bluuebunny/crossref_metadata_2025 huggingface dataset:
Retrieval of aerosol surface area and volume densities from extinction measurements: Application to POAM II and SAGE II
Authors: Steele H. M. , Lumpe J. D. , Turco R. P. , Bevilacqua R. M. , Massie S. T.
Published: September 2002

In this paper we evaluate two different methods for determining aerosol surface area and volume densities from multiwavelength extinction measurements and apply them to the Polar Aerosol and Ozone Measurement (POAM II) and Stratospheric Aerosol and Gas Experiment (SAGE II) data. Systematic and random components of the retrieval error are calculated as a function of the size distribution parameters for a unimodal lognormal size distribution using principal component analysis and an empirical formulation based on the 1 μm extinction measurement. The trade‐off between these two components of the error is demonstrated for principal component analysis by varying the degree of constraint. We show how the systematic error can exceed the random error for lognormal size distributions typical of background aerosols. Retrieved surface areas for background aerosols can be underestimated by up to 50% through principal component analysis. Random errors depend on the estimated measurement error at each wavelength but, for the instruments considered, are expected to be 15–25%. Retrieved volume densities for background aerosols are underestimated by up to 30% through principal component analysis and suffer an additional random error component of 10–15%. The empirical formulation leads to altitude dependent systematic errors since the relative error depends on the particle number density. When different techniques are used to obtain aerosol surface area and volume, there is often a greater disagreement between different methods applied to the same data than the same method applied to data recorded by two different instruments. Systematic errors arising from the retrieval methodology should therefore be carefully considered in both validation and aerosol climatology studies.
Retrieval of aerosol properties over the ocean using Global Ozone Monitoring Experiment measurements: Method and applications to test cases
Authors: Torricella Francesca , Cattani Elsa , Cervino Marco , Guzzi Rodolfo , Levoni Chiara
Published: September 2002

Satellite monitoring of aerosol properties using passive techniques is widely considered a crucial tool for the study of climatic effects of atmospheric particulate [Kaufman et al., 1997]. Only space‐based observations can provide the required global coverage information on spatial distribution and temporal variation of the aerosol field. This paper describes a method for deriving aerosol optical thickness at 500 nm and aerosol type from Global Ozone Monitoring Experiment (GOME) data over the ocean under cloud‐free conditions. GOME, flying on board the second European Remote Sensing satellite (ERS 2) since April 1995, is a spectrometer that measures radiation reflected from Earth in the spectral range 240–793 nm. The features of the instrument relevant to the aerosol retrieval task are its high relative radiometric accuracy (better than 1%), its spectral coverage, and its spectral resolution, which allows wavelengths in spectral regions free of molecular absorption (atmospheric windows) to be selected. The method presented is based on a pseudo‐inversion approach in which measured reflectance spectra are fitted to simulated equivalents computed using a suitable radiative transfer model. The crucial aspects of this method are the high accuracy and the nonapproximate nature of the radiative transfer model, which simulates the spectra during the fitting procedure, and careful selection of candidate aerosol classes. A test application of the proposed method to a Saharan dust outbreak which occurred in June 1997 is presented, showing that in spite of the instrument's low spatial resolution, information on both optical thickness and spectral characterization of the aerosol can be retrieved from GOME data. Preliminary comparisons of the results with independent estimates of the aerosol content show that a good correlation exists, encouraging planning of a systematic application of the method.
A model for the longwave radiation budget of the northern hemisphere: Comparison with Earth Radiation Budget Experiment data
Authors: Hatzianastassiou N. , Croke B. , Kortsalioudakis N. , Vardavas I. , Koutoulaki K.
Published: September 2002

A deterministic model for atmospheric longwave radiation transfer was used with climatological data to predict the mean monthly zonal (10° latitudinal zones) longwave radiation budget at the Earth's surface and at the top of the atmosphere for the Northern Hemisphere. The climatological data were obtained from the International Satellite Cloud Climatology Project (1983–1990), and from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis Project. The model's outgoing fluxes agree within 4 W m−2, on average, with the corresponding values determined from the Earth Radiation Budget Experiment (1985–1989) satellite data. The validation of the model for the top‐of‐atmosphere radiation budget allows one to obtain a better understanding of the important processes that govern the transfer of the longwave radiation for each season and zone. At the surface, validation of the predicted downwelling radiation is difficult owing to the lack of extensive ground‐based measurements. However, we have made intercomparisons with other model predictions and with ground‐based measurements that were available. The predictions of the model for the surface longwave radiation budget provide a measure against which simpler algorithms, derived from ground‐based measurements, can be compared and used to convert satellite climatologies to a globally distributed surface longwave radiation budget for climatic studies.
Tropospheric clouds and lower stratospheric heating rates: Results from late winter in the southern hemisphere
Authors: Hicke Jeffrey , Tuck Adrian
Published: September 2002

