| 1. |
- Bower, K. N., et al.
(författare)
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ACE-2 HILLCLOUD. An overview of the ACE-2 ground-based cloud experiment
- 2000
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 750-778
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Tidskriftsartikel (refereegranskat)abstract
- The ACE-2 HILLCLOUD experiment was carried out on the island of Tenerife in June-July 1997 to investigate the interaction of the boundary layer aerosol with a hill cap cloud forming over a ridge to the north-east of the island. The cloud was used as a natural flow through reactor to investigate the dependence of the cloud microphysics and chemistry on the characteristics of the aerosols and trace gases entering cloud, and to simultaneously study the influence of the physical and chemical processes occurring within the cloud on the size distribution, chemical and hygroscopic properties of the aerosol exiting cloud. 5 major ground base sites were used, measuring trace gases and aerosols upwind and downwind of the cloud, and cloud microphysics and chemistry and interstitial aerosol and gases within the cloud on the hill. 8 intensive measurement periods or runs were undertaken during cloud events, (nocturnally for seven of the eight runs) and were carried out in a wide range of airmass conditions from clean maritime to polluted continental. Polluted air was characterised by higher than average concentrations of ozone (> 50 ppbv), fine and accumulation mode aerosols (> 3000 and > 1500 cm -3 , respectively) and higher aerosol mass loadings. Cloud droplet number concentrations N, increased from 50 cm -3 in background maritime air to > 2500 cm -3 in aged polluted continental air, a concentration much higher than had previously been detected. Surprisingly, N was seen to vary almost linearly with aerosol number across this range. The droplet aerosol analyser (DAA) measured higher droplet numbers than the corrected forward scattering spectrometer probe (FSSP) in the most polluted air, but at other times there was good agreement (FSSP = 0.95 DAA with an r 2 = 0.89 for N < 1200 cm -3 ). Background ammonia gas concentrations were around 0.3 ppbv even in air originating over the ocean, another unexpected but important result for the region. NO 2 was present in background concentrations of typically 15 pptv to 100 pptv and NO 3 . (the nitrate radical) was observed at night throughout. Calculations suggest NO 3 . losses were mainly by reaction with DMS to produce nitric acid. Low concentrations of SO 2 (~30 pptv), HNO 3 and HCl were always present. HNO 3 concentrations were higher in polluted episodes and calculations implied that these exceeded those which could be accounted for by NO 2 oxidation. It is presumed that nitric and hydrochloric acids were present as a result of outgassing from aerosol, the HNO 3 from nitrate rich aerosol transported into the region from upwind of Tenerife, and HCl from sea salt aerosol newly formed at the sea surface. The oxidants hydrogen peroxide and ozone were abundant (i.e., were well in excess over SO 2 throughout the experiment). Occasions of significant aerosol growth following cloud processing were observed, particularly in cleaner cases. Observations and modelling suggested this was due mainly to the take up of nitric acid, hydrochloric acid and ammonia by the smallest activated aerosol particles. On a few occasions a small contribution was made by the in-cloud oxidation of S(IV). The implications of these results from HILLCLOUD for the climatologically more important stratocumulus Marine Boundary Layer (MBL) clouds are considered.
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| 2. |
- Flynn, Michael J., et al.
