bluuebunny/crossref_metadata_2025 huggingface dataset:
Partitioning of the reactive nitrogen reservoir in the lower stratosphere of the southern hemisphere: Observations and modeling
Authors: Gao R. S. , Fahey D. W. , Salawitch R. J. , Lloyd S. A. , Anderson D. E. , DeMajistre R. , McElroy C. T. , Woodbridge E. L. , Wamsley R. C. , Donnelly S. G. , Del Negro L. A. , Proffitt M. H. , Stimpfle R. M. , Kohn D. W. , Kawa S. R. , Lait L. R. , Loewenstein M. , Podolske J. R. , Keim E. R. , Dye J. E. , Wilson J. C. , Chan K. R.
Published: February 2004

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + …) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self‐consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NOy reservoir are well understood in the lower stratosphere.
Sponge layer feedbacks in middle‐atmosphere models
Authors: Shepherd T. G. , Semeniuk K. , Koshyk J. N.
Published: February 2004

Middle‐atmosphere models commonly employ a sponge layer in the upper portion of their domain. It is shown that the relaxational nature of the sponge allows it to couple to the dynamics at lower levels in an artificial manner. In particular, the long‐term zonally symmetric response to an imposed extratropical local force or diabatic heating is shown to induce a drag force in the sponge that modifies the response expected from the “downward control” arguments of Haynes et al. [1991]. In the case of an imposed local force the sponge acts to divert a fraction of the mean meridional mass flux upward, which for realistic parameter values is approximately equal to exp(−Δz/H), where Δz is the distance between the forcing region and the sponge layer and H is the density scale height. This sponge‐induced upper cell causes temperature changes that, just below the sponge layer, are of comparable magnitude to those just below the forcing region. In the case of an imposed local diabatic heating, the sponge induces a meridional circulation extending through the entire depth of the atmosphere. This circulation causes temperature changes that, just below the sponge layer, are of opposite sign and comparable in magnitude to those at the heating region. In both cases, the sponge‐induced temperature changes are essentially independent of the height of the imposed force or diabatic heating, provided the latter is located outside the sponge, but decrease exponentially as one moves down from the sponge. Thus the effect of the sponge can be made arbitrarily small at a given altitude by placing the sponge sufficiently high; e.g., its effect on temperatures two scale heights below is roughly at the 10% level, provided the imposed force or diabatic heating is located outside the sponge. When, however, an imposed force is applied within the sponge layer (a highly plausible situation for parameterized mesospheric gravity‐wave drag), its effect is almost entirely nullified by the sponge‐layer feedback and its expected impact on temperatures below largely fails to materialize. Simulations using a middle‐atmosphere general circulation model are described, which demonstrate that this sponge‐layer feedback can be a significant effect in parameter regimes of physical interest. Zonally symmetric (two dimensional) middle‐atmosphere models commonly employ a Rayleigh drag throughout the model domain. It is shown that the long‐term zonally symmetric response to an imposed extratropical local force or diabatic heating, in this case, is noticeably modified from that expected from downward control, even for a very weak drag coefficient.
Dispersion of aircraft emissions due to wake vortices in stratified shear flows: A two‐dimensional numerical study
Authors: Schilling V. , Siano S. , Etling D.
Published: February 2004

The development of the wake vortex system behind an airplane (B‐747) at cruising altitude (8–15 km) and the dispersion of the aircraft emissions due to this vortex system have been studied by means of a two‐dimensional numerical model. Simulation experiments are presented which examine the influence of atmospheric stratification and vertical wind shear on the combined vortex‐emission system. Although the development of the vortex wake system can be influenced by three‐dimensional effects (e.g., Crow instabilities), the undisturbed process can be approximated as a two‐dimensional phenomenon, which allows the study of details of the vortex structures at small scales (length L ≈ 1 m) and the dispersion of engine exhausts at larger scales (L ≈ 100 m). The results of simulation experiments show that the maximum lifetime of the wake vortices (120 s ≤ Tv ≲ 300 s) as well as the descending rate (1.2 m s−1 ≤ wv ≤ 2.4 m s−1) and the dispersion of the emitted substances depend on the atmospheric stratification as well as vertical wind shear, but buoyancy forces seem to dominate over shear forces. The overall dispersion of aircraft emissions due to the wake vortex system can be quantified by a vertical standard deviation for the entire process of about σz ≤ 70 m.
Potential distribution of subsurface methane in the sediments of the eastern Arabian Sea and its possible implications
Authors: Karisiddaiah S. M. , Veerayya M.
Published: February 2004

