bluuebunny/crossref_metadata_2025 huggingface dataset:
Lake‐induced atmospheric circulations during BOREAS
Authors: Sun Jielun , Lenschow Donald H. , Mahrt L. , Crawford Tim L. , Davis Kenneth J. , Oncley Steve P. , MacPherson J. I. , Wang Qing , Dobosy Ron J. , Desjardins R. L.
Published: February 2004

Lake‐induced atmospheric circulations over three lakes ranging from 3 to 10 km width are analyzed using data from three aircraft during the 1994 Boreal Ecosystem‐Atmosphere Study (BOREAS). A well‐defined divergent lake breeze circulation is observed over all three lakes during the day. Under light wind conditions, the lake breeze is not very sensitive to the water temperature, and the strength of the divergence over the lake decreases with increasing lake size. The boundary‐layer development over the surrounding land can be very important for generating a horizontal pressure difference which drives the lake breeze. Diurnal and seasonal variations of lake breezes are investigated on the basis of repeated passes from the different aircraft at different altitudes from late spring to early fall of 1994. The lake breeze divergence increases with time during the day and reaches a maximum around 1300 LST. The latent heat flux over 10‐km‐wide Candle Lake increases steadily from spring to fall as the lake temperature increases. The latent heat flux over the land reaches a maximum during the summer due to evapotranspiration. The lake effect on area‐averaged fluxes sometimes leads to a negative heat transfer coefficient for an averaging scale of several times the lake width.
Impact of air mass histories on the chemical climate of Mount Mitchell, North Carolina
Authors: Ulman J. C. , Saxena V. K.
Published: February 2004

Cloud water acidity and ionic content, as measured at the Mount Mitchell (35°44′05″N, 82°17′15″W, 2038 m msl (highest peak in the eastern United States)) State Park observing site, using a passive cloud water collector, are directly influenced by the trajectories of cloud‐forming air masses which pass over areas of varying levels of pollutant emission. Regions of the United States which are emitters of high‐level pollutants, such as SOx and NOx will thus serve to reduce observed pH levels in cloud water samples and raise the levels of acidifying ions, such as sulfate and nitrate. The 48‐hour backward trajectories for all 39 cloud events during the 1993 field season (May 15, 1993 to October 14, 1993) were computed using the hybrid singleparticle Lagrangian integrated trajectories (HY‐SPLIT) model. Three sectors, identified as the polluted sector, from 290° to 65° azimuth relative to the site, the continental sector, 240° to 290° azimuth, and the marine sector, 65° to 240° azimuth, were used to classify the cloud‐forming air masses. The polluted sector was associated with the lowest overall pH averages, with the marine sector following closely behind. The highest average pH values were received from air masses indicated as having crossed the continental and the marine sectors (in combination), with the largest portions of those air mass trajectories passing through the continental sector (exclusively continental sector air masses were also the most frequent). These observations are in agreement with findings in Colorado where aerosols produced by wind erosion were responsible for decreasing the precipitation acidity.
Special sensor microwave imager derived global rainfall estimates for climatological applications
Authors: Ferraro Ralph R.
Published: February 2004

Global monthly rainfall estimates have been produced from over 8 years of measurements from the Defense Meteorological Satellite Program series of special sensor microwave/imagers (SSM/Is) and are analyzed to depict seasonal, annual, and interannual variability. This SSM/I product is one of the components of the blended Global Precipitation Climatology Project rainfall climatology. The primary algorithm used is an 85 GHz scattering‐based algorithm over land, and a combined 85 GHz scattering and 19/37 GHz emission over ocean, both of which have been calibrated with ground‐based radar data. Errors associated with the SSM/I derived monthly rainfall are characterized through comparisons with various gauge‐based, climatological, and other satellite‐derived rainfall estimates. During the period of June 1990 to December 1991 the 85 GHz channels aboard the SSM/I failed, so no monthly rainfall estimates are available. An alternative algorithm, using a newly developed 37 GHz scattering approach over land, and emission only over ocean, was developed to obtain a continuous record of rainfall estimates for the entire SSM/I time series. Although the 37 GHz scattering algorithm is sensitive to rain rates in excess of 8 mm/h, the correlation between the 37 and 85 GHz monthly estimates over land can be as high as 0.9 (but varies regionally) when comparing both approaches during a period of useable 85 GHz measurements. The error in the monthly rainfall using this algorithm is typically larger in comparison with measurements from rain gauges. Over ocean the emission only algorithm produces a lesser amount of rain than the scattering‐based algorithm, most likely attributed to the lack of a proper beam‐filling correction. During the period of January 1992 to the present there were two SSM/I satellites in full operation, with sampling times of approximately 0600/1800 and 1000/2200 LT. Comparisons between the single and dual satellites are made and are compared with gauge data sets. In general, it is found that the dual‐satellite estimates reduce the RMS errors, although the improvements are both regionally and seasonally dependent.
Point evaluation of a surface hydrology model for BOREAS
Authors: Nijssen Bart , Haddeland Ingjerd , Lettenmaier Dennis P.
Published: February 2004

