bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the flux of different volatile sulfur gases from the ocean to the atmosphere
Authors: Kettle A. J. , Rhee T. S. , von Hobe M. , Poulton A. , Aiken J. , Andreae M. O.
Published: February 2004

Reduced sulfur gases and optical properties were measured in the upper ocean during an Atlantic Meridional Transect cruise of the RRS James Clark Ross from England to the Falkland Islands in 1998. Sea surface concentrations of carbonyl sulfide (COS) exhibited a pronounced diel variation at low latitudes but no diel cycle at mid and high latitudes possibly because of oceanic fronts and the longer hydrolysis time constant in cold water. The highest COS concentrations were observed in coastal and upwelling areas. CS2 concentrations varied less than those of COS, and the highest concentrations were found in the North African upwelling area with decreasing concentrations both northward and southward of this maximum. Dimethylsulfide (DMS) had the largest concentrations in the upper ocean, but methyl mercaptan (CH3SH) was an important reduced sulfur species in some coastal and upwelling areas. This may be associated with high bacterial growth rates. Colored dissolved organic matter (CDOM) fluorescence and absorbance also exhibit the highest values in coastal and upwelling areas and the lowest values in the southern subtropical gyre. The results suggest that carbon disulfide (CS2) outgassed from the oceans and oxidized in the atmosphere may represent a larger source of COS to the atmosphere than the direct flux of COS across the sea‐air interface.
Response of the stratospheric temperatures and ozone to past and future increases in stratospheric humidity
Authors: Dvortsov Victor L. , Solomon Susan
Published: February 2004

Balloonsonde and aircraft in situ and remote sensing measurements in the Northern Hemisphere midlatitudes show that stratospheric humidity has been increasing since 1954. Satellite data, albeit only available over a much shorter period (1992 through 1999), also suggest that water vapor has been increasing globally over much of the stratosphere. Implications of these trends for stratospheric temperatures and ozone are explored using a two‐dimensional interactive radiative‐chemical‐dynamical model. It is shown that the increase in humidity cools the model stratosphere, in agreement with previous studies. In the midlatitude lower stratosphere, increasing water vapor induces a temperature trend of about −0.25 to −0.35 K per decade, which is ∼30–50% of the observed cooling in this region. According to our results, such trends in water vapor have intensified Northern Hemisphere midlatitude ozone trends over the last few decades, mainly via the enhancement of ozone loss in HOx catalytic cycles and changes in chlorine partitioning (in spite of some buffering by concomitant increases in the O3 production in the methane oxidation cycle). Increasing humidity in the model accounts for additional depletion of midlatitude column ozone at a rate of −0.3% per decade and up to −0.7% (−1%) per decade enhancement of local ozone trends in the lower (upper) stratospheres, accordingly. It is important to investigate what will be the likely consequences for stratospheric climate and ozone if the water vapor trend continues. Our simulations suggest that smaller effects on ozone are to be expected over the 2000–2050 period as compared to 1979–1996 because of the projected reduction in the stratospheric chlorine (and bromine) loading. However, our model simulations assuming World Meteorological Organization future emission scenarios for halogenated compounds, CH4, N2O, and CO2, show that increasing humidity will induce further cooling of the stratosphere and result in about a decade of delay in the ozone recovery, all other factors being equal.
Ground measurements of surface BRF and HDRF using PARABOLA III
Authors: Abdou Wedad A. , Helmlinger Mark C. , Conel James E. , Bruegge Carol J. , Pilorz Stuart H. , Martonchik John V. , Gaitley Barbara J.
Published: February 2004

The ground‐based Portable Apparatus for Rapid Acquisition of Bidirectional Observations of Land and Atmosphere (PARABOLA), version 3, provides multiangle measurements of sky and ground radiances on a spherical grid of 5° in the zenith‐to‐nadir and azimuthal planes in eight spectral channels. The hemispherical directional reflectance factor (HDRF) can be measured directly by comparing the radiance reflected by the surface in given direction to that reflected from a reference surface simultaneously observed by the PARABOLA 3. The surface bidirectional reflectance factor (BRF) cannot be measured directly, however, because of the presence of the sky diffuse illumination. The contribution of the diffuse sky radiance to the radiance reflected by the natural target surface is computed, and removed, using an iterative technique. Two approaches are employed: the first requires knowledge of the atmospheric optical depth, and the second requires the simultaneous measurements of the radiance reflected by a standard surface panel under the same atmospheric and illumination conditions. Ground measurements of the BRF and HDRF for dry lake surfaces were obtained from the PARABOLA 3 observations with better than ±10% accuracy. The results described in this work are used primarily for the vicarious calibration of the Multiangle Imaging Spectroradiometer (MISR) onboard the Earth Observing System (EOS) Terra platform and for validation of MISR BRF retrievals of selected Earth surface targets.
A sea surface radiation data set for climate applications in the tropical western Pacific and South China Sea
Authors: Chou Ming‐Dah , Chan Pui‐King , Yan Michael M.‐H.
Published: February 2004