High‐resolution shallow seismic reflection data obtained in the continental shelf sediments off western India from 10°N to 22°N reveal the characteristic anomalous seismic signatures in the form of acoustic maskings of methane‐rich horizons. A conservative estimate of the potential subsurface methane in these gas‐charged sediments is of the order of 2.6 Tg, and its contribution to the atmosphere with an annual flux of 0.039 Tg CH4appears to be quite significant. From our limited results coupled with worldwide reports, it is concluded that the seepage of methane (8 to 65 Tg) through the seabed of the continental shelves worldwide cannot be ignored for the estimation of global oceanic flux of methane and its budget.
Analysis of small‐ and large‐scale increases of reactive nitrogen observed during the Second Airborne Arctic Stratospheric Expedition
Authors: Zheng J. , Weinheimer A. J. , Ridley B. A. , Liu S. C. , Sachse G. W. , Anderson B. E. , Collins J. E.
Published: February 2004

An analysis of the data obtained during AASE II was made to characterize small‐ (δx < 24 km) and large‐scale (30 < δx < 260 km) increases of reactive nitrogen species. By using the NOx/NOy ratio, the increases were classified into fresh emissions and aged air parcels. The sources of the NOy increases were then assessed by the freshness of the increases and by examining the correlation (or absence thereof) between NOy and other trace species including tracers of various NOx sources: for example, aircraft emissions, lightning, the stratospheric source, and sources in the boundary layer. We found that the majority (43%) of NOy increases in the upper troposphere and lower stratosphere were due to displacement of constant mixing ratio surfaces relative to isobaric flight paths. Aircraft emissions were the second most abundant (17%). The next significant contributor was surface emissions, including fossil fuel combustion and biomass burning. Only two lightning spikes were found, apparently due to the winter season and emphasis on high latitudes in the AASE II experiment. The relative contribution from each source to the increases (or positive variability) represents a measure of the relative source strength. However, it is important to note that our findings on the relative contribution of each source to the NOy increases should not be applied directly to estimating the relative source strength of the ambient or background NOy abundance. Knowledge of the detailed temporal and spatial distribution of the relative contribution of each source is needed. This requires a substantially higher precision for the instruments of tracer gases than those used in this study.
Pasture burning in Amazonia: Dynamics of residual biomass and the storage and release of aboveground carbon
Authors: Barbosa Reinaldo Imbrózio , Fearnside Philip M.
Published: February 2004

Aboveground biomass in cattle pasture converted from tropical dense forest was studied both before and after reburning in Brazilian Amazonia. In a 7‐year‐old pasture studied in Apiaú, Roraima, the aboveground dry weight of biomass (live plus dead) exposed to burning consisted of 96.3 t ha−1of original forest remains, 6.2 t ha−1of secondary successional vegetation (woody invaders in the pasture), and 8.0 t ha−1of pasture grass (carbon contents 48.2%, 45.4%, and 42.2%, respectively). In terms of carbon, burning efficiencies for these three categories were 13.2%, 66.7% and 94.6%, respectively. Net charcoal formation was 0.35 t C ha−1or 0.63% of the carbon exposed to the reburn, while the total accumulated since conversion (including the initial burn) is estimated at 2.3 t ha−1(1.82% of the predeforestation aboveground biomass carbon stock). The dynamics of the original forest remains were represented in simulations that included parameters such as charcoal formation, burning efficiency and carbon concentration in different biomass components. Releases from initial burning of the cleared forest (44.0 t C ha−1) plus releases over the course of the succeeding decade through combustion (12.5 t C ha−1) and decay (51.5 t C ha−1) total 92% of the original forest biomass carbon (126 t C ha−1). Of biomass carbon remaining after the initial burn (84.3 t C ha−1), 76.0% is released: 61.1% through decay and 14.9% through combustion in reburns, while 1.2% is net conversion to charcoal in the reburns. These results indicate an amount of charcoal accumulation that is smaller than some carbon calculations have assumed, therefore suggesting a greater impact on global warming from conversion of forest to pasture.
Polar ozone depletion: A three‐dimensional chemical modeling study of its long‐term global impact
Authors: Eckman Richard S. , Grose William L. , Turner Richard E. , Blackshear W. Thomas
Published: February 2004

The export of ozone‐poor air from the polar region following the breakup of the southern hemisphere polar vortex is examined with a three‐dimensional chemistry transport model. This volume of depleted ozone, the result of chemical processing during the southern wintertime and springtime, is long‐lived in the lower stratosphere and can affect ozone concentrations at southern middle latitudes following its transport out of the polar region. Two 5‐year simulations were performed utilizing the NASA Langley Research Center three‐dimensional chemistry transport model. One simulation included only gas phase and sulfate aerosol chemistry, while the second simulation also included reactions occurring on polar stratospheric clouds (PSCs). The model‐calculated seasonal variation of southern hemispheric O3, HNO3, and active chlorine as a result of PSC chemistry is in reasonable accord with satellite observations. The model reveals that ozone is transported equatorward following the breakup of the polar vortex to approximately 20°S latitude by the first southern summer following the activation of PSC chemistry. A residual column‐integrated ozone depletion of 9% remained by the springtime of the second year. In subsequent years, the southern ozone hole itself increased in depth from a column‐integrated depletion of 37% in the first year to 43% in the fifth year with respect to the baseline simulation with no PSC chemistry. The isopleths of column‐integrated ozone loss showed a slow equatorward movement during the 5‐year run. These model results, in general agreement with earlier model studies using parameterized chemistry, show that a potential exists for a long‐term accumulation of ozone loss in the southern polar region and a gradual increase in the global impact of polar ozone depletion. Comparison with satellite and ground‐based observations of ozone trends at midlatitudes suggests that ozone dilution may be a contributing factor. Experiments were performed to examine the sensitivity of the rate of local ozone recovery following the breakup of the vortex to the depth and spatial extent of the denitrification of polar air. These simulations revealed that deeper denitrification led to a more persistent column‐integrated ozone loss and a slight increase in its equatorward progression.
Non‐local thermodynamic equilibrium limb radiance near 10 μm as measured by UARS CLAES
Authors: Edwards D. P. , Kumer J. B. , López‐Puertas M. , Mlynczak M. G. , Gopalan A. , Gille J. C. , Roche A.
Published: February 2004

