bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of anthropogenic and biogenic sources and sinks on carbonyl sulfide in the North Pacific troposphere
Authors: Thornton Donald C. , Bandy Alan R. , Blomquist Byron W. , Anderson Bruce E.
Published: February 2004

During September–October 1991 over 500 determinations of carbonyl sulfide (OCS) were made in the troposphere over the North Pacific Ocean as part of the NASA Pacific Exploratory Mission‐West A project. Three distinct regimes were found in the distribution of OCS in the Pacific troposphere during this period. Under conditions of remote Pacific marine air, OCS had a mean of 495 parts per trillion by volume (pptv) with a standard error of the mean of 0.6 pptv and a standard deviation of 8.8 pptv. Under conditions of air transported from Asia and the North American Arctic, both elevated and depleted levels of OCS were found. Decreases in OCS of 10–20% from the remote Pacific mean were highly correlated with decreased carbon dioxide levels. Increases of 10–20% of OCS were highly correlated with increased carbon disulfide and other chemical indicators of anthropogenic sources. The constancy of the OCS mean for the remote Pacific marine air masses can be used to better understand the budget for OCS and its impact as a source of stratospheric sulfur dioxide.
Sulfur gas measurements in the eastern North Atlantic Ocean during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange
Authors: Blomquist Byron W. , Bandy Alan R. , Thornton Donald C.
Published: February 2004

Results from an intensive measurement program studying the marine stratocumulus regime in the eastern North Atlantic Ocean are reported. We observed generally high mixing ratios of sulfur dioxide (SO2) in the region, typically advected within the marine boundary layer (MBL). SO2 mixing ratios ranged from 19 pptv to 1.3 ppbv. Dimethyl sulfide (DMS) mixing ratios also were quite variable, but airborne DMS measurements were never greater than 140 pptv. The mean carbon disulfide mixing ratio was 6.5 pptv. In two intensive Lagrangian experiments, the budgets for SO2 and DMS in the MBL were examined. The observed overnight increase in DMS and the predicted increase based on a budget analysis (using a simple surface flux model) agree within the precision of the data for the first Lagrangian experiment. The photochemical oxidation rates for DMS derived from the budget analysis range from 2.5 to 4.9 μmol/m2 d. Because daytime mixing ratios of NO were seldom larger than 10–15 pptv during both experiments, nighttime oxidation of DMS by NO3 was negligible compared with daytime losses to OH. A positive surface flux is the major term in the DMS budgets. SO2 mixing ratios in the MBL were largely controlled by advected pollution from continental Europe. Deposition of SO2 to the sea surface was the major loss term in the budget analysis. Terms for photochemical production and loss of SO2 could not be independently determined in this analysis, but it is likely these terms were small compared to the surface flux. Based on the observed loss rate for SO2 in polluted European air masses, the mean lifetime of SO2 in the MBL during ASTEX/MAGE is estimated to be 15–18 hours. Our analysis suggests that the Lagrangian experimental design is a valuable tool for isolating chemical change in a dynamic meteorological system, but a budget analysis to determine photochemical production/loss terms is difficult or impossible in the presence of significant pollution. Lagrangian results highlight the potential dangers to chemical interpretation of Eulerian data sets, where advection is often important and needs to be taken into account.
Analysis of Halogen Occultation Experiment HF versus CH4 correlation plots: Chemistry and transport implications
Authors: Luo M. , Cicerone R. J. , Russell J. M.
Published: February 2004

The relationship between stratospheric CH4 and Hydrogen Fluoride (HF) observed simultaneously by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) has been examined globally. The meridional structures of the two long‐lived species for the equinox and solstice seasons are found to be very similar. Their surfaces of constant mixing ratio, however, are found to not quite coincide. The isopleth of CH4 graphed as pressure versus latitude shows a steeper slope than that of HF. This feature can be clearly seen from the scatterplots of CH4 versus HF for a sequence of latitude regions. In general, CH4‐HF correlation plots are characterized by tightly fitted curves for different latitude bands; curves for the tropics and high latitudes define the envelope for the correlations. The NCAR two‐dimensional model simulation of CH4 and HF agrees well with HALOE observations, and it shows that the altitude‐latitude dependences of CH4 removal and HF production rates play an important role in determining global CH4‐HF correlations. It is found that the CH4‐HF correlation inside the Antarctic vortex is nearly linear and is shifted from that of outside the vortex and from that of polar late‐summer before the formation of the vortex. HALOE observations of CH4 and HF indicate that the two species are not in states of perfect “slope equilibrium” or “gradient equilibrium” globally. The obvious shift of HF values on CH4 surfaces or vice versa is usually found across dynamical barriers. There is no universal relationship between CH4 and HF. The HF mixing ratios are observed to change up to 20–35% for a given CH4 from different dynamically isolated regions such as the polar vortex, midlatitudes, and the tropics, and the same magnitudes of change in CH4 could also be found for a fixed HF. Therefore one must be cautious in the usage of correlation‐inferring methods for any pair of tracers in place of unavailable measurements or for evaluating chemical disturbances.
Satellite remote sensing of fires during the SAFARI campaign using NOAA Advanced Very High Resolution Radiometer data
Authors: Justice C. O. , Kendall J. D. , Dowty P. R. , Scholes R. J.
Published: February 2004

