bluuebunny/crossref_metadata_2025 huggingface dataset:
Field observations of the vertical distribution of tropospheric ozone at the island of Reunion (southern tropics)
Authors: Baldy S. , Ancellet G. , Bessafi M. , Badr A. , Luk D. Lan Sun
Published: February 2004

An analysis of 1 year of tropospheric vertical soundings of ozone at the island of Reunion (21°S, 55°E) is presented. High values of ozone concentration are observed in the troposphere above the inversion level that caps the marine boundary layer (MBL) during the September to November period, concomitant with active biomass burning in the southeastern African continent and Madagascar. Tongues (prominences of higher values) of enhanced ozone are apparent on vertical profiles obtained during this period, and backward trajectories from tongue levels are generally traced back to these zones of intense burning. Profiles of high and almost constant ozone mixing ratio in the whole troposphere above the MBL are also obtained during this season and could not be traced back to a definite origin. Conversely, during January to March, MBL compounds and humidity are convected in the whole troposphere, and tropospheric ozone is very low. The seasonal variation of integrated tropospheric ozone is large, up to 30 Dobson units (DU) and the tropospheric contribution to total columnar ozone could be high, up to 50–55 DU. This seasonal variation is well correlated with total ozone mapping spectrometer (TOMS) data, anticorrelated with integrated water content, and approximately follows, with a small time lag, the seasonal fire activity in the southeastern Africa. Data from Reunion are in accord with equivalent results from Ascension Island (8°S, 15°W), Brazzaville (Congo; 4°S, 15°E) and Natal (Brazil; 6°S, 35°W), corroborate satellite observations, and suggest that the concentration of tropospheric ozone in the tropics is governed by the coupling of photochemical and dynamical processes.
Regional atmospheric aerosol composition and sources in the eastern Transvaal, South Africa, and impact of biomass burning
Authors: Maenhaut Willy , Salma Imre , Cafmeyer Jan , Annegarn Harold J. , Andreae Meinrat O.
Published: February 2004

As part of the Southern Africa Fire‐Atmosphere Research Initiative (SAFARI‐92), size‐fractionated aerosol samples were collected during September–October 1992 at three fixed ground‐based sites in the eastern Transvaal, i.e., at two sites within the Kruger National Park (KNP) and at a third site on the Transvaal highveld (about 150 km WSW of the KNP sites), and near a number of prescribed fires in the KNP. The collection devices consisted of stacked filter units, which separate the aerosol into a coarse (2–10 μm equivalent aerodynamic diameter (EAD)) and a fine (<2 μm EAD) size fraction, and of eight‐stage cascade impactors, which provide more detailed size fractionation. The samples were analyzed for particulate mass (PM), black carbon (BC), and up to 47 elements. The prescribed fires gave rise to high levels of airborne soil dust, but several species (elements) were particularly enriched in the pyrogenic emissions. This was the case for BC, P, K, Ca, Mn, Zn, Sr, and I in the coarse fraction, and for BC, the halogens (Cl, Br, I), K, Cu, Zn, Rb, Sb, Cs, and Pb (and in the flaming phase also Na and S) in the fine fraction. The aerosol concentrations, compositions, and time trends at the two KNP sites were quite similar, suggesting that regionally representative samples were collected. Receptor modeling calculations, using both absolute principal component analysis and chemical mass balance, indicated that the KNP coarse PM was essentially attributable to mineral dust and sea salt, with average relative apportionments of 75% and 25%, respectively. At the highveld site, mineral dust and sea salt contributed in a 99‐to‐1 ratio to the coarse PM. In the fine size fraction at all three fixed sites, four components were identified, i.e., mineral dust, sea salt, biomass burning products, and sulfate. The pyrogenic component was the dominant contributor to the atmospheric concentrations of BC, K, Zn, and I, a major source for PM, Cl, Cu, Br, and Cs, but only a minor source for S. About 40% of the fine PM was, on the average, attributed to the pyrogenic particles, and about one third of it to the sulfate component. Relation of the time trends of the various components with three‐dimensional air mass back trajectories indicated that elevated levels of pyrogenic products were mostly found in air masses arriving from the north. The levels of the sulfate component tended to be higher at the highveld site than at the two KNP sites, and this component was generally associated with continental air. It was concluded that the major contribution to this fine sulfate came from fossil fuel burning and various industrial activities on the Transvaal highveld.
Diurnal nonmigrating tidal oscillations forced by deep convective clouds
Authors: Williams Christopher R. , Avery Susan K.
Published: February 2004

The global distribution of latent heat released by the diurnal oscillations in deep convective precipitating clouds is investigated as a forcing mechanism of diurnal nonmigrating atmospheric tidal modes. The seasonal distribution of this forcing is deduced from 3‐hour temporal resolution infrared (11 μm) radiance measured by four geostationary and two polar orbiting satellites which was transformed into the zonal wavenumber domain yielding migrating and non‐migrating oscillations. The dominant wavenumbers in the forcing include the westward propagating 5, 2, and 1 oscillations, the eastward propagating 3 oscillation, and the standing oscillation. These dominant wavenumber oscillations were decomposed into Hough functions to describe their meridional structure. A vertical profile of latent heating rate was estimated and the dominant 22 tidal modes were used in an f plane model to determine the middle atmospheric response to this tropospheric forcing. The f plane model was also excited using heating rates associated with the solar insolation absorption by water vapor. The magnitude of the model atmosphere diurnal winds from both water vapor and latent heat is similar at certain locations. This response suggests that the superposition of many nonmigrating tidal modes forced by the latent heat release of precipitating clouds is important in understanding the middle atmospheric circulation.
Overview of an aircraft expedition into the Brazilian cerrado for the observation of atmospheric trace gases
Authors: Kirchhoff V. W. J. H. , Alvalá P. C.
Published: February 2004

