bluuebunny/crossref_metadata_2025 huggingface dataset:
Emissions of trace gases and particles from savanna fires in southern Africa
Authors: Sinha Parikhit , Hobbs Peter V. , Yokelson Robert J. , Bertschi Isaac T. , Blake Donald R. , Simpson Isobel J. , Gao Song , Kirchstetter Thomas W. , Novakov Tica
Published: May 2003

Airborne measurements made on initial smoke from 10 savanna fires in southern Africa provide quantitative data on emissions of 50 gaseous and particulate species, including carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, methane, ammonia, dimethyl sulfide, nonmethane organic compounds, halocarbons, gaseous organic acids, aerosol ionic components, carbonaceous aerosols, and condensation nuclei (CN). Measurements of several of the gaseous species by gas chromatography and Fourier transform infrared spectroscopy are compared. Emission ratios and emission factors are given for eight species that have not been reported previously for biomass burning of savanna in southern Africa (namely, dimethyl sulfide, methyl nitrate, five hydrocarbons, and particles with diameters from 0.1 to 3 μm). The emission factor that we measured for ammonia is lower by a factor of 4, and the emission factors for formaldehyde, hydrogen cyanide, and CN are greater by factors of about 3, 20, and 3–15, respectively, than previously reported values. The new emission factors are used to estimate annual emissions of these species from savanna fires in Africa and worldwide.
Measurements of biomass burning influences in the troposphere over southeast Australia during the SAFARI 2000 dry season campaign
Authors: Pak B. C. , Langenfelds R. L. , Young S. A. , Francey R. J. , Meyer C. P. , Kivlighon L. M. , Cooper L. N. , Dunse B. L. , Allison C. E. , Steele L. P. , Galbally I. E. , Weeks I. A.
Published: May 2003

Several studies have observed midtropospheric atmospheric composition anomalies and suggested a link to tropical biomass burning. Such anomalies complicate the use of trace gas profiles in remote regions to infer their surface sources/sinks based on the vertical gradients. The Southern African Regional Science Initiative (SAFARI 2000) campaign in Africa and coordinated downwind measurements in Australia provided an opportunity to confirm this link and elucidate the specific surface and atmospheric processes. Five aircraft missions were conducted by Commonwealth Scientific and Industrial Research Organisation (CSIRO) Atmospheric Research during the campaign. They were scheduled after African outflows of polluted air were observed in satellite images over the Indian Ocean flowing east toward Australia. Air samples collected from near the surface to 7 km were analyzed for a suite of trace gases (12CO2, CH4, CO, H2, N2O, and C2and C3hydrocarbons) and one isotopomer (13CO2) to provide vertical composition profiles. Ozone was monitored continuously during flight while a ground‐based lidar was employed in the Melbourne region to detect aerosol layers. A preliminary statistical analysis on the Australian data confirms covarying midtroposphere enhancements in the biomass burning products. Making rudimentary corrections for photochemical evolution during transit, the trace gas enhancement ratios in affected air samples are comparable to emission ratios in fresh biomass burning plumes. The13CO2/12CO2ratios are also consistent with a source from terrestrial plants. Back‐trajectory analysis for strongly enhanced samples suggests long‐range transport from tropical regions in Africa or South America, the proof of which requires a follow‐on analysis with a global chemistry transport model.
Validation of two‐channel VIRS retrievals of aerosol optical thickness over ocean and quantitative evaluation of the impact from potential subpixel cloud contamination and surface wind effect
Authors: Zhao Tom X.‐P. , Laszlo Istvan , Holben Brent N. , Pietras Christophe , Voss Kenneth J.
Published: May 2003