Observations have been made of non‐local thermodynamic equilibrium (non‐LTE) limb radiance at 923 cm−1 (10.83 μm) using the Cryogenic Limb Array Etalon Spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite (UARS). We study the relative contributions from CO2 and O3 in three CLAES channels and examine the correlation with solar zenith angle. The moderate spectral resolution of CLAES allows us to discriminate the individual radiance contributions of the CO2 isotopic and O3 hot bands. The analysis shows good agreement between measured and calculated radiances and confirms our previous theoretical modeling of the non‐LTE populations of these states. The diurnal variation of the measured emission points to solar dependent mechanisms selectively populating molecular vibrational levels in CO2 and O3. These processes are shown to affect the limb radiance for limb view tangent heights above about 38 km at the frequencies studied here. The measurements also show further experimental evidence for the excitation of the CO2 (ν3) mode by the energy transfer from electronically excited O(1D) through N2(1). This study is intended as a precursor to the inclusion of these effects in the operational CLAES data analysis.
Atmospheric fine structure during GTE TRACE A: Relationships among ozone, carbon monoxide, and water vapor
Authors: Collins James E. , Anderson Bruce E. , Sachse Glen W. , Barrick John D. W. , Wade Larry O. , Burney Lewis G. , Hill Gerald F.
Published: February 2004

A major focus of the Global Tropospheric Experiment/Transport and Chemistry Near the Equator‐Atlantic (GTE TRACE A) experiment was to determine whether the seasonal tropospheric ozone (O3) buildup over the tropical South Atlantic, observed by both satellites and sondes, is due to photochemical production of O3 from biomass burning effluents or from transport of O3 from the stratosphere. During this expedition, fast response in situ measurements were made of O3, carbon monoxide (CO), and dew point (DP) from aboard the NASA DC‐8 aircraft. Numerous vertical profiles were obtained over Brazil, Africa, and the South Atlantic to determine the origin of the observed O3 enhancement. Fine structure in these data was examined by (1) investigating differences in the species concentration (5‐s averages) and its 2 km vertical running mean during altitude profiles, (2) calculating Fishman‐Seiler coefficients for all vertical profiles with altitude range greater than 3 km, and (3) calculating linear regressions between species across short time intervals (2.5 min) using time series data. The fine structure holds information about the recent history of an air mass and therefore can indicate the “source” of tropospheric O3 enhancement: either transport from the stratosphere (negative correlation with CO and DP) or from photochemistry in the troposphere (positive correlation with CO). All three methods indicate that within the tropical South Atlantic during the TRACE A experiment, net in situ photochemical production is significantly more important than transport from the stratosphere.
Scalar multifractal radar observer's problem
Authors: Lovejoy S. , Duncan M. R. , Schertzer D.
Published: February 2004

The classical radar observer's problem in rain is to interpret the fluctuating radar echo from precipitation. Contrary to the usual homogeneity assumption involving Poisson statistics and incoherent scattering, we make a (scaling) heterogeneity assumption involving multifractal statistics and (some) coherent scattering. We consider the simplest problem, which is to relate the liquid water (σ) statistics to the (measured) effective radar reflectivity statistics (Ze) and to the (theoretical) radar reflectivity factor (Z; Ze =Z for incoherent scattering). We ignore polarization effects (that is, we use the scalar wave approximation), and denote the pulse length l, wavelength λw, the inner (homogeneity) scale of the rain field (η), and the outer (largest) scale of rain (L). For the simplest (conservative) multifractal σ the two main effects are 1) as in the standard theory, Z ≈ σ2; however, because of the strong subpulse volume gradients, there is a bias of (l/λww)Kσ(2);(Kσ(2) is the scaling exponent of σ2); 2) because of partial coherence, there is an enhancement: Ze/Z ≈ (λw/η(D‐Kσ(2) where D is the (effective) dimension of space. For nonconservative multifractals (parametrized by H) we obtain the overall bias in the means: / ≈ (λw/η)D‐Kσ(2)(L/λw)−2H. Using available data, we estimated this as typically ≈10−3 which is ≪1; Z should therefore not be used as a proxy for Ze. New theories relating radar measurements to rain must therefore be developed. Finally, we show that radar “speckle” (the drop “rearrangement” problem) is a general consequence of multifractal liquid water/ drop correlations.
A spatial and temporal continuous surface‐subsurface hydrologic model
Authors: Xiao Qing‐Fu , Ustin Susan L. , Wallender Wesley W.
Published: February 2004

