bluuebunny/crossref_metadata_2025 huggingface dataset:
On large variations in atmospheric CO2 concentration observed over the central and western Pacific Ocean
Authors: Murayama Shohei , Harada Koh , Gotoh Kouichi , Kitao Takashi , Watai Tomonori , Yamamoto Susumu
Published: May 2003

In order to examine distribution of atmospheric CO2 concentration over the central and western Pacific Ocean and elucidate factors governing the distribution, shipboard measurements were made between 1992 and 1996. Large variations in the concentration were observed in the northernmost and the tropical regions during the cruises. Also, year‐to‐year differences in the latitudinal CO2 distribution were detected. To interpret these variations, analyses were performed in terms of atmospheric transport from various source regions using meteorological and climatological data. The following results were obtained: (1) Episodic large CO2 variations appeared north of 30°N over the central and western Pacific during the periods of ship cruises. These variations were related with exchanges of continental and marine air masses associated with movements of weather systems. (2) Discontinuous changes of CO2 concentration were observed in the equatorial region during spring cruises, reflecting suppression of interhemispheric air mixing. However, the magnitude, the sharpness, and the location of these discontinuous changes were associated with variations in the strength of air convergence and the movement of enhanced convective areas, and were quite variable. (3) Differences in the latitudinal CO2 gradient from northern low latitudes to southern low latitudes were found between each spring cruise. Comparison with climatological data suggests that the difference in the CO2 gradient is related to variation in the anomaly of meridional wind component distribution over the central and western Pacific at low latitudes.
Coupled evolution of BrOx‐ClOx‐HOx‐NOx chemistry during bromine‐catalyzed ozone depletion events in the arctic boundary layer
Authors: Evans M. J. , Jacob D. J. , Atlas E. , Cantrell C. A. , Eisele F. , Flocke F. , Fried A. , Mauldin R. L. , Ridley B. A. , Wert B. , Talbot R. , Blake D. , Heikes B. , Snow J. , Walega J. , Weinheimer A. J. , Dibb J.
Published: May 2003

Extensive chemical characterization of ozone (O3) depletion events in the Arctic boundary layer during the TOPSE aircraft mission in March–May 2000 enables analysis of the coupled chemical evolution of bromine (BrOx), chlorine (ClOx), hydrogen oxide (HOx) and nitrogen oxide (NOx) radicals during these events. We project the TOPSE observations onto an O3 chemical coordinate to construct a chronology of radical chemistry during O3 depletion events, and we compare this chronology to results from a photochemical model simulation. Comparison of observed trends in ethyne (oxidized by Br) and ethane (oxidized by Cl) indicates that ClOx chemistry is only active during the early stage of O3 depletion (O3 > 10 ppbv). We attribute this result to the suppression of BrCl regeneration as O3 decreases. Formaldehyde and peroxy radical concentrations decline by factors of 4 and 2 respectively during O3 depletion and we explain both trends on the basis of the reaction of CH2O with Br. Observed NOx concentrations decline abruptly in the early stages of O3 depletion and recover as O3 drops below 10 ppbv. We attribute the initial decline to BrNO3 hydrolysis in aerosol, and the subsequent recovery to suppression of BrNO3 formation as O3 drops. Under halogen‐free conditions we find that HNO4 heterogeneous chemistry could provide a major NOx sink not included in standard models. Halogen radical chemistry in the model can produce under realistic conditions an oscillatory system with a period of 3 days, which we believe is the fastest oscillation ever reported for a chemical system in the atmosphere.
A novel approach to the polarization correction of spaceborne spectrometers
Authors: Schutgens N. A. J. , Stammes P.
Published: May 2003

We present a new polarization correction algorithm for polarization sensitive spaceborne spectrometers like Global Ozone Monitoring Experiment (GOME) or Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY). These instruments measure polarization with less spectral resolution than the radiance. As a consequence, the current GOME polarization correction algorithm allows radiance errors of 10% in the UV and 3% in the visible (VIS) and near‐IR. Using simulated spectra, we show that the continuum Stokes elements Q and U over a large wavelength range (300 to 800 nm) can be reliably retrieved from only a limited set of measurements (three to five). The interpolation to other wavelengths is made using numerically calculated polarization spectra. These polarization spectra can be calculated for Rayleigh scattering atmospheres, but we show that the retrieval is just as effective for cloudy and aerosol scenes as for clear scenes. For GOME the remaining radiance errors are less than 3% (UV) and 1% (VIS, near‐IR), and often smaller than 0.5%. The lack of actual UV (300–330 nm) polarization measurements prevents further reduction of the radiance errors. We also show how the ozone Huggins absorption band may be accounted for through a parameterization and a single polarization broadband measurement and that strong but narrow absorption bands like the O2A band maybe ignored without detrimental effect on the algorithm.
Fine‐scale study of a thick stratospheric ozone lamina at the edge of the southern subtropical barrier
Authors: Portafaix Thierry , Morel Béatrice , Bencherif Hassan , Baldy Serge , Godin‐Beekmann Sophie , Hauchecorne Alain
Published: May 2003