Detailed observations of moisture and energy fluxes made at the Boreal Ecosystem‐Atmosphere Study (BOREAS) tower flux sites offer a unique opportunity for the evaluation of hydrological models, since model process representations can be compared with observations. The distributed hydrology‐soil‐vegetation model (DHSVM) was used to simulate the latent and sensible heat fluxes at the old black spruce and old jack pine tower flux sites in the southern study area and the old black spruce tower in the northern study area during the summer of 1994. The model did a reasonable job of simulating both the seasonal average fluxes and the diurnal cycle of the surface heat fluxes. However, a lag was observed in the simulation of the sensible heat flux, which was attributed to an inadequate representation of the ground heat flux and ground heat storage. It was also noted that direct soil evaporation forms an important part of the latent heat flux simulated by the model. Incorporation of a more complete soil thermal model, and further field work in 1996 to evaluate the importance of the moss layer and the direct evaporation from the soil, is expected to lead to further improvements.
Photosynthesis and carbon isotope discrimination in boreal forest ecosystems: A comparison of functional characteristics in plants from three mature forest types
Authors: Flanagan Lawrence B. , Brooks J. Renee , Ehleringer James R.
Published: February 2004

In this paper we compare measurements of photosynthesis and carbon isotope discrimination characteristics among plants from three mature boreal forest types (Black spruce, Jack pine, and aspen) in order to help explain variation in ecosystem‐level gas exchange processes. Measurements were made at the southern study area (SSA) and northern study area (NSA) of the boreal forest in central Canada as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). In both the NSA and the SSA there were significant differences in photosynthesis among the major tree species, with aspen having the highest CO2assimilation rates and spruce the lowest. Within a species, photosynthetic rates in the SSA were approximately twice those measured in the NSA, and this was correlated with similar variations in stomatal conductance. Calculations of the ratio of leaf intercellular to ambient CO2concentration (ci/ca) from leaf carbon isotope discrimination (Δ) values indicated a relatively low degree of stomatal limitation of photosynthesis, despite the low absolute values of stomatal conductance in these boreal tree species. Within each ecosystem, leaf Δ values were strongly correlated with life‐form groups (trees, shrubs, forbs, and mosses), and these differences are maintained between years. Although we observed significant variation in the13C content of tree rings at the old Jack pine site in the NSA during the past decade (indicating interannual variation in the degree of stomatal limitation), changes in summer precipitation and temperature accounted for only 44% of the isotopic variance. We scaled leaf‐level processes to the ecosystem level through analyses of well‐mixed canopy air. On average, all three forest types had similar ecosystem‐level Δ values (average value ± standard deviation, 19.1‰±0.5‰), calculated from measurements of change in the concentration and carbon isotope ratio of atmospheric CO2during a diurnal cycle within a forest canopy. However, there were seasonal changes in ecosystem discrimination for aspen forests, while the evergreen conifer forests exhibited relatively constant discrimination values throughout the active growing season.
Local upper tropospheric/lower stratospheric clear‐sky water vapor and tropospheric deep convection
Authors: Liao Xiaohan , Rind David
Published: February 2004

Local upper tropospheric and stratospheric water vapor profile retrievals by Stratospheric Aerosol and Gas Experiment II for July 1986–1990 are compared with concurrent International Satellite Cloud Climatology Project deep convective clouds to investigate the possible impact of deep convection on upper level moisture distributions. Results show that at low latitudes, clear‐sky water vapor values in the upper troposphere (above 300 mbar level) decrease following the onset of convection, perhaps because of compensatory subsidence. The drying lasts for a few hours and then is interrupted by a moistening trend centered at 6 hours after the convection breaks out, perhaps because of the detrainment of cloud liquid water from the convective tower and spreading anvil clouds. From about 9 hours later the tropical lower stratosphere shows moistening occurring. Largely because of these effects, the tropical lower stratosphere has 20–30% more moisture at sunrise compared to sunset. The later stratospheric moistening has the largest correlation significance with convection as well as the largest sampling number, though the absolute variation is much less than the variation in the troposphere. At northern hemisphere summer middle latitudes, upper tropospheric drying follows moist convection events, without an obvious moistening trend in the upper troposphere and impact in the stratosphere. The results indicate that the relationship between local upper tropospheric moisture and convective events is timescale and latitude dependent. They illustrate the utility of high vertical and temporal resolution data for proper averaging and interpretation of convection and water vapor studies.
Separation of aerosol and gas components in the Halogen Occultation Experiment and the Stratospheric Aerosol and Gas Experiment (SAGE) II extinction measurements: Implications for SAGE II ozone concentrations and trends
Authors: Steele Helen M. , Turco Richard P.
Published: February 2004

