bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of snow and ice melt at ETH Camp (West Greenland): A study of surface albedo
Authors: Lefebre Filip , Gallée Hubert , van Ypersele Jean‐Pascal , Greuell Wouter
Published: May 2003

The objective of this paper is to present the validation over Greenland of a thermodynamic snow‐ice model that was complemented with the snow metamorphism and albedo parameterizations of the Centre d'Etudes de la Neige (Grenoble, France) in order to make the surface albedo variable and interactive. Special attention is given to the surface albedo since it is the most important parameter in energy exchanges with the atmosphere for snow and ice melt. The development of an integrated (snow, ice, and water) albedo model takes into account the different surface types observed on an ice sheet, and the snow albedo is calculated from the simulated surface snow grains. The validation for a polar site has been done at ETH Camp (West Greenland, 1155 m above sea level) during the 1990 and 1991 summer seasons. Although both ablation seasons differed greatly (in 1990 it showed a negative mass balance while in 1991 it ended with a positive mass balance), a single model configuration was able to provide good results for both 1990 and 1991. These simulations show that the snow metamorphism laws included enable an accurate simulation of the surface albedo and henceforth of the surface mass balance for a polar site, provided that the snow model is correctly forced at its surface level and that meltwater retention, percolation, and drainage are well represented in the snow model. The model results are also compared with two other modeling approaches, and differences between the three snow models are detailed.
Hydrogen in the atmosphere: Observations above a forest canopy in a polluted environment
Authors: Barnes Diana H. , Wofsy Steven C. , Fehlau Brian P. , Gottlieb Elaine W. , Elkins James W. , Dutton Geoffrey S. , Novelli Paul C.
Published: May 2003

Long‐term in situ observations of atmospheric concentrations of molecular hydrogen were monitored every 24 minutes for three years (1996–1998) above Harvard Forest, Massachusetts, in concert with measurements of carbon monoxide and twelve other trace gases. A seasonal cycle with a spring maximum and autumn minimum was observed. The diurnal cycle was characterized by a morning minimum and an afternoon maximum, reflecting the combined effects of uptake by soils and boundary height fluctuations. Enhancements of H2 concentrations in pollution events, concurrent with winds from the southwest, were typically 100–200 ppb above the background seasonal cycle. The mean molar ratio of H2 and CO (ΔH2/ΔCO) in pollution plumes was 0.396 ± 0.050 ppb/ppb. The results agree with expectations from the water‐gas equilibrium (CO + H2O ↔ CO2 + H2) for conditions in automobile engines and with car emission data. These observations suggest that automobiles are the major anthropogenic source of atmospheric hydrogen and that the ratio of ΔH2/ΔCO has changed little as emission controls have taken effect.
Size‐resolved ultrafine particle composition analysis 1. Atlanta
Authors: Rhoads K. P. , Phares D. J. , Wexler A. S. , Johnston M. V.
Published: May 2003

During August 1999 as part of the Southern Oxidants Study Supersite Experiment, our group collected size‐resolved measurements of the chemical composition of single ambient aerosol particles with a unique real‐time laser desorption/ionization mass spectrometry technique. The rapid single‐particle mass spectrometry instrument is capable of analyzing “ultrafine” particles with aerodynamic diameters ranging from 0.01 to 1.5 μm. Under the heaviest loading observed in Atlanta, particles were analyzed at a rate of roughly one per second in sizes ranging from 0.1 to 0.2 μm. Nearly 16,000 individual spectra were recorded over the course of the month during both daytime and nighttime sampling periods. Evaluation of the data indicates that the composition of the ultrafine (less than 100 nm) particles is dominated by carbon‐containing compounds. Larger particles show varied compositions but typically appeared to have organic carbon characteristics mixed with an inorganic component (e.g., crustal materials, metals, etc.). During the experiment, 70 composition classes were identified. In this paper we report the average spectra and correlations with various meteorological parameters for all major compound classes and a number of minor ones. The major composition classes are identified from the primary peaks in their spectra as organic carbon (about 74% of the particles), potassium (8%), iron (3%), calcium (2%), nitrate (2%), elemental carbon (1.5%), and sodium (1%). Many of these compound classes appeared in repeatable size ranges and quadrants of the wind rose, indicating emission from specific sources.
Size‐resolved ultrafine particle composition analysis 2. Houston
Authors: Phares Denis J. , Rhoads Kevin P. , Johnston Murray V. , Wexler Anthony S.
Published: May 2003

Between 23 August and 18 September 2000, a single‐ultrafine‐particle mass spectrometer (RSMS‐II) was deployed just east of Houston as part of a sampling intensive during the Houston Supersite Experiment. The sampling site was located just north of the major industrial emission sources. RSMS‐II, which simultaneously measures the aerodynamic size and composition of individual ultrafine aerosols, is well suited to resolving some of the chemistry associated with secondary particle formation. Roughly 27,000 aerosol mass spectra were acquired during the intensive period. These were classified and labeled based on the spectral peak patterns using the neural networks algorithm, ART‐2a. The frequency of occurrence of each particle class was correlated with time and wind direction. Some classes were present continuously, while others appeared intermittently or for very short time durations. The most frequently detected species at the site were potassium and silicon, with lesser amounts of organics and heavier metals.
Ambient aerosol sampling using the Aerodyne Aerosol Mass Spectrometer
Authors: Jimenez Jose L. , Jayne John T. , Shi Quan , Kolb Charles E. , Worsnop Douglas R. , Yourshaw Ivan , Seinfeld John H. , Flagan Richard C. , Zhang Xuefeng , Smith Kenneth A. , Morris James W. , Davidovits Paul
Published: May 2003