Tropospheric clouds can impact the radiative heating of the lower stratosphere substantially, though their effect over a winter has been estimated by previous studies to be small. In this study clouds were incorporated into radiative transfer calculations by matching computations of outgoing longwave radiation (OLR) with collocated satellite observations of OLR. Narrowband (cm−1 resolution) heating rate calculations reveal that differences in clear and cloudy heating rates occur in the ozone 9.6 μm band, where radiation exchange with the lower surface dominates the heating rate terms. By reducing the temperature of the emitting surface, clouds can decrease the heating rate by 0.6 K d−1 (dθ/dt) at 450 K for single profile calculations and have the greatest impact when over the warm, open ocean. Monthly mean calculations in the Southern Hemisphere show regions where heating rates decrease (cooling rates increase) by 0.2–0.3 K d−1 when clouds are added; these regions include areas that are equatorward of the sea ice edge but within the stratospheric polar vortex. Zonal mean heating rates display a maximum just poleward of the vortex edge during August and September 1994. Zonal monthly mean comparisons of the OLR‐matched cloudy heating rates with those using a cloud climatology show that the climatology captures 50–75% of this decrease in heating rates compared to clear skies. Differences between zonal monthly means of the daily heating rate and heating rates computed using zonal monthly inputs are small, validating the use of mean radiative heating rates in two‐dimensional monthly calculations.
Correlation between smoke and tropospheric ozone concentration in Cuiabá during Smoke, Clouds, and Radiation‐Brazil (SCAR‐B)
Authors: Longo Karla M. , Thompson Anne M. , Kirchhoff Volker W. J. H. , Remer Lorraine A. , de Freitas Saulo R. , Dias Maria A. F. Silva , Artaxo Paulo , Hart William , Spinhirne James D. , Yamasoe Márcia A.
Published: September 2002

Ozone soundings launched from Cuiabá between August 16 and September 10, 1995, during the Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) experiment show an enrichment of tropospheric ozone when compared with average wet season values and also present a great variability in concentrations depending on the dominant circulation pattern. Smoke tracers, such as aerosol optical thickness, measured from a Sun photometer installed at the Instituto Nacional de Pesquisas Espaciais‐Cuiabá site, and black carbon ground measurements, also show an enhancement of smoke during the same period. Although there is a connection between the enrichment of the tropospheric ozone around Cuiabá during the dry season and smoke from biomass burning, the correlation between ozone and smoke indicates different behavior in different periods. Trajectory analyses suggest that the strong ozone peak measured in the period between August 26 and 29, 1995, may be associated not only with direct biomass‐burning emissions but also with urban/industrial emissions from big cities on the coast of Brazil and recirculation of old smoke. This view is confirmed by measurements made from the Cloud Lidar System instrument aboard the ER‐2 aircraft.
Anthropogenic emissions of trichloromethane (chloroform, CHCl3) and chlorodifluoromethane (HCFC‐22): Reactive Chlorine Emissions Inventory
Authors: Aucott M. L. , McCulloch A. , Graedel T. E. , Kleiman G. , Midgley P. , Li Yi‐Fan
Published: September 2002

Anthropogenic emissions of trichloromethane (CHCl3, chloroform) in 1990 have been estimated with a variety of methods specific to the source category. The largest source category for CHCl3 was found to be pulp and paper manufacturing, responsible for an estimated 30±8 Gg yr−1 reactive chlorine in the form of CHCl3. Water treatment of various types was estimated to contribute another 19±12 Gg. Manufacturing facilities of products other than pulp or paper and other relatively minor sources were estimated to emit an additional 13±5 Gg yr−1, for a total of 62±25 Gg yr−1 reactive chlorine in the form of CHCl3. The global flux of chlorodifluoromethane (HCFC‐22) is well characterized from industrial and regulatory data to have been 195 Gg in 1990, equivalent to 80±0.6 Gg yr−1 as active chlorine. The fluxes of reactive chlorine from CHCl3 and HCFC‐22, distributed globally in a 1° latitude times 1° longitude grid, revealed areas highest in emissions.
Simulations of cosmogenic 14CO using the three‐dimensional atmospheric model MATCH: Effects of 14C production distribution and the solar cycle
Authors: Jöckel Patrick , Lawrence Mark G. , Brenninkmeijer Carl A. M.
Published: September 2002

Most atmospheric 14CO is produced by cosmic rays in the lowermost stratosphere and upper troposphere. The main removal process for 14CO is oxidation by OH radicals. Assuming that the spatial distribution of OH is well known, 14CO can be useful as a test‐tracer for the transport properties of a three‐dimensional chemical model. Conversely, if the transport schemes of the model are sufficiently realistic, in particular with respect to stratosphere‐troposphere exchange, the OH distribution can be evaluated. In either case, it has to be assumed that the source of 14CO is known in sufficient detail. Two presently available distributions of cosmogenic 14C production are implemented into the Model of Atmospheric Transport and Chemistry (MATCH). The tropospheric 14CO concentrations that are obtained are relatively insensitive to the source differences. The calculations for one source distribution are performed for solar minimum and solar maximum conditions. The spatial distribution of 14CO is almost unaffected by the solar activity, and the absolute concentration levels can be scaled to the actual solar cycle conditions.
Aerosol influence on the sea‐viewing wide‐field‐of‐view sensor bands: Extinction measurements in a marine summer atmosphere over the Baltic Sea
Authors: Kuśmierczyk‐Michulec J. , Krüger O. , Marks R.
Published: September 2002