The sea surface shortwave and longwave radiative fluxes have been retrieved from the radiances measured by Japan's Geostationary Meteorological Satellite 5. The surface radiation data set covers the domain 40°S‐40°N and 90°E–170°W and a period starting from January 1998. The temporal resolution is 1 day, and the spatial resolution is 0.5°×0.5° latitude‐longitude. The retrieved surface radiation has been validated with the radiometric measurements at the Atmospheric Radiation Measurement (ARM) site on Manus Island in the equatorial western Pacific. It has also been validated with the measurements at the radiation site on Dungsha Island during the South China Sea Monsoon Experiment (SCSMEX) (May and June 1998). The data set is used to study the effect of El Niño and East Asian summer monsoon on the heating of the ocean. Interannual variations of clouds associated with El Niño and the East Asian summer monsoon have a large impact on the radiative heating of the ocean, exceeding 40 W m−2 in seasonal mean over large areas. Together with the Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes at the top of the atmosphere and the radiative transfer calculations of clear‐sky fluxes, this surface radiation data set is also used to study the impact of clouds on the solar heating of the atmosphere. It is found that clouds enhance the atmospheric solar heating by ∼21 W m−2 in the tropical western Pacific and the South China Sea.
Influence of the quasi‐biennial oscillation on isentropic transport and mixing in the tropics and subtropics
Authors: Shuckburgh Emily , Norton Warwick , Iwi Alan , Haynes Peter
Published: February 2004

The influence of the quasi‐biennial oscillation (QBO) on isentropic transport and mixing in the tropical and subtropical stratosphere is investigated over a period of 6 years. The transport and mixing is quantified by the equivalent length diagnostic, calculated from tracers simulated in chemical transport models using European Centre for Medium‐Range Weather Forecasting (ECMWF) analyzed winds. A new procedure for calculating equivalent length from tracers, such as nitrous oxide (N2O), with a tropical maximum or minimum is devised. Results from different tracers and different chemical transport models demonstrate the robustness of the equivalent length diagnostic. Equivalent length calculated both from an artificial tracer and from simulated N2O indicates that, when the QBO winds are easterly, mixing is inhibited in the tropics throughout the broad region occupied by the easterlies and that, when the QBO winds are westerly, mixing is strongly inhibited within the narrow region occupied by the westerlies themselves but is enhanced in the subtropics. Examination of absolute vorticity gradients and horizontal Eliasen‐Palm (EP) fluxes (broken down into contributions from different zonal wavenumbers) suggests that, in the ECMWF analyses, barotropic shear instability of the westerly jet, as well as propagation of planetary waves from the extratropics, drives the subtropical mixing seen in the westerly phase.
Assimilation of carbon monoxide measured from satellite in a three‐dimensional chemistry‐transport model
Authors: Clerbaux Cathy , Hadji‐Lazaro Juliette , Hauglustaine Didier , Mégie Gérard , Khattatov Boris , Lamarque Jean‐François
Published: February 2004

Carbon monoxide measurements are obtained from the analysis of the spectra provided by the Interferometric Monitor for Greenhouse Gases (IMG) instrument, which flew on board the Japanese ADEOS satellite. The averaging kernel function of the instrument, which provides the sensitivity of retrieved CO to the vertical atmospheric layers, is calculated. A sequential assimilation approach is used to incorporate this CO data set, along with a detailed associated error budget, into a global three‐dimensional chemistry‐transport model (MOZART version 2). We show how data assimilation allows one to highlight the differences between modeled and observed CO global distribution. Surface CO mixing ratios computed after assimilation of total columns provided by the IMG instrument are compared with the National Oceanic and Atmospheric Administration (NOAA) ‐ Climate Monitoring and Diagnostics Laboratory (CMDL) in situ measurements, and a good agreement is found between the two data sets.
Summertime measurements of aerosol nitrate and ammonium at a northeastern U.S. site
Authors: Lefer B. L. , Talbot R. W.
Published: February 2004

Summertime measurements of the atmospheric concentrations and aerodynamic size distributions of NH4+ and NO3− and other major aerosol species were made between 1991 and 1996 at a rural site in central Massachusetts to examine the nature of aerosol chemistry at the Harvard Forest. The bulk aerosol can be described as a mixture of submicron ammonium (bi)sulfate aerosols with smaller amounts of soil‐derived particles. Approximately one third of the samples had an anion surplus of greater than 20%, which was assumed to result from unmeasured H+ ions. Aerosols in air masses from the southwest were rarely neutralized, especially when SO42− concentrations were greater than ≈75 nmol m−3. This result suggests that twice this level (i.e., 150 nmol m−3) may describe an upper limit to the amount of gaseous NH3 encountered enroute to this sampling site during the typical summer transport observed from this region. Aerosol NO3− was observed at concentrations 4–8 times lower than NH4+, and while occasionally found in the fine mode, the majority of the NO3− was associated with the water‐soluble fraction of supermicron soil‐derived Ca2+. The similarity of the ammonium and oxalate particle size distributions suggests that (NH4)2(COO)2 aerosols may result from the reaction of gaseous precursors.
Chemical characterization of pollution layers over the tropical Indian Ocean: Signatures of emissions from biomass and fossil fuel burning
Authors: Reiner T. , Sprung D. , Jost C. , Gabriel R. , Mayol‐Bracero O. L. , Andreae M. O. , Campos T. L. , Shelter R. E.
Published: February 2004