TRMM/CERES‐VIRS Single Satellite Footprint (SSF) data and AERONET Sun/sky radiometer observations from 1998 have been combined to validate SSF aerosol optical thickness (τ) retrievals over ocean along with a quantitative evaluation of the effects of potential subpixel cloud contamination and surface wind on the satellite τ retrievals. Potential subpixel cloud contamination is verified in Visible/Infrared Scanner (VIRS) SSF aerosol retrievals and constitutes a major source of systematic and random errors of the retrieval algorithm as determined from comparisons with AERONET observations. A positive correlation between the surface wind speed (which determines the roughness of the ocean surface) and the SSF τ has been observed for large surface wind speed. The validation results imply this correlation represents the real relationship between the surface wind and the wind‐driven aerosols rather than the disturbing effect of the surface reflectance associated with the rough ocean surface. After the potential subpixel cloud contamination is minimized and the effects of large surface wind are removed in the τ match‐ups, the positive biases in the SSF τ (compared to AERONET τ) for mean conditions have been reduced from 0.05 to 0.02 in VIRS channel 1 (0.63 μm) and 0.05 to 0.03 in channel 2 (1.61 μm). Random errors have also been reduced from 0.09 to 0.06 at 0.63 μm, and from 0.06 to 0.05 at 1.61 μm. The validation results support the application of the SSF aerosol data in radiation and climate studies as well as supply useful guidance for the adjustment and improvement of the aerosol retrieval algorithm.
Satellite multiangle cumulus geometry retrieval: Case study
Authors: Kassianov Evgueni , Ackerman Thomas , Marchand Roger , Ovtchinnikov Mikhail
Published: May 2003

Most satellite‐based analyses have been conducted using near‐nadir viewing sensors. The Multiangle Imaging Spectroradiometer (MISR), recently launched on the NASA Terra platform, provides high‐resolution measurements of reflectance at nine different viewing angles. In this study, we examine the possible retrieval of detailed cumulus geometry using the new and unique MISR data sets. We suggest one approach and apply it to an early MISR data set of small marine cumulus clouds. This paper also presents validation analysis of this technique with both independent, ground‐based radar measurements and a model‐output inverse problem. Collocated and coincident MISR data and ground‐based observations at the Atmospheric Radiation Measurement Tropical Western Pacific site form the basis of this validation. Future work will attempt to test the suggested approach with additional MISR scenes.
Evolution of gases and particles from a savanna fire in South Africa
Authors: Hobbs Peter V. , Sinha Parikhit , Yokelson Robert J. , Christian Ted J. , Blake Donald R. , Gao Song , Kirchstetter Thomas W. , Novakov Tica , Pilewskie Peter
Published: May 2003

Airborne measurements of particles and gases from a 1000‐ha savanna fire in South Africa are presented. These measurements represent the most extensive data set reported on the aging of biomass smoke. The measurements include total concentrations of particles (CN), particle sizes, particulate organic carbon and black carbon, light‐scattering coefficients, downwelling UV fluxes, and mixing ratios for 42 trace gases and 7 particulate species. The ratios of excess nitrate, ozone, and gaseous acetic acid to excess CO increased significantly as the smoke aged over ∼40–45 min, indicating that these species were formed by photochemistry in the plume. For 17 other species, the excess mixing ratio normalized by the excess mixing ratio of CO decreased significantly with smoke age. The relative rates of decrease for a number of chemical species imply that the average OH concentration in the plume was ∼1.7 × 107 molecules cm−3. Excess CN, normalized by excess CO, decreased rapidly during the first ∼5 min of aging, probably due to coagulation, and then increased, probably due to gas‐to‐particle conversion. The CO‐normalized concentrations of particles <1.5 μm in diameter decreased, and particles >1.5 μm diameter increased, with smoke age. The spectral depletion of solar radiation by the smoke is depicted. The downwelling UV flux near the vertical center of the plume was about two‐thirds of that near the top of the plume.
Synchrocascade pattern in the atmospheric turbulence
Authors: Zhao Songnian
Published: May 2003