This paper examines the high degree of linear dependence between multiwavelength extinction measurements of stratospheric aerosols and applies this to the problem of separating aerosol and gas contributions to the total measured extinction in the Stratospheric Aerosol and Gas Experiment (SAGE) II and Halogen Occultation Experiment (HALOE) satellite systems. Solar extinction recorded at wavelengths employed primarily for measuring gas densities inevitably includes a contribution from aerosols, whose spectral scattering behaviour depends on their unknown size distribution. Here linear relationships are determined to extract the aerosol contribution from the total extinction at the centers of the SAGE II ozone channel and the HALOE nitrogen dioxide and ozone broadband channels. The derived relationships are applied to both background and volcanic conditions. For the HALOE system we show how the currently employed two‐wavelength ratio gives accurate results for most commonly encountered particles sizes in the stratosphere. Although the use of multiple channels can improve the accuracy to which aerosols can be removed from HALOE gas channels, the sensitivity of the relationships to aerosol composition makes them impractical for routine processing. For the SAGE II experiment we show how inaccuracies in aerosol removal have affected the retrieved ozone concentration in the lower stratosphere. Under background conditions, SAGE II ozone concentrations are shown to be biased low by several percent, whereas in postvolcanic periods they are biased high. Prior to the eruption of Mount Pinatubo, SAGE II ozone concentrations below 20 km should be adjusted upward by up to 15% as too much of the measured 0.6 μm extinction has been attributed to aerosol. This change would exacerbate the discrepancy between SAGE II and ozonesonde data in the lower stratosphere throughout the 1980s. In the aftermath of Pinatubo the SAGE II ozone concentrations need to be adjusted downward by up to 15% as too little aerosol extinction was removed from the ozone channel. This shifting bias in the removal of aerosols by the SAGE II retrieval algorithm introduces an apparent downward trend in lower stratospheric ozone concentrations throughout the 1980s and early 1990s as the aerosol size distribution evolves during postvolcanic recovery periods. Trends as large as −2% per year have previously been reported from SAGE II data below 20 km. We show how a significant proportion of this could be explained by the incorrect aerosol removal.
Age scale of the air in the summit ice: Implication for glacial‐interglacial temperature change
Authors: Schwander J. , Sowers T. , Barnola J.‐M. , Blunier T. , Fuchs A. , Malaizé B.
Published: February 2004

The air occluded in ice sheets and glaciers has, in general, a younger age (defined as the time after its isolation from the atmosphere) than the surrounding ice matrix because snow is first transformed into open porous firn, in which the air can exchange with the atmosphere. Only at a certain depth (firn‐ice transition) the pores are pinched off and the air is definitely isolated from the atmosphere. The firn‐ice transition depth is at around 70 m under present climatic conditions at Summit, central Greenland. The air at this depth is roughly 10 years old due to diffusive mixing, whereas the ice is about 220 years old. This results in an age difference between the air and the ice of 210 years. This difference depends on temperature and accumulation rate and did thus not remain constant during the past. We used a dynamic firn densification model to calculate the firn‐ice transition depth and the age of the ice at this depth and an air diffusion model to determine the age of the air at the transition. Past temperatures and accumulation rates have been deduced from the δ18O record using time independent functions. We present the results of model calculations of two paleotemperature scenarios yielding a record of the age difference between the air and the ice for the Greenland Ice Core Project (GRIP) and the Greenland Ice Sheet Project Two (GISP2) ice cores for the last 100,000 years. During the Holocene, the age difference stayed rather stable around 200 years, while it reached values up to 1400 years during the last glaciation for the colder scenario. The model results are compared with age differences obtained independently by matching corresponding climate events in the methane and δ18O records assuming a very small phase lag between variations in the Greenland surface temperature and the atmospheric methane. The past firn‐ice transition depths are compared with diffusive column heights obtained from δ15N of N2 measurements. The results of this study corroborate the large temperature change of 20 to 25 K from the coldest glacial to Holocene climate found by evaluating borehole temperature profiles.
Wintertime planetary wave propagation in the lower stratosphere and its observed effect on northern hemisphere temperature‐ozone correlations
Authors: Sabutis J. L. , Turco R. P. , Kar S. K.
Published: February 2004