A large‐scale transport event resulting in a thick ozone lamina originating from midlatitudes is observed in the tropical stratosphere over Reunion island (55°E, 21°S). This isentropic transport was detected from stratospheric balloon‐borne ozone measurements that showed the occurrence of the lamina and was investigated using different tools based on Ertel's potential vorticity (Epv) analyses. An original software (DYBAL) using surface coordinate and the equivalent length of Epv contours as diagnostic tools in conjunction with high‐resolution outputs from an Epv advection model MIMOSA allows us to specify the origin of the lamina. The results indicate that a broad layer of stratospheric air was isentropically advected from midlatitudes across the southern edge of tropical reservoir and reached Reunion island on 12 July 2000. In addition, Eliassen‐Palm's flux vectors, calculated from ECMWF analysis, show that planetary wave activity was quite large during that time period, with wave‐breaking occurring around 30 km, and could have driven that exchange. In contrast with analyses of filamentation events based on model and satellite data, the present study focuses on a fine‐scale vertical survey from in situ measurements. The filament reported in this paper is characterized by a large vertical extension and is located around the maximum of ozone concentration in the tropical stratosphere (600 K). The analysis of such events, poorly documented in the tropics, could complement satellite studies and contribute to a better determination of the transport between the tropics and the midlatitudes.
Tropospheric aerosol impacts on trace gas budgets through photolysis
Authors: Bian Huisheng , Prather Michael J. , Takemura Toshihiko
Published: May 2003

Aerosols affect the global budgets of O3, OH, and CH4 in part through their alteration of photolysis rates and in part through their direct chemical interactions with gases (i.e., “heterogeneous chemistry”). The first effect is evaluated here with a global tropospheric chemistry transport model using recently developed global climatologies of tropospheric aerosols: a satellite‐derived aerosol climatology over the oceans by advanced very high resolution radiometer and a model‐generated climatology for land plus oceans by the Center for Climate System Research. Globally averaged, the impact of aerosols on photolysis alone is to increase tropospheric O3 by 0.63 Dobson units and increase tropospheric CH4 by 130 ppb (via tropospheric OH decreases of 8%). These greenhouse gas increases lead to an aerosol indirect effect (counting both natural and anthropogenic aerosols) of +0.08 W/m2. Although the CH4 increases are, of course, global, the changes in tropospheric OH and O3 are mainly regional, with the largest impacts in northwest Africa for January and in India and southern Africa for July. The influence of aerosols is greater in July than in January and greater in the Northern Hemisphere than in the Southern Hemisphere, as expected given the pollution sources in the Northern Hemisphere. The predominant impact is due to the aerosols over land; aerosols over the ocean contribute less than a third to globally integrated changes.
Modeling the plasma response to small‐scale aerosol particle perturbations in the mesopause region
Authors: Lie‐Svendsen Ø. , Blix T. A. , Hoppe U.‐P. , Thrane E. V.
Published: May 2003

We have developed a numerical model that solves the time‐dependent, one‐dimensional, coupled continuity and momentum equations for an arbitrary number of charged and neutral particle species. The model includes production and loss of particles due to ionization, recombination, and attachment of ions and electrons by heavy aerosol particles, and transport due to gravity and multipolar diffusion. The model is used to study the response of the mesopause plasma to small‐scale, aerosol particle density perturbations. We find that for aerosol structures on the order of a few meters, electron attachment and ambipolar diffusion are the dominant processes, leading to small‐scale electron perturbations that can cause polar mesosphere summer echoes (PMSEs). Moreover, for small aerosol particles, with radii on the order of 10 nm or less, ambipolar diffusion leads to an anticorrelation between electron and ion densities, which is in agreement with most rocket observations. These small‐scale structures persist as long as the aerosol layer persists, which will be limited by aerosol particle diffusion. For 10‐nm particles, this diffusive lifetime will be on the order of hours. The few instances where rocket observations find instead a correlation between electron and ion densities can be explained either by the aerosol particles becoming large, on the order of 50 nm or more, in which case ion attachment becomes important, or by rapid evaporation of aerosol particles. In the latter case, evaporation must be sufficiently fast to overcome ambipolar diffusion.
North Pacific–North Atlantic relationships under stratospheric control?
Authors: Castanheira J. M. , Graf H.‐F.
Published: May 2003

Based on a linear regression/correlation analysis of monthly mean atmospheric sea level pressure (SLP) data from the National Centers for Environmental Prediction (NCEP) reanalysis (1948–2000), we find a significant anticorrelation between pressure in the northern North Atlantic and North Pacific only if the stratospheric circulation is in the “strong polar vortex” regime but not when the vortex is weak. Since some general circulation models (GCMs) (e.g., European Center/Hamburg (ECHAM4)) are biased toward the strong vortex regime (SVR), they tend to reproduce this anticorrelation already in the mean. The pattern of the “Arctic Oscillation” (AO) is shown to be consistent with the mean surface pressure differences between the two stratospheric regimes. The typical SW‐NE tilt of the node line of the North Atlantic Oscillation (NAO) found with linear analyses (i.e., with such that do not take the regime character of the stratospheric circulation into account) in Northern Hemisphere winter is due to a superposition of correlation patterns based on physical processes working in the troposphere (a strictly meridional dipole and the pattern resulting from planetary wave refraction in the strong vortex regime) and those produced by the rapid transition from one stratospheric regime to the other with subsequent downward propagation of the signal. This result underlines the necessity of the application of nonlinear statistics or the restriction of linear statistics to variations in the stable (quasi‐linear) environment of natural regimes.
Ozone absorption around 10 μm
Authors: Flaud J. M. , Wagner G. , Birk M. , Camy‐Peyret C. , Claveau C. , De Backer‐Barilly M. R. , Barbe A. , Piccolo C.
Published: May 2003