Active fires in southern Africa were detected using daily NOAA advanced very high resolution radiometer (AVHRR) 1‐km satellite data. The active fire distribution during the period of the SAFARI intensive field campaign in September and October 1992 is described. The distribution of fires for the period of the campaign is presented along with a comparison for the same period in 1989. For the latitudinal belt between 15° and 30°S which was affected by drought in 1992, there was an average of 49% fewer fires in 1992 than in 1989. However, most of the burning in southern Africa takes place between 5° and 20°S with peak activity between the months of July and September. The interannual variability in the amount and timing of fires was noted. The relationship between fires, rainfall, and vegetation state for the two years are described for sample locations. The extent of the 1992 drought and its impact on the occurrence of fire are also discussed.
Three‐dimensional simulation of the influence of a cutoff low on the distribution of northern hemisphere processed air in late January 1992
Authors: Cerniglia Mark C. , Rood Richard B. , Douglass Anne R.
Published: February 2004

The NASA Goddard three‐dimensional chemistry and transport model (3D CTM), utilizing winds and temperatures from a stratospheric data assimilation, is used to investigate the influence of a large cutoff low (COL) system on the transport of chemically processed stratospheric air. The conversion of hydrogen chloride to reactive chlorine is simulated for the early winter of 1991/1992. This heterogeneously converted air is defined as being processed. Throughout December and early January, simulated processed air remained nearly isolated within the Arctic vortex. In late January there were intrusions of midlatitude air across the boundary of the vortex over the North Atlantic and northwestern Europe. These intrusions, which are associated with horizontal transport associated with the COL system, dilute regions of highly processed air within several days. The simulation demonstrates the importance of synoptic scale events on processed air distribution within the vortex as well as transport out of the vortex base into the upper troposphere and midlatitudes.
Some features observed by the L‐band push broom microwave radiometer over the Konza Prairie during 1985–1989
Authors: Wang J. R.
Published: February 2004

Airborne L‐band radiometric measurements were conducted over the Konza Prairie near Manhattan, Kansas, in the summers of 1985, 1987, 1988, and 1989 to study the relationship among surface microwave emission, soil moisture, and vegetation cover. The annual surface treatments that were applied to the watersheds in the experimental area appeared to show a significant impact on the surface microwave emission. A watershed that was burned every year showed a better sensitivity to soil moisture variation than those burned less frequently. This feature persisted even though the radiometric measurements were made over those watersheds that were burned in the same year. It was concluded that the burning process might not completely remove a thatch layer of efficient microwave absorption, which was developed through years of accumulation of senescent vegetation. Results from the analysis of these radiometric data sets also suggest the need of an adequate estimation of vegetation biomass in order to obtain a reliable retrieval of surface soil moisture from L‐band radiometric measurements. On the basis of the data acquired from the 1987 and 1989 field campaigns, the push broom microwave radiometer (PBMR) measurements are likely to give errors of the order of ±0.065 g/cm3 in surface soil moisture estimation if there are no measurements of vegetation biomass. Measurements of vegetation biomass to an accuracy of ±0.46 kg/m2 improve the corresponding PBMR estimation of surface soil moisture to an accuracy of ±0.032 g/cm3.
Sensitivity analysis of a radiation parameterization
Authors: Živković Marina , Louis Jean‐François , Moncet Jean‐Luc
Published: February 2004

An assessment of the forecast sensitivity to model and radiation parameters is critical to validating climate change studies. This paper quantifies forecast first‐order sensitivity to the input to the radiation calculations in a numerical weather prediction model. The forecast aspects of interest are the temperature at the surface and near the tropopause. The model used here is a single column model, the AER Local Forecast and Assimilation (ALFA) model, which emulates a grid box of a general circulation model. It includes the NASA Ames rapid model as a broadband radiation parameterization. The sensitivities are calculated for a single time step (tendency) by the adjoint method. They reflect interactions of parameterized physical processes, since they are derived from a single iteration of the forward model and its adjoint. The sensitivities are distinguished by their sign as positive and negative responses to initial perturbation. When the atmosphere is cloudy, the surface temperature tendency shows the highest sensitivity to the single‐scattering albedo in the band centered at 0.69 μm (14,492 cm−1) in the visible window region. When the atmosphere is clear, the highest sensitivity is to the water vapor path in the continuum band, but 1 order of magnitude smaller. Also, in the clear case, the temperature tendency just below the tropopause is most sensitive to the water vapor path in the rotational absorption band. Again, this sensitivity is smaller than the sensitivity to a single‐scattering albedo in a cloud at the same altitude.
Variability of mesospheric CO in the fall and winter as observed with ground‐based microwave radiometry at 115 GHz
Authors: Aellig Christoph P. , Kämpfer Niklaus , Hauchecorne Alain
Published: February 2004