This study examines temporal and spatial correlations between TOMS total ozone and MSU4 brightness temperature data for the seven‐years 1980–1986. These data sets are separated into monthly mean and transient time series, and a Monte Carlo method is used to determine the statistical significance of the observed correlations. Monthly mean data have large areas of positive correlations during NH summer months, and during SH springtime months. Both the NH and SH have smaller areas of monthly mean positive correlations during winter. The NH has large areas of transient correlations during October, November and April, and the SH during September, October and November. One result of this analysis is that monthly mean and transient total ozone and brightness temperature show little correlation in the NH during January and the SH during July. To examine the role that planetary waves play in these correlations during January, LIMS data are used to calculate the wave activity. It is found that the NH regions of significant total ozone‐temperature positive correlations correspond to regions (corridors) in the stratosphere where large vertical planetary wave propagation takes place. Monthly mean correlations are found in the corridors over north central Asia, northeastern Pacific and northern Atlantic Oceans. Transient correlations are found over northern Canada. The northern Atlantic Ocean region is characterized by downward, and the remaining three regions are dominated by upward propagating wave activity. Trajectory calculations are used to examine the observed LIMS temperature and ozone trends. This analysis shows that as air parcels pass through the corridor over the northern Atlantic Ocean, they rise and cool. This unique region of downward wave activity and subsequent upward trajectory motion may be important when considering the processing of air by polar stratospheric clouds.
The climatological distribution of tropospheric ozone derived from satellite measurements using version 7 Total Ozone Mapping Spectrometer and Stratospheric Aerosol and Gas Experiment data sets
Authors: Fishman Jack , Brackett Vincent G.
Published: February 2004

The climatological distribution of tropospheric ozone derived from satellite observations has been updated using the reprocessed version 7 Total Ozone Mapping Spectrometer (TOMS) gridded data. The use of version 7 of the archive has not changed any of the climatological features first identified using earlier archived versions of the TOMS data. In general, however, the absolute values of the amount of ozone in the troposphere are decreased by ∼5 Dobson units (DU). In areas of persistent marine stratus clouds, the climatological values are decreased by an additional 2–3 DU.
Recent observations of mesospheric temperature inversions
Authors: Leblanc Thierry , Hauchecorne Alain
Published: February 2004

The recent results of observed mesospheric temperature inversions are presented. Using two Rayleigh lidars (located in the south of France) and ISAMS (Improved Stratospheric And Mesospheric Sounder) and HALOE (Halogen Occultation Experiment) temperature measurements from UARS, a new detailed climatology of the inversions (occurring between 65 and 85 km of altitude) has been developed. A strong annual cycle is observed at midlatitudes, with a maximum during the winter months (monthly mean amplitude of 15 K observed by lidar at 44°N, 5°E). This annual cycle is also observed by ISAMS and HALOE for all longitudes, so that a midlatitude belt of strong inversions forms during the southern and northern winters. In addition, a strong semiannual cycle is observed by ISAMS and HALOE at lower latitudes, with its maxima 1 month after the equinoxes. Both solstice and equinoctial events are the most significant observed signatures of the inversions. The frequency of occurrence of the inversions follows the same annual and semiannual cycles. The winter inversion events are located about 70 km of altitude, and the equinoctial events are located 5–10 km above, suggesting that different processes could be involved. The winter events observations are consistent with some of the proposed mechanisms, involving the breaking gravity waves, while no evidence of similar mechanisms was found for the equinoctial events.
Organic aerosols in the Caribbean trade winds: A natural source?
Authors: Novakov T. , Corrigan C. E. , Penner J. E. , Chuang C. C. , Rosario O. , Bracero O. L. Mayol
Published: February 2004

Mass concentrations of carbonaceous and inorganic components of submicron (aerodynamic diameters < 0.6 μm) aerosol particles were measured at Cape San Juan, a coastal site located on the extreme northeastern tip of Puerto Rico. Additionally, carbonaceous aerosols and condensation nuclei (CN) were measured offshore during a limited shipboard sampling experiment at an Atlantic Ocean site away from the coast. Both sites were exposed to trade winds during the sampling periods. Under these conditions no obvious upwind anthropogenic sources should impact the sites. From the analyses of collected filter samples, mass concentrations of major inorganic anions and filterable particulate organic aerosol material (OCp) were determined. The derived OCp concentrations may represent lower limits because of the uncertainty in the collection of semivolatile organic material lost from the particles during sampling. Analyses of Cape San Juan samples show that (1) mass concentrations of submicron OCp (average about 390 ng m−3) exceed sulfate concentrations (average about 270 ng m−3); (2) this organic aerosol material is water soluble (and the particles act as effective cloud condensation nuclei); and (3) primary combustion aerosol does not appear to be a major contributor to OCp. The fact that OCp concentrations measured at the coastal site are similar to OCp concentrations (330–400 ng m−3) measured at an Atlantic Ocean site removed from the coast suggests that a substantial fraction of the OCp in the Caribbean trade winds may be associated with natural oceanic emissions. Results imply that background organic marine aerosol should be included in estimating the indirect forcing of climate by anthropogenic sulfate aerosol.
Ventilation of liquefied petroleum gas components from the Valley of Mexico
Authors: Elliott Scott , Blake Donald R. , Rowland F. Sherwood , Lu Rong , Brown Michael J. , Williams Michael D. , Russell Armistead G. , Bossert James E. , Streit Gerald E. , Santoyo Marisa Ruiz , Guzman Francisco , Porch William M. , McNair Laurie A. , Keyantash John , Kao Chih‐Yue Jim , Turco Richard P. , Eichinger William E.
Published: February 2004