A careful comparison of four sets of ozone line intensities measured independently in the 10 μm region has been achieved. It is demonstrated that three of the experimental sets agree to better than 2% whereas the last one is consistently 4.4% higher. This is also the case for the ozone line intensities given in the HITRAN database, which are about 4% higher than the values given in the three experimental sets in agreement. New and more accurate transition moment constants for the ν1 and ν3 bands of 16O3 were derived and used to generate new line positions and intensities. These new spectroscopic parameters allow one to simulate atmospheric spectra recorded by the Atmospheric Trace Molecule Spectroscopy Experiment better than the existing HITRAN spectroscopic parameters, showing that on a relative basis the new spectral parameters are of better quality.
Measurement of the timescale of hygroscopic growth for atmospheric aerosols
Authors: Chuang Patrick Y.
Published: May 2003

The rate of condensational growth is relevant to a variety of atmospheric processes, in particular the activation of cloud condensation nuclei to form cloud droplets. It has been hypothesized that the presence of organic films on the surface of aerosols can strongly inhibit condensational growth, but few relevant observations of atmospheric aerosol growth rates appear to have been previously reported. A brief review of the literature on the effects of films on the mass transfer of water is presented. A novel experiment based on tandem differential mobility analysis for the measurement of the timescale for condensational growth (τg) for ambient aerosols is introduced. Measurements were taken during the wet season (25–27 September 2000) and dry season (16–17 November 2000) in Mexico City for particles with diameters of 50 and 100 nm. The results show that most of the particles exhibit τg < 2 to 3 s. However, a small number (between 0 and 2.0% depending on particle size and season) do exhibit timescales larger than this. The accommodation coefficient of this minority of particles is estimated to be approximately in the range of 1 to 4 × 10−5, which is in the lowest range of observed values for laboratory aerosols. The observations show a strong dependence of the occurrence of such particles on season and time of day. It is hypothesized that these measurements suggest that an even larger concentration of particles exhibiting accommodation coefficients in the range of 10−5 to 10−4 may exist. The existence of such particles would be important to the indirect effect of aerosols on climate.
Aerosol formation via aqueous‐phase chemical reactions
Authors: Anttila Tatu , Kerminen Veli‐Matti
Published: May 2003

A theoretical study investigating the growth of nano‐size particles via aqueous‐phase chemical reactions was carried out. These reactions were assumed to involve semivolatile, water‐soluble organic compounds and lead to the production of nonvolatile compounds that stay in particles, thereby making them grow effectively. By using a mathematical framework developed earlier, quantitative estimates for the conditions under which the considered mechanism is able to induce a significant particle growth were derived. In addition to the reaction rate itself, important parameters in this respect were the gas/particle‐partitioning coefficient of a reacting semivolatile compound, its gas‐phase concentration, and mass accommodation coefficient, as well as the particle diameter and chemical composition. For particles <10 nm in diameter, the Kelvin effect supresses effectively the growth via condensation of semivolatile compounds that subsequently react in the particle aqueous phase. Therefore other heterogeneous mechanisms might be more viable for the rapid growth of such small particles; for example, they might involve chemical reactions that take place in the gas‐liquid interface. The derived estimates were presented in a form where they can be directly applied to interpret experimental data. As an example of this, results of a recent laboratory study investigating the formation of organic compounds in the aerosol aqueous phase were analyzed.
Ozone profile differences between Europe and New Zealand: Effects on surface UV irradiance and its estimation from satellite sensors
Authors: McKenzie Richard , Smale Dan , Bodeker Greg , Claude Hans
Published: May 2003

Substantial differences in summertime surface UV irradiance between New Zealand and Europe have been reported previously. The main contributors to these differences are differences in total column ozone, differences in Sun‐Earth separation between the Southern Hemisphere summer (December/January) and the Northern Hemisphere summer (June/July), and differences in tropospheric pollution. Differences due to higher Northern Hemisphere aerosol extinction have been well documented. Here we present a climatology of ozone profiles measured by balloon‐borne sensors launched from Lauder, New Zealand, and from Hohenpeissenberg, Germany, to show that there are also substantial differences in the shapes of ozone profiles, especially during the summer months. A radiative transfer model is then used to investigate the extent to which these profile shape differences contribute to observed UV differences. It is found that the differences in the vertical distribution of ozone amplify existing Northern and Southern Hemisphere differences in UV. Effects can be significant in the UV‐B region, but the sign of the effect depends on the solar zenith angle. Consequently, the effect on daily doses of biologically harmful UV radiation is suppressed somewhat, and the differences are responsible for differences in erythemally weighted UV of only a percent or two, which is small compared with other effects. While these effects are relatively small, differences in the vertical profile of ozone can affect the accuracy of satellite retrievals of total column ozone. This analysis shows that the lower tropospheric ozone amounts at Lauder may lead to underestimations of summertime UV from satellite by ∼4% at that site.
Satellite observations of daytime and nighttime ozone in the mesosphere and lower thermosphere
Authors: Kaufmann M. , Gusev O. A. , Grossmann K. U. , Martín‐Torres F. J. , Marsh D. R. , Kutepov A. A.
Published: May 2003