We have performed airborne measurements of atmospheric trace gases and aerosol composition on the National Center for Atmospheric Research C‐130 research aircraft over the tropical Indian Ocean during the Indian Ocean Experiment (INDOEX) intensive field phase in February and March 1999. Gases measured included acetone, acetonitrile, sulfur dioxide, and carbon monoxide. The aerosol composition was analyzed for water‐soluble ions, and black and organic carbon. South of the Intertropical Convergence Zone (ITCZ), we sampled pristine air originating from the remote southern Indian Ocean. North of the ITCZ, signatures of heavy pollution were evident over large areas of the Indian Ocean. Heavy pollution was present in the marine boundary layer as well as in the free troposphere at altitudes up to almost 4000 m. Outflow from the Indian subcontinent as well as from other source regions (Arabian Sea, Southeast Asia) could be identified by back trajectory calculations using the Hybrid Single Particle Lagrangian Integrated Trajectory model. The highest pollutant concentrations were observed in a free tropospheric pollution layer (“residual layer”), which originated from the Indian continental boundary layer. High mixing ratios of acetonitrile (up to 0.8 ppb) and submicron aerosol potassium (up to 0.6 ppb) indicate an important contribution from biomass or biofuel burning sources. On the other hand, high mixing ratios of sulfiir dioxide (up to 1.5 ppb) and aerosol sulfate (up to 3 ppb) indicate the influence of fossil fuel burning. During most flights the contributions from these two sources were well mixed within the same air mass, suggesting that the sources on the ground are also close to each other. This is consistent with the assumption that biomass is mainly burnt as biofuel for domestic use in populated areas, where fossil fuel is also used. The ratiosdX/dCQ (X=acetone, acetonitrile, sulfur dioxide, potassium, or sulfate) measured during the flights indicate that most of the CO in the continental outflow is due to biomass or biofuel burning, whereas the majority of the aerosols results from fossil fuel burning.
On the origin of mesospheric bores
Authors: Dewan E. M. , Picard R. H.
Published: February 2004

A dramatic front of airglow radiance and wave structure reported by Taylor et al. [1995] was attributed, in a previous paper of ours [Dewan and Picard, 1998], to a manifestation of an internal undular bore in the mesosphere. In the current paper we address the question of what physical process could be responsible for generating such a bore at that altitude. While it is relatively easy to find sources of internal tropospheric bores, including the dramatic “morning glory,” the same cannot be said for mesospheric bores. It will be argued here that a likely candidate for the generator of such bores is the interaction of gravity waves with the mean flow at a critical layer. This interaction could take place within an already existing inversion layer, the latter playing the role of the “channel” in which the bore propagates. As Huang et al. [1998] have shown, a similar wave/critical‐level interaction may be responsible for the inversion layer in question. Hence we are proposing that the physical process producing the channel is the same as the one responsible for subsequently generating the bore.
N2O record spanning the penultimate deglaciation from the Vostok ice core
Authors: Sowers Todd
Published: February 2004

Nitrous oxide (N2O) is an important atmospheric trace gas whose concentration is determined by numerous sources and sinks. Over the past 200 years, N2O has increased by 17±3% due primarily to increased anthropogenic emissions. Over the last glacial/interglacial transition, data from ice cores show that N2O increased by 35%. This increase may be related to increased terrestrial N2O emissions resulting from a global climate amelioration. Here I describe a new dry extraction technique for measuring the elemental and isotopic composition of N2O in ice core samples. Results from a shallow GISP II ice core spanning the last 200 years provide an estimate for the preanthropogenic N2O concentration of 266±4 ppb. In addition, 11 ice samples from the last interglacial period show fairly uniform N2O values (269±9 ppb). During the penultimate glacial period (131–160 ka), N2O concentrations of air trapped in the glacier fluctuated between 190 ppb and 320 ppb, while CO2 and CH4 concentrations were relatively low and stable. Two local N2O maxima were observed during the penultimate glacial period that actually exceeded “normal” interglacial N2O values (∼265 ppb). The maxima were located in portions of the core which exhibit both elevated dust concentrations and elevated bacterial counts. The δ15N and δ18O of N2O in this portion of the Vostok core were 15‰ higher and 12‰ lower than during the warm Eemian period, respectively. The isotopic data and coincidence between the elevated N2O concentrations and the high bacterial counts may be related to in situ N2O production by bacteria. The lower δ18O values are consistent with the isotopic composition of N2O produced by in‐situ nitrification.
Effect of coagulation on the particle charge distribution and air conductivity
Authors: Dhanorkar Savita , Kamra A. K.
Published: February 2004