The saturated hydrocarbons propane and the butane isomers are both indirect greenhouse gases and key species in liquefied petroleum gas (LPG). Leakage of LPG and its component alkanes/alkenes is now thought to explain a significant fraction of the volatile organic burden and oxidative potential in the basin which confines Mexico City. Propane and the butanes, however, are stable enough to escape from the basin. The gas Chromatographie measurements which have drawn attention to their sources within the urban area are used here to estimate rates of ventilation into the free troposphere. The calculations are centered on several well studied February/March pollution episodes. Carbon monoxide observations and emissions data are first exploited to provide a rough time constant for the removal of typical inert pollutant species from the valley. The timescale obtained is validated through an examination of meteorological simulations of three‐dimensional flow. Heuristic arguments and transport modeling establish that propane and the butanes are distributed through the basin in a manner analogous to CO despite differing emissions functions. Ventilation rates and mass loadings yield outbound fluxes in a box model type computation. Estimated in this fashion, escape from the Valley of Mexico constitutes of the order of half of 1% of the northern hemispheric inputs for both propane and n‐butane. Uncertainties in the calculations are detailed and include factors such as flow into the basin via surface winds and the size of the polluted regime. General quantification of the global propane and butane emissions from large cities will entail studies of this type in a variety of locales.
The effects of clouds on aerosol and chemical species production and distribution: 1. Cloud model formulation, mixing, and detrainment
Authors: Taylor Gregory R. , Kreidenweis Sonia , Zhang Yiping
Published: February 2004

Clouds play an important role in tropospheric chemical processes and in the modulation of global climate via transport of reactive species from lower levels of the troposphere to higher altitudes and by modification of boundary layer gas and aerosol concentrations by aqueous phase reactions in cloud and precipitation. We present here the initial results of a study of the effects of deep convective clouds upon transport of aerosols and aerosol precursor gases along with a discussion of the formulation of the two‐dimensional Eulerian model dynamics and two‐moment bulk microphysics parameterization. Results from a test run using data from the Cooperative Convective and Precipitation Experiment show reasonable agreement with observations, although comparison with aircraft observations show the model cannot resolve saturated downdrafts. Comparison with the Taylor and Baker [1991] detrainment criterion shows good agreement for water vapor, a passive tracer, and cloud condensation nuclei.
Potential origin of organic cloud condensation nuclei observed at marine site
Authors: Andrews Elisabeth , Kreidenweis Sonia M. , Penner Joyce E. , Larson Susan M.
Published: February 2004

Observations by Novakov and Penner [1993] (hereinafter, NP) suggest that organic aerosol particles may make up a significant portion of cloud condensation nuclei (CCN), comparable perhaps to the sulfate aerosol contribution to CCN. Because organic CCN would influence the albedo and radiative properties of clouds and play a role in climate change, it is important to identify the sources of these aerosols. In their research, Novakov and Penner showed that particles larger than 0.05 μm could act as CCN at supersaturation ratios of 0.5% water vapor. Here we use model simulations to investigate the origins of the nucleation mode aerosol (0.03<dp<0.1 μm) observed at a marine site in Puerto Rico by NP. NP measured the size segregated mass and composition of the atmospheric aerosol at this site and found that organic aerosol mass dominated the total mass in the nucleation mode. The presence of organics in this size range may be the result of nucleation of a gas phase organic and/or condensational growth. Therefore identifying sources of the gas phase precursors is important to determining the origins of the organic CCN. Back trajectory analysis (J. Merrill, private communication, 1994) shows that the air mass that Novakov and Penner studied was without continental contact for 8–12 days prior to being sampled. This implicates two possible sources for the gas phase organic: biogenic emissions from the Puerto Rican forest upwind of the mountain sampling site and emissions from the ocean surface. In this study both the forest and ocean source scenarios are explored. Using input parameters taken from the literature, it is shown that an assumed organic vapor flux for the forest scenario, very similar to the measured biogenic fluxes reported by Zimmerman et al. [1988], generated size distributions similar to the observed aerosol. In contrast, literature estimates for the n‐alkane vapor flux from the ocean are not consistent with the observed size distribution at the mountain site.
The Milan photooxidant plume
Authors: Prévôt André S. H. , Staehelin Johannes , Kok Gregory L. , Schillawski Richard D. , Neininger Bruno , Staffelbach Thomas , Neftel Albrecht , Wernli Heini , Dommen Josef
Published: February 2004