The Aerodyne Aerosol Mass Spectrometer (AMS) has been designed to measure size‐resolved mass distributions and total mass loadings of volatile and semivolatile chemical species in/on submicron particles. This paper describes the application of this instrument to ambient aerosol sampling. The AMS uses an aerodynamic lens to focus the particles into a narrow beam, a roughened cartridge heater to vaporize them under high vacuum, and a quadrupole mass spectrometer to analyze the vaporized molecules. Particle size is measured via particle time‐of‐flight. The AMS is operated in two modes: (1) a continuous mass spectrum mode without size information; and (2) a size distribution measurement mode for selected m/z settings of the quadrupole. Single particles can also be detected and sized if they have enough mass of a chemical component. The AMS was deployed at a ground sampling site near downtown Atlanta during August 1999, as part of the Environmental Protection Agency/Southern Oxidant Study Particulate Matter “Supersite” experiment, and at a suburban location in the Boston area during September 1999. The major observed components of the aerosol at both sites were sulfate and organics with a minor fraction of nitrate, consistent with prior studies and colocated instruments. Different aerosol chemical components often had different size distributions and time evolutions. More than half of the sulfate mass was contained in 2% of the ambient particles in one of the sampling periods. Trends in mass concentrations of sulfate and nitrate measured with the AMS in Atlanta compare well with those measured with ion chromatography‐based instruments. A marked diurnal cycle was observed for aerosol nitrate in Atlanta. A simple model fit is used to illustrate the integration of data from several chemical components measured by the AMS together with data from other particle instruments into a coherent representation of the ambient aerosol.
Semicontinuous aerosol carbon measurements: Comparison of Atlanta Supersite measurements
Authors: Lim Ho‐Jin , Turpin Barbara J. , Edgerton Eric , Hering Susanne V. , Allen George , Maring Hal , Solomon Paul
Published: May 2003

An intensive field campaign of the Atlanta Supersite Experiment was carried out at a ground‐based measurement site on Jefferson Street in midtown Atlanta, Georgia, from 3 August to 1 September 1999. This paper examines the semicontinuous particulate organic and elemental measurements that were made as a part of the experiment. Measurements were made using a Rutgers University/Oregon Graduate Institute in situ thermal‐optical carbon analyzer, Rupprecht and Patashnick 5400 ambient carbon particulate monitor, Radiance Research particle soot absorption photometer, Aerosol Dynamics flash vaporization carbon analyzer, and Magee Scientific AE‐16 Aethalometer. The “intersampler precision” with which semicontinuous particulate total carbon (TC), organic carbon (OC), and elemental carbon (EC) were measured is 7, 13, and 26%, expressed as pooled coefficients of variation of 2, 3, and 4 instruments, respectively. Correlations between pairs of OC measurements are moderate (R2 = 54–73%), and correlations between pairs of EC measurements are high (R2 = 74–97%). Differences in reported OC concentrations are small compared to differences in EC concentrations; intersampler EC concentration differences result from differences (1) in the operational definitions of OC and EC, (2) in the calibration of optical instruments, and (3) because EC values are closer to limits of detection. This agreement between semicontinuous samplers is quite good, especially in light of previous particulate carbon comparisons. Reasons for measurement differences and benefits of automated time‐resolved measurements are discussed.
Comparison of integrated samplers for mass and composition during the 1999 Atlanta Supersites project
Authors: Solomon Paul , Baumann Karsten , Edgerton Eric , Tanner Roger , Eatough Delbert , Modey William , Maring Hal , Savoie Dennis , Natarajan Sanjay , Meyer Michael B. , Norris Gary
Published: May 2003

The first of the U.S. Environmental Protection Agency's (EPA) Particulate Matter (PM) Supersites projects was established in Atlanta, GA, during the summer of 1999 in conjunction with the Southern Oxidants Study. The short‐term primary focus was a one month intensive field campaign to evaluate advanced PM measurement methods for measuring PM mass and the chemical and physical properties of PM. Long‐term objectives are being met through coordination and cooperation with existing programs in Atlanta and the southeastern United States. Three categories of PM instruments were deployed during August 1999: time‐integrated or discrete filter‐based methods like those used in EPA's PM2.5 Chemical Speciation Network; continuous or semicontinuous species specific methods, most of which are still in development; and single particle mass spectrometers, the most advanced methods looking at the chemical composition of single particles. The focus of this paper is on comparison of the discrete filter‐based methods. Samples were collected by 12 discrete filter‐based samplers on an every other day basis during the study period at the Jefferson Street Southeastern Aerosol Research and Characterization (SEARCH) study site. Samples were analyzed for PM2.5 mass, sulfate, nitrate, ammonium, organic carbon, elemental carbon, and trace elements, the latter by XRF. Samplers used a variety of filters; denuder‐filter combinations in the case of nitrate and organic carbon, particle size fractionating devices, and flow rates. Ambient concentrations for most species were sufficiently above detection limits for testing comparability among samplers, with nitrate being the most notable exception for the major components having an average reported value of 0.5 μg/m3. Several trace species, e.g., As and Pb, also were often below limits of detection of the analysis method. Results indicate that real differences exist among the samplers tested for most species, with sulfate and ammonium being the exceptions, under the conditions tested. Differences are due to sampler design, and in the case of elemental carbon, also due to the use of different chemical analysis methods. Comparability among most of the samplers for a given species was: mass (±20%); sulfate (±10%); nitrate (±30–35%); ammonium (±10–15%); organic carbon either with or without denuders (±20%) or including samplers both with and without denuders (±35–45%); elemental carbon (±20 to ±200%, the latter if different analysis methods are used); and minor and trace elements (±20–30%). A net organic carbon‐sampling artifact on quartz‐fiber filters was estimated from the comparison of denuded versus undenuded samples and is in the range of 1–4 μg/m3.
An algorithm for retrieval of cloud microphysics using 95‐GHz cloud radar and lidar
Authors: Okamoto Hajime , Iwasaki Suginori , Yasui Motoaki , Horie Hiroaki , Kuroiwa Hiroshi , Kumagai Hiroshi
Published: May 2003