(författare)
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Modelling cloud processing of aerosol during the ACE-2 HILLCLOUD experiment
- 2000
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 52:2, s. 779-800
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Tidskriftsartikel (refereegranskat)abstract
- A numerical model has been used to simulate the conditions observed during the ACE-2 Hillcloud experiment and to study the processes which may be taking place. The model incorporates gas phase chemistry of sulphur and nitrogen compounds upstream of the cloud, and the interaction of aerosol, precursor trace gases and oxidants within the cloud. Gas phase and aerosol inputs to the model have been provided from measurements made in the field. Dynamics of the air flow over the hill consisted of simple prescribed dynamics based on wind speed measurements, and also for some cases modelled dynamics. In this modelling study, it was found that during clean case studies particles down to 40-55 nm diameter were activated to form cloud droplets, the total number of droplets formed ranging from 200 to 400 drops/cm3. Significant modification of the aerosol spectra due to cloud processing was observed. In polluted cases particles down to 65-80 nm diameter were activated to form cloud droplets, the total number of droplets ranging from 800 to 2800 drops/cm3. Modification of the aerosol spectra due to cloud processing was slight. In all cases, changes in the aerosol spectra were due to both the uptake of HNO3, HCl, NH3 and SO2 from the gas phase, (the SO2 being oxidised to sulphate) and the repartitioning of species such as HNO3, HCl, and NH3 from larger particles onto smaller ones. Modelling results have been compared with observations made. Modelled droplet numbers are typically within 20% of the best measured values. The mode of the droplet distribution typically around 10-20 μm for clean cases and 4-8 μm for polluted cases was found to be in good agreement with the measured values of 10-25 μm for clean cases, but not in such good agreement for polluted cases. Measurements of upwind and interstitial aerosol distributions showed that the smallest particles activated were 30 and 50 nm for clean and polluted cases respectively, slightly smaller than the model values quoted above. Measured upwind and downwind aerosol spectra showed similar modification to that predicted by the model in eight out of the eleven model runs carried out. Chemistry measurements also give general evidence for both the uptake of species from the gas phase, and repartitioning of species from large particles onto smaller ones, though comparisons for individual cases are more difficult. From this modelling study, it can be concluded that in general, in the remote environment the exchange of hydrochloric acid, nitric acid and ammonia between aerosol particles and take up from the gas phase in the vicinity of cloud may be a very important mechanism in regulating the evolution of the aerosol spectrum. Further, the much more linear relationship between cloud droplet and accumulation mode aerosol number, which was observed in the measurements made during the ACE-2 HILLCLOUD project is supported by these modelling results. The implications of this for the indirect effect will be explored in future work.
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| 3. |
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| 4. |
- Bäckstrand, Kristina, et al.
(författare)
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Non-methane volatile organic compound flux from a subarctic mire in Northern Sweden
- 2008
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:2, s. 226-237
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Tidskriftsartikel (refereegranskat)abstract
- Biogenic NMVOCs are mainly formed by plants and microorganisms. They have strong impact on the local atmospheric chemistry when emitted to the atmosphere. The objective of this study was to determine if there are significant emissions of non-methane volatile organic compounds (NMVOCs) from a subarctic mire in northern Sweden. Subarctic peatlands in discontinuous permafrost regions are undergoing substantial environmental changes due to their high sensitivity to climate warming and there is need for including NMVOCs in the overall carbon budget. Automatic and manual chamber measurements were used to estimate NMVOC fluxes from three dominating subhabitats on the mire during three growing seasons. Emission rates varied and were related to plant species distribution and seasonal net ecosystem exchange of carbon dioxide. The highest fluxes were observed from wetter sites dominated by Eriophorum and Sphagnum spp. Total NMVOC emissions from the mire (similar to 17 ha) is estimated to consist of similar to 150 kgC during a growing season with 150 d. NMVOC fluxes can account for similar to 5% of total net carbon exchange (-3177 kgC) at the mire during the same period. NMVOC emissions are therefore a significant component in a local carbon budget for peatlands.
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| 5. |
- Börjesson, Gunnar, et al.
(författare)
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A national landfill methane budget for Sweden based on field measurements, and an evaluation of IPCC models
- 2009
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Ingår i: Tellus, Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 61:2, s. 424-435
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Tidskriftsartikel (refereegranskat)abstract
- Seven Swedish landfills were investigated from 2001 to 2003. On each landfill, a measure of the total methane production was calculated from data on: (1) methane emissions (leakage); (2) methane oxidation and (3) from gas recovery. Methane emissions were determined via a tracer gas (N2O) release-based remote sensing method. N2O and CH4 were measured with an Fourier Transform infrared detector at a distance of more than 1 km downwind from the landfills. Methane oxidation in the landfill covers was measured with the stable carbon isotope method. The efficiency in gas recovery systems proved to be highly variable, but on an average, 51% of the produced landfill gas was captured. A first-order decay model, based on four fractions (waste from households and parks, sludges and industrial waste), showed that the use of a degradable organic carbon fraction (DOCf) value of 0.54, in accordance with the default value for DOCf of 0.50 in the latest IPCC model, gave an emission estimate similar to the official national reports.