We report on observations of the J = 1 → 0 emission line of terrestrial mesospheric CO at 115 GHz. The measurements were made in the fall of 1993 and in February 1994 from Bern (47°N, 7.5°E). Column densities above 65 km as well as mesospheric vertical distributions were derived from the measured spectra. Between the end of September and middle November an increase by a factor of 2 of the column density was detected, in accordance with theory and previous observations. The February measurements exhibited a short‐term variation on a timescale of a few days which may be explained by a combination of horizontal advection of air and gravity wave activity.
April 1993 Arctic profiles of stratospheric HCl, ClONO2, and CCl2F2 from atmospheric trace molecule spectroscopy/ATLAS 2 infrared solar occultation spectra
Authors: Rinsland C. P. , Gunson M. R. , Abrams M. C. , Lowes L. L. , Zander R. , Mahieu E. , Goldman A. , Irion F. W.
Published: February 2004

Partitioning among the major components of the stratospheric odd chlorine family inside and outside of the remanent Arctic vortex has been studied on the basis of infrared solar occultation measurements obtained by the atmospheric trace molecule spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS 2 shuttle mission (April 8–17, 1993). Profiles of hydrogen chloride (HCl) and simultaneous profiles of chlorine nitrate (ClONO2) and CFC‐12 (CCl2F2) are reported for examples of in‐vortex and out‐of‐vortex conditions. Increased ClONO2 volume‐mixing ratios (VMRs) are measured in the vortex below 20 mbar (∼25 km altitude) with a peak ClONO2 VMR of 2.05±0.45 ppbv (10−9 per volume) at 56 mbar (∼19 km altitude). The reported error correspond to 1σ uncertainties. Simultaneous CCl2F2 and N2O measurements, combined with published empirical relations, indicate that only 0.34±0.15 ppbv, about 10% of total chlorine, was bound in organic species at the ClONO2 VMR peak in the vortex. A colocated vortex profile of HCl, referenced to simultaneous N2O VMR measurements, has been used to derive a HCl mixing ratio of 1.21±0.12 ppbv corresponding to the ClONO2 VMR peak. The internal consistency of the ATMOS measurements is demonstrated by the agreement between the total chlorine mixing ratio of 3.60±0.72 ppbv derived at the ClONO2 VMR peak in the vortex and HCl measurements of 3.37±0.37 and 3.76±0.41 ppbv at 0.56 mbar, where HCl is the only significant chlorine‐bearing molecule. Outside the vortex the mixing ratio of HCl exceeds the mixing ratio of ClONO2 throughout the stratosphere.
The long‐range transport of southern African aerosols to the tropical South Atlantic
Authors: Swap R. , Garstang M. , Macko S. A. , Tyson P. D. , Maenhaut W. , Artaxo P. , Kållberg P. , Talbot R.
Published: February 2004

Two episodes of long‐range aerosol transport (4000 km) from southern Africa into the central tropical South Atlantic are documented. Stable nitrogen isotope analysis, multielemental analysis, and meteorological observations on local and regional scales are used to describe the observed surface aerosol chemistry during these transport episodes. The chemical, kinematic, and thermodynamic analyses suggest that for the central tropical South Atlantic, west Africa between 0° and 10°S is the primary air mass source region (over 50%) during austral spring. Over 70% of all air arriving in the lower and middle troposphere in the central tropical South Atlantic comes from a broad latitudinal band extending from 20°S to 10°N. Air coming from the east subsides and is trapped below the midlevel and trade wind inversion layers. Air from the west originates at higher levels (500 hPa) and contributes less than 30% of the air masses arriving in the central tropical South Atlantic. The source types of aerosols and precursor trace gases extend over a broad range of biomes from desert and savanna to the rain forest. During austral spring, over this broad region, processes include production from vegetation, soils, and biomass burning. The aerosol composition of air masses over and the atmospheric chemistry of the central South Atlantic is a function of the supply of biogenic, biomass burning, and aeolian emissions from tropical Africa. Rainfall is a common controlling factor for all three sources. Rain, in turn, is governed by the large‐scale circulations which show pronounced interannual variability. The field measurements were taken in an extremely dry year and reflect the circulation and transport fields typical of these conditions.
Long‐term changes in the acid and salt concentrations of the Greenland Ice Core Project ice core from electrical stratigraphy
Authors: Wolff Eric W. , Moore John C. , Clausen Henrik B. , Hammer Claus U. , Kipfstuhl Josef , Fuhrer Katrin
Published: February 2004