Based on the analytical results of wavelet transform from data of the atmospheric turbulence experiments on a near‐ground surface, it is found that the high‐frequency components of the turbulent velocity fluctuation make no contribution to the energy cascade, which is governed only by the low‐frequency components in nature. The power density spectrum of turbulence velocity shows that if the timescale of wavelet transform varies as 2j(j = 1,2,…), the eddy will cascade in a manner of (2j−1− 1). The results of wavelet transform using different basis function of wavelet are consistent with each other. In order to characterize the new pattern of turbulence cascade, synchrocascade pattern, a so‐called Cantor complementary set is constructed from Cantor middle third set C. The set is a geometric representation of the hierarchical structures and multiscale properties of turbulence. Using transfer probability as a mathematical tool, we strictly derived the turbulence scaling law for high‐order moment from such a geometric pattern. It is easy to determine all parameters contained in the scaling law using intuitive geometric relationship. The synchrocascade pattern, which is very different from Richardson‐Kolmogorov's models [Richardson, 1922; Kolmogorov, 1941], shows that the energy of turbulence is fractal, intermittent, and nonuniform. At the same time, some predictions can be made from the new cascade pattern, especially from the fact that the measure of Cantor complementary set is equal to 1, which means that the whole physical space of the fluid will be gradually filled with smaller and smaller eddies, as the scale gradually approaches Kolmogorov dissipative scale η. It agrees quite well with the actual picture observed in practical turbulence.
Seasonal variation and origins of dicarboxylic acids in the marine atmosphere over the western North Pacific
Authors: Mochida Michihiro , Kawabata Aki , Kawamura Kimitaka , Hatsushika Hiroaki , Yamazaki Koji
Published: May 2003

Concentrations of homologous (C2–C11) dicarboxylic acids were measured in the atmosphere over Chichi‐jima Island (27°04′N, 142°13′E), western North Pacific, from April 1990 to November 1993. The monthly averaged concentrations of straight‐chain C2–C7 dicarboxylic acids, and some branched, keto‐, and unsaturated dicarboxylic acids showed a maximum in winter to spring and a minimum in the summer season. In contrast, straight‐chain C8–C11 dicarboxylic acids showed an opposite trend with a maximum in spring to summer. Principal component analysis revealed that there is a source characterized by a strong contribution of C2–C7 dicarboxylic acids, phthalic acid, some keto‐dicarboxylic acids, and unsaturated‐dicarboxylic acids, whereas there seems to be another source(s) for the C8–C11 dicarboxylic acids. A combined model of backward trajectories and emission inventories was used to better understand the sources and source regions of the dicarboxylic acids. The results show that concentrations of various C2–C7 dicarboxylic acids in the western North Pacific atmosphere are largely controlled by their emissions and/or their precursor emissions from anthropogenic sources in the Asian continent, followed by long‐range atmospheric transport. On the other hand, longer‐chain dicarboxylic acids cannot be explained by long‐range atmospheric transport from a continental region, which implies emissions and/or formation from natural sources, possibly from the ocean.
Quantitative sampling using an Aerodyne aerosol mass spectrometer 1. Techniques of data interpretation and error analysis
Authors: Allan James D. , Jimenez Jose L. , Williams Paul I. , Alfarra M. Rami , Bower Keith N. , Jayne John T. , Coe Hugh , Worsnop Douglas R.
Published: May 2003

The aerosol mass spectrometer (AMS), manufactured by Aerodyne Research, Inc., has been shown to be capable of delivering quantitative information on the chemical composition and size of volatile and semivolatile fine airborne particulate matter with high time resolution. Analytical and software tools for interpreting the data from this instrument and generating meaningful, quantitative results have been developed and are presented here with a brief description of the instrument. These include the conversion of detected ion rates from the quadrupole mass spectrometer during the mass spectrum (MS) mode of operation to atmospheric mass concentrations of chemical species (in μg m−3) by applying calibration data. It is also necessary to correct for variations in the electron multiplier performance, and a method involving the measurement of the instrument's response to gas phase signals is also presented. The techniques for applying particle velocity calibration data and transforming signals from time of flight (TOF) mode to chemical mass distributions in terms of aerodynamic diameter (dM/dlog(Da) distributions) are also presented. It is also possible to quantify the uncertainties in both MS and TOF data by evaluating the ion counting statistics and variability of the background signal, respectively. This paper is accompanied by part 2 of this series, in which these methods are used to process and analyze AMS results on ambient aerosol from two U.K. cities at different times of the year.
Gravity‐wave influences on Arctic mesospheric clouds as determined by a Rayleigh lidar at Sondrestrom, Greenland
Authors: Thayer Jeffrey P. , Rapp Markus , Gerrard Andrew J. , Gudmundsson Eggert , Kane Timothy J.
Published: May 2003