We develop a new forward algorithm for the retrieval of effective size and ice water content (IWC) of ice crystals in clouds by using collocated 95‐GHz (3.16 mm) cloud radar and lidar with the wavelength of 0.532 μm. Use of radar or lidar alone has a fundamental difficulty to obtain cloud microphysics because of the wide variety of size distributions of cloud particles, though it is effective to obtain cloud macrophysical information such as cloud boundaries. The combined use of radar and lidar can overcome this problem. One unique feature of the algorithm is the attenuation‐correction to the lidar signals according to the cloud microphysics determined by look‐up tables of backscattering and extinction for the radar and lidar signals. Consequently, the combined system enables the retrieval of vertical profiles of the effective radius (reff) and ice water content (IWC). We perform several numerical analyses of the retrieved values for potential sources of errors, that is, the shape of the size distribution, biases in the radar and lidar signals, and the effect of multiple scattering. Then we provide the formulations that describe the retrieval errors as a function of the given bias and optical thickness. Finally, we demonstrate retrieval of microphysics for ground‐based observation of cirrus clouds in February 2000 in Kashima, Japan. We examine the vertical distributions of reff, IWC, fall velocity, and depolarization ratio as well as the interrelationships between them. The radius of the particles turns out to be the largest near the cloud bottom, and the fall velocity also shows a trend consistent with the reff tendency. There are no in situ measurements to validate the retrieved parameters for the observations. Instead, supporting arguments are given on the basis of information about the expected behavior of the relationships between the cloud microphysical parameters from the literature.
Inorganic trace gases and peroxy radicals during BERLIOZ at Pabstthum: An investigation of the photostationary state of NOx and O3
Authors: Volz‐Thomas Andreas , Pätz Hans‐Werner , Houben Norbert , Konrad Stephan , Mihelcic Djuro , Klüpfel Thomas , Perner Dieter
Published: May 2003

Meteorological and chemical measurements, including peroxy radicals, made during the Berlin Ozone Experiment (BERLIOZ) in summer 1998 at Pabstthum, a rural site about 50 km NW of the city, are described. The analytical techniques and data quality are discussed, including the comparison of different methods deployed side by side at Pabstthum. The highest concentrations of NOx (>20 ppb) and other precursors were observed on days when relatively young air was advected to Pabstthum from the greater Berlin area. NOx often increased during the night due to emissions from the surrounding soils under stagnant conditions with a shallow boundary layer as is evident in the strong negative correlation between nocturnal NO mixing ratios and product of ozone and wind speed. The ozone production rate (PO3) calculated from the photostationary state (PSS) of NOx and O3 increased with NO and reached values of up to 90 ppb h−1. PO3 calculated from NO and the measured peroxy radical concentrations was much lower, around or below 10 ppb h−1. The lower production rates obtained from the peroxy radical measurements are consistent with the ozone budget in the city plume of Berlin. The new JPL recommendation for the rate coefficient of the reaction of NO with O3 slightly improves the disagreement between PSS and measured peroxy radicals. However, another enhancement of 10–20% in the rate coefficient would be required in order to match the results within the uncertainty of the measurements in the high NOx regime. Even then, PSS remains to overpredict PO3 by a factor of 2 at low NOx concentrations. Hence, a yet unidentified process must exist in the atmosphere that converts NO to NO2 without leading to a net production of ozone. The PSS results from other studies are similar as at Pabstthum, suggesting that the overestimation of peroxy radicals and PO3 by the PSS approach is not a particular feature of the conditions at the site.
Interactions between tropospheric chemistry and aerosols in a unified general circulation model
Authors: Liao Hong , Adams Peter J. , Chung Serena H. , Seinfeld John H. , Mickley Loretta J. , Jacob Daniel J.
Published: May 2003