Measurements of atmospheric extinction at sea‐viewing wide‐field‐of‐view sensor wavelengths were carried out during the Lagrangian Experiment on the Baltic Sea within the Baltic Sea System Study project, July 2–15, 1997. The empirical orthogonal functions method was applied to the aerosol optical thickness spectra, allowing three air mass types, containing different aerosol types, to be distinguished: continental, continental‐maritime, and maritime, corresponding to different residence times of air masses over the Baltic Sea. The amplitude of the aerosol optical thickness, describing the temporal variability, was found to be strongly affected by the atmospheric stability. The contribution of the aerosol radiance to the atmospheric radiance depends directly on the aerosol type, the wavelength λ, and the solar zenith angle θs. The most significant contribution of more than 30% was detected for the continental and continental‐maritime aerosol types, for θs = 30°, and at λ = 865 nm.
Ozone and aerosol distributions and air mass characteristics over the South Pacific during the burning season
Authors: Fenn Marta A. , Browell Edward V. , Butler Carolyn F. , Grant William B. , Kooi Susan A. , Clayton Marian B. , Gregory Gerald L. , Newell Reginald E. , Zhu Yong , Dibb Jack E. , Fuelberg Henry E. , Anderson Bruce E. , Bandy Alan R. , Blake Donald R. , Bradshaw John D. , Heikes Brian G. , Sachse Glen W. , Sandholm Scott T. , Singh Hanwant B. , Talbot Robert W. , Thornton Donald C.
Published: September 2002

In situ and laser remote measurements of gases and aerosols were made with airborne instrumentation to establish a baseline chemical signature of the atmosphere above the South Pacific Ocean during the NASA Global Tropospheric Experiment (GTE)/Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A) conducted in August‐October 1996. This paper discusses general characteristics of the air masses encountered during this experiment using an airborne lidar system for measurements of the large‐scale variations in ozone (O3) and aerosol distributions across the troposphere, calculated potential vorticity (PV) from the European Centre for Medium‐Range Weather Forecasting (ECMWF), and in situ measurements for comprehensive air mass composition. Between 8°S and 52°S, biomass burning plumes containing elevated levels of O3, over 100 ppbv, were frequently encountered by the aircraft at altitudes ranging from 2 to 9 km. Air with elevated O3 was also observed remotely up to the tropopause, and these air masses were observed to have no enhanced aerosol loading. Frequently, these air masses had some enhanced PV associated with them, but not enough to explain the observed O3 levels. A relationship between PV and O3 was developed from cases of clearly defined O3 from stratospheric origin, and this relationship was used to estimate the stratospheric contribution to the air masses containing elevated O3 in the troposphere. The frequency of observation of the different air mass types and their average chemical composition is discussed in this paper.
Constraints on the age and dilution of Pacific Exploratory Mission‐Tropics biomass burning plumes from the natural radionuclide tracer210Pb
Authors: Dibb Jack E. , Talbot Robert W. , Meeker L. David , Scheuer Eric M. , Blake Nicola J. , Blake Donald R. , Gregory Gerald L. , Sachse Glen W.
Published: September 2002

During the NASA Global Troposphere Experiment Pacific Exploratory Mission‐Tropics (PEM‐Tropics) airborne sampling campaign we found unexpectedly high concentrations of aerosol‐associated210Pb throughout the free troposphere over the South Pacific. Because of the remoteness of the study region, we expected specific activities to be generally less than 35 μBq m−3but found an average in the free troposphere of 107 μBq m−3. This average was elevated by a large number of very active (up to 405 μBq m−3) samples that were associated with biomass burning plumes encountered on nearly every PEM‐Tropics flight in the southern hemisphere. We use a simple aging and dilution model, which assumes that222Rn and primary combustion products are pumped into the free troposphere in wet convective systems over fire regions (most likely in Africa), to explain the elevated210Pb activities. This model reproduces the observed210Pb activities very well, and predicts the ratios of four hydrocarbon species (emitted by combustion) to CO to better than 20% in most cases. Plume ages calculated by the model depend strongly on the assumed222Rn activities in the initial plume, but using values plausible for continental boundary layer air yields ages that are consistent with travel times from Africa to the South Pacific calculated with a back trajectory model. The model also shows that despite being easily recognized through the large enhancements of biomass burning tracers, these plumes must have entrained large fractions of the surrounding ambient air during transport.
Atmospheric processing of organic aerosols
Authors: Ellison G. Barney , Tuck Adrian F. , Vaida Veronica
Published: September 2002