The steady state charge distribution on submicron‐size charged aerosols is calculated from the ion‐aerosol balance equations including the effects of both the ion‐particle charging mechanism as well as the coagulation of charged aerosols. The particle charge distribution is found to depend on the aerosol concentration and the ionization rate. The results show that for a given ionization rate the fraction of singly charged aerosols increases up to a critical value of aerosol concentration and then decreases with further increase in the aerosol concentration. However, the fractions of multiply charged aerosols show a steady increase with the aerosol concentration. The variation of the polar conductivity with aerosol concentration shows that the inverse relationship between them exists only up to a critical value of aerosol concentration which is decided by the prevailing ionization rate. Above this critical value the polar conductivity shows an increase with the aerosol concentration. Further, it is shown that though the polar conductivity is mainly due to small ions in a clean environment, the charged aerosols may dominantly contribute to the polar conductivity in a polluted atmosphere. For aerosols having larger mean radii the contribution of multiply charged aerosols becomes appreciable for higher values of aerosol concentration and is almost comparable to that of the small ions.
A seasonal climatology of effective diffusivity in the stratosphere
Authors: Allen Douglas R. , Nakamura Noboru
Published: February 2004

A 7‐year (1992–1998) seasonal climatology of effective horizontal diffusivity is presented for the stratosphere (350–1900 K). As in previous studies, the diagnosis is based on the equivalent length of a test tracer advected on isentropic surfaces, in this case using the van Leer flux‐limiting scheme driven by the United Kingdom Meteorological Office assimilated winds. Although the magnitude of equivalent length is resolution dependent, its structure is shown to be reasonably robust for quantifying the inhomogeneous mixing in the stratosphere. The van Leer calculation agrees well with a more expensive spectral transform calculation at a comparable resolution, suggesting that the diagnostic is not sensitive to the advection scheme or subgrid representation of the models. A first attempt is also made at estimating the implicit numerical diffusion of the van Leer scheme, which is necessary to convert equivalent length to effective diffusivity. Compared with the spectral calculations with a constant diffusion coefficient, the van Leer results show notably greater diffusivity within the winter polar vortices despite the comparable equivalent lengths, suggesting that the scheme may be overdiffusing in the vicinities of mobile tracer extrema. The climatology of equivalent length is then presented, and the seasonal evolution is discussed in detail for the lower, middle, and upper stratosphere. The major mixing barriers (winter and summer polar vortices and tropical eddy transport barrier) are easily identified, as well as the strong mixing regions (surf zones). Generally, equivalent length tends to be small in regions of strong zonal wind and large in regions of weak wind. Large values of equivalent length are observed in the summer lower stratosphere and in the middle stratosphere during the breakup of the polar vortices. Interhemispheric asymmetry is observed both after the winter polar vortex breakup, where in the middle stratosphere the Southern Hemisphere shows much larger equivalent lengths, and in the summer tropical region, where larger equivalent lengths are observed in the Northern Hemisphere, likely related to the monsoon circulation. A monthly averaged equivalent length climatology is presented, and implications for two‐dimensional stratospheric chemistry‐transport modeling are discussed.
Direct observations of clear‐sky aerosol radiative forcing from space during the Indian Ocean Experiment
Authors: Rajeev K. , Ramanathan V.
Published: February 2004

This study presents the regional estimates of the seasonal and diurnal mean broadband (0.3–5.0 μm) clear‐sky aerosol radiative forcing at the top of atmosphere (TOA) due to both the natural and the anthropogenic aerosols over the tropical Indian Ocean from 25°N to 25°S. We propose two new methods, the slope method and the differencing method, to obtain clear sky aerosol forcing from solely satellite measurements. The focus of the study is January to March 1997, 1998, and 1999. The TOA clear‐sky aerosol forcing was obtained by integrating satellite data for aerosol optical depth (AOD) and the broadband radiation budget. Over 30,000 pixels were collocated to estimate that the diurnal and seasonal mean reflected broadband solar radiation at TOA increases by about 24 W m−2 per unit increase in AOD at the wavelength of 500 nm. The observed TOA clear‐sky aerosol forcing varied between −4 and −14 W m−2 in the Northern Hemisphere (NH) and between 0 and −6 Wm−2 in the Southern Hemisphere. Assuming a ratio of surface to TOA clear‐sky aerosol forcing of 3 which was observed over Kaashidhoo Climate Observatory (4.96°N, 73.46°E) during the same period [Satheesh and Ramanathan, 2000], this leads to a clear‐sky aerosol forcing of −12 to −42 Wm−2 at the surface in the NH. The difference between the TOA forcing and the surface forcing is the atmospheric forcing. As a result, the atmosphere is subject to a large net forcing of about 8–28 Wm−2 in the NH, largely due to the presence of black carbon. Of equal importance is the fact that the Indian Ocean aerosols introduce a large interhemispheric gradient in the solar heating during the wintertime. The implications for climate and monsoonal circulation may be major and need to be explored with coupled model studies.
A reconstruction of the winter North Atlantic Oscillation index back to A.D. 1501 using documentary data in southern Spain
Authors: Rodrigo F. S. , Pozo‐Vázquez D. , Esteban‐Parra M. J. , Castro‐Díez Y.
Published: February 2004

In this work a reconstruction of seasonal rainfall in Andalusia (southern Spain) from 1501 to 1997 is presented. This reconstruction is based on the analysis of a wide variety of documentary data. Qualitative data are translated into numerical indices to elaborate time series of rainfall for each season of the year. Because of the strong relationship between Andalusian rainfall and the North Atlantic Oscillation (40% of the winter rainfall variance is explained by the NAO index behavior), it is possible to use these rainfall series to reconstruct the seasonal NAO index back to 1501. The results are compared with other analyses reported in the literature.
Total ozone determinations from National Oceanic and Atmospheric Administration operational solar backscattered ultraviolet 2 instrument observations: An update
Authors: Planet W. G. , Miller A. J. , Horvath K. , Nagatani R. , Flynn L. E. , Hilsenrath E. , Kondragunta S. , Cebula R. P. , DeLand M. T.
Published: February 2004