The global distribution of mesospheric and lower thermospheric ozone 9.6 μm infrared emissions was measured by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment during two Space Shuttle missions in November 1994 and August 1997. The radiances measured by CRISTA have been inverted to O3 number densities in the 50–95 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved O3 number densities has been carried out. The ozone abundance profiles show volume mixing ratios of 1–2 ppmv at the stratopause, 0.5 ppmv or less around 80 km, and typically 1 ppmv during daytime and 10 ppmv during nighttime at the secondary maximum. The agreement with other experiments is typically better than 25%. The global distribution of upper mesospheric ozone shows significant latitudinal gradients and an enhancement in the equatorial upper mesosphere. At the polar night terminator a third ozone maximum is observed. Three‐dimensional model results indicate that the latitudinal gradients are significantly influenced by solar tides.
Consistency of MODIS surface bidirectional reflectance distribution function and albedo retrievals: 1. Algorithm performance
Authors: Jin Yufang , Schaaf Crystal B. , Gao Feng , Li Xiaowen , Strahler Alan H. , Lucht Wolfgang , Liang Shunlin
Published: May 2003

The first consistent year (November 2000 to November 2001) of global albedo product was produced at 1‐km resolution every 16 days from the observations of the Moderate‐Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA's Terra spacecraft. We evaluated the quality of the operational albedo retrievals in two ways: (1) by examining the algorithm performance using the product quality assurance (QA) fields (this paper) and (2) by comparing retrieved albedos with those observed at ground stations and by other satellite instruments (in a companion paper). The internal diagnostics of the retrieval algorithm adequately reflect the goodness of the model fit and the random noise amplification in the retrieved albedo. Global QA statistics show that the RossThick‐LiSparse‐Reciprocal model fits the atmospherically corrected surface reflectances very well, and the random noise amplification factors for white sky albedo and reflectance are generally less than 1.0. Cloud obscuration is the main reason for the activation of the backup magnitude retrieval algorithm. Over the 60°S to 60°N latitude band, 50% of the land pixels acquire more than six clear looks during 14–29 September 2001, and only 5% of these pixels are inverted with the backup algorithm. The latitude dependence and temporal distribution of the QA fields further demonstrate that the retrieval status mainly follows the pattern of angular sampling determined by cloud climatology and the instrument/orbit characteristics. A case study over the west coast of the United States shows that white sky shortwave albedos retrieved from magnitude inversions agree on average with those from full inversions to within 0.033 in reflectance units and have a slightly lower bias ranging from 0.014 to 0.023. We also explored the effect of residual cloud and aerosol contamination in the atmospherically corrected surface reflectance inputs in another case study over southern Africa. The quality assurance procedure of the operational MODIS bidirectional reflectance distribution function and albedo algorithm compensates for some of these residual effects and improves the albedo retrieval results by an order of 0.005 (10%) in the visible for more than 12% of pixels.
Consistency of MODIS surface bidirectional reflectance distribution function and albedo retrievals: 2. Validation
Authors: Jin Yufang , Schaaf Crystal B. , Woodcock Curtis E. , Gao Feng , Li Xiaowen , Strahler Alan H. , Lucht Wolfgang , Liang Shunlin
Published: May 2003