We suggest a chemical model for the composition, structure, and atmospheric processing of organic aerosols. This model is stimulated by recent field measurements showing that organic compounds are a significant component of atmospheric aerosols. The proposed model organic aerosol is an ‘inverted micelle’ consisting of an aqueous core that is encapsulated in an inert, hydrophobic organic monolayer. The organic materials that coat the aerosol particles are surfactants of biological origin. We propose a chemical mechanism by which the organic surface layer will be processed by reactions with atmospheric radicals. The net result of an organic aerosol being exposed to an oxidizing atmosphere is the transformation of an inert hydrophobic film to a reactive, optically active hydrophilic layer. Consequently, processed organic aerosols can grow by water accretion and form cloud condensation nuclei, influencing atmospheric radiative transfer. Radiative transfer may be affected directly by the chromophores left on the surface of the aerosol after chemical transformation. The chemical model yields certain predictions which are testable by observations. Among them is a curve of the percent organic material as a function of particle diameter which predicts that a high fraction of the mass of the upper tropospheric aerosol will be organic. Atmospheric processing of organic aerosols will lead to the release of small organic fragments into the troposphere which will play a subsequent role in homogeneous chemistry. Organic aerosols are likely to act as a transport vehicle of organics and other water insoluble compounds into the atmosphere. We speculate that biomass burning will produce a similar coating of surfactants derived from land sources. Finally, it is pointed out that the radical‐induced transformation of the surface layer of aerosol particles from hydrophobic to hydrophilic offers an additional means by which the biosphere, through atmospheric chemistry, can affect the radiative balance.
Arctic lower tropospheric aerosol trends and composition at Alert, Canada: 1980–1995
Authors: Sirois Alain , Barrie Leonard A.
Published: September 2002

Fifteen years (1980 to 1995) of observations of weekly mean concentrations of 18 constituents in the aerosol of the lower Arctic troposphere at Alert, Canada, have been analyzed by time series analysis for seasonal and long‐term trends and by positive matrix factorization for aerosol components. The dominant anthropogenic constituent measured is SO42− which is composed of two major components: a neutralized ammonium sulphate salt and a highly acidic sulphate salt. The latter component becomes increasingly prominent as the Arctic atmosphere goes from complete darkness in January to complete sunlight in April and SO2 is oxidized to sulphuric acid in the northern troposphere. In winter/spring the 18 observed constituents are associated with 10 distinct aerosol factors (components). They are as follows: PHOTO‐S (i.e., anthropogenic sulphur from oxidation of SO2 in the Arctic), ANTHRO‐S, MIXED PHOTO‐S/SEA‐SALT, MSA (i.e., biogenic sulphur), SEA‐SALT, SMELTER, SOIL, NITRATE, BROMINE, and IODINE. Most winter/spring pollution comes to Alert from Eurasia. In the 1980s, trends in the winter/spring levels of anthropogenic constituents are evident for some (Pb, Zn, Cu, xV, and xMn) but not for SO42−. The lack of trend in SO42− is consistent with no change in emissions in the former Soviet Union between 1985 and 1990. However, since 1991, all of these constituents show a marked decrease suggesting that the collapse of industry in the early years of the new Eurasian republics has left its mark in the Arctic. The exception to this explanation is Pb which has clearly seen a major decline (70%) due to decreased use of Pb additives in automobile fuel in western Europe. Natural aerosol components are SEA‐SALT, SOIL, MSA, BROMINE, and IODINE. The first two are related to mechanical generation of aerosols and long‐range transport. SEA‐SALT peaks in late autumn and winter due to highest winds in the North Atlantic and North Pacific Ocean source regions. SOIL is composed of a local component and a long‐range Asian dust component that peaks in spring. MSA is a product of marine biogenic production and shows two peaks: one in May due to long‐range transport from the North Atlantic and one in summer due to more local sources in the Arctic Ocean. BROMINE and IODINE aerosol components are associated with lower tropospheric ozone depletion at polar sunrise. In autumn, aerosol iodine but not bromine has a secondary peak.
Dust sources and deposition during the last glacial maximum and current climate: A comparison of model results with paleodata from ice cores and marine sediments
Authors: Mahowald Natalie , Kohfeld Karen , Hansson Margaret , Balkanski Yves , Harrison Sandy P. , Prentice I. Colin , Schulz Michael , Rodhe Henning
Published: September 2002

Mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean. Ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2–20 times greater during glacial periods, raising the possibility that mineral aerosols might have contributed to climate change on glacial‐interglacial time scales. To address this question, we have used linked terrestrial biosphere, dust source, and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum (LGM) climates. We obtain a 2.5‐fold higher dust loading in the entire atmosphere and a twenty‐fold higher loading in high latitudes, in LGM relative to present. Comparisons to a compilation of atmospheric dust deposition flux estimates for LGM and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations; differences suggest where further improvements in the simple dust model could be made. The simulated increase in high‐latitude dustiness depends on the expansion of unvegetated areas, especially in the high latitudes and in central Asia, caused by a combination of increased aridity and low atmospheric [CO2]. The existence of these dust source areas at the LGM is supported by pollen data and loess distribution in the northern continents. These results point to a role for vegetation feedbacks, including climate effects and physiological effects of low [CO2], in modulating the atmospheric distribution of dust.
Ozone transport during the California Ozone Deposition Experiment
Authors: Sun Jielun , Massman William
Published: September 2002