A hydrologic model integrating surface‐subsurface processes was developed based on spatial and temporal continuity theory. The raster‐based mass balance hydrologic model consists of several submodels which determine spatial and temporal patterns in precipitation, surface flow, infiltration, subsurface flow, and the linkages between these submodels. Model parameters and variables are derived directly or indirectly from satellite remote sensing data, topographic maps, soil maps, literature, and weather station data and are stored in a Geographic Information System (GIS) database used for visualization. Surface resolution of cells in the model is 20 m by 20 m (pixel resolution of the Systeme Probatoire d'Observation de la Terre (SPOT) satellite image) over a 2511 km2 study area around the Crazy Mountains, Alaska, a watershed on the Arctic Circle draining into the Yukon River. The outputs from this model illustrate the interaction of physical and biologic factors on the partitioning of hydrologic components in a complex landscape.
Observations of diurnal oscillations with a meteor wind radar and radiosondes in Indonesia
Authors: Tsuda Toshitaka , Nakamura Takuji , Shimizu Atsushi , Yoshino Tetsuo , Harijono Sri Woro B. , Sribimawati Tien , Wiryosumarto Harsono
Published: February 2004

We constructed a meteor wind radar in an observatory near Jakarta, Indonesia, through collaboration between Japan and Indonesia, which has been operating continuously since November 1992. Horizontal wind velocity fluctuations were determined for altitudes between 75 and 100 km with time and height resolutions of 1 hour and 4 km, respectively. We also launched radiosondes from Bandung, four times a day from November 1992 to April 1993, and obtained profiles of horizontal wind velocity and temperature at 0–35 km with a height resolution of 150 m. Further, the data collected during the Tropical Ocean and Global Atmosphere/Coupled Ocean‐Atmosphere Response Experiment (TOGA/COARE) campaign have been particularly used to investigate the horizontal variations of diurnal oscillations. Overall structure of the observed wind velocity profiles agreed well with the model diurnal winds above 20 km, with a dominant vertical wavelength of 25–30 km. However, disagreements appeared below 20 km, showing significantly larger amplitudes and complicated phase structures, which may suggest the effects of nonmigrating tides. Diurnal oscillations of the temperature in the lower atmosphere were described very well by a numerical model.
New particle formation at a remote continental site: Assessing the contributions of SO2 and organic precursors
Authors: Marti James J. , Weber Rodney J. , McMurry Peter H. , Eisele Fred , Tanner David , Jefferson Anne
Published: February 2004

Ultrafine aerosols, with diameters less than 10 nm, nucleate from gas phase species. The composition of newly formed ultrafine atmospheric aerosols is not known with certainty; new particles have variously been conjectured to be sulfates, organic compounds, and sulfate/organic mixtures. The 1993 Tropospheric OH Photochemistry Experiment at Idaho Hill, Colorado, provided an opportunity to examine the question of which class of compounds, i.e., sulfates or organics, make the major contribution to new particle formation in the unpolluted troposphere. This study compared the production rates of sulfuric acid (from the oxidation of sulfur dioxide) and oxidized organic compounds to gauge their relative contributions to the formation of ultrafine particles. Potential organic precursor species examined in this study were the naturally occurring terpenes α– and β pinene, and the anthropogenic hydrocarbons toluene, m‐xylene, ethyl benzene, 1,2,4 trimethyl benzene, and methylcyclohexane. The calculated production of oxidized organics appeared well correlated with total particle surface area and volume, suggesting that at least some of the organic compounds formed in gas phase reactions condensed upon the preexisting aerosol. New particle formation was found to be more highly associated with elevated production of gas phase sulfuric acid (via the SO2‐OH reaction) than with production of oxidized organic products, although data from one day, during which sulfuric acid production and total aerosol surface area were both lower than usual, provided evidence for the involvement of terpene species in new particle formation. The results suggest that for this continental site, sulfuric acid was probably responsible for most of the observed new ultrafine particle formation. Low‐volatility organic compounds may have caused particle formation under the right conditions, but were more likely to condense upon preexisting particles.
Accuracy of spectral UV model calculations: 2. Comparison of UV calculations with measurements
Authors: Weihs Philipp , Webb Ann R.
Published: February 2004