The evaluation of the first available satellite‐based global albedo product at 1‐km resolution is essential for its application in climate studies. We evaluate the accuracy of the Moderate‐Resolution Imaging Spectroradiometer (MODIS) albedo product using available field measurements at Surface Radiation Budget Network (SURFRAD) and Cloud and Radiation Testbed–Southern Great Plains (CART/SGP) stations and examine the consistency between the MODIS surface albedos and the Clouds and Earth's Radiant Energy System (CERES) top‐of‐the‐atmosphere albedos as well as historical global albedos from advanced very high resolution radiometer (AVHRR) and Earth Radiation Budget Experiment (ERBE) observations. A comparison with the field measurements shows that the MODIS surface albedo generally meets an absolute accuracy requirement of 0.02 for our study sites during April–September 2001, with the root mean square errors less than 0.018. Larger differences appear in the winter season probably due to the increased heterogeneity of surface reflectivity in the presence of snow. To examine the effect of spatial heterogeneity on the validation of the MODIS albedos using fine resolution field measurements, we derive an intermediate albedo product from four Landsat Enhanced Thematic Mapper Plus (ETM+) images at 30‐m spatial resolution as a surrogate for the distributed field measurements. The surface albedo is relatively homogeneous over the study stations in growing seasons, and therefore the validation during April–September is supported. A case study over three SURFRAD stations reveals that the MODIS bidirectional reflectance distribution function model is able to capture the solar zenith angle dependence of surface albedo as shown by the field measurements. We also find that the MODIS surface shortwave albedo is consistent with the contemporary and collocated CERES top‐of atmosphere albedos derived directly from broadband observations. The MODIS albedo is also well correlated with historical surface albedos derived from AVHRR and ERBE observations, and a high bias of 0.016 and a low bias of 0.034 compared to those of the latter albedos are reasonable considering the differences in instruments and retrieval algorithms as well as environmental changes.
Results from the first ARM diffuse horizontal shortwave irradiance comparison
Authors: Michalsky J. J. , Dolce R. , Dutton E. G. , Haeffelin M. , Major G. , Schlemmer J. A. , Slater D. W. , Hickey J. R. , Jeffries W. Q. , Los A. , Mathias D. , McArthur L. J. B. , Philipona R. , Reda I. , Stoffel T.
Published: May 2003

The first intensive observation period (IOP) dedicated exclusively to the measurement of diffuse horizontal shortwave irradiance was held in the Fall 2001 at the central facility of the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site with the cooperation of the Baseline Surface Radiation Network (BSRN) community. The purpose of the study was to compare diffuse irradiance measurements among most commercial pyranometers and a few prototypes calibrated independently using current practices. The hope was to achieve a consensus for this measurement with the goal of improving the uncertainty of shortwave diffuse irradiance measurements. All diffuse broadband measurements were made using the same type of two‐axis tracker with the direct beam blocked by shading balls. Tracking was excellent during the IOP with no lost data associated with tracker problems. Fourteen simultaneous measurements were obtained over a two‐week period under mostly clear skies with low to moderate aerosol loading. Totally overcast data were obtained during the morning of one day. Five of the measurements are reproducible to about 2 W/m2 at the 95% confidence level. Three more agree with the mean of these five to about 4 W/m2 at the 95% confidence level after correction for thermal offsets.
In situ observations of ClO near the winter polar tropopause
Authors: Thornton Brett F. , Toohey Darin W. , Avallone Linnea M. , Harder Hartwig , Martinez Monica , Simpas James B. , Brune William H. , Avery Melody A.
Published: May 2003

Significant abundances of chlorine oxide (ClO) were observed throughout the lowermost stratosphere at high latitudes during winter from the NASA DC‐8 aircraft during the SAGE III—Ozone Loss and Validation Experiment and Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) campaign. Mixing ratios of ClO averaging 15–20 parts per trillion by volume (pptv) were observed near the tropopause, a region where ClO abundances are usually only a pptv or less at lower latitudes. The ratio of ClO to inferred inorganic chlorine ([ClO]/[Cly]) was found to be largest (∼7%) in air characterized by low abundances of ozone (∼100–250 parts per billion by volume (ppbv)). This was the region where cirrus clouds were also observed occasionally during the measurement period, although abundances of ClO directly within cirrus clouds were not significantly different than background abundances. Nonzero instrument signals during darkness are attributed to detection of ∼5–15 pptv of OClO. BrO mixing ratios between 2 and 4 pptv are sufficient to produce these amounts of OClO, assuming daytime mixing ratios of ClO between 15 and 20 pptv. At these levels of ClO and BrO, approximately 10% of the ozone at these altitudes is chemically destroyed per month in springtime by reactions of ClO and BrO, representing an effective loss process for ozone near the high‐latitude tropopause.
Survey of whole air data from the second airborne Biomass Burning and Lightning Experiment using principal component analysis
Authors: Choi Yunsoo , Elliott Scott , Simpson Isobel J. , Blake Donald R. , Colman Jonah J. , Dubey Manvendra K. , Meinardi Simone , Rowland F. Sherwood , Shirai Tomoko , Smith Felisa A.
Published: May 2003

Hydrocarbon and halocarbon measurements collected during the second airborne Biomass Burning and Lightning Experiment (BIBLE‐B) were subjected to a principal component analysis (PCA), to test the capability for identifying intercorrelated compounds within a large whole air data set. The BIBLE expeditions have sought to quantify and understand the products of burning, electrical discharge, and general atmospheric chemical processes during flights arrayed along the western edge of the Pacific. Principal component analysis was found to offer a compact method for identifying the major modes of composition encountered in the regional whole air data set. Transecting the continental monsoon, urban and industrial tracers (e.g., combustion byproducts, chlorinated methanes and ethanes, xylenes, and longer chain alkanes) dominated the observed variability. Pentane enhancements reflected vehicular emissions. In general, ethyl and propyl nitrate groupings indicated oxidation under nitrogen oxide (NOx) rich conditions and hence city or lightning influences. Over the tropical ocean, methyl nitrate grouped with brominated compounds and sometimes with dimethyl sulfide and methyl iodide. Biomass burning signatures were observed during flights over the Australian continent. Strong indications of wetland anaerobics (methane) or liquefied petroleum gas leakage (propane) were conspicuous by their absence. When all flights were considered together, sources attributable to human activity emerged as the most important. We suggest that factor reductions in general and PCA in particular may soon play a vital role in the analysis of regional whole air data sets, as a complement to more familiar methods.
In situ measurements of bromine oxide at two high‐latitude boundary layer sites: Implications of variability
Authors: Avallone Linnea M. , Toohey Darin W. , Fortin Tara J. , McKinney Karena A. , Fuentes Jose D.
Published: May 2003