Tropospheric trace gases were measured from an aircraft platform. The flights were organized to sample air masses from the geographic area of central Brazil, where the vegetation, a savanna‐type environment with the local name of “cerrado”, is subject to burning every year, especially through August, September, and October. These measurements were made as a Brazilian local contribution to the international field campaign organized by NASA, the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) mission, and the Southern African Fire Atmospheric Research Initiative (SAFARI). The major NASA TRACE A mission used the NASA DC 8 aircraft, with most flights over the South Atlantic Ocean region. In Brazil, missions using small aircraft measured ozone and carbon dioxide continuously, and carbon monoxide, nitrous oxide, and methane using grab sampling. In addition, ground‐based measurements were made continuously over most of the dry months of 1992, and ozonesondes were launched at three different sites. Geostationary Operational Environment Satellite‐East (GOES E) images and a special network of radio soundings provided meteorological information, and advanced very high resolution radiometer (AVHRR) images indicated the distribution of fire pixels in the region of interest. Most of the biomass burning in 1992 occurred in the state of Tocantins, with about 22% of all the burning in Brazil. The state of Mato Grosso was second, with 19% of all burning. The Brazilian aircraft was used mostly in these two states, near the cities of Porto Nacional and Cuiabá, for in situ sampling; 31 vertical profiles were made in air masses considered to be well mixed, that is, not in fresh plumes. Although the major interest was the dry season, sampling was also made during the previous wet season period in April 1992 for comparison; 10 vertical profiles were obtained using the same aircraft and measurement techniques. There is a clear difference between these two opposite seasonal periods, most evident in the O3and CO data. Both Cuiabá and Porto Nacional show some 30–60 parts per billion by volume (ppbv) larger methane concentrations, for example, during the dry season, in comparison to the wet season, the difference at Cuiabá being larger. The methane data for the wet season show no significant differences between Cuiabá and Porto Nacional mixing ratios, which seems to exclude the existence of significant sources or sinks at these sites during this wet season. The ozone mixing ratios vary around 15 ± 5 ppbv in the wet season, and from a minimum of 35 to a maximum of 70 ± 10 ppbv, depending on height, in the dry season. The largest variability is seen in the carbon monoxide mixing ratios which vary from 90–100 ppbv in the wet season to maxima of 300 at 3.3 km and 600 ppbv at 1.2 km height in the dry season.
Three‐dimensional numerical study of shallow convective clouds and precipitation induced by land surface forcing
Authors: Avissar Roni , Liu Yongqiang
Published: February 2004

A state‐of‐the‐art mesoscale atmospheric model was used to investigate the three‐dimensional structure and evolution of shallow convective clouds and precipitation in heterogeneous and homogeneous domains. In general, the spatial distribution of clouds and precipitation is strongly affected by the landscape structure. When the domain is homogeneous, they appear to be randomly distributed. However, when the landscape structure triggers the formation of mesoscale circulations, they concentrate in the originally dry part of the domain, creating a negative feedback which tends to eliminate the landscape discontinuities, and spatially homogenize the land water content. The land surface wetness heterogeneity of the domain and the toted amount of water vapor present in the atmosphere (locally evapotranspired and/or advected) affect the precipitation regime. In general, the upward motion of mesoscale circulations generated by landscape heterogeneities is stronger than thermal cells induced by turbulence. Furthermore, their ability to transport moist, warm air to higher elevations increases the amount of water that can be condensed and precipitated. The evolution of shallow convective clouds and precipitation consists of a “build‐up phase” during which turbulence is predominant and responsible for the moistening of the atmosphere. In heterogeneous domains, it is also responsible for the creation of horizontal pressure gradients leading to the generation of mesoscale circulations. This phase occurs during the morning hours. From about 1200 until 1600 LST, clouds develop and most of the precipitation is produced. This is the “active phase.” After 1600 LST, the horizontal thermal and pressure gradients, which fed the energy necessary to create and sustain the mesoscale circulations, gradually disappear. This is the “dissipation phase.” The differences and similarities obtained between three‐dimensional and two‐dimensional simulations were also studied. These simulations indicate that, unless the landscape presents a clear two‐dimensional structure, the use of such a two‐dimensional model is not appropriate to simulate this type of clouds and precipitation. Conversely, two‐dimensional simulations can be confidently used, provided that the simulated domain presents a two‐dimensional heterogeneity.
Atomic hydrogen and ozone concentrations derived from simultaneous lidar and rocket airglow measurements in the equatorial region
Authors: Takahashi Hisao , Melo Stella M. L. , Clemesha B. R. , Simonich D. M. , Stegman J. , Witt G.
Published: February 2004