Since 1994, Rayleigh lidar measurements of the Arctic middle atmosphere have been conducted at the Sondrestrom research facility near Kangerlussuaq, Greenland (67.0N,50.9W). The summer lidar observations typically cover the late June through August period. From these observations, 220 hours of noctilucent clouds (NLCs) have been detected by the lidar spanning 16 hours of local time. Organizing the cloud characteristics irrespective of local time reveals the most common cloud height as 82.5 km, the most common full‐width‐half‐maximum (FWHM) as 0.7 km, and the most common peak volume backscatter coefficient as 20.0 × 10−11 m−1sr−1. The FWHM is noticeably thinner than determined by other lidar observations of NLCs in Norway and the South Pole. We found the mean backscatter strength to increase and the FWHM to decrease with decreasing cloud height. In addition, the cloud slopes with time are greater for the thicker weaker clouds at higher altitudes than the thinner stronger clouds at lower altitudes. Gravity‐wave signatures are routinely observed in the cloud detections. Upon estimating stratospheric wave activity in the data, we observed stronger cloud backscatter during low gravity‐wave activity and weak cloud backscatter during high gravity‐wave activity. To help support these results, simulations from a microphysical cloud model were performed under summer mesospheric conditions with and without gravity‐wave activity. Upon including short‐period (∼2–3 hours) gravity‐wave activity, the model simulation reproduced the behavior observed in the ensemble cloud properties by producing a broader altitude distribution, weaker backscatter strength, and thinner clouds.
Forty years of noctilucent cloud observations near Moscow: Database and simple statistics
Authors: Romejko V. A. , Dalin P. A. , Pertsev N. N.
Published: May 2003

The observation procedure and relevant database of Moscow (56°N, 37°E) noctilucent cloud (NLC) systematic observations (1962–2001) are described. The long‐term series of Moscow NLC data are analyzed and compared to the observations in western Europe. Statistical analysis of seasonally averaged parameters of the NLCs is carried out. Characteristic periods in interannual variability of the integral NLC brightness fluctuation are extracted. Particular attention is paid to decadal (∼10 years) periodicity in the NLC occurrence and their brightness. A distinct difference between decadal periodicity in NLC parameters and solar activity is found and its possible origin is discussed.
Arctic Transitions in the Land–Atmosphere System (ATLAS): Background, objectives, results, and future directions
Authors: McGuire A. D. , Sturm M. , Chapin F. S.
Published: May 2003

This paper briefly reviews the background, objectives, and results of the Arctic Transitions in the Land–Atmosphere System (ATLAS) Project to date and provides thoughts on future directions. The key goal of the ATLAS Project is to improve understanding of controls over spatial and temporal variability of terrestrial processes in the Arctic that have potential consequences for the climate system, i.e., processes that affect the exchange of water and energy with the atmosphere, the exchange of radiatively active gases with the atmosphere, and the delivery of freshwater to the Arctic Ocean. Three important conclusions have emerged from research associated with the ATLAS Project. First, associated with the observation that the Alaskan Arctic has warmed significantly in the last 30 years, permafrost is warming, shrubs are expanding, and there has been a temporary release of carbon dioxide from tundra soils. Second, the winter is a more important period of biological activity than previously appreciated. Biotic processes, including shrub expansion and decomposition, affect snow structure and accumulation and affect the annual carbon budget of tundra ecosystems. Third, observed vegetation changes can have a significant positive feedback to regional warming. These vegetation effects are, however, less strong than those exerted by land–ocean heating contrasts and the topographic constraints on air mass movements. The papers of this special section provide additional insights related to these conclusions and to the overall goal of ATLAS.
Interannual variability and timing of growing‐season CO2 exchange in a boreal forest
Authors: Suni Tanja , Berninger Frank , Markkanen Tiina , Keronen Petri , Rannik Üllar , Vesala Timo
Published: May 2003