In Switzerland, measurement campaigns including aircraft measurements were carried out in the summers of 1992 and 1993 as part of the Pollution and Meteorology (POLLUMET) study. Ozone (O3) concentrations, up to 185 ppb, with a large spatial variability were found south of the Alps in the afternoon. Comparison to measurements north of the Alps shows that these concentration levels are extraordinarily high for central Europe. Backward trajectories reveal that the highest O3 levels were found 4–5 hours downwind of Milan, Italy. The measurements suggest a reactive organic gas (ROG) sensitive O3 production regime 1–3 hours downwind in the plume, and a NOx (sum of nitrogen oxide (NO) and nitrogen dioxide (NO2)) limitation in air masses not affected by the Milan plume. Air masses originating north of Milan are probably close to the transition zone between the two photochemical regimes. This was found by using measurements of total odd nitrogen (NOy,), NO, NO2, formaldehyde (HCHO), and hydrogen peroxide (H2O2) yielding indicators for ROG and NOx sensitive O3 production. The slope of ozone versus NOz (=NOy−NOx: photochemical products of NOx) were markedly higher in NOx limited conditions (ΔO3/ΔNOz=13.6) than in air masses close to the transition zone (ΔO3/ΔNOz=4.2).
Synoptic‐scale mass exchange from the troposphere to the stratosphere
Authors: Rood Richard B. , Douglass Anne R. , Cerniglia Mark C. , Read William G.
Published: February 2004

The transport of material between the troposphere and the stratosphere is studied with an off‐line chemical transport model which uses winds from a global assimilated meteorological data set. The focus is on the role of rapidly growing synoptic waves in the maintenance of lower stratospheric tracer distributions in the extratropics. Satellite observations are used to establish that the modeled transport represents the observed tracer variability with sufficient accuracy to justify more quantitative analysis. Diabatic trajectory calculations are then used to understand the transport mechanisms in the model. Two rapidly developing surface cyclones are specifically studied and found to have qualitatively different impact on the tracer distribution. A strong storm in the Pacific Ocean perturbs the tropopause region, and because it remains relatively stationary, ultimately has transport characteristics similar to a cutoff low. The explosively developing synoptic wave responsible for the March 1993 blizzard in the eastern United States causes large‐scale transport between the troposphere and stratosphere. There are two notable characteristics of the transport associated with the U.S. blizzard: (1) The U.S. blizzard moves across many degrees of latitude. This storm develops in the subtropics, with a high tropopause, and later decays in a subpolar environment where the tropopause is naturally much lower. (2) Diabatic processes are crucial to the long‐range transport and ultimate transfer of mass to the stratosphere. The transport studied in connection with the United States requires consideration of the entire life cycle of the storm from subtropical cyclogenesis to subpolar decay. The fact that storms that are similar to the U.S. blizzard are quite common and that the transport is consistent with available tracer observations suggest that the large‐scale transport of air from the troposphere to the stratosphere is plausible. Further investigation with more sophisticated models and tracer observations is needed to verify the importance of the modeled transport.
High bromine aerosol concentrations near Lake Huron from long‐range transport from the Arctic during polar sunrise
Authors: Biegalski S. R. , Landsberger S. , Hoff R.
Published: February 2004

Aerosol samples were collected at the Burnt Island sampling station in the northern part of Lake Huron, Canada. These samples were analyzed for trace elements via neutron activation analysis and aerosol concentrations were determined for the time period from 1992 through 1994. The seasonal trends of these aerosols were investigated and the results for bromine indicated seasonal highs in the month of March. This was different from the trend displayed by sodium whose peak was not as pronounced. Sodium was an indicator of the salt component of the aerosol that Br was associated with at this site. Wind trajectory end‐point analysis was utilized to show that the high Br aerosol concentrations originate from the Arctic where Br aerosols have seasonal highs in the spring due to the photo‐induced production of particulate Br. This research shows that the highest levels of the Br aerosol in the rural north Lake Huron area originate from the production of Br in the Arctic.
The influence of soil gas transport properties on methane oxidation in a selection of northern European soils
Authors: Ball B. C. , Smith K. A. , Klemedtsson L. , Brumme R. , Sitaula B. K. , Hansen S. , Priemé A. , MacDonald J. , Horgan G. W.
Published: February 2004

The oxidation of atmospheric methane in soils was measured in situ at a selection of sites in northern Europe, mainly under forest but also under moorland and agricultural arable land and grassland. Our objective was to examine how land use, soil type, and location affected methane oxidation through their impact on gas diffusivity and air permeability. Gas diffusivity at the soil surface and, in some cases, after removal of any surface organic layer was measured in situ using Freon‐22 tracer in a portable probe. For about half of the sites, gas diffusivity was also measured in intact topsoil core samples in the laboratory using krypton 85. Air permeability and porosity were also measured on these cores. Although the method of measurement of CH4 oxidation varied between sites, the same techniques were used to measure soil physical properties at all sites. CH4 oxidation rates ranged from 0 to 2.5 mg m−2 d−1. Diffusivity also covered a very wide range, being lowest in loam cores from wet grassland in Norway and highest in relatively dry, sandy soils in Denmark and Scotland. CH4 oxidation tended to increase with gas diffusivity measured in situ at the soil surface, though the relationship was poor at high diffusivities, presumably because CH4 oxidation was not limited by diffusion. Removal of the surface organic layer reduced in situ diffusivity at the surface and improved its relationship with CH4 oxidation rate. Sites where soils had well‐developed structure and a loose and permeable organic layer at the surface tended to have the highest CH4 oxidation rates. Core measurements, particularly of air permeability, could not be obtained at some sites owing to the inability to take suitable samples. Diffusivity measured in cores generally decreased with increasing depth of sampling in the topsoil, with the 50‐to 100‐mm depth giving the best correlation with CH4 uptake; cores from within this layer also gave the highest CH4 oxidation during laboratory incubation. Effective comparisons between sites were hampered by the differing responses of CH4 oxidation and diffusivity to soil properties. However, multivariate cluster analysis that included the above transport variables plus others relevant to CH4 oxidation (namely, soil texture; bulk density; airfilled porosity; pH; carbon, nitrogen, and water contents; presence and depth of organic layers; and N deposition) confirmed the importance of soil water content, structure and texture in distinguishing different soil and site conditions.
Comments on some recent measurements of anomalously steep N2O and O3 tracer spectra in the stratospheric surf zone
Authors: Ngan Keith , Shepherd Theodore G.
Published: February 2004