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| 6. |
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| 7. |
- Freud, E., et al.
(författare)
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Anthropogenic aerosol effects on convective cloud microphysical properties in southern Sweden
- 2008
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:2, s. 286-297
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we look for anthropogenic aerosol effects in southern Scandinavia's clouds under the influence of moderate levels of pollution and relatively weak dynamic forcing. This was done by comparing surface aerosol measurements with convective cloud microphysical profiles produced from satellite image analyses. The results show that the clouds associated with the anthropogenic-affected air with high PM0.5, had to acquire a vertical development of similar to 3.5 km before forming precipitation-sized particles, compared to less than 1 km for the clouds associated with low PM0.5 air-masses. Additionally, a comparison of profiles with precipitation was done with regard to different potentially important parameters. For precipitating clouds the variability of the cloud thickness needed to produce the precipitation (Delta h(14)) is directly related to PM0.5 concentrations, even without considering atmospheric stability, the specific aerosol size distribution or the aerosols' chemical composition. Each additional 1 mu g m(-3) of PM0.5 was found to increase Delta h(14) by similar to 200-250 m. Our conclusion is that it is indeed possible to detect the effects of anthropogenic aerosol on the convective clouds in southern Scandinavia despite modest aerosol masses. It also emphasizes the importance of including aerosol processes in climate-radiation models and in numerical weather prediction models.
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| 8. |
- Hermann, M, et al.
(författare)
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Submicrometer aerosol particle distributions in the upper troposphere over the mid-latitude North Atlantic - Results from the third route of 'CARIBIC'
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:1, s. 106-117
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Tidskriftsartikel (refereegranskat)abstract
- Particle number and mass concentrations of submicrometer aerosol particles were determined for the upper troposphere over the mid-latitude North Atlantic within the Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container project (CARIBIC, http://www.caribic-atmospheric.com). Between May 2001 and April 2002, 22 flights from Germany to the Caribbean were conducted using an automated measurement container on a B767 passenger aircraft. Spatial and seasonal probability distributions for ultrafine and Aitken mode particles as well as mass concentrations of particulate sulphur in 8-12 km altitude are presented. High particle number concentrations (mostly 2500-15 000 particles cm(-3) STP) are particularly found in summer over the western North Atlantic Ocean close to the North American continent. The distributions together with an analysis of particle source processes show that deep vertical transport is the dominant process leading to most of the events with high particle number concentrations (greater than or similar to 8000 particles cm(-3) STP) for ultrafine particles as well as for Aitken mode particles. This study emphasizes the importance of deep vertical transport and cloud processing for the concentration of aerosol particles in the upper troposphere.
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| 9. |
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| 10. |
- Lindroth, Anders
(författare)
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Foreword
- 2007
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59:5, s. 787-787
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 11. |
- Svenningsson, Birgitta, et al.
(författare)
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Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland-forest mosaic
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60, s. 353-364
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- An analysis of particle formation (PF) events over a subarctic mire in northern Sweden was performed, based on number size distributions of atmospheric aerosol particles (10-500 nm in diameter) and ions (0.4-40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005- September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis concentrates on calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm/h) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions repeated particle formation events were observed within one day, with differences in onset time of a few hour. These high growth rates were only observed when the condensation sink was higher than 0.001 s-1.
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| 12. |
- Swietlicki, Erik, et al.
(författare)
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Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments : a review
- 2008
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 432-469
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Forskningsöversikt (refereegranskat)abstract
- The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the size-resolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.
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| 13. |
- Thum, T., et al.
