författare)
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Total hydrocarbon flux dynamics at a subarctic mire in northern Sweden
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113, s. G03026-
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Tidskriftsartikel (refereegranskat)abstract
- This is a study of the spatial and temporal variability of total hydrocarbon (THC) emissions from vegetation and soil at a subarctic mire, northern Sweden. THCs include methane (CH4) and nonmethane volatile organic compounds (NMVOCs), both of which are atmospherically important trace gases and constitute a significant proportion of the carbon exchange between biosphere and atmosphere. Reliable characterization of the magnitude and the dynamics of the THC fluxes from high latitude peatlands are important when considering to what extent trace gas emissions from such ecosystems may change and feed back on climate regulation as a result of warmer climate and melting permafrost. High frequency measurements of THC and carbon dioxide (CO2) were conducted during four sequential growing seasons in three localities representing the trophic range of plant communities at the mire. The magnitude of the THC flux followed the moisture gradient with increasing emissions from a dry Palsa site (2.2 +/- 0.1 mgC m(-2) d(-1)), to a wet intermediate melt feature with Sphagnum spp. (28 +/- 0.3 mgC m(-2) d(-1)) and highest emissions from a wet Eriophorum spp. site (122 +/- 1.4 mgC m(-2) d(-1)) (overall mean +/- 1 SE, n = 2254, 2231 and 2137). At the Palsa site, daytime THC flux was most strongly related to air temperature while daytime THC emissions at the Sphagnum site had a stronger relation to ground temperature. THC emissions at both the wet sites were correlated to net ecosystem exchange of CO2. An overall spatial correlation indicated that areas with highly productive vegetation communities also had high THC emission potential.
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| 7. |
- Bastviken, D., et al.
(författare)
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Fates of methane from different lake habitats : Connecting whole-lake budgets and CH4 emissions
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:G2
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Tidskriftsartikel (refereegranskat)abstract
- Methane (CH4) represents a major product of organic matter decomposition in lakes. Once produced in the sediments, CH4 can be either oxidized or emitted as a greenhouse gas to the atmosphere. Lakes represent an important source of atmospheric CH4, but the relative magnitudes of the internal pathways that lead to CH4 emissions are not yet clear. We quantified internal cycling and methane emissions in three lakes during summer stratification. These methane budgets included: sediment release of CH4 at different depths; water column transport patterns and methane oxidation; methane storage in the water column; and methane emissions to the atmosphere by diffusion and ebullition. The contribution of CH4 carbon, via oxidation by methanotrophic bacteria, to pelagic food webs was also estimated. Despite the very low concentration of CH4 in surface waters, shallow, epilimnetic sediments were major contributors of CH4 to the atmosphere. While 51 - 80% of the CH4 produced in deep sediments was oxidized in the water column, most of the CH4 released from shallow sediment escaped oxidation and reached the atmosphere. Epilimnetic sediments accounted for 100% of CH4 emitted during summer stratification, and 14 - 76% considering the release of CH4 stored in deep water layers during lake circulation after the stratification period; diffusive emission accounted for 26 - 48% and ebullition the remainder. These results indicate that it is important to address transport rates of CH4 from the shallow sediment along with the production-consumption processes when trying to understand methane dynamics and the regulation of lake methane emissions.
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| 8. |
- Benze, Susanne, et al.
(författare)
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On the onset of polar mesospheric cloud seasons as observed by SBUV
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D07104-
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes an investigation using data from the Solar Backscatter Ultraviolet (SBUV) satellite instruments to explore and understand variations in the timing of the onset of Polar Mesospheric Cloud (PMC) seasons. Previous work has shown that for several recent southern hemisphere (SH) seasons, the PMC season onset was controlled by the timing of the shift from winter to summer zonal wind flow in the SH stratosphere. We extend the analysis of PMC season onset to 28 years of SBUV observations, including both hemispheres. A multiple linear regression analysis of SBUV data from 1984 to 2011 suggests that the SH PMC season onset is delayed by one day for every day that the zonal wind at 65 degrees S and 50 hPa (similar to 20 km) remains in a winter-like state. In addition, we find that the solar cycle plays a role: The SH season onset is delayed by about ten days at solar maximum compared to solar minimum. In the NH, the PMC season onset is delayed by similar to 7 days at solar maximum compared to solar minimum; variations in the NH stratospheric wind, however, are not correlated with the NH onset date. On the other hand, inter-hemispheric teleconnections are important in the NH; a one-day shift in the NH season onset corresponds to a shift of similar to 1.4 m/s in the SH stratospheric wind at 60.0 degrees S and 20 hPa (similar to 26 km). Neither the NH nor the SH season onset date is correlated with the Quasi-Biennial Oscillation, North Atlantic Oscillation, Arctic Oscillation, or El Nino Southern Oscillation.
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| 9. |
- Bosson, Emma, et al.
(författare)
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Influences of shifts in climate, landscape, and permafrost on terrestrial hydrology
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117
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Tidskriftsartikel (refereegranskat)abstract
- This study has simulated the terrestrial hydrology associated with different climate, landscape, and permafrost regime scenarios for the field case example of the relatively well characterized coastal catchment of Forsmark, Sweden. The regime scenarios were selected from long-term simulation results of climate, topographical, shoreline, and associated Quaternary deposit and vegetation development in this catchment with a time perspective of 100,000 years or more and were used as drivers for hydrological simulations with the three-dimensional model MIKE SHE. The hydrological simulations quantify the responses of different water flow and water storage components of terrestrial hydrology to shifts from the present cool temperate climate landscape regime in Forsmark to a possible future Arctic periglacial landscape regime with or without permafrost. The results show complexity and nonlinearity in the runoff responses to precipitation changes due to parallel changes in evapotranspiration, along with changes in surface and subsurface water storage dynamics and flow pathways through the landscape. The results further illuminate different possible perspectives of what constitutes wetter/drier landscape conditions, in contrast to the clearer concept of what constitutes a warmer/colder climate.
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| 10. |
- Bromley, T., et al.
(författare)
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Shipboard measurements and modeling of the distribution of CH4 and (CH4)-C-13 in the western Pacific
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D04307-
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of methane (CH4) mixing ratio and C-13/C-12 isotopic ratios in CH4 (delta C-13) data from a collaborative shipboard project using bulk carrier ships sailing between Nelson, New Zealand, and Osaka, Japan, in the western Pacific Ocean. Measurements of the CH4 mixing ratio and delta C-13 in CH4 were obtained from large clean-air samples collected in each 2.5 degrees to 5 degrees of latitude between 30 degrees S and 30 degrees N on eight voyages from 2004 to 2007. The data show large variations in CH4 mixing ratio in the tropical western Pacific, and data analysis suggests that these large variations are related to the positions and strengths of the South Pacific Convergence Zone and the Intertropical Convergence Zone, with variability in the sources playing a much smaller role. These measurements are compared with results from a modified version of the Unified Model (UMeth) general circulation model along two transects, one similar to the ship transects and another 18.75 degrees to the east. Although UMeth was run to a steady state with the same sources and sinks each year, the gradient structures varied considerably from year to year, supporting our conclusion that variability in transport is a major driver for the observed variations in CH4. Simulations forced with an idealized representation of the El Nino-Southern Oscillation (ENSO) suggest that a large component of the observed variability in latitudinal gradients of CH4 and its delta C-13 arises from intrinsic variability in the climate system that does not occur on ENSO time scales.
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