Continuous electrical records covering a climatic cycle are presented for the Greenland Ice Core Project deep ice core from Greenland. Electrical conductivity measurement (ECM) measures the acid content of the ice, and the dielectric profile (DEP) responds to acid, ammonium, and chloride. All features seen can be explained by chemical changes in the ice, and there is no evidence so far for any major change in electrical response with depth or age of the ice. Both records are dominated by the acidity of the ice which varies strongly from acidic in warm periods to alkaline in cold periods, controlled by neutralization by alkaline dust (calcareous and other mineral dust). When Ca is low, the acidity (mainly nitric acid) has a fairly constant background level throughout the cycle, with slightly lower values in ice believed to be from the last interglacial. Ca has to rise only slightly to neutralize the available acidity, so that acidity is a highly nonlinear reflection of climate changes. If neutralization occurred in the aerosol (rather than in the ice), then the number of cloud condensation nuclei over parts of the northern hemisphere could have been reduced, leading to reduced cloud albedo. This nonlinear feedback may have some importance for modeling of climate change. When both acid and ammonium levels are low, the DEP signal can be used to give a rapid indication of chloride trends.
Constraints on droplet growth in radiatively cooled stratocumulus clouds
Authors: Austin P. H. , Siems S. , Wang Y.
Published: February 2004

Radiative cooling near the top of a layer cloud plays a dominant role in droplet condensation growth. The impact of this cooling on the evolution of small droplets and the formation of precipitation‐sized drops is calculated using a microphysical model that includes radiatively driven condensation and coalescence. The cloud top radiative environment used for these calculations is determined using a mixed‐layer model of a marine stratocumulus cloud with a subsiding, radiatively cooled inversion. Calculations of the radiatively driven equilibrium supersaturation show that net long wave emission by cloud droplets produces supersaturations below 0.04% for typical nocturnal conditions. While supersaturations as low as this will force evaporation for droplets smaller than ≈ 5 μm, radiatively enhanced growth for larger droplets can reduce the time required to produce precipitation‐sized particles by a factor of 2–4, compared with droplets in a quiescent cloud without flux divergence. The impact of this radiative enhancement on the acceleration of coalescence is equivalent to that produced in updrafts of 0.1–0.5 ms−1, and varies linearly with the total emitted flux (the “radiative exchange”).
Stratospheric trace constituents simulated by a three‐dimensional general circulation model: Comparison with UARS data
Authors: Eckman Richard S. , Grose William L. , Turner Richard E. , Blackshear W. Thomas , Russell James M. , Froidevaux Lucien , Waters Joe W. , Kumer J. B. , Roche Aidan E.
Published: February 2004

Constituent distributions are presented from the NASA Langley three‐dimensional general circulation model, incorporating a comprehensive chemistry scheme. A 7‐year, gas phase model simulation was performed to investigate long‐term model stability. In addition, a 1‐year simulation was made using parameterized polar heterogeneous processes and reactions occurring on sulfate aerosols. The results of these simulations are compared with species climatologies and with satellite data sets in order to characterize and evaluate model performance and identify aspects of the chemical scheme requiring improvement. The agreement between the modeled seasonal variation of total ozone and the measurement climatologies is satisfactory but with some differences with respect to the depth and persistence of the southern springtime ozone depletion. Comparisons of the model simulation with observations made from UARS were performed. There is good accord between the microwave limb sounder observations of ozone and the model. Areas of agreement and disagreement are revealed between the model and the cryogenic array etalon spectrometer measurements of HNO3 and ClONO2, suggesting the need for a more detailed representation of sulfate aerosol processes in the model. The comparison between the modeled and the measured partitioning of odd chlorine species is improved in the upper stratosphere by the inclusion of an additional pathway to HCl from the reaction of ClO + OH.
High‐resolution measurements of vertical velocity with the European incoherent scatter VHF radar: 1. Motion field characteristics and measurement biases
Authors: Hoppe Ulf‐Peter , Fritts David C.
Published: February 2004

European incoherent scatter VHF radar measurements of vertical velocities were made under polar mesopause summer echo (PMSE) conditions enabling spatial and temporal resolution of 300 m and 2 s and accuracies of 0.1 ms−1 or better. Our observations revealed vertical motions with periods ranging from hours to tens of seconds and vertical wave structure exhibiting both ducted and vertically propagating behavior. Significant correlations were found between the low‐pass vertical velocity and velocity uncertainties, velocity variances at high frequencies, radar backscatter power, and radar spectral widths. Specifically, upward motions at lower frequencies correlated with larger uncertainties, high‐frequency variances, and radar spectral widths, while downward motions correlated best with larger backscatter power. We show these correlations to lead to biases in the determination of mean vertical motions when data are thresholded by any of the above quantities. We also suggest that these correlations arise from a tendency for turbulence to be associated primarily with the upward phase of wave motions at lower frequencies. A companion paper by Fritts and Hoppe presents a spectral analysis of this same data set.
High‐resolution measurements of vertical velocity with the European incoherent scatter VHF radar: 2. Spectral observations and model comparisons
Authors: Fritts David C. , Hoppe Ulf‐Peter
Published: February 2004