In this work, spectral UV calculations based on the discrete ordinate model by Stamnes et al. [1988] are compared with measurements from two different campaigns in Panorama (Greece) and on Jungfraujoch (Switzerland). Ozone input data were taken from Brewer or spectrophotometer measurements; spectral aerosol optical depths were measured by sunphotomelers and by direct spectral irradiance measurements. The single‐scattering albedo(SSA) and the reflectance were inverted using the procedure by King and Herman [1979]. The cosine error for global irradiance is taken into account and a correction is applied to the data if needed. We analyze the uncertainty interval of calculations as well as the uncertainty interval of measurements. We find deviations of the UV calculations around ±10% or slightly more in Panorama and ±5% to 10% at Jungfraujoch. Taking into consideration the uncertainty interval of the measurements, there is a large probability of reaching agreement between calculations and measurements. Comparisons of the UV calculations performed in this study with calculations performed with SSA and asymmetry model input parameters taken from aerosol climatology by d'Almeida and from IAMAP show that the calculated UV irradiances differ by up to 14% between model runs.
Climatological significance of δ18O in north Tibetan ice cores
Authors: Yao Tandong , Thompson Lonnie G. , Mosley‐Thompson Ellen , Zhihong Yang , Xingping Zhang , Lin Ping‐Nan
Published: February 2004

Oxygen isotopic ratios (δ18O) of precipitation samples collected over several years at three meteorological stations on the northern Tibetan Plateau were used to conduct the first investigation of the relationship between δ18O and contemporaneous air temperatures (Ta). Inferring past temperatures from δ18O measured in recently acquired Tibetan ice cores necessitates establishing whether a δ18O‐Ta relationship exists. For each station a strong temporal relationship is found between δ18O and Ta, particularly for monthly averages which remove synoptic‐scale influences such as changes in condensation level, condensation temperature, and moisture sources. Moisture source is identified as a major factor in the spatial distribution of δ18O, but air temperature determines the temporal fluctuations of δ18O at individual sites on the northern Tibetan Plateau. The 30‐year records of annually averaged δ18O from three different ice coring sites are not correlated significantly with contemporaneous air temperature records from their closest meteorological station (150 to 200 km). However, since 1960 the three air temperature records reveal a modest warming trend, while the three contemporaneous δ18O records show a modest 18O enrichment.
Synthetic satellite radiances using the radiance sampling method
Authors: Tjemkes Stephen A. , Schmetz Johannes
Published: February 2004

A statistical method to calculate the radiance at the top of the atmosphere is described. This method solves the monochromatic radiative transfer equation at selected wavenumbers. A comparison with line‐by‐line calculations shows that the method is stable and converges to the line‐by‐line results with increasing number of selected points. The method has the advantage over other statistical methods that it is a strict monochromatic method, such that the exact information at the selected wavenumber is retained. This implies that overlapping absorption bands of different gases can be treated in a simple manner, which is exact at the selected wavenumbers. Since the method retains the correspondence of a monochromatic calculation to wavenumber, a folding of radiance simulations with the exact filter function of a satellite sensor is easily performed. The method is applied to simulate radiances of the future European geostationary meteorological satellites Meteosat Second Generation and to study the possibility of cross calibration of similar satellite sensors aboard different satellites.
Climatic effect of water vapor release in the upper troposphere
Authors: Rind D. , Lonergan P. , Shah K.
Published: February 2004

Water vapor is released into the Goddard Institute for Space Studies (GISS) global climate middle atmosphere model at the locations and cruise altitude of subsonic aircraft. A range of water vapor values is used to simulate not only current and 2015 projected emissions but also to provide larger signal‐noise ratios. The results show that aircraft water vapor emissions do not significantly affect the model's climate, either at the surface or in situ. With emissions some 15 times higher than the 2015 projection, a small impact is observed, amounting to a few tenths degrees Celsius globally and locally, while with emissions 300 times the 2015 values, a global warming of 1°C results. However, with releases this large, only about 5% actually stays in the atmosphere. The larger emissions increase the specific humidity most in the tropical lower troposphere, partly as a result of increased evaporation due to the global warming; at flight altitudes, relative humidity and cloud cover increase at latitudes of emission, and temperature decreases. Surface warming is relatively independent of latitude, and only a slight longitudinal aircraft footprint is found in the warming for the most extreme experiment. Comparison to increased CO2experiments of similar magnitude warming shows that the upper tropospheric response is greater in the water vapor release experiments, but the high‐latitude surface temperature response is larger with increased CO2due to more effective cryospheric feedbacks.
Applications of radiative perturbation theory to changes in absorbing gas
Authors: Box M. A. , Loughlin P. E. , Samaras M. , Trautmann T.
Published: February 2004

The perturbation formulations presented in papers published by Box et al. have been investigated for homogeneous and real atmospheres by perturbing the optical thickness of an absorbing gas, with the emphasis in this paper on ozone changes. Both exponential and linear perturbation formulations were investigated for a model with plane parallel geometry and different solar zenith angles. The results for the exponential perturbation predictions for net surface fluxes were very good in all cases where the solar zenith angle was less than 60°. However, where the solar zenith angle was increased past 60°, the range of validity of the perturbation models was clearly reduced. Applications to action spectrum integrals are presented which show that the approach is able to provide good results for zenith angles up to 60°, with accuracy past this angle being better than for nonintegrated effects.
Impact of Asian emissions on the remote North Pacific atmosphere: Interpretation of CO data from Shemya, Guam, Midway and Mauna Loa
Authors: Jaffe Daniel , Mahura Alexander , Kelley Jennifer , Atkins John , Novelli Paul C. , Merrill John
Published: February 2004