A unified tropospheric chemistry‐aerosol model has been developed within the Goddard Institute for Space Studies general circulation model (GCM). The model includes a detailed simulation of tropospheric ozone‐NOx‐hydrocarbon chemistry as well as aerosols and aerosol precursors. Predicted aerosol species include sulfate, nitrate, ammonium, black carbon, primary organic carbon, and secondary organic carbon. The partitioning of ammonia and nitrate between gas and aerosol phases is determined by on‐line thermodynamic equilibrium, and the formation of secondary organic aerosols is based on equilibrium partitioning and experimentally determined parameters. Two‐way coupling between aerosols and chemistry provides consistent chemical fields for aerosol dynamics and aerosol mass for heterogeneous processes and calculations of gas‐phase photolysis rates. Although the current version of the unified model does not include a prognostic treatment of mineral dust, we include its effects on photolysis and heterogeneous processes by using three‐dimensional off‐line fields. We also simulate sulfate and nitrate aerosols that are associated with mineral dust based on currently available chemical understanding. Considering both mineral dust uptake of HNO3 and wet scavenging of HNO3 on ice leads to closer agreement between predicted gas‐phase HNO3 concentrations and measurements than in previous global chemical transport model simulations, especially in the middle to upper troposphere. As a result of the coupling between chemistry and aerosols, global burdens of both gas‐phase and aerosol species are predicted to respond nonlinearly to changing emissions of NOx, NH3, and sulfur.
Relationship between aerosol number concentrations and convergence fields in winter monsoon seasons
Authors: Kikuchi Katsuhiro , Matsuoka Seiki , Uyeda Hiroshi , Kikuchi Osamu , Lee Dong‐In
Published: May 2003

Observations of snow clouds and the number concentrations of aerosol particles were conducted during two winter seasons, at Rebun Island in 1991 and at Ishikari Bay in 1992 on the west coast of Hokkaido, Japan. A significant increase of 1 to 2 orders of magnitude in the number concentration of relatively large aerosol particles was recorded in several 10‐min intervals during the observation period. However, there was only a poor direct correlation between the number concentrations of large particles greater than 0.5 μm in diameter and wind speed. In contrast, the increase in number concentration was correlated with a convergence field calculated by the velocity azimuth display method using a Doppler radar. These results imply that the large and giant aerosol particles, including sea‐salt nuclei which were generated by wind stress near the sea surface under winter monsoon periods, which is known as a typical pressure pattern of “west‐high and east‐low” (as shown in Figure 2), were transported and were then gathered under the convergence field of unstable/convective meteorological systems with developing cumulus cloud cells.
Scattering of light by large Saharan dust particles in a modified ray optics approximation
Authors: Nousiainen Timo , Muinonen Karri , Räisänen Petri
Published: May 2003

Single scattering by randomly oriented Saharan sand, silt, and clay particles is studied at 441.6 nm wavelength. Numerical simulations using the ray optics approximation and the Lorenz‐Mie theory are compared with laboratory measurements of scattering matrix elements reported in the literature. The ray optics approximation is modified with ad hoc simple schemes of Lambertian surface elements and internal screens to study the effect of small‐scale surface roughness and internal structures, respectively. Two different Lambertian reflection/refraction matrices with varying depolarization characteristics are applied. Model particle shapes are based on a tentative shape analysis of real Saharan particles. It is found that the traditional ray optics approximation agrees well with measurements only if unrealistically spiky particle shapes and an imaginary part of the refractive index (Im(m)) that is rather small compared with the typical values given in the literature are used. When the Lambertian schemes are applied, the agreement with measurements clearly improves. More importantly, good agreement can then be achieved using realistic particle shapes; this too requires a rather small Im(m). If Im(m) values corresponding to typical values in the literature are used, good fits can be achieved, but unrealistically spiky particle shapes have to be used. Our findings also indicate that sophisticated single‐scattering modeling is important even below the ray optics domain. Finally, we demonstrate the importance of sophisticated single‐scattering modeling for radiative flux and radiance calculations.
Extratropical low‐frequency variability in a three‐level quasi‐geostrophic atmospheric model with different spectral resolution
Authors: Weisheimer Antje , Kurgansky Michael V. , Dethloff Klaus , Handorf Dörthe
Published: May 2003

Apart from variations of external forcing components and interactions between climate subsystems, natural atmospheric fluctuations with periods of years, decades and centuries can also be generated by inherent atmospheric dynamical instabilities of the flow. The objective of this study is to investigate the spatial and temporal structure of internal low‐frequency atmospheric variability of the Northern Hemisphere using a minimum‐complexity model of the extratropical circulation. Here, the main focus is the influence of varying spectral horizontal resolution on the formation of dominant patterns of variability. For this purpose, a three‐level quasi‐geostrophic atmospheric model with idealized thermal and orographic forcing has been integrated over 1,000 years under perpetual winter conditions with T5, T10, T15, and T21 resolutions. It has been shown that for the crude resolution T5 a rather strong bias occurs, whereas starting with T10 resolution, the nonlinear feedback between large‐ and small‐scale features is reasonably well described. At this resolution a sort of plateau in the model performance has been reached, in respect to both the model climatology and the spatiotemporal structure of variability. Ultralow‐frequency variability is most pronounced in the model's stratosphere and is associated with changes in the polar vortex strength and shape caused by vertically propagating planetary waves. Rossby wave trains in the lee of the model large‐scale orography are the most dominant structures of long‐period fluctuations in the middle troposphere. The results show that interannual‐ and decadal‐scale variations can, in substantial part, be considered as a manifestation of the natural variability of the extratropical atmosphere. The inclusion of a seasonal cycle of the model's diabatic heating increases the interannual and interdecadal variability.
Filling in of Fraunhofer lines by plant fluorescence: Simulations for a nadir‐viewing satellite‐borne instrument
Authors: Sioris Christopher E. , Bazalgette Courrèges‐Lacoste Grégory , Stoll Marc‐Philippe
Published: May 2003