We present an analysis of the spectral characteristics of the vertical motion field observed with the European incoherent scatter VHF radar near the summer mesopause. The data were collected in a mode permitting very precise measurements of vertical velocities with very high spatial and temporal resolution. High measurement accuracies resulted in broad spectral sensitivity extending well into acoustic wave frequencies. High spatial resolution in addition provided sensitivity to more than a decade of vertical wavenumbers. Mean frequency spectra exhibit a rapid decrease in amplitude near the buoyancy frequency, suggesting weak Doppler shifting conditions. Frequency spectra also display high vertical coherence and variable noise levels, implying coherent motions at large scales and geophysical modulation of velocity estimates at smaller spatial and larger temporal scales. Vertical wavenumber spectra reveal a sharp contrast between ducted and vertically propagating motion fields. Spectra of propagating motions exhibit a steep slope consistent with vertical wavenumber spectra of horizontal motions. A separable model spectrum is seen to be consistent with the observed vertical velocity characteristics and spectra.
A simulation of the surface energy budget and soil water content over the Hydrologic Atmospheric Pilot Experiments‐Modélisation du Bilan Hydrique forest site
Authors: Kim Jinwon , Ek Mike
Published: February 2004

The surface energy budget and soil water content variation are simulated for a two month period during the 1986 Hydrologic Atmospheric Pilot Experiment‐Modélisation du Bilan Hydrique (HAPEX‐MOBILHY) (J.C. André et al., 1988) using the Oregon State University Coupled Atmosphere Plant Snow (CAPS) model. When initialized and driven by the observed soil water content and atmospheric forcing, the CAPS model closely simulated the observed surface energy budget and the variation of soil water content. Lateral transports of soil water may cause significant impacts on the simulated soil water content during the later part of the simulation. Vegetation appears to significantly affect the surface energy budget and temporal variation of soil water content. We found two major mechanisms by which vegetation controls the surface energy budget and soil water content: (1) dependencies of transpiration on ambient conditions, and (2) direct hydrological coupling between the atmosphere and deep soil water through the root structure. Compared to the simulation without vegetation, net effects of vegetation are (1) sustained evaporation over the entire simulation period, (2) more gradual variation of near surface soil water content, and (3) continued reduction of deep soil water content through transpiration. Soil heat flux becomes an important component of the surface energy budget over a bare soil surface. The simulated surface energy budget is strongly dependent on the initial soil water content, however, dependence of the simulated surface energy budget on the initial soil temperature was relatively minor.
Representation of localized aircraft NOy emissions in a two‐dimensional model of stratospheric ozone
Authors: Plumb R. Alan , Ko Malcolm K. W. , Shia Run‐Li
Published: February 2004

Oxides of nitrogen deposited into the lower stratosphere by supersonic aircraft can affect ozone. The effect can be estimated using two‐dimensional chemistry‐transport models in which the transport of the deposited material is simulated by zonal‐mean advection and eddy transport. In these assessment studies, the localized three‐dimensional injection is usually introduced into the model simply by specifying the zonal average of the actual three‐dimensional sources as input to the model. In the presence of substantial stratospheric wave activity, this procedure may be inaccurate as the emissions will rapidly be transported away from the initial locations through short‐term processes not incorporated in two‐dimensional transport parameterizations. Here we use a potential vorticity/potential temperature mapping technique to determine the effective zonally averaged sources appropriate for input to a two‐dimensional model. Using projected source scenarios for NOy emissions and a two‐dimensional chemistry transport model, we conclude that this effect has little impact on projections of ozone depletion.
Using coincident multispectral satellite data to assess the accuracy of special sensor microwave imager liquid water path measurements
Authors: Miletta Jennifer , Katsaros Kristina B.
Published: February 2004

We present techniques to identify and reduce the sources of error in the liquid water path (LWP) of marine stratocumulus clouds retrieved from the special sensor microwave imager (SSMI), using coincident high‐resolution visible and infrared data provided by the operational linescan system (OLS). The OLS data are used to identify cloud‐free areas in order to determine the degree of error in the estimated clear sky polarization difference, an important parameter in the SSMI retrieval algorithm. The retrieval algorithm is refined by including the cloud top temperature derived from the OLS infrared data. Errors in the LWP measurements owing to broken or inhomogeneous clouds are difficult to quantify, but a subpixel analysis of cloud type and spatial variability reveals which measurements are more likely to be biased. The application of these techniques on a set of sample images confirms that the relationships between the liquid water path and other cloud parameters are most robust in overcast conditions.
Overview of UARS ozone validation based primarily on intercomparisons among UARS and Stratospheric Aerosol and Gas Experiment II measurements
Authors: Cunnold D. M. , Froidevaux L. , Russell J. M. , Connor B. , Roche A.
Published: February 2004