We studied the interannual variability of cumulative net ecosystem CO2 exchange (NEE) and its connection with cumulative or average climatic variables during five growing seasons. The analysis was based on a 5‐year‐long time series of CO2 flux measured from April 1996 to April 2001 in a Scots pine forest in southern Finland by the eddy covariance technique. The onset of the ecosystem growing season was best connected with air temperature, and the end of the growing season was best connected with day length. With these variables we were able to predict the timing and the length of each growing season within 0–3 days. The forest was a sink of carbon with little interannual variability: The uptake during the four full growing seasons varied by 80 g C m−2, ranging from 230 to 310 g C m−2. The estimated winter release each year varied between 60 and 90 g C m−2. The interannual variation in seasonal (spring, summer, autumn) carbon exchange ranged from 30 g C m−2 in autumn and spring to 80 g C m−2 in summer. The average climatic variables explained the variability of the seasonal or growing‐season cumulative NEE only partly. Both the daytime and the nighttime CO2 fluxes contributed markedly to the variability in carbon exchange, indicating that photosynthesis and respiration have an equally important influence on NEE.
Airborne spectral measurements of surface–atmosphere anisotropy for several surfaces and ecosystems over southern Africa
Authors: Gatebe Charles K. , King Michael D. , Platnick Steve , Arnold G. Thomas , Vermote Eric F. , Schmid Beat
Published: May 2003

The Cloud Absorption Radiometer (CAR) was flown aboard the University of Washington Convair CV‐580 research aircraft during the Southern Africa Regional Science Initiative 2000 (SAFARI 2000) dry season campaign and obtained measurements of bidirectional reflectance distribution function (BRDF) for a variety of natural surfaces and ecosystems in southern Africa. To measure the BRDF of the surface–atmosphere system, the University of Washington CV‐580 banked at a roll angle of ∼20° and flew circles about 3 km in diameter above the surface, taking approximately 2 min. Multiple circular orbits were acquired over selected surfaces so that average BRDFs could be acquired, smoothing out small‐scale surface and atmospheric inhomogeneities. In this paper, we present results of BRDFs taken over two Earth Observing System (EOS) validation sites: Skukuza tower, South Africa (25.0°S, 31.5°E) and Mongu tower, Zambia (15.4°S, 23.3°E). Additional sites are discussed and include the Maun tower, Botswana (20.0°S, 23.6°E), Sua Pan, Botswana (20.6°S, 25.9°E), Etosha Pan, Namibia (19.0°S, 16.0°E), and marine stratocumulus clouds off the west coast of Namibia (20.5°S, 13.1°E). Results clearly show anisotropy in reflected solar radiation over the various surfaces types: savanna, salt pans, and cloud. The greatest anisotropy is observed over marine stratus clouds, which exhibit strong forward scattering as well as important water cloud scattering features such as the rainbow and glory. The BRDF over savanna is characterized by a distinct backscattering peak in the principal plane and shows directional and spectral variations. Over the pans, the BRDF is more enhanced in the backscattering plane than forward scattering plane and shows little directional variation.
Layering accompanying turbulence generation due to shear instability and gravity‐wave breaking
Authors: Fritts David C. , Bizon Chris , Werne Joseph A. , Meyer Christian K.
Published: May 2003

We describe and compare idealized high‐resolution simulations of turbulence arising due to Kelvin‐Helmholtz shear instability and gravity‐wave breaking, believed to be the two major sources of turbulence generation near the mesopause. The two flows both share characteristics related to turbulence transition, evolution, and duration and exhibit a number of differences that have important implications for layering, layered structures, and atmospheric observations at mesopause altitudes. Common features related to layering include sharp local gradients in turbulent kinetic energy production, dissipation, and magnitude and a clear spatial separation of the maxima of turbulent kinetic energy dissipation and thermal dissipation accompanying vigorous turbulence. Differences arise because shear instability causes turbulence and mixing confined by stratification to a narrow layer, whereas gravity‐wave breaking leads to a maximum of turbulence activity that moves with the phase of the wave. As a result, the effects of turbulence due to shear instability likely persist for much longer than those of turbulence due to gravity‐wave breaking. We also discuss the implications of these results for a number of atmospheric measurements employing radar.
Persistent ice cloud in the midsummer upper mesosphere at high latitudes: Three‐dimensional modeling and cloud interactions with ambient water vapor
Authors: von Zahn U. , Berger U.
Published: May 2003