Bromine oxide (BrO) was measured in situ during the Arctic Tropospheric Ozone Chemistry (ARCTOC) '96 campaign in Ny Ålesund, Spitsbergen (April–May 1996), and during the Alert 2000 Polar Sunrise Experiment in Alert, Nunavut, Canada (April–May 2000). Measurements were made in near‐surface air during low‐ozone events in early May at both sites. The average of the in situ concentrations of BrO at Ny Ålesund is consistent with the path average of near‐simultaneous long‐path differential optical absorption spectroscopy measurements, but there is considerable scatter in a point‐by‐point comparison. The differences between these observations are consistent with a strong surface influence on reactive bromine. We see similar variability of the in situ measurements at Alert, which reflects the real variability of both surface sources and sinks. The fluctuations of BrO abundances are used to assess the expected loss rates and associated lifetimes of ozone during depletion events. We show that ozone loss will be underpredicted by any temporal or spatial average of BrO.
Effects of absorbing aerosols on the determination of the surface solar radiation
Authors: Feng Jian , Leighton Henry G.
Published: May 2003

Coincident and collocated measurements of solar radiation from the Scanner for Radiation Budget (ScaRaB) on Meteor‐3 and from towers in a boreal forest region during the Boreal Ecosystems and Atmosphere Study (BOREAS) period are used to evaluate an algorithm of Li et al. [1993a] which was developed to derive the net surface solar radiation flux from satellite measurements. The analysis shows that after correcting for mismatching between the footprints of the tower measurements and the satellite pixels, there is a substantial bias that is due to the presence of absorbing aerosols. Application of the aerosol correction term of Masuda et al. [1995] reduces the mean bias to about 5 W m−2. Cloud radiation forcing ratio R has been used in many studies to address the issue of a cloud absorption anomaly. Three methods, each with a different approach to the consideration of the effect on radiative fluxes by absorbing aerosols, are used to calculate R. Methods that account inadequately for aerosol effects when applied to the coincident and collocated tower and satellite measurements give large values of R (1.28–1.42) under conditions of heavy aerosol loading, which could be interpreted as an indication of a cloud absorption anomaly. However, application of the method that accounts best for aerosol effects gives values of R within the range 1.08∼1.18 and so does not support the idea of anomalous cloud absorption.
On the nature of PMSE: Electron diffusion in the vicinity of charged particles revisited
Authors: Rapp Markus , Lübken Franz‐Josef
Published: May 2003

Triggered by recent experimental evidence showing that some parts of the Cho et al. [1992] theory describing electron diffusion in the vicinity of charged aerosol particles cannot be correct, we reconsider the process of electron diffusion under the conditions of the polar summer mesopause region. The key idea is that perturbations in the distribution of charged aerosol particles created for example by neutral air turbulence almost immediately lead to (anticorrelated) perturbations in the electron number density due to simple charge neutrality and zero net current arguments. We obtain analytical solutions of the coupled diffusion equations for electrons, charged aerosol particles, and positive ions subject to the initial condition of anticorrelated perturbations in the charged aerosol and electron distribution. The main signatures of these solutions are in line with available in situ evidence of small‐scale plasma structures in the vicinity of polar mesosphere summer echoes (PMSE), i.e., electron perturbations are anticorrelated to both perturbations in the distributions of negatively charged aerosol particles and positive ions. The lifetime of these perturbations is proportional to the square of the aerosol particle radius such that the presence of particles with radii larger than ∼10 nm allows for the existence of electron number density perturbations up to several hours after the initial creation mechanism has stopped. These results are almost independent of the ratio between the aerosol charge number density and the number density of free electrons. These electron perturbations potentially give rise to a radar reflectivity comparable to values observed with 50 MHz VHF radars. Our model results can readily explain why in situ measurements of neutral air turbulence have repeatedly shown active turbulence only in the upper part of the PMSE layer whereas turbulence was basically absent in the lower part. Furthermore, our model concept qualitatively yields the correct altitude profile of the mean PMSE occurrence frequency based on the measured altitude profile of the turbulence occurrence frequency.
A monodisperse aerosol dynamics module, a promising candidate for use in long‐range transport models: Box model tests
Authors: Pirjola L. , Tsyro S. , Tarrason L. , Kulmala M.
Published: May 2003