Comparisons among Stratospheric Aerosol and Gas Experiment (SAGE) II, microwave limb sounder (MLS) (version 3), cryogenic limb array etalon spectrometer (CLAES) (version 7), improved stratospheric and mesospheric sounder (ISAMS) (version 10), and Halogen Occultation Experiment (HALOE) (version 17) ozone profiles are reported with the emphasis being on the periods of January 9–11, April 15–20, and August 25–30, 1992, which were selected for analysis at four UARS validation workshops. The differences with respect to SAGE II are consistent with the conclusions of those workshops. MLS values are found to be systematically approximately 5% larger than SAGE II values except at 1 mbar (where they are approximately 5% smaller) and at 46 mbar in the tropics where they are approximately 20% too small (perhaps with some time dependence to this difference). HALOE values are systematically approximately 5% lower than SAGE II values, with a tendency for this difference to increase slightly in the upper part of the altitude range. CLAES values are approximately 15% high near 4.6 mbar and at 46 mbar in the tropics and are approximately 20% low near 0.32 mbar but show small differences near 1 and 10 mbar. ISAMS produced considerably more variable differences with respect to the other sensors both in space and in time. There remains clear evidence of Pinatubo aerosol contamination of ISAMS values at 10 mbar (the lowest level of the v10 retrievals) in January. The standard deviations of the differences between the coincidentally measured ozone profiles are generally consistent with the prescribed profile error bars of better than 5% from approximately 46 to 0.46 mbar for HALOE and from 1.5 to 15 mbar for MLS (and to approximately 0.46 mbar for the 183‐GHz measurements). For ISAMS also, the error bars of 10–15% are consistent with the standard deviations of the differences, but for CLAES, the precision seems to be approximately 10% and would be approximately 20% if the relatively systematic, vertical structure differences were to be included in the error bars.
Validation of temperature measurements from the Halogen Occultation Experiment
Authors: Hervig M. E. , Russell J. M. , Gordley L. L. , Drayson S. R. , Stone K. , Thompson R. E. , Gelman M. E. , McDermid I. S. , Hauchecorne A. , Keckhut P. , McGee T. J. , Singh U. N. , Gross M. R.
Published: February 2004

The Halogen Occultation Experiment (HALOE) onboard UARS measures profiles of limb path solar attenuation in eight infrared bands. These measurements are used to infer profiles of temperature, gas mixing ratios of seven species, and aerosol extinction at five wavelengths. The objective of this paper is to validate profiles of temperature retrieved from atmospheric transmission measurements in the 2.80‐μm CO2 band. Temperatures are retrieved for levels above where aerosol affects the signals (35 km) to altitudes where the signal‐to‐noise decreases to unity (∽85 km). At altitudes from 45 to 35 km the profile undergoes a gradual transition from retrieved to National Meteorological Center (NMC) temperatures and below 35 km the profile is strictly from the NMC. This validation covers the uncertainty analysis, internal validations, and comparisons with independent measurements. Monte Carlo calculations using all known random and systematic errors determine typical measurement uncertainties of 5 K for altitudes below 80 km. Comparisons of coincident HALOE sunrise and sunset measurements are an indicator of the upper limit of measurement uncertainty. The sunrise‐sunset comparisons have random and systematic differences which are less than 10 K for altitudes below 80 km. Comparisons of HALOE to lidar and rocket measurements typically have random differences of ∽5 K for altitudes below 65 km. The mean differences for the correlative comparisons indicate that HALOE temperatures have a cold bias (2 to 5 K) in the upper stratosphere and stratopause.
Field comparison of static and flow‐through chamber techniques for measurement of soil NO emission
Authors: Valente Ralph J. , Thornton Frank C. , Williams Eric J.
Published: February 2004

A field comparison of flow‐through and static chamber techniques for measuring soil emissions of NO was performed on fertilized soil at a commercial cotton (Gossypium hirsutum L.) farm near Muscle Shoals, Alabama, during July 1992. The purpose of the study was to compare soil NOx. emissions data taken using two different techniques at a common field site. Emission rates with collocated chambers using the two techniques were compared, and spatial means were also compared for 17 National Oceanic and Atmospheric Administration (NOAA) plots and 10 Tennessee Valley Authority (TVA) plots. Emission rates of NO at the site covered a broad spectrum, ranging from less than 1 to greater than 100 ng N m−2 s−1. Data from collocated TVA static and NOAA flow‐through chambers showed a correlation coefficient of 0.98 with a linear regression slope of 0.97. A t test indicated that the mean difference was not statistically different than zero. The plot mean emission rates were 17.7 and 18.0 ng N m−2 s−1 for the TVA and NOAA chambers, respectively, for an 8‐day comparison period. These findings indicate that data sets collected with these methods are comparable and may be combined without concern for differences in technique. These results also reveal that the techniques used by each group in attempting to characterize overall site mean emissions are remarkably similar, despite differences in chamber size, plot location, extent of areal coverage, and random error associated with the measurements. This finding is significant in that it means that field data used to characterize emissions estimates by both protocols can be pooled to better estimate regional soil NO emission inventories.
Global methane emissions from minor anthropogenic sources and biofuel combustion in residential stoves
Authors: Piccot Stephen D. , Beck Lee , Srinivasan Sridhar , Kersteter Sharon L.
Published: February 2004