Total ozone amounts have been derived from observations of the Solar Backscattered Ultraviolet 2 (SBUV/2) instruments on National Oceanic and Atmospheric Administration (NOAA) operational satellites since 1985. The data from the NOAA‐9 instrument for the period 1985–1997 have been reprocessed using instrument characterizations based on in‐orbit operation and comparisons with Shuttle Solar Backscattered Ultraviolet (SSBUV) observations. The data from the NOAA‐11 satellite for the period 1989–1994 have also been reprocessed using mainly internal spacecraft information. The data from the NOAA‐14 satellite for the period 1995–1998 have been reprocessed using complete instrument characterization. The NOAA‐11 and NOAA‐14 data for 1998 to the present, briefly discussed herein, are preliminary. The calibration adjustments used in the reprocessing of NOAA‐9, NOAA‐11, and NOAA‐14 total ozone data are internal, with the exception of those derived from SSBUV analysis, and are independent of Dobson and Total Ozone Mapping Spectrometer (TOMS) total ozone measurements. The reprocessed data have been validated with ground‐based Dobson spectrophotometer observations, and are compared to other sources of total column ozone amounts. The mean bias between NOAA‐9 data and Dobson data is 1.9%±0.6% over the 12‐year record with a trend of 0.1% per year. The mean bias between NOAA‐11 and Dobson data is 0.8%±0.2% with a near‐zero trend. The mean bias between NOAA‐14 and Dobson data is 1.5%±0.3% with a trend of 0.2% per year; the NOAA‐14 calibration and characterization data for the period 1998 to the present are not yet fully analyzed. The methods used in the validations are discussed here, as are some reasons for the results. Finally, a recommendation is made for the use of a relatively continuous total ozone data set.
A study of formaldehyde chemistry above a forest canopy
Authors: Sumner Ann Louise , Shepson Paul B. , Couch Tara L. , Thornberry Troy , Carroll Mary Anne , Sillman Sandy , Pippin Margaret , Bertman Steven , Tan David , Faloona Ian , Brune William , Young Valerie , Cooper Owen , Moody Jennie , Stockwell William
Published: February 2004

Gas‐phase formaldehyde (HCHO) was measured at a mixed deciduous/coniferous forest site as a part of the PROPHET 1998 summer field intensive. For the measurement period of July 11 through August 20, 1998, formaldehyde mixing ratios ranged from 0.5 to 12 ppb at a height ∼10 m above the forest canopy, with the highest concentrations observed in southeasterly air masses. Concentrations varied on average from a mid‐afternoon maximum influenced by photochemical production of 4.0 ppb, to a late night minimum of 2.2 ppb, probably resulting from dry depositional loss. An analysis of local HCHO sources revealed that isoprene was the most important of the measured formaldehyde precursors, contributing, on average, 82% of the calculated midday HCHO production rate. We calculate that the nighttime HCHO dry deposition velocity is 2.6 times that of ozone, or approximately 0.65 cm/s. In the daytime, photolysis, dry deposition, and reaction with hydroxyl radical (OH) are roughly equally important as loss processes. Explicit calculations of HCHO chemical behavior highlighted the probable importance of transport and surface deposition to understanding the diel behavior of formaldehyde.
Global tropospheric NO2 column distributions: Comparing three‐dimensional model calculations with GOME measurements
Authors: Velders Guus J. M. , Granier Claire , Portmann Robert W. , Pfeilsticker Klaus , Wenig Mark , Wagner Thomas , Platt Ulrich , Richter Andreas , Burrows John P.
Published: February 2004

Tropospheric NO2 columns derived from the data products of the Global Ozone Monitoring Experiment (GOME), deployed on the ESA ERS‐2 satellite, have been compared with model calculations from two global three‐dimensional chemistry transport models, IMAGES and MOZART. The main objectives of the study are an analysis of the tropospheric NO2 data derived from satellite measurements, an interpretation of it and evaluation of its quality using global models, and an estimation the role of NO2 in radiative forcing. The measured and modeled NO2 columns show similar spatial and seasonal patterns, with large tropospheric column amounts over industrialized areas and small column amounts over remote areas. The comparison of the absolute values of the measured and modeled tropospheric column amounts are particularly dependent upon uncertainties in the derivation of the tropospheric NO2 columns from GOME and the difficulty of modeling the boundary layer in global models, both of which are discussed below. The measured tropospheric column amounts derived from GOME data are of the same order as those calculated by the MOZART model over the industrialized areas of the United States and Europe, but a factor of 2–3 larger for Asia. The modeled tropospheric NO2 columns from MOZART as well as the column amounts measured by GOME are in good agreement with NO2 columns derived from observed NO2 mixing ratios in the boundary layer in eastern North America. The comparison of the models to the GOME data illustrates the degree to which present models reproduce the hot spots seen in the GOME data. The radiative forcing of NO2 has been estimated from the calculated tropospheric NO2 columns. The local maxima in the radiative forcing of tropospheric NO2 for cloud‐free conditions over the eastern United States and western Europe represent 0.1–0.15 W m−2, while values of 0.04–0.1 W m−2 are estimated on a continental scale in these regions, of the same order of magnitude as the forcing of N2O and somewhat smaller than the regional forcing of tropospheric ozone. The globally averaged radiative forcing of tropospheric NO2 is negligible, ∼0.005 W m−2.
Isotopic composition of stratospheric water vapor: Measurements and photochemistry
Authors: Johnson David G. , Jucks Kenneth W. , Traub Wesley A. , Chance Kelly V.
Published: February 2004