In this study we look at the concentration of CO at four remote stations in the North Pacific to evaluate the impact of Asian industrial emissions on the remote atmosphere. Using a locally weighted smoothing technique to identify individual data outliers from the seasonal cycle, we have identified 22–92 outliers or “events” (greater than 5 ppbv above the seasonal cycle) at each site for the 3–6 year data records. Using isentropic back trajectories, we identify a possible source region for each event and present a distribution of the trajectory types. For the events at Midway, Mauna Loa, Guam, and Shemya, we are able to identify a source region for the elevated CO in 82, 72, 65, and 50% of the events, respectively. At Mauna Loa and Midway a majority of the events occur during spring and are usually associated with transport from Asia. These events bring the highest CO mixing ratios observed at any time during the year to these sites, with CO enhancements up to 46 ppb. At Guam, easterly trade winds are the norm, but occasionally synoptic events bring Asian emissions to the island, generally during late summer and fall, from either East Asia or Southeast Asia (e.g., Indonesia). These events bring with them the largest CO enhancements of any of the four sites considered in this paper, up to 58 ppb. Finally, to examine the robustness of our conclusions, we redo our analysis using the more stringent definition that an event must be either 10 or 15 ppb above the seasonal cycle. Although this reduces the number of events identified at each site, it does not significantly change the fraction of events which can be attributed to a known source.
Effects of clouds, ice sheet, and sea ice on the Earth radiation budget in the Antarctic
Authors: Yamanouchi Takashi , Charlock Thomas P.
Published: February 2004

The effects of clouds, the continental ice sheet, and sea ice on the radiation budget in the Antarctic are examined by using Earth Radiation Budget Experiment, International Satellite Cloud Climatology Project, and special sensor microwave/imager data in 1987/1988. The continental ice sheet affects not only the albedo but also the surface temperature because of elevation and hence the outgoing longwave radiation (OLR). The high elevation of the Antarctic continent makes the radiation budget in both polar regions asymmetric. At elevations below 2 km the OLR is reduced at the rate of 5–10 W/m2/km; above 2 km the rate is about 20 W/m2/km. Sea ice, which is a critical climate feedback factor, appears to have less impact on radiation than do clouds. Between 60° and 65°S in October, sea ice increases the top of the atmosphere albedo by about 0.2 and reduces the OLR by 7–10 W/m2; this seems smaller than the formal cloud forcing, which increases the albedo by 0.3 and reduces the OLR by 30–40 W/m2. However, these numbers do not fully differentiate the independent effects of sea ice and cloudiness. A more detailed analysis shows that the independent effect of sea ice is as large as clouds, with clouds masking the radiative effect of sea ice by more than one half.
Distributions of beryllium 7 and lead 2109, and soluble aerosol‐associated ionic species over the western Pacific: PEM West B, February‐March 1994
Authors: Dibb J. E. , Talbot R. W. , Lefer B. L. , Scheuer E. , Gregory G. L. , Browell E. V. , Bradshaw J. D. , Sandholm S. T. , Singh H. B.
Published: February 2004

Aerosol sampling for the determination of the concentrations of soluble ionic species and the natural radionuclides 7Be and 210Pb was conducted from the NASA DC‐8 over the western Pacific as part of GTE/PEM‐West B during February‐March 1994. Concentrations of most soluble ionic species in the free troposphere were higher in samples collected on flights originating from Hong Kong and Japan than those collected further east over the open ocean. In both regions the measured concentrations were higher than those found during PEM‐West A (fall 1991). Activities of 210Pb, a tracer of air masses influenced by sources on the Asian continent, showed the same patterns. These data indicate the effect of stronger continental outflow from Asia over the western Pacific during the spring compared to fall season. For readily scavenged aerosol‐associated species and soluble acidic gases the strongest indications of Asian outflow were restricted to altitudes below 6 km. The distribution of the continental tracer 210Pb was also compared to those of a large number of gas phase species measured on the DC‐8. Relatively strong correlations were found with O3 and peroxyacetylnitrate (PAN), but only during the flights over the remote Pacific. During PEM‐West A, similar correlations were seen, but they were stronger near Asia. We believe that these correlations are a signature of continental air that has been processed by deep wet convection over land before being advected over the ocean. One flight over the Sea of Japan provided the opportunity to sample upper troposphere/lower stratosphere air in and around a tropopause fold. Concentrations of 7Be reached 7 pCi m−3 STP, and peak O3 mixing ratios of 480 ppb were encountered at 10.7 km. The 7Be data are used to estimate the fraction of stratospheric air mixed down into the troposphere by circulation in the fold.
Transport‐induced interannual variability of carbon monoxide determined using a chemistry and transport model
Authors: Allen Dale J. , Kasibhatla Prasad , Thompson Anne M. , Rood Richard B. , Doddridge Bruce G. , Pickering Kenneth E. , Hudson Robert D. , Lin Shian‐Jiann
Published: February 2004