Nighttime atomic hydrogen and ozone concentrations are derived from simultaneous measurements of the vertical profiles of upper mesospheric airglow emissions and atmospheric sodium. The airglow profiles were obtained in a sounding rocket experiment launched from Alcântara (2.5°S, 44.2°W) on May 31, 1992. A lidar operating at the launch site was used to measure sodium at the time of the rocket experiment. A total of 10 airglow photometers, 6 forward looking and 4 side looking, observed the OI 557.7 nm, O2 Herzberg and O2 atmospheric (0,0) bands, sodium D lines, OI 630 nm, OH(8,3) band, and the airglow continuum. The simultaneous ground‐based sodium lidar and onboard sodium airglow measurements made it possible to derive the ozone concentration at heights between 85 and 100 km. The hydrogen concentrations were then calculated from the O2 atmospheric (0,0), OH(8,3) and the ozone profiles. The results suggest that the hydrogen concentration varied from 1 × 109 cm−3 at 85 km to 1 × 108 cm−3 at 100 km, values much higher than those suggested by recent model atmospheres and by some rocket observations at middle and high latitudes. Although the method of obtaining the concentrations of the minor constituents in the upper atmosphere is an indirect optical technique, this is the first time that these concentrations have been measured by rocket in the equatorial region.
Sensitivity analysis of the biosphere‐atmosphere transfer scheme
Authors: Gao Xiaogang , Sorooshian S. , Gupta H. V.
Published: February 2004

The biosphere‐atmosphere transfer scheme (BATS) land surface parameterization was developed to provide a realistic representation of hydrometeorology at the atmosphere‐land interface for coupling with general circulation models. This paper presents the results of a comprehensive sensitivity analysis of BATS for the conditions of midlatitude land surface and climatology. The analysis employs visual “feature‐curve” representations to study the sensitivity of key model outputs to variations over a range of model parameters, atmospheric forcings, and model initialization conditions. The analysis provides insights into the behavior of the model and indicates that (1) the dominant energy flux shifts from being the soil sensible heat flux in arid/semiarid regions to evapotranspiration in rain forest regions; (2) in off‐line studies the absence of important feedback mechanisms may result in unrealistic results at extreme climatic conditions; (3) the model functions which determine the atmosphere‐controlled and soil moisture limited latent heat fluxes from soil and vegetation may need to be refined in order to obtain a more realistic modeling of the energy fluxes from the land surface; and (4) certain components of the model can possibly be simplified. The results also show that the influence of errors in the initial state estimates can persist for several years, indicating that caution should be exercised when attempting to validate or calibrate BATS using incomplete observation data and short‐term simulation runs.
Use of volcanic aerosols to study the tropical stratospheric reservoir
Authors: Grant William B. , Browell Edward V. , Long Craig S. , Stowe Larry L. , Grainger R. G. , Lambert Alyn
Published: February 2004

Aerosol data obtained by the advanced very high resolution radiometer on NOAA 11, the improved stratospheric and mesospheric sounder on the upper atmospheric research satellite, one airborne lidar system, and several ground‐based lidar systems up to 2‐1/2 years after the eruption of Mount Pinatubo are used to study stratospheric dynamics. In particular, this study focuses on the tropical stratospheric reservoir and transport from it to northern midlatitudes following the eruption of Mount Pinatubo. This includes: The build‐up and removal rates for sulfate aerosol, the position and motion of the center of the reservoir, and the position and width of its boundaries at altitudes of the volcanic aerosols. Ozone data from the total ozone mapping spectrometer were also used to study the position and width of the reservoir boundaries. In addition, ground‐based lidar stratospheric aerosol data are used to study aerosol transport from the reservoir to the northern hemisphere as it relates to winds in the tropical stratosphere. Finally, historical in situ and satellite data were used to examine how the time and location of volcanic injections into the stratosphere affect the aerosol decay rates and seasonal variations of aerosol optical depth in the midlatitude stratosphere.
Origin of tropospheric ozone at remote high northern latitudes in summer
Authors: Mauzerall D. L. , Jacob D. J. , Fan S.‐M. , Bradshaw J. D. , Gregory G. L. , Sachse G. W. , Blake D. R.
Published: February 2004

We quantify the tropospheric ozone budget over remote high northern latitudes in summer using chemical and meteorological measurements between 0 and 6‐km made during the summer of 1990 Arctic Boundary Layer Expedition (ABLE 3B). We include all components of the ozone budget, both sinks (in situ photochemical loss and deposition); and sources (in situ photochemical production, advection of pollution ozone into the region, production in biomass wildfire plumes, and downwards transport from the upper troposphere/stratosphere). In situ production and loss of ozone are calculated with a photochemical model. The net influx of pollution ozone from North America and Eurasia is estimated from the average enhancement ratio of ΔO3/ΔC2Cl4 observed in pollution plumes and scaled by the net influx of C2Cl4. The contribution of ozone produced in biomass wildfire plumes is estimated from the average enhancement ratio of ΔO3/ΔCO in aged fire plumes. Regional photochemical production and loss in the 0–6 km column are found to be approximately equal; hence, net photochemical production is near zero. However, when ozone production and loss terms are separated, we find that dispersed in situ photochemical production driven by background NO levels (5–10 pptv) is the largest source term in the ozone budget (62%). Influx of stratospheric ozone is of secondary importance (27%), long‐range transport of pollution ozone makes a small contribution (9%), and photochemical production of ozone within biomass wildfire plumes is a relatively negligible term (2%) in the budget. Biomass fires and transport of anthropogenic pollution into the region may however have a major effect on the ozone budget through enhancement of background NO, mixing ratios which increase dispersed photochemical production. Using a 1‐D time‐dependent photochemical model between 0 and 6 km, we obtain good agreement between the observed and model‐generated vertical ozone profiles. We find that in situ photochemistry within the 0–6 km column accounts for nearly 90% of the ozone mixing ratio within the boundary layer, while above 5 km it accounts for only about 40%. Although photochemical production of ozone within the 0–6 km column is larger than the other source terms combined, the 1‐D model results indicate that influx from above is necessary to account for the observed increase in ozone mixing ratios with altitude.
Three‐dimensional view of the large‐scale tropospheric ozone distribution over the North Atlantic Ocean during summer
Authors: Kasibhatla P. , Levy H. , Klonecki A. , Chameides W. L.
Published: February 2004