We present a photochemical model describing the changes in the isotopic composition of stratospheric water vapor that result from methane oxidation and reactions with O(1D). We then compare model calculations with measurements made with the Smithsonian Astrophysical Observatory far‐infrared spectrometer during seven balloon flights that took place between 1989 and 1997. The agreement between the model calculations and measurements establishes the validity of the model and the internal consistency of the data set. Finally, we use the model and measurements together to estimate the mixing ratio and isotopic composition of water vapor entering the stratosphere and find that the average over all flights of the water vapor mixing ratio, δD, δ18O, and δ17O are 3.48±0.15 parts per million by volume, −679±20‰, −128±31‰, and −84±31‰, respectively, where the errors indicate the estimated accuracy.
A simulation of bromoform's contribution to stratospheric bromine
Authors: Nielsen J. Eric , Douglass Anne R.
Published: February 2004

The chlorine and bromine that are contained in gases emitted at the Earth's surface enter the stratosphere in two ways. First, those gases that are inert in the troposphere may be transported to the stratosphere before they are oxidized or photolyzed. In this case these compounds act as an in situ source of stratospheric reactive chlorine and bromine. Second, the chlorine and bromine that are released into the troposphere from those gases that are reactive in the troposphere may also be subsequently transported to the stratosphere. We evaluate the relative influence of these processes on stratospheric bromine in a three‐dimensional chemistry and transport model that simulates the distribution of bromoform (CHBr3). Many of the observed features of CHBr3 are simulated well, and comparisons with observations show that the model represents aspects of transport in the upper troposphere and lower stratosphere that are critical to the evaluation. In particular, the model maintains the observed troposphere‐stratosphere distinctness in transport pathways and reproduces the observed seasonal dependence of the mixture of air in the middle‐ and high‐latitude lowermost stratosphere. CHBr3 is short‐lived and is destroyed by photolysis and by reaction with hydroxyl (OH), which yields inorganic bromine (Bry). In our simulations, stratospheric destruction of CHBr3 produces Bry in amounts that are comparable to that transported into the stratosphere after photolysis and oxidation of CHBr3 in the troposphere. The mass of Bry produced from the destruction of CHBr3 does not exceed the mass of Bry produced from the destruction of the long‐lived brominated compounds (halons and methyl bromide) globally at any level in the stratosphere. However, Bry from the loss of CHBr3 accounts for approximately one third of the total Bry in the lowest kilometer of the stratosphere. We estimate that adding CHBr3 to models that already include the long‐lived organic brominated compounds will increase the simulated stratospheric mass of Bry by, at most, 15%.
Altitude distribution of tropospheric ozone over the northern hemisphere during 1996, simulated with a chemistry‐general circulation model at two different horizontal resolutions
Authors: Kentarchos A. S. , Roelofs G. J. , Lelieveld J.
Published: February 2004

The spatial/temporal variability of the vertical distribution of tropospheric ozone in the Northern Hemisphere (NH) over a period of 1 year (1996) is studied with a coupled chemistry‐general circulation model. The model is used at two different horizontal resolutions (T30: 3.75°×3.75° and T63: 1.875°×1.875°) and is nudged towards European Centre for Medium Range Weather Forecasts analyses for 1996, using a four‐dimensional assimilation technique (newtonian relaxation), to enable direct comparisons of observations and model results. Overall, the model reproduces satisfactorily the magnitude and seasonal variability of the vertical ozone distribution observed at six selected locations. Discrepancies occur, however, at remote locations in the subtropical Atlantic and tropical Pacific where ozone concentrations throughout the free troposphere are overestimated by the fourth version of the European Centre Hamburg Model (ECHAM4)‐T30. A considerable improvement is evident at T63, which can be attributed, at least partially, to less efficient transport of ozone precursors from the polluted continents at higher resolution. In the upper troposphere/tropopause region, short‐term ozone variations are better reproduced at higher resolution. The origin of tropospheric ozone is examined by decomposing its seasonal variation in the model into ozone from the stratosphere and ozone produced within the troposphere. Differences in the NH annual tropospheric ozone budget for 1996, between T30 and T63 mean amounts are relatively small. The tropospheric ozone budget is dominated by photochemical production and destruction (2716 and 2684 Tg, respectively), while the net ozone flux from the stratosphere is estimated to be 436 Tg, and dry deposition is estimated to be 487 Tg.
Effects of land‐use modification on potential increase of convection: A numerical mesoscale study over south Israel
Authors: Perlin Nataly , Alpert Pinhas
Published: February 2004