Recent aircraft measurements, primarily in the extratropics, of the horizontal variance of nitrous oxide (N2O) and ozone (O3) in the middle stratosphere indicate that horizontal spectra of the tracer variance scale nearly as k−2, where k is the spatial wavenumber along the aircraft flight track [Strahan and Mahlman, 1994; Bacmeister et al., 1996]. This spectral scaling has been regarded as inconsistent with the accepted picture of stratospheric tracer motion; large‐scale quasi‐two‐dimensional tracer advection typically yields a k−1 scaling (i.e., the classical Batchelor spectrum). In this paper it is argued that the nearly k−2 scaling seen in the measurements is a natural outcome of quasi‐two‐dimensional filamentation of the polar vortex edge. The accepted picture of stratospheric tracer motion can thus be retained: no additional physical processes are needed to account for deviations from the Batchelor spectrum. Our argument is based on the finite lifetime of tracer filaments and on the “singularity spectrum” associated with a one‐dimensional field composed of randomly spaced jumps in concentration.
Atmospheric absorption during the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE)
Authors: Zender Charles S. , Bush Brett , Pope Shelly K. , Bucholtz Anthony , Collins William D. , Kiehl Jeffrey T. , Valero Francisco P. J. , Vitko John
Published: February 2004

The objectives of the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE) are to directly measure clear and cloudy sky shortwave atmospheric absorption and to quantify any absorption found in excess of model predictions. We undertake detailed model comparisons to near‐infrared and total solar flux time series observed by surface and airborne radiometric instruments during the ARESE campaign. Model clear‐sky absorption biases generally fall within the range of uncertainty generated by sample size, and assumptions of aerosol properties and surface albedo. Direct measurements by stacked aircraft on the overcast day of October 30, 1995, confirm the detection of enhanced cloud shortwave absorption during ARESE. The detection is substantiated by, and consistent with, three independent measures of cloudy sky absorption estimated in previous studies: cloud forcing ratio, insolation forcing ratio, and albedo/transmission slope. A significant portion of the enhanced absorption occurs at visible wavelengths. Collocated measurements of liquid water path (LWP) suggest the magnitude of the enhanced absorption increases with LWP.
Mean winds in the tropical stratosphere and mesosphere during January 1993, March 1994, and August 1994
Authors: Hitchman Matthew H. , Kudeki Erhan , Fritts David C. , Kugi Joleen M. , Fawcett Clint , Postel Gregory A. , Yao Chia‐Yi , Ortland David , Riggin Dennis , Harvey V. Lynn
Published: February 2004

Radar observations of winds and momentum fluxes in the stratosphere and mesosphere at the Jicamarca Radio Observatory in Peru ( JRO; 12°S, 77°W) were taken during three 10 day campaigns in January 1993, March 1994, and August 1994. In order to interpret features in the campaign mean JRO wind profiles, we examined global circulation patterns as depicted by long time series of radiosonde profiles, analyses from the European Center for Medium Range Weather Forecasting (ECMWF), and winds from the High Resolution Doppler Imager (HRDI) aboard the Upper Atmosphere Research Satellite. In the tropical stratosphere, large‐scale analyses show that a geographically varying annual cycle significantly affects winds over JRO, as does the quasi‐biennial oscillation ( QBO). The spatial structure of the annual cycle and QBO is shown for the three campaigns, emphasizing the upward influence of subtropical tropospheric monsoon anticyclones. These anticyclones tilt poleward and merge zonally, underlying the zonal summer easterlies, which also merge zonally and tilt poleward with altitude. The annual cycle at Singapore includes a substantial easterly acceleration during March‐August, which causes an apparent stalling of descending QBO westerlies or a more rapid descent of QBO easterlies. In the mesosphere, JRO and HRDI winds agree reasonably well, with zonal winds over JRO varying on a semiannual basis and meridional winds exhibiting structures expected from the diurnal tide. For vertical motion, separate north‐south and east‐west beam pair estimates agree, yet campaign‐averaged vertical motions are large: ∼1–5 cm/s in the stratosphere and ∼ 10–50 cm/s in the mesosphere. In both the stratosphere and mesosphere, vertical winds are anticorrelated with horizontal wind. Possible explanations for the large vertical motions include aspect sensitivity and the diurnal tide. Uncertainties in the meaning of radar vertical motions create a challenge for interpreting momentum fluxes.
Thermodynamic and optical properties of sea salt aerosols
Authors: Tang I. N. , Tridico A. C. , Fung K. H.
Published: February 2004