Solar‐excited plant fluorescence in the red/near‐infrared is known to fill Fraunhofer lines at ground level. In this paper, it is shown that red/near‐infrared fluorescence by vegetation can fill Fraunhofer lines much more effectively than rotational Raman scattering (RRS) by air (Ring effect) for nadir viewing from satellite altitudes. Thus, similarly to RRS, plant fluorescence can be remotely sensed from an orbiting spectrometer, and may impact the retrieval of atmospheric trace gases such as water vapor by high‐resolution spectroscopy over vegetated land.
Mathematical investigation of mass transfer for atmospheric pollutants into a fixed droplet with aqueous chemistry
Authors: Sportisse Bruno , Djouad Rafik
Published: May 2003

The objective of this article is to investigate some of the classical parameterizations used for modeling mass transfer between interstitial gas and cloud droplets for aqueous‐phase models in Air Pollution Modeling [Schwartz, 1986]. After an appropriate scaling of the initial model (a set of two coupled Partial Differential Equations), we apply the singular perturbation theory and some theoretical results of Reaction‐Diffusion models with large diffusion coefficients. This justifies the use of classical parameterizations in a large range of parameters. Moreover, we propose a new parameterization of mass transfer, taking into account aqueous‐phase diffusion limitations. This parameterization is based on a double‐film model and may have an impact for some species, as it is illustrated with a simple box model.
Signatures of tropopause folding in satellite imagery
Authors: Wimmers Anthony J. , Moody Jennie L. , Browell Edward V. , Hair Johnathan W. , Grant William B. , Butler Carolyn F. , Fenn Martha A. , Schmidt Christopher C. , Li Jun , Ridley Brian A.
Published: May 2003

A satellite‐based conceptual picture of the stratospheric contribution to the spring ozone peak is presented through a survey of flight measurements and satellite imagery from the Tropospheric Ozone Production about the Spring Equinox (TOPSE) program. We address the stratospheric contribution through the process of tropopause folding across air mass boundaries (the arctic and polar tropopause break) in the polar and midlatitude upper troposphere. These boundaries and the boundaries of their related outgrowing streamers are easily identifiable as sharp gradients in the altered water vapor (AWV) imagery, a linear modification of the GOES water vapor channel that represents upper tropospheric specific humidity. The close relationship between altered brightness temperature and total ozone (from the Total Ozone Mapping Spectrometer (TOMS) and the GOES sounder) along this gradient confirms the utility of AWV imagery in detecting the tropopause break. Transects constructed from aircraft lidar and in situ observations of ozone illustrate the existence of tropopause folding along the AWV gradient. Ten out of ten available transects during the February to May study period show tropopause folding where indicated by the satellite imagery. This is strong evidence that folding is ubiquitous across the polar/stratospheric air mass boundary during the study period, and that the associated intrusions of stratospheric air into the troposphere can be located continuously using AWV imagery.
Seasonal distributions of fine aerosol sulfate in the North American Arctic basin during TOPSE
Authors: Scheuer Eric , Talbot Robert W. , Dibb Jack E. , Seid Garry K. , DeBell Linsey , Lefer Barry
Published: May 2003

We used the mist chamber/ion chromatography technique to quantify fine aerosol SO4= (<2.7 μm) in the Arctic during the Tropospheric Ozone Production about the Spring Equinox Experiment (TOPSE) with about 2.5 min time resolution. Our effective sample area ranged from 50° to 86°N and 53° to 100°W. The seasonal evolution of fine aerosol sulfate in the Arctic troposphere during TOPSE was consistent with the phenomenon of Arctic haze. Arctic haze has been attributed to pollution from sources in the Arctic and pollution transported meridionally along stable isentropes into the Arctic in geographically broad but vertically narrow bands. These layers became more prevalent at higher altitudes as the season progressed toward summer, and the relevant isentropes are not held so close to the surface. Mean fine particle SO4= mixing ratios during TOPSE in February below 1000 m were elevated (112 pptv) and highly variable (between 28 and 290 pptv) but were significantly lower at higher altitudes (about 40 pptv). As the season progressed, elevated mixing ratios and higher variability were observed at higher altitudes, up to 7 km. In May, mixing ratios at the lowest altitudes declined but still remained higher than in February at all altitudes. The high variability in our measurements likely reflects the vertical heterogeneity of the wintertime Arctic atmosphere as the airborne sampling platform passed in and out of these layers. It is presumed that mixing ratios and variability will continue to decline at all altitudes into the summer as wet deposition processes become important in removing aerosol SO4= from the troposphere.
Vertical and latitudinal distributions of tropospheric ozone over the western Pacific: Case studies from the PACE aircraft missions
Authors: Tsutsumi Yukitomo , Makino Yukio , Jensen Jørgen B.
Published: May 2003