The current research was designed to examine the potential of modified surface conditions in semiarid and arid central‐southern Israel to enhance convective development and rainfall. The fifth‐generation mesoscale model (MM5), coupled with a sophisticated land‐surface submodel, is applied for the three‐dimensional high resolution simulations of two convective rain case studies, on October 27, 1990 and October 18, 1987. Three surface conditions are modeled to examine the relative influence of land‐use changes, which are present‐time land‐use (1990s), preirrigation time (1930s), and the hypothetical case of extended irrigated agricultural lands. The main conclusion of the study is that there exists a positive influence of the anthropogenic land‐use changes on the enhancement of thermal convection and associated rainfall. Modification of surface parameters from semiarid land conditions to cultivated lands tends to consistently increase the potential for moist convection during the daytime heating hours, as expressed in the evolution of the PBL structure and the growth of convective available potential energy (CAPE), as well as the area‐averaged rainfall. The model seems to accurately reproduce the observed atmospheric situations and rainfall, lending confidence to the assertion that these land‐atmosphere effects can be quantified with an advanced mesoscale modeling system. This work is the first numerical mesobeta scale 3‐D study over the south Israel area with its relatively sharp spatial change in land use as well as in climatic zone. It is believed to be a region, possibly the only in the world, where mesoscale surface and planetary boundary layer processes were suggested as causes for observed anti‐desertification gains.
Absolute intensities of 16O3 lines in the 9–11 μm region
Authors: Smith M. A. H. , Devi V. Malathy , Benner D. Chris , Rinsland C. P.
Published: February 2004

Absolute intensities of 376 16O3 lines in the 9–11 μm region have been determined from high‐resolution infrared absorption spectra recorded at room temperature using a Fourier transform spectrometer. The ozone samples were contained in a glass cell having crossed IR‐transmitting and UV‐transmitting paths, and the UV absorption at 254 nm was used to monitor ozone concentrations in the cell. A multispectrum nonlinear least squares fitting procedure was used to determine intensities for 366 lines in the ν3 fundamental band and 10 lines in the ν1 band. The absolute accuracy of these intensity values ranges from 2% for the strongest, most well determined lines to 4 or 5% for the weakest lines measured. On average, our measured intensities are approximately 1% larger than the values on current spectroscopic databases.
Model analysis of trace gas measurements and pollution impact during INDOEX
Authors: de Laat A. T. J. , de Gouw J. A. , Lelieveld J. , Hansel A.
Published: February 2004

An analysis of acetone (CH3COCH3) and acetonitrile (CH3CN) measurements, performed during the Indian Ocean Experiment (INDOEX), using a chemistry general circulation model is presented. A comparison with measurements indicates that the model simulates realistic CO and acetone distributions, except toward the Indian west coast near the surface. The latter may be related to a sea breeze circulation at the Indian west coast, which is not resolved by the model. A comparison of the measured and modeled correlation between CO and acetone indicates the presence of a background marine acetone source. A model sensitivity study suggests a global marine emission strength of 15–20 Tg acetone yr−1, which is a significant contribution to the estimated global acetone source of 56 (37–80) Tg acetone yr−1. The comparison of measured and modeled CO‐acetonitrile correlation from surface measurements indicates that a model sink of acetonitrile in the marine boundary layer is missing. A model sensitivity study suggests that this could be dry deposition (deposition velocity estimate: 0.01–0.05 cm s−1) on the ocean surface. A comparison of measured and modeled tropospheric acetonitrile indicates that the model overestimates the free tropospheric acetonitrile mixing ratios up to a factor of 3, which points to a missing free tropospheric sink of acetonitrile in the model. A possible explanation may be stratospheric loss and subsequent stratosphere‐troposphere exchange, which was not included in the model.
Comparison of satellite ozone observations in coincident air masses in early November 1994
Authors: Manney G. L. , Michelsen H. A. , Bevilacqua R. M. , Gunson M. R. , Irion F. W. , Livesey N. J. , Oberheide J. , Riese M. , Russell J. M. , Toon G. C. , Zawodny J. M.
Published: February 2004