Sea salt particles are constantly produced from ocean surfaces by wave‐wind interactions and removed by deposition and precipitation scavenging. These particles constitute the background aerosol for light scattering in the marine boundary layer. In this work, the thermodynamic and optical properties of sea salt aerosol particles generated from seawater samples are measured at 25°C as a function of relative humidity, using a single‐particle levitation technique. Water activities, densities, and refractive indices of aqueous solution droplets containing a single salt NaCl, Na2SO4, MgCl2, or MgSO4 are also reported as a function of concentration. The light‐scattering properties of the sea salt aerosol are modeled by the external mixture of these four salt systems selected to approximate the sea salt composition. Good agreements are obtained. It follows that in either visibility reduction or radiative forcing calculations, both freshly produced and aged sea salt aerosols may be modeled by external mixtures of the appropriate inorganic salts, whose solution properties are now available in the literature.
Spatiotemporal analysis and processing of thermometric data over Belgium
Authors: Bogaert P. , Christakos G.
Published: February 2004

Thermometric measurements over Belgium provide a considerable amount of spatiotemporal data, the study of which can provide valuable information for a variety of atmospheric studies, agricultural activities, pollution control, etc. In this work, a data set that includes a year of daily temperature measurements at 121 stations and shows a complicated variation in space and time is selected and analyzed using a spatiotemporal random field model. This model has three random components and a space/time mean function, which allow considerable flexibility in analytical calculations and rigorous assessment of the spatiotemporal variation of temperature. A space/time estimation system is formulated and solved to provide detailed temperature maps over the whole country. The composite space/time analysis offers valuable physical insight that could not have been obtained on the basis of a purely spatial or a purely temporal analysis of the temperature data set. The variability between successive days at a monitoring station is considerably more important than spatial variability throughout the country at a given day, and therefore limited improvements should be expected regarding temperature forecasting and interpolation by focusing only on the spatial aspect of the temperature variation.
A new inverse method for trace gas flux estimation: 1. State‐space model identification and constraints
Authors: Mulquiney John E. , Norton John P.
Published: February 2004

A new method for estimating time‐varying fluxes of atmospheric trace gases using an atmospheric transport model and observed concentrations is presented. Specifically Kaiman filtering is used to estimate inputs from a state‐space model identified using unit‐pulse response functions from a transport model. The method is new in that no assumptions about initial concentrations in the model are required, although this in turn means that all flux processes must be explicitly modeled as inputs linearly related to concentrations. This also means that at least one extra measuring‐site or other measurement variable (e.g. a linear combination of emissions) than the number of input‐fluxes being estimated, is required to ensure a stable Kaiman filter.
Scavenging of aerosol particles by large water drops: 3. Washout coefficients, half‐lives, and rainfall depths
Authors: Pranesha T. S. , Kamra A. K.
Published: February 2004

Using the average values of collection efficiencies obtained from our experiments [Pranesha and Kamra, 1996, this issue] washout coefficients for the drops in the diameter (D) range 3.6≤D≤5.0 mm collecting micron‐sized aerosol particles have been calculated when the drops are neutral, charged, or falling in an electric field. Compared with the neutral case, the values of washout coefficients are higher in both electrical cases, the increase being more pronounced for smaller particles. Washout coefficients show a maximum for a drop charge of 10−12 to 10−11 C. With an increase in electric field, the washout coefficients increase linearly for ∼1‐μm particles, show a maximum for ∼4‐μm particles, and change insignificantly for ∼7‐μm particles. Combining our experimental values of collection efficiencies with the theoretical collision efficiencies of McGann and Jennings [1991] for smaller drops, washout coefficients, half‐lives, and rainfall depths have been computed for the raindrop size distribution extending from 0.1‐ to 5 mm‐diameter. Results show that raindrops of diameter >1 mm contribute dominantly in removing particles of diameter 1–2 μm and their contributions increase with the rainfall rate. When the effect of the raindrops of diameter >1 mm is included, the values of washout coefficient increase by about 2 orders of magnitude for particles of diameter 1–2 μm and by about 1 order of magnitude for particles of diameter >2 μm. It can be concluded from the estimates of rainfall depth that a heavy rainfall over a short duration is more efficient in removing the particles of diameter <2.2 μm, whereas a lower rainfall spread over a longer duration is more efficient in removing the particles of diameter >2.2 μm.