Most global methane (CH4) budgets have failed to include emissions from a diverse group of minor anthropogenic sources. Individually, these minor sources emit small quantities of CH4, but collectively, their contributions to the budget may be significant. In this paper, CH4 emissions are estimated for a wide variety of individual minor emissions sources on a country‐specific basis. Emissions from biomass combustion in the residential sector are also examined. The minor sources examined include fuel combustion in furnaces, vehicles, aircraft, ship, rail systems, industrial waste treatment and combustion processes, various industrial manufacturing processes (e.g., chemical manufacturing), on‐site residential waste burning, forest wildfires, and prescribed burning activities, oil refining, and the storage/distribution of oil‐derived products, coke production, and charcoal production. Country‐specific emissions associated with residential wood, charcoal, and dung combustion are also estimated. The total annual CH4 emissions from all sources examined here are estimated to be about 40 Tg. Almost half of this total is due to residential fossil fuel and biofuels combustion.
Assessment of TOVS‐derived stratospheric temperatures up to 10 hPa for episodes of the European Arctic Stratospheric Ozone Experiment campaign
Authors: Claud Chantal , Ovarlez Joelle , Scott Noelle A.
Published: February 2004

The European Arctic Stratospheric Ozone Experiment (EASOE) campaign, conducted during the winter of 1991–1992 to study the evolution of the Arctic stratosphere, has provided the scientific community with a large data set and, in particular, radiosonde reports which yield information up to the lower stratosphere, thereby allowing the validation of satellite‐derived products. Global observations from the satellites of the TIROS N series for several episodes of the EASOE campaign have been analyzed using the improved initialization inversion (3I) algorithm. The use of both the high‐resolution infrared radiometer sounder (HIRS‐2) and the microwave sounding unit (MSU) radiometric observations permits the determination of the temperature profile up to about 10 hPa (about 30 km). The evolution of the thermal fields in the stratosphere is examined for two stratospheric cooling events and a minor stratospheric warming, along with more standard conditions for midwinter and end of winter. For all these cases, colocations between 3I‐retrieved temperature profiles and radiosonde reports, as well as comparisons with analyzed temperatures in the low stratosphere provided by the Stratospheric Research Group of the Free University of Berlin, are presented and discussed in order to assess the accuracy of the retrievals in this part of the atmosphere. The TIROS N operational vertical sounder is able to resolve the stratospheric coolings and warming, but not always with the right intensity. The agreement with the Berlin analyses is better in the layer 50–30 hPa than in the layer 30–10 hPa and better for “regular” than for disturbed situations.
Measurements of water vapor distributions by the improved stratospheric and mesospheric sounder: Retrieval and validation
Authors: Goss‐Custard M. , Remedios J. J. , Lambert A. , Taylor F. W. , Rodgers C. D. , Lopez‐Puertas M. , Zaragoza G. , Gunson M. R. , Suttie M. R. , Harries J. E. , Russell J. M.
Published: February 2004

The Improved Stratospheric and Mesospheric Sounder (ISAMS) measured emissions from the 6.3‐μm band of water vapor using the pressure modulation technique. The particular form of the technique employed by ISAMS produces two signals: a pressure‐modulated signal and a wideband signal. Water vapor retrievals from the wideband signal are presented here since data from the former are still under investigation. The data are also restricted to nighttime because of the significant nonthermal emission processes which govern the daytime water vapor emissions at this wavelength. In this paper the retrieval method for the wideband water vapor retrievals is discussed in detail and an internal error budget is derived based on results for version 9 of the ISAMS data set. Comparisons are also made with available coincident measurements during the ISAMS period of observations from September 1991 to July 1992, including data from other instruments on the Upper Atmosphere Research Satellite.
A simulated spectrum of convectively generated gravity waves: Propagation from the tropopause to the mesopause and effects on the middle atmosphere
Authors: Alexander M. Joan
Published: February 2004

This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. [1995] that simulated a two‐dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.
Emissions of trace gases and aerosol particles due to vegetation burning in southern hemisphere Africa
Authors: Scholes R. J. , Ward D. E. , Justice C. O.
Published: February 2004

The emissions of trace gases and particles resulting from extensive vegetation fires in southern and central Africa are estimated from the amount of fuel consumed and emission factors determined during the Southern Africa Fire‐Atmosphere Research Initiative (SAFARI‐92) field campaign. The fuel consumption estimates are from the modeling approach ofScholes et al.[this issue]. The emission factors are a function of the “combustion efficiency,” a measure of the oxygenation state of the fire. Combustion efficiency is in turn related to the types of fuel consumed. Most of the burning in southern Africa takes place in savannas during the dry season. The main fuel is dry grass, which burns with high efficiency and produces relatively low emissions of methane, carbon monoxide, and aerosols per unit mass of fuel consumed. The combination of the reduced estimates of amount of biomass burned and the low emission factors results in subcontinental emission estimates for CH4, CO, NOx, and aerosols which are substantially lower than previous estimates. The estimates for the nominal year 1989 are 14.9 Tg CO, 0.500 Tg CH4, 1.06 Tg NOx, and 1.08 Tg particles (<2.5 μm). Approximately 324 Tg CO2is released by vegetation fires and, in the absence of evidence to the contrary, is assumed to be reabsorbed by subsequent regrowth. The pyrogenic emissions are concentrated in the area between 5° and 20°S and in the months between June and October, with a peak in August.
A three‐dimensional study of the tropospheric sulfur cycle
Authors: Pham M. , Müller J.‐F. , Brasseur G. P. , Granier C. , Mégie G.
Published: February 2004