Three Pacific atmospheric chemistry experiments (PACE I, II, and III) were conducted each in January 1994, October 1994, and July 1995. The objective was to investigate the latitudinal distribution, transportation, and possible sources of tropospheric ozone over the western Pacific. Measurements of ozone using UV absorption method were taken by an aircraft flying at a maximum altitude of 6000 m between the Southern Hemisphere (SH) and the Northern Hemisphere (NH) (38°S–38°N) and within the longitudinal range of 120°E–150°E. The PACE aircraft missions first provide the middle troposphere (5000–6000 m) ozone distributions in three different seasons over this region in relatively short periods of time (within 9 days). On the basis of one‐minute average data, ozone mixing ratios in the middle troposphere were significantly higher in the NH midlatitudes (39–92 ppbv) and the SH midlatitudes (30–71 ppbv) than in the tropics (10–35 ppbv) during three different seasons. In particular, an air mass with low ozone mixing ratios (2–28 ppbv) extended from 7°S to 29°N in July during PACE III, in contrast to the air mass with higher ozone mixing ratios (39–57 ppbv) observed in the NH midlatitudes (>21°N) in January during PACE I. Several episodes of increased ozone were observed during the PACE missions. In the SH subtropics (16°S–22°S), photochemical ozone production in a biomass‐burning smoke, probably emitted from the northwest part of Australia, caused relatively high ozone mixing ratios (maximum 89 ppbv) at 5200 m during PACE II. In contrast, ozone transport over a long distance from the upper troposphere south of Africa brought about a maximum ozone mixing ratio of 64 ppbv in the same geographical region above 4500 m during PACE III. Large‐scale circulation coupled with a typhoon was found to impact ozone transport from the NH midlatitudes to the tropics. An air mass with ozone mixing ratios averaging about 50 ppbv at 5200 m, which originated over the Asian continent in the NH midlatitudes, was transported to the tropical western Pacific region (9°N–14°N) by a circulation coupled with a typhoon during PACE II. Summer observations of tropopause folding over the western Pacific are rare, yet high potential vorticity (PV) value (>1 PV unit) above 600 hPa level at 35°N shows that the tropopause folding beneath the subtropical jet occurred in the NH midlatitudes over the western Pacific in summer during PACE III. In this measurement, the increased ozone (maximum 92 ppbv) combined with decreased water vapor mixing ratio (<3.0 g/kg) and large potential temperature gradient (0.083 K/m) was observed above 3800 m. These facts suggest stratospheric influenced air descended to 3800 m. The source region of the high ozone observed over the tropical region (5°S–9°S) during PACE II has not been confirmed, but it is thought to have originated from biomass burning and might be influenced by circulation associated with El Nino.
Evaluation of algorithms for fire detection and mapping across North America from satellite
Authors: Li Zhanqing , Fraser R. , Jin J. , Abuelgasim A. A. , Csiszar I. , Gong P. , Pu R. , Hao W.
Published: May 2003

This paper presents an evaluation of advanced very high resolution radiometer (AVHRR)‐based remote sensing algorithms for detecting active vegetation fires [Li et al., 2000a] and mapping burned areas [Fraser et al., 2000] throughout North America. The procedures were originally designed for application in Canada with AVHRR data aboard the NOAA 14 satellite. They were tested here with both NOAA 11 and NOAA 14 covering the period 1989–2000. It was found that the active fire detection algorithm performs well with low commission and omission error rates over forested regions in the absence of cloud cover. Moderate errors were found over semi‐arid areas covered by thin clouds, as well as along rivers and around lakes observed from sun‐glint angles. A modification to a fire algorithm threshold and the addition of a new test can significantly improve the detection accuracy. Burned areas mapped by satellite were compared against extensive fire polygon data acquired by U.S. forest agencies in five western states. The satellite‐based mapping matches nearly 90% of total forested burned area, with the difference being mainly attributable to omission of some nonburned islands and patches within the fire polygons. In addition, it maps a significant area of burning outside the fire polygons that appear to be true fires. The 10% omission error was found to be caused mainly by three factors: lack or insufficient number of active fires, partial burning, and vegetation recovery after early season burning. In addition to total area, the location and shapes of burned scars are consistent with the ground‐based maps. Overall, the two algorithms are competent for detecting and mapping forest fires in North America north of Mexico with minor modifications.
Absorption of solar radiation by the clear and cloudy atmosphere during the Atmospheric Radiation Measurement Enhanced Shortwave Experiments (ARESE) I and II: Observations and models
Authors: Valero Francisco P. J. , Pope Shelly K. , Bush Brett C. , Nguyen Quyen , Marsden David , Cess Robert D. , Simpson‐Leitner A. Sabrina , Bucholtz Anthony , Udelhofen Petra M.
Published: May 2003