The high correlation between the canopy stomatal uptake and ozone deposition velocity is found to be strongly dominated by their diurnal variations. By averaging observed variables over the daytime periods to remove the correlations simply due to their individual diurnal variations, we found that the ozone deposition velocity is highly correlated with the buoyancy flux during the daytime. As canopy stomata are closed at night, the ozone deposition velocity is found to be related to the friction velocity. Interpretation of the derivation of the ozone deposition velocity, expressed in terms of the traditional three resistances, is reanalyzed to explain the role of the turbulence strength in the ozone deposition velocity. We find that the resistance rc is the dominant resistance for the ozone deposition, not only due to the ozone uptake through biophysical processes, but also due to its role in the turbulent ozone transport.
Analysis of the atmospheric energy budget: A consistency study of available data sets
Authors: Yu Rucong , Zhang Minghua , Cess Robert D.
Published: September 2002

This study examines the following question: Are the recently available climate data sets consistent with each other in describing the atmospheric energy budget? If they are not, what is the sign of the systematic bias and how large is it? The atmospheric radiative cooling in this budget analysis is derived from satellite measurements of radiative fluxes at the top of the atmosphere and satellite‐algorithm products at the surface. Atmospheric transports are derived from the National Centers for Environmental Protection/National Center for Atmospheric Research and the European Centre for Medium‐Range Weather Forecasts reanalysis products. Surface turbulent heat fluxes are derived from products on the basis of Comprehensive Ocean‐Atmosphere Data Sets and reanalysis. Spatial and temporal averaging is performed to reduce random uncertainties in each data set. It is found that these data sets result in an unbalanced atmospheric budget with a residual of 20 W m−2 when averaged from 50°N to 50°S. The sign and magnitude of this systematic bias are shown to be consistent with the recently debated insufficient absorption of solar radiation in the atmosphere.
Dimethyl sulfide emissions to the atmosphere from lakes of the Canadian boreal region
Authors: Sharma S. , Barrie L. A. , Hastie D. R. , Kelly C.
Published: September 2002

Dimethyl sulfide (DMS) concentrations were measured over 2 years in 10 lakes situated in northwestern Ontario. Concentrations varied from 0.1 nmol L−1 to 100 nmol L−1 (geometric mean of 1.2 nmol L−1) during the ice‐free season (April to November) of 1995 and 1996. Shallow (1–5 m depth and 1–5 ha area) and medium depth (5–10 m depth and 5–15 ha area) lakes exhibited higher surface water DMS concentrations than deeper and larger lakes (32 m depth and 20–56 ha area). During the fall in the medium size lakes (5–12 m depth and <15 ha area), DMS concentrations increased markedly by a factor of as much as 100 because of circulation of deeper, high‐DMS water from the hypolimnion (lake turnover). The estimated seasonal mean fluxes of DMS from shallow and medium depth lakes to the atmosphere ranged between 0.058 and 15 μmol S m−2 d−1 respectively. The shallow and medium depth lakes tend to release higher DMS than the large and deeper lakes. Extrapolation of flux estimates indicates that the lakes of the Canadian Boreal Shield emit 1.5 Gg yr−1 biogenic sulfur (DMS) to the atmosphere, and this is approximately 83% of the total annual biogenic sulfur (DMS) emissions from the Canadian Boreal Shield (lakes plus terrestrial). Compared to the annual anthropogenic emissions by five smelters in the boreal region, these emissions are small (0.08%).
The UIUC three‐dimensional stratospheric chemical transport model: Description and evaluation of the simulated source gases and ozone
Authors: Rozanov Eugene V. , Zubov Vladimir A. , Schlesinger Michael E. , Yang Fanglin , Andronova Natalia G.
Published: September 2002

A new University of Illinois at Urbana‐Champaign (UIUC) three‐dimensional stratospheric chemical transport model is presented. The model consists of (1) a hybrid transport routine; (2) a chemical routine that includes the principal gas‐phase and heterogeneous reactions; and (3) the circulation, temperature, and tropospheric humidity fields acquired from the UIUC 24‐layer general circulation model. The model is applied to study chemistry‐transport processes in the stratosphere. The results of an 8‐year steady state simulation with 1995 boundary conditions are analyzed, and the distributions of three source gases, methane, water vapor, and nitrous oxide, and ozone are evaluated in comparison with appropriate UARS measurements. The comparison shows that the model is able to reproduce the main features of the distributions of long‐lived species obtained from satellite measurements, namely, the location of the tropical extremes in the summer hemisphere, the high horizontal gradient in the subtropics, the winter midlatitude mixing zone, and the high‐latitude minimum (or maximum) regions. The model also well captures the observed features of the ozone distribution in the stratosphere, including the intensity and location of the tropical maximum, the depletion in the lower stratosphere of the Southern Hemisphere, and the seasonal variations in the middle stratosphere. The magnitudes of the mixing ratios of the long‐lived species are found to be in reasonable agreement with the observed values, although the model overestimates the N2O mixing ratio over high latitudes and slightly underestimates the H2O mixing ratio in the stratosphere. Also, the simulated ozone mixing ratio is overestimated in the middle stratosphere and underestimated in the upper stratosphere by 5–15%. However, analysis and comparison of the simulated and observed species distributions and tracer‐to‐tracer correlations show a very good overall performance of the model.
Thermodynamics of heterogeneous binary condensation on insoluble nuclei
Authors: Djikaev Y. S. , Donaldson D. J.
Published: September 2002