The global tropospheric distributions of seven important sulfur species were simulated with a global three‐dimensional chemistry‐transport model (IMAGES). Surface emission and deposition velocity maps were established for use as lower boundary conditions in the model. While anthropogenic SO2 emissions are by far the largest sulfur source in the northern midlatitudes, reduced sulfur compounds, notably dimethyl sulfide (DMS) predominate over most remote areas. Simulations were performed for the present‐day (∼ 1985) atmosphere. The calculated distributions are compared with available observations. The model results are found to be generally within a factor of (at most) 2–3 of long‐term observations. Comparison with campaign measurements is more difficult, mostly due to the strong dependence of sulfur species concentrations on local meteorological conditions. The results, however, indicate the need for future model refinements, especially with respect to biogenic emission estimates and parameterization of cloud processes. A sensitivity study is presented to discuss the uncertainties of the results related to several parameters (the decoupling of wet scavenging and convective transport for soluble species, volcanoes emission and deposition velocities). Results are also discussed in terms of global budgets and related variables and processes. Around 125 Tg S/yr of non‐sea‐salt (nss) sulfur compounds (DMS, CS2, H2S, COS, and SO2) are injected into the atmosphere. The balance is mainly maintained by nss‐sulfates wet and dry deposition, and by SO2 dry deposition (94% of total sulfur deposition). It is found that DMS oxidation represents the main contribution to SO2 chemical production (80% of the chemical sources), and that the major sink of SO2 is provided by in‐cloud oxidation (90% of the chemical sinks), under the assumption that all SO2 incorporated into clouds is oxidized. The calculated annual wet deposition of sulfates reaches 3 g S m−2 yr−1 over Europe and North America, while it is usually lower than 0.5 g S m−2 yr−1 in remote parts of the world. Estimations for the global lifetimes are 0.9 day for DMS, 4 days for CS2, 2.2 days for H2S, 0.6 day for SO2, 0.18 day for DMSO, 6.1 days for MSA, and 4.7 days for nss‐sulfates.
Contribution of primary aerosol emissions from vegetation‐derived sources to fine particle concentrations in Los Angeles
Authors: Hildemann Lynn M. , Rogge Wolfgang F. , Cass Glen R. , Mazurek Monica A. , Simoneit Bernd R. T.
Published: February 2004

Field measurements of the n‐alkanes present in fine atmospheric aerosols show a predominance of odd carbon numbered higher molecular weight homologues (C27–C33) that is characteristic of plant waxes. Utilizing a local leaf wax n‐alkane profile in conjunction with an air quality model, it is estimated that, at most, 0.2–1.0 μg m−3 of the airborne fine particulate matter (dp < 2.1 μm) present in the Los Angeles basin could originate from urban vegetative detritus; this corresponds to approximately 1–3% of the total ambient fine aerosol burden. However, some of the observed vegetation aerosol fingerprint in the Los Angeles air may be due in part to emissions from food cooking rather than plant detritus. Seasonal trends in the ambient n‐alkane patterns are examined to seek further insight into the relative importance of anthropogenic versus natural sources of vegetation‐derived fine particulate matter.
Spatial variation in high‐latitude methane flux along a transect across Siberian and European tundra environments
Authors: Christensen T. R. , Jonasson S. , Callaghan T. V. , Havström M.
Published: February 2004

This paper reports results from a transect of methane flux measurements across tundra environments in Siberia and the European Arctic during July and August 1994. Overall, mean CH4 emission was 2.3±0.7 mg m−2 day−1 for the mesic tundra sites and 46.8±5.9 for the wet habitats with large intersite variability. The general scale of emissions was somewhat low compared to assumptions made about them in global methane budgets and models. In particular, the mesic tundra fluxes were lower than what would be expected based on data from similar environments in North America, and there are indications that these environments may be significant atmospheric methane consumers. Consistent consumption rates in combination with the large expanse of dry/mesic tundra environments suggest that it may be necessary to incorporate a high‐latitude soil sink term in global methane budgets. However, the wet tundra emissions found between 67° and 77°N in this study were consistently higher than recent findings in comparable environments at much lower latitudes (50°–55°N). High northern latitudes therefore represent a very important player in the global methane budget. When compared across both mesic and wet sites, methane emission increased with increasing soil organic content, soil temperature, and soil moisture. The relationship between soil temperature and methane flux at the wet sites alone was highly significant, and the flux also increased with increasing soil moisture and organic content. No correlations were found between flux and the measured environmental parameters at the mesic sites when treated separately.