A global chemical transport model is used to study the three‐dimensional structure of the tropospheric ozone (O3) distribution over the North Atlantic Ocean during summer. A simplified representation of summertime O3photochemistry appropriate for northern hemisphere midlatitudes is included in the model. The model is evaluated by comparing simulated O3mixing ratios to summertime O3measurements taken in and near the North Atlantic Ocean basin. The model successfully reproduces (1) the means and standard deviations of ozonesonde measurements over North America at 500 mbar; (2) the statistical characteristics of surface O3data at Sable Island off the coast of North America and at Bermuda in the western North Atlantic; and (3) the mean midtropospheric O3measured at Bermuda and also at the Azores in the eastern North Atlantic. The model underestimates surface O3in the eastern North Atlantic, overestimates O3in the lower free troposphere over the western North Atlantic, and also has difficulty simulating the upper tropospheric ozonesonde measurements over North America. An examination of the mean summertime O3distribution simulated by the model shows a significant continental influence on boundary layer and free‐tropospheric O3over the western North Atlantic. The model has also been exercised using a preindustrial NOxemission scenario. By comparing the present‐day and preindustrial simulations, we conclude that anthropogenic NOxemissions have significantly perturbed tropospheric O3levels over most of the North Atlantic. We estimate that present‐day O3levels in the lower troposphere over the North Atlantic are at least twice as high as corresponding preindustrial O3levels. We find that the anthropogenic impact is substantial even in the midtroposphere, where modeled present‐day O3mixing ratios are at least 1.5 times higher than preindustrial O3levels.
Major optical depth perturbations to the stratosphere from volcanic eruptions: Pyrheliometric period, 1881–1960
Authors: Stothers Richard B.
Published: February 2004

A detailed chronology of major stratospheric dust veils from 1881 to 1960 has been constructed by searching the primary literature for relevant observational data of various kinds, especially pyrheliometry. Data from 23 observing sites in both hemispheres have been reduced in a rigorous fashion to yield a table of pyrheliometric optical depth perturbations as a function of year, month, and latitude band. To convert to visual reference wavelengths, the tabular entries should be multiplied by a time‐dependent factor that is somewhat greater than unity. Ten measurable volcanic dust veils have been established in this manner and have been analyzed as to their generation, transport, decay, and total mass. These clouds arose from eruptions of Krakatau (1883), an unidentified volcano (1890), Soufrière and Pelée (1902), Santa Maria (1902), Ksudach (1907), Katmai (1912), Puyehue (1921), Paluweh (1928), Komagatake (1929), and Quizapu (1932). Other turbidity indicators have also been used in the analysis, including starlight extinction, purple twilight glows, color of Sun and Moon, polarization of blue sky light, Bishop's ring around the Sun, and dark lunar eclipses. Global stratospheric aerosol loadings have been computed from the peak turbidities. Agreement with the aerosol masses derived from polar ice cores is good in the important cases of Krakatau, Santa Maria, and (after a major correction of the ice core value) Katmai. During the long period 1881–1992, about 80% of all stratospheric aerosols generated by the largest sulfur‐producing eruptions were emplaced during the two short time intervals 1883–1902 and 1982–1991. The long‐term (1881–1992) average annual production rate of stratospheric SO2 from the largest eruptions was 0.8 Tg yr−1, about half the average rate since 1981. Implications of the principal results are discussed.
Fast response resonance fluorescence CO measurements aboard the C‐130: Instrument characterization and measurements made during North Atlantic Regional Experiment 1993
Authors: Gerbig Christoph , Kley Dieter , Volz‐Thomas Andreas , Kent Joss , Dewey Ken , McKenna Danny S.
Published: February 2004