We consider heterogeneous binary condensation as the formation of wetting films of arbitrary thickness on insoluble nuclei. Using this approach, we show that the concurrence of the capillary and disjoining pressures in thin films plays a key role in the thermodynamics of the whole process. The limiting partial supersaturations necessary for barrierless condensation are obtained as functions of the droplet composition and an explicit expression for the formation free energy of a binary droplet on an insoluble nucleus is derived. The surface describing the formation free energy as a function of film thickness and composition has a minimum and a saddle point whose coordinates correspond to droplets in stable and unstable equilibria, respectively, with the vapor mixture. Equations for determining the coordinates of the well and saddle points are presented. The theoretical results are illustrated with numerical calculations for the butanol‐hexanol and butanol‐water droplets formation on quartz particles.
Radiative transfer modeling for the EOS Terra satellite Measurement of Pollution in the Troposphere (MOPITT) instrument
Authors: Edwards D. P. , Halvorson C. M. , Gille J. C.
Published: September 2002

This paper describes the radiative transfer modeling effort in support of the EOS Measurements of Pollution in the Troposphere (MOPITT) instrument. MOPITT is due to be launched on the AM‐1 Terra platform in the summer of 1999 and is a nadir‐viewing gas correlation radiometer designed to measure CO and CH4 in the troposphere using a CO thermal channel at 4.7 μm and reflected solar channels for CO at 2.3 μm and CH4 at 2.2 μm. We describe the spectroscopic considerations and radiative transfer studies that have been performed for this instrument and the implications for operational algorithm design. We outline the construction of MOPITT project forward models, both the research codes and the fast transmittance module that forms part of the operational retrieval algorithm. Several different approaches have been considered for these models: full line‐by‐line calculations using the general purpose line‐by‐line transmittance and radiance model GENLN2, absorption coefficient look‐up tables, and regression techniques using a recurrence parameterization of transmittance. These models are capable of reproducing MOPITT channel signals and their dependence on temperature, viewing geometry, and the mixing ratios of target and contaminating gases.
Seasonal and diurnal variation of aerosol size distributions (10<D<750 nm) at a high‐alpine site (Jungfraujoch 3580 m asl)
Authors: Weingartner E. , Nyeki S. , Baltensperger U.
Published: September 2002

During an extended field campaign at a high‐alpine site (Jungfraujoch; 3580 m asl, Switzerland) from March 1997 to May 1998, the particle number size distribution (diameter D = 18–750 nm) and number concentration N (D>10 nm) were measured on a continuous basis. The number size distribution was dominated by particles with D<100 nm, while most of the surface area was in the accumulation mode size range (0.1–1 μm). Average size distributions exhibited a distinct bimodal shape which is generated and maintained by cloud processes and is less distinct in the free troposphere. Fitted modal diameters and standard deviations σ of the Aitken (20–100 nm) and accumulation modes were surprisingly constant throughout the year (DAit = 43±3 nm; DAcc = 140±6 nm; σAit = 2.13±0.11; σAcc = 1.61±0.03). The relative number concentrations in both modes are responsible for the seasonally observed in the shape of the size distribution. The high seasonality of NAcc with summer and winter values of ∼260 and ∼40 cm−3, respectively, is mainly due to transport of planetary boundary layer air to the station. In contrast, new particle formation is responsible for the high concentrations of nucleation mode particles (D<20 nm) which exhibited a maximum during the winter months. The relatively low seasonality found for NAit (summer, winter values: ∼530, ∼310 cm−3) is due to gas‐to‐particle conversion as well as transport processes. An analysis showed that a significant fraction of nucleation mode particles were formed by photochemical reactions.
Large injection of carbon monoxide into the upper troposphere due to intense biomass burning in 1997
Authors: Matsueda Hidekazu , Inoue Hisayuki Y. , Ishii Masao , Tsutsumi Yukitomo
Published: September 2002

Air samples at 8–13 km were collected regularly using a commercial airliner to obtain long‐term measurements of carbon monoxide (CO) mixing ratio in the upper troposphere over the western Pacific between Australia and Japan during April 1993‐December 1997. The measurements in 1997 clearly reveal an anomalous CO increase during September to November in the Southern Hemisphere, with a maximum of 320–380 ppb around 20°S in October. Tropical biomass burning, not urban/industrial emissions, was the main source for the enhanced CO in 1997. A similar southern‐spring increase due to biomass burning was observed in previous years. The peaks showed a large interannual variation associated with the El Niño/Southern Oscillation (ENSO) events. The largest CO spring peak appeared during the strong El Niño event in 1997, while the weak La Niña year of 1996 was marked by a largely suppressed CO spring peak. The outgoing longwave radiation (OLR) anomaly is largest during the El Niño events indicating that the events cause a longer drought in the tropics and significantly influence the enlargement of biomass burning in tropical Southeast Asia. Thus the most likely cause for the ENSO‐cycle CO variability is a year‐to‐year change of biomass‐burning emissions mainly from Southeast Asia. The appearance of the CO spring peak in the southern subtropics is discussed on the basis of the possible long‐range transport of biomass‐burning CO from Southeast Asia to the upper troposphere over the western South Pacific.
Evaluating the performance of a land Surface / ecosystem model with biophysical measurements from contrasting environments
Authors: Delire Christine , Foley Jonathan A.
Published: September 2002