Air quality models used as a scientific basis for air pollution strategy development need physically sound and computationally efficient schemes to describe aerosol formation, interaction, and evolution. In this work, we present and evaluate an aerosol dynamics module MONO32, which is designed for use in regional air pollution models. The module presents aerosol size distribution with four monodisperse modes and characterizes aerosol chemical composition with seven components, so 32 prognostic equations are needed to describe particle mass and number concentration. MONO32 accounts for nucleation, condensation, and coagulation processes. Two different time integration schemes, a FORTRAN NAG‐library routine and a two‐step scheme, were tested. Both integration methods showed the same accuracy in calculating particle number and size evolution, while the two‐step scheme was computationally much more efficient. A mode‐merging method was implemented in MONO32 to account for the transfer of aerosol mass and number to a larger mode as particles grow by condensation and coagulation. MONO32 compared reasonably well with the sectional model AEROFOR2 with 54 sections; for example, difference in the total number concentration after 24‐hour simulation was less than 15–25%. MONO32 was also verified against measurements available from the Biogenic Aerosol Formation in the Boreal Forest 3 (BIOFOR3) campaign. Two typical nucleation episodes were chosen for testing, and by using the nucleation rate and the condensable vapor source rate calculated from the measurements, MONO32 was able to predict the evolution of the total number concentration and the growth rate of the nucleation mode quantitatively in good agreement with the observations. Deviations in the resulting nucleation mode diameter were 11–16%. However, the results appeared to be quite sensitive to the hygroscopic properties of the condensable organic vapor. MONO32 showed an acceptable accuracy for long‐range transport modeling in describing aerosol dynamics while being computationally efficient. Therefore it is recommended for implementation and further testing in the regional three‐dimensional Eulerian model.
A model study of the effects of climatic precipitation changes on ground temperatures
Authors: Lin Xiaohua , Smerdon Jason E. , England Anthony W. , Pollack Henry N.
Published: May 2003

Temperature changes at the Earth surface propagate into the subsurface and leave a thermal signature in the underlying soil and rock. Inversions of subsurface temperature measurements yield reconstructions of ground surface temperature (GST) histories that provide estimates of climatic changes. A question remaining in the interpretation of reconstructed GST histories is the extent to which GST changes reflect changes principally in surface air temperature (SAT), or whether other factors may be significant. Here we use a Land Surface Processes (LSP) model to examine the influence of precipitation changes on GST and subsurface temperature and moisture fields on annual to decadal timescales. We model soil and vegetation conditions representative of a prairie region in the southern Great Plains of North America and force the model with meteorological data synthesized from a typical year in the region. Model responses are observed after changes in the amount of daily precipitation, the intensity and frequency of daily precipitation, and the diurnal and seasonal timing of precipitation. We show that: (1) increasing daily precipitation cools mean annual GST, (2) increasing the intensity and reducing the frequency of daily precipitation, while holding the annual amount of precipitation constant, cools mean annual GST, and (3) shifting maximum precipitation to occur in the warmest months cools mean annual GST. We compare modeled results to observed precipitation changes during the 20th century and conclude that the observed precipitation changes would cause only small changes to GST within the modeled region, on the order of 0.1 K or less.
On the detection of water vapor profiles and thin moisture layers from atmospheric radio occultations
Authors: de la Torre Juárez M. , Nilsson M.
Published: May 2003

GPS radio occultations provide high‐resolution vertical profiles of the atmospheric refraction index that can be used to extract vertical profiles of tropospheric moisture content. A physical method to extract water abundances from refraction index profiles without using ancillary data or model input is described. The ability to capture sharp water structures in the upper troposphere is illustrated by comparisons with current approaches, individual radiosonde measurements, and statistics against global circulation analyses from the National Centers for Environmental Prediction and European Centre for Medium‐Range Weather Forecasts. It is shown that thin layers of significant moisture variability can be detected and that atmospheric water profiles can be retrieved even in cases where the ancillary data are not optimal.
Comparison between active sensor and radiosonde cloud boundaries over the ARM Southern Great Plains site
Authors: Naud Catherine M. , Muller Jan‐Peter , Clothiaux Eugene E.
Published: May 2003

In order to test the strengths and limitations of cloud boundary retrievals from radiosonde profiles, 4 years of radar, lidar, and ceilometer data collected at the Atmospheric Radiation Measurements Southern Great Plains site from November 1996 through October 2000 are used to assess the retrievals of Wang and Rossow [1995] and Chernykh and Eskridge [1996]. The lidar and ceilometer data yield lowest‐level cloud base heights that are, on average, within approximately 125 m of each other when both systems detect a cloud. These quantities are used to assess the accuracy of coincident cloud base heights obtained from radar and the two radiosonde‐based methods applied to 200 m resolution profiles obtained at the same site. The lidar/ceilometer and radar cloud base heights agree by 0.156 ± 0.423 km for 85.27% of the observations, while the agreement between the lidar/ceilometer and radiosonde‐derived heights is at best −0.044 ± 0.559 km for 74.60% of all cases. Agreement between radar‐ and radiosonde‐derived cloud boundaries is better for cloud base height than for cloud top height, being at best 0.018 ± 0.641 km for 70.91% of the cloud base heights and 0.348 ± 0.729 km for 68.27% of the cloud top heights. The disagreements between radar‐ and radiosonde‐derived boundaries are mainly caused by broken cloud situations when it is difficult to verify that drifting radiosondes and fixed active sensors are observing the same clouds. In the case of the radar the presence of clutter (e.g., vegetal particles or insects) can affect the measurements from the surface up to approximately 3–5 km, preventing comparisons with radiosonde‐derived boundaries. Overall, Wang and Rossow [1995] tend to classify moist layers that are not clouds as clouds and both radiosonde techniques report high cloud top heights that are higher than the corresponding heights from radar.
A model for studies of tropospheric ozone and nonmethane hydrocarbons: Model description and ozone results
Authors: von Kuhlmann Rolf , Lawrence Mark G. , Crutzen Paul J. , Rasch Philip J.
Published: May 2003