Ozone observed by seven satellite instruments, the Atmospheric Trace Molecule Spectroscopy instrument (ATMOS), Stratospheric Aerosol and Gas Experiment (SAGE) II, Polar Ozone and Aerosol Measurement (POAM) II instrument, Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS), Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA), and Millimeter‐wave Atmospheric Sounder (MAS), during early November 1994 is mapped in equivalent latitude/potential temperature (EqL/θ) space to facilitate nearly global comparisons of measurements taken in similar air masses. Ozone from all instruments usually agrees to within 0.5 ppmv (∼5%) in the upper stratosphere and ∼0.25 ppmv in the lower stratosphere; larger differences in the midstratosphere are primarily due to sampling differences. Individual profile comparisons, selected to match meteorological conditions, show remarkably good agreement between all instruments that sample similar latitudes, although some small differences do not appear to be related to sampling differences. In the Southern Hemisphere (SH) midstratosphere, the instruments (ATMOS, SAGE II, and POAM II) with observations confined to high latitudes measured low EqLs in air drawn up from low latitudes that had formed a “low‐ozone pocket”; they measured much lower ozone at low EqL than those that sampled low latitudes. A low‐ozone pocket had also formed in the Northern Hemisphere (NH) midstratosphere (a month earlier than this phenomenon has previously been reported), also resulting in differences between instruments based on their sampling patterns. POAM II sampled only high latitudes in the NH, where extravortex sampling did not include tropical, high‐ozone air, and thus measured lower ozone at a given EqL than other instruments. Ozone laminae appear in coincident profiles from multiple instruments, confirming atmospheric origins for these features and agreement in some detail between ozone observed by several instruments; reverse trajectory calculations indicate such laminae arise from filamentation in and around the polar vortices. Both EqL/θ and profile comparisons indicate overall excellent agreement in ozone observed by all seven instruments in early November 1994. When care is taken to compare similar air masses and to understand sampling effects, much useful information can be obtained from comparisons between instruments with very different observing patterns.
Dust and pollution transport on global scales: Aerosol measurements and model predictions
Authors: Clarke A. D. , Collins W. G. , Rasch P. J. , Kapustin V. N. , Moore K. , Howell S. , Fuelberg H. E.
Published: February 2004

Vertical profiles of aerosol and gas phase species were measured on flights near Hawaii on April 9 and 10, 1999, during NASA's Pacific Exploratory Mission (PEM) Tropics B program. These measurements characterized aerosol microphysics, inferred chemistry, optical properties, and gases in several extensive dust and pollution plumes, also detected by satellites, which had 10,000‐km trajectories back to sources in Asia. Size‐resolved measurements indicative of aerosol sulfate, black carbon, dust, light scattering, and absorption allowed determination of their concentrations and contributions to column aerosol optical depth. A new Chemical Transport Model (CTM) that includes aerosol, meteorological fields, dynamics, gas and particle source emissions, a chemistry component (MATCH), and assimilated satellite data was used to predict aerosol and gas concentrations and the aerosol optical effects along our flight path. Flight measurements confirmed the “river‐like” plume structures predicted by the CTM and showed close agreement with the predicted contributions of dust and sulfate to aerosol concentrations and optical properties for this global‐scale transport path. Consistency between satellite, model and in situ assessment of aerosol optical depth was found, with noted exceptions, within ∼25%. Both observations and model results confirmed that this aerosol was being entrained into the marine boundary layer between Hawaii and California where it can be expected to modify the type and concentration of cloud condensation nuclei in ways that may alter properties of low‐level clouds. These observations document the significance and complexity of long‐range aerosol transport and highlight the potential of emerging CTM models to extend observational data and address related issues on global scales.
Evolution of the vertical profile and flux of large sea‐salt particles in a coastal zone
Authors: Reid Jeffrey S. , Jonsson Haflidi H. , Smith Michael H. , Smirnov Alexander
Published: February 2004

In the vicinity of the North Carolina Outer Banks we observed both steady onshore flow conditions and a continental air mass transition into a marine boundary layer. Using the CIRPAS Twin Otter aircraft, we measured changes in the column burden of sea salt as the air mass was advected out to sea. We also measured the flux of whitecap‐generated sea‐salt particles in neutrally stable atmosphere at wind speeds of 4, 8, and 12 m s−1. Production of salt particles as small as 0.27 μm in diameter was observed. Furthermore, we measured salt particle size distributions at various wind speeds during along shore wind and near steady state conditions. Using these measurements as a frame of reference, we discuss the very large differences in the reported size and flux of sea salt presented in the literature. The disagreement in reported salt fluxes is larger for smaller‐ sized particles (almost an order of magnitude) and is most likely due to assumptions made when the fluxes were computed, especially the particle dry deposition velocity and air mass history. However, for giant salt particles with short atmospheric lifetimes (>∼10 μm in diameter), there is general agreement between fluxes and size distributions measured in this study and previous ones. Reported salt particle size distributions in the literature also vary considerably under similar steady wind and stability conditions. From these and our results it is clear that no more than half of the variance in salt particle concentration can be explained by wind speed alone, suggesting that the idea of “steady state” in the marine boundary layer rarely exists at midlatitudes.
Evolution of the mode of convection within terrestrial planets
Authors: Sleep Norman H.
Published: February 2004

Magma oceans, plate tectonics, and stagnant‐lid convection have transferred heat out of the terrestrial planets at various times in their histories. The implications of the existence of multiple branches are graphically illustrated by approximating the globally averaged mantle heat flow as a function of the interior potential temperature. For this assumption to be valid, the mantle heat flow needs to be able to change rapidly relative to the potential temperature, or, equivalently, lithosphere needs to be a small fraction of the mass planet. This criterion is satisfied by the Earth, Venus, and Mars, but not the Moon. At a given potential temperature the function may be multivalued with a separate branch representing each mode of convection. The heat flow evolves along a branch as the potential temperature changes depending on whether the heat flow is greater or less than the global radioactive heat generation. When the end of a branch is reached, the state of the system jumps to another branch, quickly changing the global heat flow. Examples include transitions from a magma ocean to plate tectonics, probably on the Earth and Mars, and conceivably Venus; and the transition from a stagnant‐lid planet to a magma ocean on Venus and the eventual return to a stagnant‐lid planet.