As a follow‐on to the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE) I, which provided atmospheric shortwave measurements from collocated aircraft, ARESE II performed similar measurements with a single aircraft flying at an altitude of 7 km over an instrumented surface site. ARESE I and ARESE II absorptance measurements are found to agree with each other and, when converted to top of the atmosphere (TOA) instantaneous column absorption, are also consistent with GOES 8 and Scanner for Radiation Budget (ScaRaB) satellite observations. Measurements are compared to calculations performed with five different radiative transfer models. It is found that the calculated absorption differs systematically from the observations in cloudy conditions, with models underpredicting the absorption. In particular, all the models tested here underpredict the measured instantaneous cloudy column absorption by amounts ranging from 17 to 61 W m−2, depending on the models and cases studied. The various models, using identical input, differ among themselves; for example, for the same cloudy case, absorptance estimates range from 0.22 to 0.27 for the atmospheric column from the surface to the TOA. It is also found that model‐calculated absorptances appear not as well correlated to cloud optical depth variations as the measured absorptances appear to be. Measured and calculated clear‐sky absorptances agree well within the uncertainties. Cloudy‐sky absorptances in the visible spectral region (300 to 700 nm) reach values of as much as 0.02 during ARESE II while the equivalent measurements for ARESE I range around 0.06. This visible absorptance may be related to aerosols and their day‐to‐day and seasonal variability.
A timescale investigation of volatile chemical retention during hydrometeor freezing: Nonrime freezing and dry growth riming without spreading
Authors: Stuart A. L. , Jacobson M. Z.
Published: May 2003

Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversion of liquid water to ice in clouds can impact the poststorm distributions of chemicals in the troposphere and in precipitation. In this paper, we use a timescale‐based methodology to determine the key physical parameters involved in retention and derive the dependence of retention on these parameters for nonrime freezing and rime freezing when droplet spreading is minimal. We calculate a dimensionless retention indicator for SO2, H2O2, NH3, and HNO3, for a variety of conditions relevant to natural clouds. We find that solute properties, particularly the effective Henry's constant, likely have a large impact on retention. Chemicals with very high effective Henry's constants (e.g., HNO3) will likely be retained completely under all conditions. For chemicals with lower effective Henry's constants, freezing conditions (including pH, temperature, magnitude of the hydrometeor velocity in air, and drop size) will likely have significant impacts on retention, while air pressure has only a small effect. The dependence on velocity and drop size depends on the limiting mass transport regime and is nonmonotonic due to the competing effects of ventilation on heat and mass transport. The formation of a complete or partial ice shell likely also affects retention significantly. Comparison of our results with available experimental data provides possible explanations of the trends and apparent disagreement found in the studies. The theory‐based analysis and methodology presented in this paper can be used to improve experimental design and parameterization of retention in cloud models.
Models‐3 Community Multiscale Air Quality (CMAQ) model aerosol component 1. Model description
Authors: Binkowski Francis S. , Roselle Shawn J.
Published: May 2003

The aerosol component of the Community Multiscale Air Quality (CMAQ) model is designed to be an efficient and economical depiction of aerosol dynamics in the atmosphere. The approach taken represents the particle size distribution as the superposition of three lognormal subdistributions, called modes. The processes of coagulation, particle growth by the addition of mass, and new particle formation, are included. Time stepping is done with analytical solutions to the differential equations for the conservation of number, surface area, and species mass. The component considers both PM2.5 and PM10 and includes estimates of the primary emissions of elemental and organic carbon, dust, and other species not further specified. Secondary species considered are sulfate, nitrate, ammonium, water, and secondary organics from precursors of anthropogenic and biogenic origin. Extinction of visible light by aerosols is represented by two methods: a parametric approximation to Mie extinction and an empirical approach based upon field data. The algorithms that simulate cloud interactions with aerosols are also described. Results from box model and three‐dimensional simulations are exhibited.
Models‐3 Community Multiscale Air Quality (CMAQ) model aerosol component 2. Model evaluation
Authors: Mebust Michelle R. , Eder Brian K. , Binkowski Francis S. , Roselle Shawn J.
Published: May 2003

An initial evaluation of the Models‐3 Community Multiscale Air Quality (CMAQ) model aerosol component reveals CMAQ's varying ability to simulate observed visibility indices and aerosol species concentrations. The visibility evaluation, using National Weather Service observations from 139 airports for 11–15 July 1995, shows that CMAQ reasonably captured the general spatial and temporal patterns of visibility degradation, including major gradients, maxima and minima. However, CMAQ's two visibility prediction methods, Mie theory approximation and mass reconstruction, both underpredict visibility degradation (i.e., overpredict visibility). The mean bias, normalized mean bias (NMB), mean error and normalized mean error (NME) for the Mie calculations are −5.9 dv, −21.7%, 7.0 dv and 25.4%, respectively. For the reconstruction simulations, these statistics are −9.8 dv, −35.5%, 10.0 dv and 36.2%, respectively. Most simulated values (∼90% Mie and ∼85% reconstruction) fall within a factor of two of the observations, although r2 = 0.25 (Mie) and r2 = 0.24 (reconstruction). The speciated aerosol evaluation uses observations of sulfate, nitrate, PM2.5, PM10 and organic carbon obtained from 18 stations of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network in June 1995. This evaluation reveals that, with the exception of sulfate (mean bias: 0.15 μg/m3, NMB: 3.1%), the model consistently underpredicts aerosol concentrations of nitrate (−0.10 μg/m3, −33.1%), PM2.5 (−3.9 μg/m3, −30.1%), PM10 (−5.66 μg/m3, −29.2%) and organic carbon (−0.78 μg/m3, −33.7%). Sulfate was simulated best by the model (r2 = 0.63, mean error = 1.75 μg/m3, NME = 36.2%), followed by PM2.5 (0.55, 5.00 μg/m3, 38.5%), organic carbon (0.25, 0.94 μg/m3, 40.6%), PM10 (0.13, 9.85 μg/m3, 50.8%) and nitrate (0.01, 0.33 μg/m3, 104.3%). Except for nitrate, 75–80% of simulated concentrations fall within a factor of two of the IMPROVE observations.
Regional background ozone and carbon monoxide variations in remote Siberia/East Asia
Authors: Pochanart Pakpong , Akimoto Hajime , Kajii Yoshizumi , Potemkin Vladimir M. , Khodzher Tamara V.
Published: May 2003