The resonance fluorescence instrument for the measurement of atmospheric CO described by Volz and Kley [1985] was characterized in the laboratory and adapted for use on aircraft. A major finding was that the background signal is largely due to continuum resonance Raman scattering by molecular oxygen and thus cannot be reduced by better design. The instrument was deployed on the United Kingdom Meteorological Office (UKMO) C‐130 Hercules during August 1993 and in subsequent missions. The instrument achieved a detection limit (3σ) of 5 ppb at a time resolution of 30 s. For a typical CO concentration of 100 ppb, the signal‐to‐noise ratio (1σ) was 15 for an integration time of 2 s, which was the minimum time resolution that could be obtained during the flights because of limited pump capacity. Data collected over the North Atlantic show distinct layers of CO above the atmospheric boundary layer (ABL) that are well correlated with enhanced NOy mixing ratios and indicate transport of pollution from the American continent. Such layers, albeit much less pronounced, were encountered in westerly flow in the midtroposphere west of the coast of Portugal. Fairly high mixing ratios were observed in the lower troposphere associated with transport from southern Europe.
Analysis of the distribution of ozone over the southern Atlantic region
Authors: Olson Jennifer Richardson , Fishman Jack , Kirchhoff Volker W. J. H. , Nganga Dominique , Cros Bernard
Published: February 2004

Tropospheric ozone data measured by ozonesondes during the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) field mission and the multiyear pre‐TRACE A program are analyzed jointly with tropospheric ozone amounts derived from remote satellite data (“residuals”). We present here the first detailed analysis of the entire Ascension Island pre‐TRACE A data set. Data from the three pre‐TRACE A ozonesonde sites are used to establish a coherent spatial and temporal climatology of ozone in the southern tropical Atlantic region. This analysis shows a significant ozone seasonality over the Atlantic region, with a period of maximum values that extends from the austral winter through at least October at Natal, Brazil, and Ascension Island. Concentrations begin to decline somewhat earlier at Brazzaville, Congo, especially at lower altitudes. Although Natal exhibits a significantly lower annual average than Ascension Island or Brazzaville by about 4 Dobson Units (DU), the magnitude of the seasonal amplitude at Natal is the largest of the three stations. Additionally, more of the seasonal amplitude at Natal is due to a contribution from ozone in the middle and upper troposphere than at either Ascension Island or Brazzaville. Amplitudes as large as 15 DU are measured at individual sites, and the residuals show an average amplitude over the southern tropical Atlantic region of 10–12 DU. Statistical comparison of the residuals to the ozonesonde climatology show that while the residuals tend to underpredict both the means and the seasonal amplitudes compared to the in situ data, they provide a good representation of the variance of ozone in this region and predict the local annual and seasonal means to within better than 10% and seasonal amplitudes to within 15%.
Observational evidence of plane parallel model biases: Apparent dependence of cloud optical depth on solar zenith angle
Authors: Loeb Norman G. , Davies Roger
Published: February 2004

This study directly compares plane parallel model calculations with 1 year of Earth Radiation Budget Satellite shortwave observations at nadir over ocean between 30°S and 30°N. When plane parallel model calculations are matched to the observations on a pixel‐by‐pixel basis by adjusting cloud fraction and cloud optical depth, the resulting frequency distributions of cloud optical depth show a systematic shift towards larger values with increasing solar zenith angle, regardless of the assumptions made in the calculations. This dependence is weak for thin clouds but gets progressively stronger as the clouds become thicker. For the thinnest 50% of the clouds (optical depths ≲6), it occurs only at oblique solar zenith angles, whereas it is observed at all solar zenith angles for the thickest 10% of clouds (optical depths ≳12). On average, the increase is extremely large for solar zenith angles ≳63°. Such behavior is unrealistic since average cloud optical depths from such an extensive data set should be almost independent of solar zenith angle. The cause is traced to a fundamental flaw in plane parallel theory applied to real clouds: the solar zenith angle dependence of model reflectance is opposite to that of the observations. The one‐dimensional nadir reflectance remains within 10% of the observed reflectance for solar zenith angles ≲53° when applied to a general ensemble of real clouds, and for solar zenith angles ≲63° when applied to the thinnest 50% of such clouds. Uncertainties are found to increase rapidly as the Sun becomes more oblique, easily reaching 30% at the lowest solar elevations. Based on results from theoretical studies, it is concluded that three‐dimensional cloud structures not accounted for by plane parallel theory have a statistically important effect on the radiation field. As a minimum requirement, application of one‐dimensional theory to the remote sensing of cloud optical thickness from measurements of nadir reflectance should therefore be restricted to thin clouds and small solar zenith angles.
Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12°S, 135°W): A comparison of field data and model results: 1. Dimethylsulfide
Authors: Yvon S. A. , Saltzman E. S. , Cooper D. J. , Bates T. S. , Thompson A. M.
Published: February 2004

Shipboard measurements of atmospheric and seawater DMS were made at 12°S, 135°W for 6 days during March 1992. The mean seawater DMS concentration during this period was 4.1 ± 0.45 nM (1σ, n = 260) and the mean atmospheric DMS mole fraction was 453 ± 93 pmol mol−1 (1σ, n = 843). Consistent atmospheric diel cycles were observed, with a nighttime maximum and daytime minimum and an amplitude of approximately 85 pmol mol−1. Photochemical box model calculations were made to test the sensitivity of atmospheric DMS concentrations to the following parameters: 1) sea‐to‐air flux, 2) boundary layer height, 3) oxidation rate, and 4) vertical entrainment velocities. The observed relationship between the mean oceanic and atmospheric DMS levels require the use of an air‐sea exchange coefficient which is at the upper limit end of the range of commonly used parameterizations. The amplitude of the diel cycle in atmospheric DMS is significantly larger than that predicted by a photochemical model. This suggests that the sea‐to‐air DMS flux is higher than was previously thought, and the rate of daytime oxidation of DMS is substantially underestimated by current photochemical models of DMS oxidation.
A comparison of sources of odd nitrogen production from 1974 through 1993 in the Earth's middle atmosphere as calculated using a two‐dimensional model
Authors: Vitt Francis M. , Jackman Charles H.
Published: February 2004