Transport‐induced interannual variability of carbon monoxide (CO) is studied during 1989–1993 using the Goddard chemistry and transport model (GCTM) driven by assimilated data. Seasonal changes in the latitudinal distribution of CO near the surface and at 500 hPa are captured by the model. The annual cycle of CO is reasonably well simulated at sites of widely varying character. Day to day fluctuations in CO due to synoptic waves are reproduced accurately at remote North Atlantic locations. By fixing the location and magnitude of chemical sources and sinks, the importance of transport‐induced variability is investigated at CO‐monitoring sites. Transport‐induced variability can explain 1991–1993 decreases in CO at Mace Head, Ireland, and St. David's Head, Bermuda, as well as 1991–1993 increases in CO at Key Biscayne, Florida. Transport‐induced variability does not explain decreases in CO at southern hemisphere locations. The model calculation explains 80–90% of interannual variability in seasonal CO residuals at Mace Head, St. David's Head, and Key Biscayne and at least 50% of variability in detrended seasonal residuals at Ascension Island and Guam. Upper tropospheric interannual variability during October is less than 8% in the GCTM. Exceptions occur off the western coast of South America, where mixing ratios are sensitive to the strength of an upper tropospheric high, and just north of Madagascar, where concentrations are influenced by the strength of offshore flow from Africa.
Modeling the diurnal variability in cloud microphysics in boundary layer clouds
Authors: Considine Geoffrey D.
Published: February 2004

The purpose of this study is to understand and model the diurnal cycle in the microphysics of boundary layer clouds that has been inferred from recent remote sensing studies. To assess the modeled diurnal variation in cloud drop size, a one‐dimensional cloud microphysics model is initialized with dynamical conditions that are typical of the contrast between daytime and nighttime clouds. The model‐generated microphysics show a shift in droplet sizes from day to night that is consistent with that observed in satellite retrievals. The results indicate that the diurnal cycle in droplet size results from the shift in dynamical structure associated with the cloud becoming decoupled from the subcloud boundary layer during the day, along with an associated decrease in cloud‐top entrainment. The effect of decoupling on drop size is also enhanced by a decreased concentration of activated droplets at cloud base associated with the characteristically smaller vertical updraft velocities for the decoupled clouds.
Tomography of the Earth's atmosphere by the spaceborne occultation radiometer ORA: Spatial inversion algorithm
Authors: Fussen Didier , Arijs Etienne , Leclere Fabienne , Nevejans Dennis , Bingen Christine
Published: February 2004

The occultation radiometer ORA was designed to perform measurements of O3, NO2, H2O, number density, and aerosol extinction altitude profiles in the Earth's atmosphere through the occultation method viewing the full solar disk. The experiment was mounted on the EURECA satellite and measured the relative transmission of light during about 7000 orbital sunsets and sunrises from August 11, 1992, to May 13, 1993. The spatial inversion algorithm developed to retrieve the total extinction altitude profiles from these data is described here. It is shown that the signal measured by an instrument having a large field of view can be successfully processed to give a much better altitude resolution than the one related to the angular size of the Sun. The main difficulties concern the inclusion of all refractive effects, the application of a new inversion scheme and its associated mapping strategy to refine the aerosol layer detection. The algorithm applies to fully nonlinear occultation experiments requiring global and nonheuristic inversion schemes.
Chemical and size effects of hygroscopic aerosols on light scattering coefficients
Authors: Tang Ignatius N.
Published: February 2004

The extensive thermodynamic and optical properties recently reported [Tang and Munkelwitz, 1994a] for sulfate and nitrate solution droplets are incorporated into a visibility model for computing light scattering by hygroscopic aerosols. The following aerosol systems are considered: NH4HSO4, (NH4)2SO4, (NH4)3H(SO4), NaHSO4, Na2SO4, NH4NO3, and NaNO3. In addition, H2SO4 and NaCl are included to represent freshly formed sulfate and background sea‐salt aerosols, respectively. Scattering coefficients, based on 1 μg dry salt per cubic meter of air, are calculated as a function of relative humidity for aerosols of various chemical compositions and lognormal size distributions. For a given size distribution the light scattered by aerosol particles per unit dry‐salt mass concentration is only weakly dependent on chemical constituents of the hygroscopic sulfate and nitrate aerosols. Sulfuric acid and sodium chloride aerosols, however, are exceptions and scatter light more efficiently than all other inorganic salt aerosols considered in this study. Both internal and external mixtures exhibit similar light‐scattering properties. Thus for common sulfate and nitrate aerosols, since the chemical effect is outweighed by the size effect, it follows that observed light scattering by the ambient aerosol can be approximated, within practical measurement uncertainties, by assuming the aerosol being an external mixture. This has a definite advantage for either visibility degradation or climatic impact modeling calculations, because relevant data are now available for external mixtures but only very scarce for internal mixtures.
Hydrogen peroxide in the marine atmospheric boundary layer during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic
Authors: Martin Daniel , Tsivou Maria , Bonsang Bernard , Abonnel Christian , Carsey Thomas , Springer‐Young Margie , Pszenny Alex , Suhre Karsten
Published: February 2004