Continuous measurements of O3 and CO were made during 1997–1999 at Mondy, a remote mountain site in East Siberia, in order to quantify their mixing ratios and their climatology in the “background” troposphere of continental Eurasia. The seasonal cycles of O3 and CO show the spring maximum‐summer minimum similar to that previously reported in the remote Northern Hemisphere. The influences of Siberian forest fires on the variations of CO mixing ratios at Mondy were observed both on a local and a regional scale during spring 1997 and fall 1998, respectively. We further evaluate the possible impact of European pollution export to the remote atmosphere of Siberia using trajectory analysis. It was found that the O3 and CO mixing ratios in the air masses transported from Europe are higher than those from Siberia and high‐latitude regions for most of the year. The medians of O3 and CO mixing ratios associated with the European air masses are 44.2 and 134 ppb, respectively, in comparison with 42.7 and 128 ppb in the Siberian air masses, and 41.0 and 110 ppb in the high‐latitude air masses. The residence time analysis of air masses transported from the European continent indicates that CO mixing ratios significantly decrease with longer transport time of air masses from Europe, while rapid air motion retains higher CO mixing ratios in every season due to the admixture of polluted European air into the continental background air during air mass transport over Eurasia and photochemical loss by OH. Because of a shorter lifetime in summer, CO mixing ratios decrease at a rate of 6–7 ppb per day, while they decrease at a rate of 2–4 ppb per day in winter and spring. The similar trend is found for O3 but only in summer, at a rate of 2–3 ppb per day. From this analysis, we are able to identify that European pollution exerts an influence, though not very strong, on the background O3 and CO at Mondy in remote Siberia/East Asia.
Improved hydrological modeling for remote regions using a combination of observed and simulated precipitation data
Authors: van der Linden Sandra , Christensen Jens Hesselbjerg
Published: May 2003

Precipitation, as simulated by climate models, can be used as input in hydrological models, despite possible biases both in the total annual amount simulated as well as the seasonal variation. Here we elaborated on a new technique, which adjusted precipitation data generated by a high‐resolution regional climate model (HIRHAM4) with a mean‐field bias correction using observed precipitation. A hydrological model (USAFLOW) was applied to simulate runoff using observed precipitation and a combination of observed and simulated precipitation as input. The method was illustrated for the remote Usa basin, situated in the European part of Arctic Russia, close to the Ural Mountains. It was shown that runoff simulations agree better with observations when the combined precipitation data set was used than when only observed precipitation was used. This appeared to be because the HIRHAM4 model data compensated for the absence of observed data from mountainous areas where precipitation is orographically enhanced. In both cases, the runoff simulated by USAFLOW was superior to the runoff simulated within the HIRHAM4 model itself. This was attributed to the rather simplistic description of the water balance in the HIRHAM4 model compared to a more complete representation in USAFLOW.
An estimate of the stratospheric contribution to springtime tropospheric ozone maxima using TOPSE measurements and beryllium‐7 simulations
Authors: Allen Dale J. , Dibb Jack E. , Ridley Brian , Pickering Kenneth E. , Talbot Robert W.
Published: May 2003

Measurements of tropospheric ozone (O3) between 30°N and 70°N show springtime maxima at remote locations. The contribution of seasonal changes in stratosphere–troposphere exchange (STE) to these maxima was investigated using measurements from the Tropospheric Ozone Production about the Spring Equinox Experiment (TOPSE) campaign and the beryllium‐7 (7Be) distribution from a calculation driven by fields from the Goddard Earth Observing System Data Assimilation System (GEOS DAS). Comparison with TOPSE measurements revealed that upper tropospheric model‐calculated 7Be mixing ratios were reasonable (a change from previous calculations) but that lower tropospheric mixing ratios were too low most likely due to an overestimation of scavenging. Temporal fluctuations were well captured although their amplitudes were often underestimated. Analysis of O3 measurements indicated that O3 mixing ratios increased by 5–10% month−1 for θ < 300 K (the underworld) and by 10–15% month−1 for θ > 300 K (the tropospheric middleworld). 7Be mixing ratios decreased with time for θ < 290 K and increased with time for θ > 300 K. Model‐calculated middleworld increases of 7Be were a factor of 2 less than measured increases. 7Be with a stratospheric source (strat‐7Be) increased by 4.6–8.8% month−1 along TOPSE flight paths within the tropospheric middleworld. Increases in strat‐7Be were not seen along TOPSE flight paths in the underworld. Assuming changes in tropospheric O3 with a stratospheric source are the same as changes in strat‐7Be and that 50% of O3 in the region of interest is produced in the stratosphere, changes in STE explain 20–60% of O3 increases in the tropospheric middleworld and less than 33% of O3 increases in the underworld.