(författare)
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Spring initiation and autumn cessation of boreal coniferous forest CO2 exchange assessed by meteorological and biological variables
- 2009
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 61:5, s. 701-717
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Tidskriftsartikel (refereegranskat)abstract
- We studied the commencement and finishing of the growing season using different air temperature indices, the surface albedo, the chlorophyll fluorescence (Fv/Fm) and the carbon dioxide (CO2) tropospheric concentration, together with eddy covariance measurements of CO2 flux. We used CO2 flux data from four boreal coniferous forest sites covering a wide latitudinal range, and CO2 concentration measurements from Sammaltunturi in Pallas. The CO2 gas exchange was taken as the primary determinant for the growing season to which other methods were compared. Indices based on the cumulative temperature sum and the variation in daily mean temperature were successfully used for approximating the start and cessation of the growing season. The beginning of snow melt was a successful predictor of the onset of the growing season. The chlorophyll fluorescence parameter Fv/Fm and the CO2 concentration were good indicators of both the commencement and cessation of the growing season. By a derivative estimation method for the CO2 concentration, we were also able to capture the larger-scale spring recovery. The trends of the CO2 concentration and temperature indices at Pallas/Sammaltunturi were studied over an 11-yr time period, and a significant tendency towards an earlier spring was observed. This tendency was not observed at the other sites.
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| 14. |
- Delmas, RJ, et al.
(författare)
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Bomb-test Cl-36 measurements in Vostok snow (Antarctica) and the use of Cl-36 as a dating tool for deep ice cores
- 2004
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 56:5, s. 492-498
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Tidskriftsartikel (refereegranskat)abstract
- A large pulse of atmospheric Cl-36 generated by a limited number of nuclear tests peaked in the late 1950s to early 1960s. The corresponding enhanced Cl-36 deposition is seen in various glaciological archives in the Northern Hemisphere. The profile of the bomb spike recorded in firn layers at Vostok Station, central East Antarctica. has been measured by employing accelerator mass spectrometry (AMS). The records obtained front two well-dated data sets collected in snow pits in 1997 and 1998 show a broad Cl-36 peak, beginning as early as the 1940s and reaching its maximum in the 1960s. The signal is followed by a long-lasting tail up to the surface. This pattern is totally unexpected. We show that the results, unlike the Greenland data, can be explained by a mobility of HCl in the Antarctic firn. This experiment demonstrates the instability of gaseous Cl- deposits. a phenomenon which has important implications for the use of natural cosmogenic Cl-36 radionuclides as a reliable dating tool for deep ice cores from low-accumulation areas. However, during glacial times, under favourable atmospheric chemistry conditions this dating method may still be applicable. Snow metamorphism and ventilation are assumed to be the two main physical processes responsible for the observed patterns.
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| 15. |
- Grelle, A., et al.
(författare)
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Large carbon-sink potential by Kyoto forests in Sweden - A case study on willow plantations
- 2007
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Ingår i: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59:5, s. 910-918
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Tidskriftsartikel (refereegranskat)abstract
- Fluxes of CO were measured in a 75-ha short-rotation willow plantation at Enkoping, central Sweden. The plantation was irrigated with wastewater for fertilization and water-filtering purposes. The harvested biomass was used locally for combined heat and power production. The plantation was a sink of ca. 8 tonnes C ha(-1) during 2003, of which ca. 50% was estimated to be attributed to fertilization. Biomass increment by shoot growth was 5 tonnes C ha-1 during the same year. Belowground carbon allocation was estimated to 3 tonnes C ha(-1) yr(-1) by a model that relates carbon allocation to shoot growth. Thus, the ecosystem carbon balance was closed by these estimations. The carbon uptake by the willow plantation was 5.5 times as high compared to a normally managed spruce forest, but only half as high as from an experimental, well-roanaged willow plantation in the same region. This illustrates the vast potential of short-rotation willow plantations for CO2 uptake from the atmosphere.
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| 16. |
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| 17. |
- Kristensson, Adam, et al.
(författare)
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Characterization of New Particle Formation Events at a Background Site in Southern Sweden: Relation to Air Mass History
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 330-344
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Tidskriftsartikel (refereegranskat)abstract
- Particle formation events were analysed from aerosol number size distribution data collected at a background station in southern Sweden between February 2001 and May 2004. Events occurred on about 36% of all days and were favoured by high global radiation values. The clearest events (class I, 20% of all days) were observed when the formation rate of activated hypothetical clusters around 1 nm diameter, J(1) was higher than 10((180*CondS-0.60)), where CondS is the condensation sink (in s(-1)). The median condensable vapour concentration, observed formation rate at 3 nm, and growth rate during class I events were 3.0 x 10(7) cm(-3), 1.1 cm(-3) s(-1) and 2.1 nm h(-1), respectively. On 7% of all days, it was possible to observe growth of the newly formed particles exceeding 30 nm geometric mean diameter during event days in the evening, which is important for the regional particle population, and thereby the climate. A trajectory analysis revealed that cleaner air masses were relatively more important for the contribution of Aitken mode particles than polluted ones. Class I events were registered on 36% of all days when trajectories had passed over the open sea, indicating that ship traffic can contribute to particle formation and growth.