Gas phase H2O2 was measured in surface air on the NOAA ship Malcolm Baldrige from June 8 to 27, 1992 (Julian days 160–179), during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic region. Average H2O2 mixing ratios observed were 0.63±0.28 ppbv, ranging between detection limit and 1.5 ppbv. For the entire experiment, only weak or no correlation was found between H2O2 mixing ratio and meteorological parameters (pressure, temperature, humidity, or UV radiation flux) as well as with tracers of continental air masses (CO, black carbon, radon). The average daily H2O2 cycle for the entire period exhibits a maximum of 0.8±0.3 ppbv near sunset and a minimum of 0.4±0.2 ppbv 4–5 hours after sunrise. Several clear H2O2 diurnal variations have been observed, from which a first‐order removal rate of about 1×10−5 s−1 for H2O2 can be inferred from nighttime measurements. This rate compares well with those deduced from measurements taken at Cape Grim (Tasmania, 41°S) and during the Soviet‐American Gas and Aerosol III experiment (equatorial Pacific Ocean).
On the origin of midlatitude ozone changes: Data analysis and simulations for 1979–1993
Authors: Callis Linwood B. , Natarajan Murali , Lambeth James D. , Boughner Robert E.
Published: February 2004

Satellite data show large declines in global (4.5%) and midlatitude (10%) ozone in the mid‐1980s and during 1992 and 1993. Analyses of ozone, temperature, and aerosol records and two‐dimensional chemical transport simulations have been carried out to develop an understanding of the causes of these changes. Simulations include contemporary homogeneous and heterogeneous chemistry. Also included are the effects of trace gas increases, dilution and denitrification associated with the Antarctic ozone destruction, solar cycle effects including relativistic electron precipitation (REP), variable diabatic transport fields and temperature, and variable sulfate aerosol surface area density and acidity. Simulated global and midlatitude ozone agree very well with observations for the entire period. Mid‐1980s near‐global ozone declines calculated by the model were found to be due to solar cycle (including REP) effects, −1.9%; volcanic effects, −1.5%; dilution effects, −1.1%; transport and temperature effects, −1%; and trace gas effects, −0.2%. The maximum effects of these different processes occur at different times. The observed 10% reductions in midlatitude ozone are reproduced in the simulations and are primarily due to 1 to 2‐year transport and temperature variations.
Intercomparison of ozone measurements in the lower stratosphere from the UARS Halogen Occultation Experiment and the ER‐2 UV absorption photometer
Authors: Grose William L. , Lingenfelser Gretchen S. , Russell James M. , Pierce R. Bradley , Fairlie T. Duncan , Proffitt Michael H.
Published: February 2004

Ozone data obtained by the Halogen Occultation Experiment (HALOE) on the NASA Upper Atmosphere Research Satellite (UARS) have been compared with ozone data obtained by the NOAA dual‐beam, UV absorption photometer on the NASA ER‐2 aircraft during the 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign. This paper describes the measurement characteristics of the two instruments and the precision and accuracy of the two data sets. A total of 26 cases are discussed in which the two different measurements occur within 24 hours, 2.5° latitude, and 10° longitude of each other. Generally, agreement between the two data sets improved the closer in time and space the two measurements occurred. The agreement was better than 10% at ER‐2 cruise altitudes (∼50–70 mbar) where the error estimated for HALOE is slightly larger than 18%.
Temperature dependent NO2 cross sections at high spectral resolution
Authors: Harder J. W. , Brault J. W. , Johnston P. V. , Mount G. H.
Published: February 2004

The importance of nitrogen dioxide in both the troposphere and the stratosphere has been known for some years, and since the early 1970s, spectroscopic determinations have played an important role in understanding NOX chemistry. Spectroscopic measurements of the atmosphere have improved in quality in recent years to the point that an accurate determination of the NO2 absorption cross section is essential to accurate retrievals of not only NO2 but also less abundant species in the troposphere and stratosphere. NO2 is such a large absorber (approximately 1% at large air mass) in the stratosphere at twilight or in the troposphere under even mildly polluted conditions, that if it is not properly removed from observed spectra, the spectra of the more subtle species are masked and cannot be measured at all. We present cross sections of NO2 in the spectral region 350–585 nm at four temperatures between 217 and 298 K and total pressures between 100 and 600 torr at a mixing ratio of 84.1 ppmv and at a spectral resolution sufficient for accurate convolution with instruments typically used to measure atmospheric NO2. Data will be presented to demonstrate the presence of NO2 pressure dependence in high resolution. A detailed comparison with commonly used literature cross sections is made to show how such instrument parameters as wavelength accuracy, resolution, spectrograph scattered light, and data sampling affect the usefulness of the observed cross section.