We infer from the observed occurrence frequency of polar mesosphere summer echoes and from the three‐dimensional (3‐D) modeling of conditions in the high‐latitude mesopause region that a persistent layer of icy particles exists in midsummer at all latitudes poleward of about 60°N at and a few kilometers below the mesopause. All of these icy particles are transported equatorward by the climatological mean winds. At the same time, many of the larger icy particles possess a high enough sedimentation velocity to induce a net downward transport of water vapor. Both types of particle motions cause the mesopause region to become substantially dryer than without these transports of icy particles. We follow the interactions between water vapor and icy particles by means of a 3‐D dynamical and chemical model, which includes a module for the formation, growth, and sublimation of icy particles. For midsummer conditions and poleward of 67°N latitude, the model predicts (1) a strongly dehydrated region, typically above 84 km, in which the water vapor mixing ratio can fall below 0.2 ppmv and (2) atmospheric regions with enhanced water vapor abundance near both the lower and the equatorward borders of the icy particle layer.
First in situ temperature measurements in the summer mesosphere at very high latitudes (78°N)
Authors: Lübken Franz‐Josef , Müllemann Arno
Published: May 2003

A total of 24 temperature profiles from ∼92 to 55 km were obtained from falling sphere flights in Longyearbyen (Svalbard, 78°N) from 16 July to 14 September 2001. The thermal structure of the upper mesosphere during the summer season (here from mid‐July to 23 August) is characterized by very low temperatures and little variability. The mesopause temperature decreases slightly from ∼130 K in mid‐July to 126–128 K in late July/beginning of August. The mesopause altitude in summer is ∼89 km. Compared to 10° further south (69°N, Andøya), the mesopause temperature is very similar in mid‐July but is significantly colder by 6–8 K in the second half of July and in August. Part of this difference (especially in late August) is due to the later transition from summer to winter in Longyearbyen. The mesopause altitude is higher by approximately 1 km at Longyearbyen compared to Andøya. At 82 km, the temperature in summer is very close to 150 K, very similar to other Arctic and Antarctic stations (“equithermal submesopause”). The temperatures in the upper mesosphere are significantly lower compared to COSPAR International Reference Atmosphere (CIRA, 1986) by up to 20 K. Assuming model water vapor concentrations, we derived the degree of saturation of water vapor (S). In summer, there is an extended altitude range (82–92 km) with supersaturation (S > 1). Occasionally, very high supersaturation was derived (S > 100). Our temperature measurements are in general agreement with the occurrence morphology of polar mesosphere summer echoes (PMSE). However, double layered structures frequently observed in PMSEs are not a prominent feature of the temperatures in the upper mesosphere.
Measurement of positively and negatively charged particles inside PMSE during MIDAS SOLSTICE 2001
Authors: Smiley B. , Robertson S. , Horányi M. , Blix T. , Rapp M. , Latteck R. , Gumbel J.
Published: May 2003

A magnetically shielded, charge collecting rocket probe was used on two flights in the MIddle Atmosphere Dynamics and Structure (MIDAS) Studies of Layered STructures and ICE (SOLSTICE) 2001 rocket campaign over Andøya, Norway. The probe was a graphite collection surface with a permanent magnet underneath to deflect electrons. The first MIDAS was launched 17 June 2001 into a strong, multiply layered PMSE. The probe measured negative particles inside an electron biteout within the PMSE, having a peak charge number density of −1500 charges per cubic centimeter. The second MIDAS was launched 24 June 2001 into another strong, multiply layered PMSE. The probe saw a band of positive particles centered in the lowest radar echo maximum, and a negative particle layer accompanied by a positive ion excess. The charge number densities for the positive and negative PMSE particles were several thousand charges per cubic centimeter. Unexpectedly, 2 km beneath the PMSE, the probe also found a very pronounced negative layer, which was probably an NLC. Computer simulations of incoming, negatively charged ice grains were performed using a rarefied flow field representative of the MIDAS payload at zero angle of attack. Ice grains ≤1 nm in radius were diverted by the leading shock front, indicating the smallest detectable ice particle by this probe.
A database of spectral surface reflectivity in the range 335–772 nm derived from 5.5 years of GOME observations
Authors: Koelemeijer R. B. A. , de Haan J. F. , Stammes P.
Published: May 2003