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| 18. |
- Kulmala, Liisa, et al.
(författare)
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H2O and CO2 fluxes at the floor of a boreal pine forest
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:2, s. 167-178
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Tidskriftsartikel (refereegranskat)abstract
- We measured H2O and CO2 fluxes at a boreal forest floor using eddy covariance (EC) and chamber methods. Maximum evapotranspiration measured with EC ranged from 1.5 to 2.0 mmol m(-2) s(-1) while chamber estimates depended substantially on the location and the vegetation inside the chamber. The daytime net CO2 exchange measured with EC (0-2 mu mol m(-2) s(-1)) was of the same order as measured with the chambers. The nocturnal net CO2 exchange measured with the chambers ranged from 4 to 7 mu mol m(-2) s(-1) and with EC from similar to 4 to similar to 5 mu mol m(-2) s(-1) when turbulent mixing below the canopy was sufficient and the measurements were reliable. We studied gross photosynthesis by measuring the light response curves of the most common forest floor species and found the saturated rates of photosynthesis (P-max) to range from 0.008 (mosses) to 0.184 mu mol g(-1) s(-1) (blueberry). The estimated gross photosynthesis at the study site based on average leaf masses and the light response curves of individual plant species was 2-3 mu mol m(-2) s(-1). At the same time, we measured a whole community with another chamber and found maximum gross photosynthesis rates from 4 to 7 mu mol m(-2) s(-1).
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| 19. |
- Kulmala, Markku, et al.
(författare)
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Overview of the biosphere-aerosol-cloud-climate interactions (BACCI) studies
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60:3, s. 300-317
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Forskningsöversikt (refereegranskat)abstract
- Here we present research methods and results obtained by the Nordic Centre of Excellence Biosphere-Aerosol-Cloud-Climate Interactions (BACCI) between 1 January 2003 and 31 December 2007. The centre formed an integrated attempt to understand multiple, but interlinked, biosphere-atmosphere interactions applying inter and multidisciplinary approaches in a coherent manner. The main objective was to study the life cycle of aerosol particles and their importance on climate change. The foundation in BACCI was a thorough understanding of physical, meteorological, chemical and ecophysiological processes, providing a unique possibility to study biosphere-aerosol-cloud-climate interactions. Continuous measurements of atmospheric concentrations and fluxes of aerosol particles and precursors and, CO2/aerosol trace gas interactions in different field stations (e.g. SMEAR) were supported by models of particle thermodynamics, transport and dynamics, atmospheric chemistry, boundary layer meteorology and forest growth. The main progress was related to atmospheric new particle formation, existence of clusters, composition of nucleation mode aerosol particles, chemical precursors of fresh aerosol particles, the contribution of biogenic aerosol particles on the global aerosol load, transport, transformation and deposition of aerosol particles, thermodynamics related to aerosol particles and cloud droplets, and the microphysics and chemistry of cloud droplet formation.
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| 20. |
- Lagergren, Fredrik, et al.
(författare)
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Biophysical controls on CO2 fluxes of three Northern forets based on long-term eddy covariance data.
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 60:2, s. 143-152
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedSix to nine years of net ecosystem carbon exchange (NEE) data from forests in Hyytiala in Finland, Soro in Denmark and Norunda in Sweden were used to evaluate the interannual variation in the carbon balance. For half-monthly periods, average NEE was calculated for the night-time data. For the daytime data parameters were extracted for the relationship to photosynthetic active radiation (PAR). The standard deviation of the parameters was highest for Norunda where it typically was around 25% of the mean, while it was ca. 15% for Hyytiala and Soro. Temperature was the main controller of respiration and photosynthetic capacity in autumn, winter and spring but explained very little of the interannual variation in summer. A strong correlation between respiration and photosynthesis was also revealed. The start, end and length of the growing season were estimated by four different criteria. The start date could explain some of the variation in yearly total NEE and gross primary productivity (GPP) in Hyytiala and Soro, but the average maximum photosynthetic capacity in summer explained more of the variation in annual GPP for all sites than start, end or length of the growing season.