Five sets of biophysical and hydrological measurements from across the globe are used to test the performance of the Integrated Biosphere Simulator (IBIS) [Foley et al., 1996] in reproducing short‐term and long‐term evolution of soil moisture and temperature, surface energy fluxes and CO2 fluxes. The sites include a soybean crop in southwestern France (HAPEX‐MOBILHY, 1986), a meadow in the Netherlands (Cabauw, 1987), a grassland in Russia (Valday‐Usadievskiy, 1966–1983), a prairie in Kansas (FIFE, site 16, 1987–1989), and a tropical forest in Brazil (ABRACOS, Reserva Jaru, 1992–1993). IBIS adequately reproduces the evolution of the soil moisture together with the surface fluxes for those five different sites while only imposing a small number of site specific parameters describing vegetation characteristics and soil texture. The quality of the simulations is improved when detailed information regarding soil texture, rooting profiles, and leaf area index are available.
Long‐term observation of the atmospheric exchange of CO2 with a temperate deciduous forest in southern Ontario, Canada
Authors: Lee Xuhui , Fuentes Jose D. , Staebler Ralf M. , Neumann Harold H.
Published: September 2002

This paper reports the results of the analysis of eddy covariance CO2 data obtained at a successional forest of maple and aspen at Camp Borden in southern Ontario, Canada, between July 1995 and December 1997. Main findings are (1) The Michaelis‐Menton model explains >50–65% of the observed variance of the daytime net ecosystem carbon exchange (NEE) during the growing season; leaf wetness appears to be an important variable contributing to the remaining variance. (2) The whole‐ecosystem respiration rate as a function of the 5‐cm soil temperature shows a seasonal “hysteresis” (higher rate in the later part of the year), suggesting a nonnegligible contribution by deep soil/roots and the influence of litter age. (3) There is evidence of photosynthetic activities immediately after the spring snowmelt/soil warming, but the daily NEE did not switch sign till about 40 days later; our best estimates of the annual net carbon uptake by the ecosystem (net ecosystem production (NEP)) are −1.0, −1.2, and −2.8 t C ha−1 yr−1 for the periods July 19, 1995, to July 18, 1996, January 1 to December 31, 1996, and January 1 to December 31, 1997, respectively, with an uncertainty of ±0.4 t C ha−1 yr−1. (4) The higher NEP value in 1997 than in 1996 was caused by lower growing season soil temperature, cooler spring and fall transitional periods, and higher photon flux in 1997; possible enhancement in canopy photosynthetic capacity may also have played a role. In addition, three main sources of uncertainties, data gap, fetch, and mass flow, are discussed. It is suggested that collective use of the methods available for assessing the whole‐ecosystem respiration (friction velocity threshold, mass flow theory, and dark respiration from the forest light response) may increase the confidence level of NEP estimates.
Design of the Mexico City UV monitoring network: UV‐B measurements at ground level in the urban environment
Authors: Acosta L. R. , Evans W. F. J.
Published: September 2002

Although there is concern for future stratospheric ozone depletion, several large urban populations are already being exposed to very high UV levels due to geographical factors. In Mexico City, ultraviolet radiation (UV) plays an important role in the generation of high levels of tropospheric ozone and other photochemical pollutants. The measurement of ultraviolet‐B radiation in Mexico began in the spring 1993, as a pilot project for ultraviolet‐B (UV‐B) monitoring and as support for the first Hispanic public information program on the UV index through the Televisa (Mexican television network, which covers the Spanish speaking world). In 1996, based on our preliminary measurements, the Mexico City government commissioned the authors to design the Valley of Mexico UV‐monitoring Network. The design of the network is presented. The preliminary measurements show that biologically active (UV‐B) solar radiation can reach levels above 5 minimum erythemal dose (MED/hour) or 12 UV index units during spring and summer months. Annual UV measurements have shown seasonal variations of 40% between winter and summer months. Strong attenuation of UV‐B radiation at ground level in the urban troposphere has been detected under polluted conditions. Measurements of the morphology of UV‐B radiation have been taken at downtown and suburban monitoring stations, over diurnal, monthly and yearly periods. The network measurements show that the downtown UV‐B levels are 20% lower than suburban levels on a seasonal basis, but differences can be greater than 40% on polluted days. The relationship between the Total Ozone Mapping Spectrometer (TOMS) total ozone column and tropospheric ozone concentrations in Mexico City is also discussed.
Uncertainty in the simulation of runoff due to the parameterization of frozen soil moisture using the Global Soil Wetness Project methodology
Authors: Pitman A. J. , Slater A. G. , Desborough C. E. , Zhao M.
Published: September 2002