The odd nitrogen source strengths associated with solar proton events (SPEs), galactic cosmic rays (GCRs), and the oxidation of nitrous oxide in the Earth's middle atmosphere from 1974 through 1993 have been compared globally, at middle and lower latitudes (<50°), and at polar regions (>50°) with a two‐dimensional photochemical transport model. As discovered previously, the oxidation of nitrous oxide dominates the global odd nitrogen source, while GCRs and SPEs are significant at polar latitudes. The horizontal transport of odd nitrogen, produced by the oxidation of nitrous oxide at latitudes <50°, was found to be the dominant source of odd nitrogen in the polar regions, with GCRs contributing substantially during the entire solar cycle. The source of odd nitrogen from SPEs was more sporadic; however, contributions during several years (mostly near solar maximum) were significant in the polar middle atmosphere.
Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn
Authors: Etheridge D. M. , Steele L. P. , Langenfelds R. L. , Francey R. J. , Barnola J.‐M. , Morgan V. I.
Published: February 2004

A record of atmospheric CO2 mixing ratios from 1006 A.D. to 1978 A.D. has been produced by analysing the air enclosed in three ice cores from Law Dome, Antarctica. The enclosed air has unparalleled age resolution and extends into recent decades, because of the high rate of snow accumulation at the ice core sites. The CO2 data overlap with the record from direct atmospheric measurements for up to 20 years. The effects of diffusion in the firn on the CO2 mixing ratio and age of the ice core air were determined by analyzing air sampled from the surface down to the bubble close‐off depth. The uncertainty of the ice core CO2 mixing ratios is 1.2 ppm (1 σ). Preindustrial CO2 mixing ratios were in the range 275–284 ppm, with the lower levels during 1550–1800 A.D., probably as a result of colder global climate. Natural CO2 variations of this magnitude make it inappropriate to refer to a single preindustrial CO2 level. Major CO2 growth occurred over the industrial period except during 1935–1945 A.D. when CO2 mixing ratios stabilized or decreased slightly, probably as a result of natural variations of the carbon cycle on a decadal timescale.
A global three‐dimensional model study of carbonaceous aerosols
Authors: Liousse C. , Penner J. E. , Chuang C. , Walton J. J. , Eddleman H. , Cachier H.
Published: February 2004

We have developed detailed emission inventories for the amount of both black and organic carbon particles from biomass burning sources (wood fuel, charcoal burning, dung, charcoal production, agricultural, savanna and forest fires). We have also estimated an inventory for organic carbon particles from fossil fuel burning and urban activities from an existing inventory for fossil fuel sources of black carbon. We also provide an estimate for the natural source of organic matter. These emissions have been used together with our global aerosol model to study the global distribution of carbonaceous aerosols. The accuracy of the inventories and the model formulation has been tested by comparing the model simulations of carbonaceous aerosols in the atmosphere and in precipitation with observations reported in the literature. For most locations and seasons, the predicted concentrations are in reasonable agreement with the observations, although the model underpredicts black carbon concentrations in polar regions. The predicted concentrations in remote areas are extremely sensitive to both the rate of removal by wet deposition and the height of injection of the aerosols. Finally, a global map of the aerosol single scattering albedo was developed from the simulated carbonaceous particle distribution and a previously developed model for aerosol sulfates. The computed aerosol single scattering albedos compare well with observations, suggesting that most of the important aerosol species have been included in the model. For most locations and seasons, the single scattering albedo is larger than 0.85, indicating that these aerosols, in general, lead to a net cooling.
Measurement of peroxides and related species in the 1993 North Atlantic Regional Experiment
Authors: Weinstein‐Lloyd Judith B. , Daum Peter H. , Nunnermacker Linda J. , Lee Jai H. , Kleinmann Lawrence I.
Published: February 2004

Gaseous peroxides were measured during the North Atlantic Regional Experiment (NARE) aboard the Department of Energy's Gulfstream G‐1 aircraft in August 1993. Rights originated in Halifax, Nova Scotia and covered a region extending several hundred kilometers from the eastern edge of the North American continent. Total peroxide concentration was dominated by H2O2. Median H2O2 concentration for all flights was 2.5 parts per billion by volume (ppbv), with the highest concentrations observed in spatially extensive layers between 250 and 1750 m above sea level. In the clean free troposphere, H2O2 concentration correlates strongly with the product O3*H2O, consistent with our understanding of the formation mechanism. The median peroxide concentration was 4 ppbv in pollutant plumes, with excursions above 11 ppbv. The high concentration of H2O2 observed, and its covariance with concentrations of anthropogenic species such as O3, NOy, and aerosol particles is attributed to the aging of polluted air masses advected from the continent in stable layers.
MICADO wind measurements from Observatoire de Haute‐Provence for the validation of WINDII green line data
Authors: Thuillier G. , Fauliot V. , Hersé M. , Bourg L. , Shepherd G. G.
Published: February 2004