We have developed a global three‐dimensional chemistry‐meteorology model for studies of ozone and hydrocarbons in the troposphere, called Model of Atmospheric Transport and Chemistry‐Max‐Planck‐Institute for Chemistry Version (MATCH‐MPIC). The model currently calculates the distributions of 54 species and 141 reactions using a new flexible chemical integration method in connection with a fast general Rosenbrock solver. The reactions can be easily expanded for future studies with the model. The model includes updated emission inventories, an explicit dry deposition scheme, online photolysis rates, extensive budgeting capabilities and a correction for the so‐called “mass‐wind inconsistency” problem. One‐year simulations at two different horizontal resolutions, approximately 1.9° × 1.9° (T63) and 5.6° × 5.6° (T21), both with 28 vertical levels, are extensively evaluated with available observations from surface stations, ozonesondes, and field campaigns. The model is generally able to reproduce the observations of ozone to within 10 nmol/mol, but it overestimates upper tropospheric ozone at northern high‐latitude stations in winter and spring and tends to underestimate the summer maximum in the free troposphere. In the tropics the chemical tropopause is sometimes too low. Generally, the low‐resolution run yields only slightly worse agreement with observations compared to the higher‐resolution run, thus making it suitable for further sensitivity studies. In a simulation using different meteorological data, O3 agrees much better with observations in the upper troposphere, possibly because of the higher resolution near the tropopause. The net ozone production integrated over all tropospheric regions with a net production and loss separately reveals that the calculated chemically induced redistribution of ozone in the troposphere is 2–3 times larger than the net stratospheric influx. Even in the upper troposphere, photochemical production is of similar magnitude to the stratospheric influence.
Two‐day wave observations of UARS Microwave Limb Sounder mesospheric water vapor and temperature
Authors: Limpasuvan Varavut , Wu Dong L.
Published: May 2003

A two‐day wave disturbance is observed in the mesospheric temperature and water vapor on the basis of new version data from the Upper Atmosphere Research Satellite Microwave Limb Sounder. Using two data segments during the austral summers (January–February of 1992 and 1993) and the asynoptic mapping method, a strong wave signal is identified as having zonal wave number 3 and a westward period of about 2.1 days. The wave amplitudes are located near the core of the summer easterly jet with strongest wave amplitudes (as large as 11 K and 0.35 part per million by volume) near the mesopause. The temperature and water vapor wave strengths are highly correlated in time, but their peaks are almost longitudinally out of phase. Poleward heat flux associated with upward wave energy propagation in the Southern Hemisphere points to baroclinic instability as the cause for the wave appearance. A growing wave signature in water vapor is observed in regions of strong meridional gradient of water vapor. Near the mesopause, wave breaking is suggested as moist polar air is displaced into the much drier subtropics and wave amplitude decays.
Simultaneous spectral albedo measurements near the Atmospheric Radiation Measurement Southern Great Plains (ARM SGP) central facility
Authors: Michalsky J. , Min Q. , Barnard J. , Marchand R. , Pilewskie P.
Published: May 2003

During the second Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE II), measurements were obtained during low‐altitude passes of the Twin Otter aircraft directly over the central facility of the ARM Southern Great Plains (SGP) site. One set of measurements taken from this platform was the spectral irradiance pointing in the nadir and in the zenith with moderate spectral resolution from about 350 to 1670 nm using the NASA Ames solar spectral flux radiometer (SSFR). Routine measurements are made at the central facility (CF) of the ARM SGP site using two multifilter radiometer (MFR) heads with six narrowband filters covering portions of the spectrum between 415 and 940 nm. One measures upwelling spectral irradiance above an ungrazed pasture, and the other measures that above a wheat field. In addition, on one of the cloudy days during ARESE II (3 March 2000), measurements were made with a hand‐held, commercial spectrometer above wheat, pasture, and dry corn stalks in and around the CF site between the wavelengths of 350 and 2340 nm. A needed input to radiation modeling at the top of the atmosphere and at the surface is the effective spectral surface albedo. In the calculation of downwelling radiation at the surface it is important to correctly specify surface albedo in overcast and clear conditions. This paper will examine the level of agreement among different spectral albedo measurements. The effect of the differences on calculated downwelling surface irradiance will be analyzed for thin and heavy overcast. Finally, the importance of spectral albedo versus a single‐valued broadband albedo on modeled, clear‐sky diffuse irradiance is demonstrated.