Four simulations of the region 30°N–90°N are performed using the Global Soil Wetness Project methodology and a single land surface scheme. Four methods are used to represent soil ice: an explicit representation of the thermal and hydrological effects of soil ice; two implicit methods (which only account for the hydrological effects); and finally the simplest approach where soil ice is not accounted for. Substantial impacts on total runoff, evaporation and temperature result from the choice of parameterization. The partitioning of total runoff between drainage and surface runoff is also changed. The impacts on temperature are large enough to cause problems for “fingerprinting” of global change while the change in the runoff generation process, and the timing of maximum runoff are large enough to concern ocean modelers. Evidence presented here and elsewhere indicates that land surface schemes should include the thermal effects of soil ice melting and freezing. However, the hydrological effects of soil ice suppressing infiltration and encouraging surface runoff may be based on observations taken at a scale inappropriate to climate model parameterization. We show that for one basin, the Mackenzie, a land surface model which ignores soil ice entirely simulates runoff better than the other methodologies tested here. We therefore hypothesize that it may be preferable to not include soil ice in the runoff formulations used in land surface models until we have more observations at an appropriate spatial scale. Testing of frozen soil moisture parameterizations in other catchments with high‐quality observed runoff data should be conducted to test this hypothesis.
Warm climate transitions: A general circulation modeling study of the Late Paleocene Thermal Maximum (∼56 Ma)
Authors: Huber Matthew , Sloan L. Cirbus
Published: September 2002

A unique opportunity to study rapid climate transitions in a warm climate world is provided by the Late Paleocene Thermal Maximum (LPTM), a ∼100,000 year interval during which high‐latitude temperatures suddenly rose to their highest levels in the Cenozoic. In order to explore the processes and feedbacks which may have generated or limited this brief warming event, we model the atmosphere in equilibrium with sea surface temperatures (SSTs) derived for LPTM and for conditions more representative of the late Paleocene or early Eocene. Our model results suggest that conditions during the LPTM were more equable relative to the late Paleocene or early Eocene, with the mean annual temperature range reduced by more than 5°C over much of the continental interiors and precipitation over land increased by 5–10%. Nevertheless, despite specifying warm polar SSTs which exclude sea‐ice, the model produces January continental interior temperatures less than −13°C, in contrast to proxy data estimates of higher temperatures. The zonal wind strength is drastically reduced during the LPTM, and during Northern Hemisphere winter, deep atmospheric convection over the Arctic Sea is generated owing to the specified warm SSTs. We calculate substantial wind‐driven ocean circulation response to model‐produced wind fields for these time intervals, including increases in inferred western boundary current strength of 8–28%. In general, our results are in agreement with deep‐sea sediment‐derived clay and eolian records which suggest warm, wet conditions with less vigorous atmospheric circulation during these time periods. However, major changes in the high‐latitude hydrological cycle found in our LPTM experiment results raise important questions about high‐latitude stable isotopic paleoclimate interpretations.
Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO): An overview
Authors: Delmas R. A. , Druilhet A. , Cros B. , Durand P. , Delon C. , Lacaux J. P. , Brustet J. M. , Serça D. , Affre C. , Guenther A. , Greenberg J. , Baugh W. , Harley P. , Klinger L. , Ginoux P. , Brasseur G. , Zimmerman P. R. , Grégoire J. M. , Janodet E. , Tournier A. , Perros P. , Marion Th. , Gaudichet A. , Cachier H. , Ruellan S. , Masclet P. , Cautenet S. , Poulet D. , Biona C. Bouka , Nganga D. , Tathy J. P. , Minga A. , Loemba‐Ndembi J. , Ceccato P.
Published: September 2002

This paper presents an overview of the Experiment for Regional Sources and Sinks of Oxidents (EXPRESSO) including the objectives of the project, a detailed description of the characteristics of the experimental region and of field instrumentation deployed, and a summary of the main results of all components of the experiment. EXPRESSO is an international, multidisciplinary effort to quantify and better understand the processes controlling surface fluxes of photochemical precursors emitted by vegetation and biomass burning along a tropical forest to savanna gradient in central Africa. The experiment was conducted at the beginning of the dry season in November‐December 1996. Three main research tools were deployed during this period: (1) the French research aircraft (Avion de Recherche Atmosphérique et de Télédétection, Fokker 27), instrumented for chemistry and flux measurements (CNRS‐ France), (2) two satellite receivers for in situ acquisition of National Oceanic and Atmospheric Administration‐advanced very high resolution radiometer (NOAA‐AVHRR) imagery for fire detection (EC‐JRC, Ispra, Italy), and (3) a 65‐m walkup tower installed at a tropical forest site in the Republic of Congo (National Center for Atmospheric Research, Boulder, Colorado). Average dynamic and turbulence characteristics over savanna and forest ecosystems were retrieved from aircraft measurements. They illustrate the complex atmospheric circulation occurring in this region in the vicinity of the Intertropical Convergence Zone. Satellite receivers were operated three times a day to produce maps of fire distribution. Statistics and mapping of burned surfaces from NOAA‐AVHRR and ERS‐Along Track Scanning Radiometer space systems have been developed. The influence of biogenic and biomass burning sources on the chemical composition of the lower atmosphere was studied through both aircraft and tower measurements. The EXPRESSO field campaign was followed by modeling efforts (regional and global scales) in which model components are evaluated using the experimental data.