The WINDII instrument measures the velocity of the meridional and zonal components of the wind as a function of altitude using a Michelson interferometer. Such an instrument is calibrated in the laboratory before launch. For several reasons, it is important to compare the WINDII data with other independent measurements. This should allow the confirmation of either the accuracy of the space measurements, the detection of some systematic offset, or an aging as a function of time. The MICADO interferometer has been running since the beginning of the UARS mission at Observatoire de Haute‐Provence (France). The data provided by this instrument are used to perform this study. For nighttime measurements, no aging has been detected and it is found that WINDII overestimates the two components of the wind by 10 m s−1 at the latitude and longitude of the ground‐based observations. This corresponds to an offset of 9 m s−1 for both fields of view. Amplitude and phase of the semidiurnal tide have also been derived from the WINDII and MICADO data as a function of season. Comparable results were obtained.
Methane in the tropical South Atlantic: Sources and distribution during the late dry season
Authors: Bartlett Karen B. , Sachse Glen W. , Collins James E. , Harriss Robert C.
Published: February 2004

Methane (CH4) mixing ratios in the South Atlantic basin were sampled from a DC‐8 aircraft during the TRACE A expedition over the months of September and October 1992. This high‐precision (±0.1%), high‐resolution data set (independent measurements every 5 s) includes a total of 67,335 observations and ranges from 1586.6 to 2152.8 parts per billion by volume (ppbv). The observed values were influenced by emissions from biomass burning and local urban/industrial areas, stratosphere‐troposphere exchange, active convective mixing, and possible long‐range transport of pollution. Average mixing ratios increased from the atmospheric mixed layer (0–2 km) to the free troposphere (2–6 km) and were greatest at altitudes above 6 km. A longitudinal trend observed between 5°N and 40°S latitude suggests that CH4inputs were greater on the South American side of the basin. A latitudinal trend in values between the near‐surface and 11 km exhibits the expected gradient from north to south, but differs from the latitudinal gradient observed in surface level clean air at this time. Higher concentrations at altitude, at least at this time of year, indicate that ground‐based atmospheric monitoring sites may underestimate pollution inputs to the region.
Modeling of particle size distribution and its influence on the radiative properties of mineral dust aerosol
Authors: Tegen Ina , Lacis Andrew A.
Published: February 2004

The radiative parameters of mineral aerosols are strongly dependent on particle size. Therefore explicit modeling of particle size distribution is needed to calculate the radiative effects and the climate impact of mineral dust. We describe a parameterization of the global mineral aerosol size distribution in a transport model using eight size classes between 0.1 and 10 μm. The model prescribes the initial size distribution using soil texture data and aerosol size measurements close to the ground. During transport, the size distribution changes as larger particles settle out faster than smaller particles. Results of Mie scattering calculations of radiative parameters (extinction efficiency, single scattering albedo, asymmetry parameter) of mineral dust are shown at wavelengths between 0.3 and 30 μm for effective particle radii between 0.1 and 10 μm. Also included are radiative properties (reflection, absorption, transmission) calculated for a dust optical thickness of 0.1. Preliminary studies with the Goddard Institute for Space Studies (GISS) general circulation model (GCM), using two particle size modes, show regional changes in radiative flux at the top of the atmosphere as large as +15 W m−2 at solar and +5 W m−2 at thermal wavelengths in the annual mean, indicating that dust forcing is an important factor in the global radiation budget.
Comparison of CLAES preliminary N2O5 data with correlative data and a model
Authors: Kumer J. B. , Mergenthaler J. L. , Roche A. E. , Nightingale R. W. , Zele F. , Gille J. C. , Massie S. T. , Bailey P. L. , Connell P. S. , Gunson M. R. , Abrams M. C. , Toon G. C. , Sen B. , Blavier J.‐F. , Smith S. E. , Taylor F. W.
Published: February 2004

The cryogenic limb etalon array spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite (UARS) has made near‐global measurements of N2O5. Data for 388 days have been processed to version 7 (V7) for the period from January 9, 1992, to April 25, 1993. Results from UARS instruments, including CLAES and the improved stratospheric and mesospheric sounder (ISAMS) provide the first near‐global N2O5 measurements. Retrieval below 3.16 mbar is adversely affected by aerosols and above 1.47 mbar by lack of signal and possible instrument effects, so data usage is recommended for just the three “UARS pressure surfaces” 3.16, 2.15, and 1.47 mbar. A comparison of the diurnal data variation with the model suggests there are offsets in the data that are to first order diurnally independent. These offsets are tabulated to facilitate subtraction, which is recommended for most data applications. Candidate mechanisms for the offsets are discussed. Comparisons of CLAES data with the offsets subtracted, with profiles obtained by the shuttle‐deployed Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment and concurrent ISAMS profiles, and with a profile obtained by the balloon‐borne NASA Jet Propulsion Laboratory (JPL) MARK IV instrument, show poorest agreement in equatorial regions at 3.15 mbar where CLAES values are larger by about 30 to 40%. At higher altitudes and latitudes the comparison improves and tends toward consistency with systematic error estimates that are based on instrument and retrieval process characterization and range from 14% at 3.16 mbar to 21% at 1.47 mbar. A similar estimate of random CLAES error ranges from 7% at 3.16 mbar to 26% at 1.47 mbar. By comparison, the average values of the error estimates generated by the production processing algorithm at 3.16 and 1.47 mbar are 8 and 36%, respectively, and the average values derived from the observed data variability are 19 and 24%. Confidence is enhanced by the good global scale agreement and correlation of CLAES and ISAMS during an N2O5 enhancement event in early–mid‐January 1992 polar winter, in which values >5.5 parts per billion at 3.16 mbar by volume are observed. A description of artifacts that may occur at 3.16 mbar and much less frequently at 2.15 mbar, during this and other enhancement conditions, and the demonstrated approach to eliminate these in future versions, is given in the text.
Mesospheric gravity waves at Saskatoon (52°N), Kyoto (35°N), and Adelaide (35°S)
Authors: Nakamura T. , Tsuda T. , Fukao S. , Manson A. H. , Meek C. E. , Vincent R. A. , Reid I. M.
Published: February 2004