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| 21. |
- Launiainen, S, et al.
(författare)
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Vertical variability and effect of stability on turbulence characteristics down to the forest floor of a pine forest.
- 2007
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59, s. 919-936
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Tidskriftsartikel (refereegranskat)abstract
- Among the fundamental problems in canopy turbulence, particularly near the forest floor, remain the local diabatic effects and linkages between turbulent length scales and the canopy morphology. To progress on these problems, mean and higher order turbulence statistics are collected in a uniform pine forest across a wide range of atmospheric stability conditions using five 3-D anemometers in the subcanopy. The main novelties from this experiment are: (1) the agreement between second-order closure model results and measurements suggest that diabatic states in the layer above the canopy explain much of the modulations of the key velocity statistics inside the canopy except in the immediate vicinity of the trunk space and for very stable conditions. (2) The dimensionless turbulent kinetic energy in the trunk space is large due to a large longitudinal velocity variance but it is inactive and contributes little to momentum fluxes. (3) Near the floor layer, a logarithmic mean velocity profile is formed and vertical eddies are strongly suppressed modifying all power spectra. (4) A spectral peak in the vertical velocity near the ground commensurate with the trunk diameter emerged at a moderate element Reynolds number consistent with Strouhal instabilities describing wake production.
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| 22. |
- Lund, Magnus, et al.
(författare)
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Annual CO2 balance of a temperate bog
- 2007
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 59, s. 804-811
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Tidskriftsartikel (refereegranskat)
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| 23. |
- Tunved, Peter, et al.
(författare)
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The natural aerosol over Northern Europe and its relation to anthropogenic emissions - implications of important climate feedbacks
- 2008
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 60 B:4, s. 473-484
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Tidskriftsartikel (refereegranskat)abstract
- We use a recently developed parametrization to estimate the regional particle field in the summer time troposphere over Scandinavia that would result if the forest were the only source of particles. The calculated field is compared with available observational data. It is concluded that the needle leaf forest above 58 degrees N alone is capable of producing aerosol mass concentrations corresponding to 12-50% of today's values in the boundary layer over Scandinavia. We also demonstrate that the forest itself could produce up to 200 CCN per cubic centimetre on average over Scandinavia and further show that an increase in temperature by 5.8 degrees C compared to today's average temperature could increase this CCN population by 40%. The study shows that we are able to approximate the natural aerosol field resulting from biogenic emissions over the boreal forest in the northern hemispheric region. This information provide an important contribution in the evaluation of the climate effect caused by anthropogenic emissions of particles over the forest and also opens the possibility to better address the climate feedbacks believed to be associated with the boreal region.
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| 24. |
- Lundén, Jenny, et al.
(författare)
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The vertical distribution of atmospheric DMS in the high Arctic summer
- 2010
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 62:3, s. 160-171
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Tidskriftsartikel (refereegranskat)abstract
- The vertical structure of gas-phase dimethyl sulfide, DMS(g), in the high Arctic atmosphere is investigated during a summer season. The model results show that the near-surface DMS(g) concentration over open ocean is very variable both in time and space, depending on the local atmospheric conditions. Profiles over ocean have typically highest concentration near the surface and decrease exponentially with height. Over the pack-ice, the concentrations are typically lower and the vertical structure changes as the air is advected northward. Modeled DMS(g) maxima above the local boundary layer were present in about 3\% of the profiles found over the pack-ice. These maxima were found in association to frontal zones. Our results also show that DMS(g) can be mixed downward by turbulence into the local boundary layer and act as a local near--surface DMS(g) source over the pack-ice and may hence influence the growth of cloud condensation nuclei and cloud formation in the boundary layer. Profile observations are presented in support to the model results. They show that significant DMS(g) concentrations exist in the Arctic atmosphere at altitudes not to be expected when only considering vertical mixing in the boundary layer.
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| 25. |
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