The gravity waves with periods of 10 min to 8 hours in the mesosphere (67–80 km) are studied using observations from the Adelaide MF radar (35°S), Saskatoon MF radar (52°N), and the middle and upper atmosphere (MU) radar at Shigaraki, near Kyoto (35°N). The seasonal variations of the gravity wave intensity deduced from the horizontal wind velocities showed semiannual variations with solstitial maxima and equinoctial minima at all three locations, but the month of maximum intensity in the year depends on the locations and wave frequency. The kinetic energy due to gravity waves showed similar amplitude between Kyoto and Adelaide, but smaller at Saskatoon, which agrees well with the results of the preliminary comparison using a limited frequency range and limited observation periods by Nakamura et al. [1993a, b]. The horizontal propagation direction of these gravity waves showed small seasonal variations and significant dependency with wave periods at Saskatoon but showed more frequent variation without a large frequency dependency at Kyoto and Adelaide. These characteristics indicate that at the lower latitudes gravity wave activity is larger, as pointed out by Tsuda et al. [1994] from various observational techniques. Also, the frequent changes of the gravity wave intensities at the lower latitudes suggest that there are strong influences of the background wind variation in the middle atmosphere such as semiannual oscillation, mesospheric semiannual oscillation and other wind variations in the low latitudes.
A reexamination of the relationship between eddy mixing and O2 in the Martian middle atmosphere
Authors: Rosenqvist Jan , Chassefière E.
Published: February 2004

A value of the eddy diffusion coefficient K of ≈1.5×106 cm2 s−1 in the middle atmosphere of Mars was obtained from Phobos 2 solar occultation measurements of dust, ozone, and clouds at low latitude. The aim of the present study is to complete this picture by using a steady state photochemical one‐dimensional model. The main regulation mechanism of O2 is the reaction of O with itself, whose rate depends on the value of K in the middle atmosphere. By comparing calculated and observed values of the O2 abundance, an upper limit of ≈2×107 cm−2 s−1 on K is inferred. By including an additional constraint provided by H2 balance, a lower limit of ≈4×106 cm−2 s−1 may be placed. It results from the present analysis that the most realistic value of K to be used in works resorting to one‐dimensional modeling (long‐term evolution, escape, surface/atmosphere exchanges) is ≈107 cm2 s−1 rather than ≈106 cm2 s−1. The difference between theoretical and observational values might be due to the regular occurrence of global dust storms, whose effect should be to increase the yearly average value of K. The present study suggests less than 3 precipitable micrometer (pr‐μm) of the yearly averaged water vapor column, unless H2O is confined in a layer near the ground. Although the first possibility seems more probable, the second hypothesis cannot be ruled out. It could reflect a continuous supply of H2O from the regolith to the atmosphere on a seasonal scale. The loss to production ratio of CO, which has a lifetime of ≈5 years, is shown to depart from unity by no more than ≈10% over a wide range of atmospheric conditions. The stability of the Martian atmosphere is therefore realized in the classical frame of homogeneous chemistry.
A case for ancient evaporite basins on Mars
Authors: Forsythe Randall D. , Zimbelman James R.
Published: February 2004

Observations indicate that a Martian analog to the Earth's salt pans and saline lakes of arid regions may have existed in crater‐basins during Mars' early (Noachian) epoch. Terraced and channelized crater‐basins point to ponding of surface water as well as possible prolonged and evolving base levels. In addition, supportive (evaporite basin) analogs are offered for three other morphologic features of Martian crater‐basins. An evaporite basin model for crater‐basins on Mars has major implications for the mechanical, chemical, and even biological processes that potentially have operated in Mars' past, and represent a spectrum of potential mineral resources.
Mass of dust in the Martian atmosphere
Authors: Martin Terry Z.
Published: February 2004

Estimates of the mass of dust suspended in the Martian atmosphere are derived from global and regional 9‐μm opacity maps produced from Viking Infrared Thermal Mapper data. During the peak of the 1977b storm, a total dust mass of approximately 4.3 × 1014 g was suspended, equivalent to 4.3 × 10−4 g/cm2, or a layer 1.4 μm thick. During a local dust storm near Solis Planum at LS 227°, approximately 1.3 × 1013 g of dust were lofted, equal to about a 6‐μm layer in that vicinity.