A global database of Lambert‐equivalent reflectivity (LER) of the Earth's surface has been constructed by analyzing observations of the reflectivity at the top of the atmosphere made by the Global Ozone Monitoring Experiment (GOME). Since its launch on board the ERS‐2 satellite in April 1995, the GOME instrument has been measuring spectra of the Earth between 237 and 794 nm, with a spectral resolution between 0.2 and 0.4 nm and a spatial resolution between 40 × 80 and 40 × 320 km2. The LER database covers eleven 1‐nm‐wide wavelength bins centered at 335, 380, 416, 440, 463, 494.5, 555, 610, 670, 758, and 772 nm, which were selected for various retrieval applications. The database has a spatial resolution of 1° × 1°, is made for each month of the year, and pertains to the period June 1995–December 2000. Typical spectra of various surface types are presented. Attention is paid to instrument degradation and residual cloud contamination. We have found satisfactory agreement between our database at 380 nm and the Total Ozone Mapping Spectrometer (TOMS) LER database at 340–380 nm, with negligible average difference and a standard deviation of 0.013. The database presented here can be used to improve retrievals of trace gases, clouds and aerosols from GOME, Scanning Imaging Absorption Spectrometer or Atmospheric Cartography (SCIAMACHY), Ozone Monitoring Instrument (OMI), and GOME‐2.
Trace gas chemistry in a young biomass burning plume over Namibia: Observations and model simulations
Authors: Jost Christof , Trentmann Jörg , Sprung Detlev , Andreae Meinrat O. , McQuaid James B. , Barjat Hannah
Published: May 2003

We investigated trace gas emissions from a biomass fire near Otavi, northern Namibia, on 13 September 2000 as part of the Southern African Regional Science Initiative 2000 (SAFARI 2000). Observations included fast measurements of carbon monoxide (CO), ozone (O3), acetone (propanone, CH3COCH3), and acetonitrile (ethanenitrile or methyl cyanide, CH3CN). Additionally, flask samples were taken and analyzed for nonmethane hydrocarbons (NMHCs). Measurements close to the fire were used to quantify the emissions of the different compounds. Several transects were flown through the plume downwind to study the chemical changes in the plume during the first 2 hours after the emission. Fast production of O3was observed, with the O3/CO molar enhancement ratioER(O3/CO) reaching ∼0.10 in the plume after 2 hours. Acetone molar enhancement ratios (ER(acetone/CO) were ∼5 × 10−3in the very young plume but ∼9 × 10−3after 1–2 hours of aging, pointing to a substantial fast secondary acetone formation. To understand the chemical processes occurring in the plume, we simulated the plume chemistry with a dilution box model. The fast O3production is well reproduced, whereas acetone mixing ratios in the aging plume are underestimated by the model. This points to additional yet unidentified acetone precursors. The model suggests an overall molar enhancement ratio of these compounds with respect to CO of 7.5 × 10−3and a reaction rate coefficient of 6 × 10−11cm3s−1for the reaction with HO radicals. The secondary acetone production may cause the net acetone source from biomass burning to be underestimated when only data from observations immediately near the fires are considered. The atmospheric implications of these findings are discussed.
Impact of the heterogeneous hydrolysis of N2O5 on chemistry and nitrate aerosol formation in the lower troposphere under photosmog conditions
Authors: Riemer N. , Vogel H. , Vogel B. , Schell B. , Ackermann I. , Kessler C. , Hass H.
Published: May 2003

The impact of the heterogeneous hydrolysis of N2O5 on tropospheric gas phase and particle phase chemistry was investigated by performing model simulations with two comprehensive model systems and taking into account recent findings on the heterogeneous reaction probability of N2O5. Hereby, we focused on photosmog conditions in the lower troposphere. Chemistry box model runs were carried out neglecting transport and deposition processes. The heterogeneous hydrolysis of N2O5 leads to a decrease of ozone under low‐NOx conditions and to a strong increase of ozone under high‐NOx conditions. One‐dimensional simulations were performed to take into account vertical mixing processes, deposition, and temporal changes of the emissions. The rate constant for the heterogeneous hydrolysis was determined depending on the simulated aerosol surface area density. A large impact of the heterogeneous hydrolysis on the nocturnal concentrations of N2O5, NO3, HNO3, and the surface area density and nitrate content of the aerosol is found. However, the effect of the hydrolysis of N2O5 on ozone decreases considerably compared to the box model simulations. Three‐dimensional simulations for a typical summer smog situation for the southwestern part of Germany and on the European scale, which cover a variety of atmospheric and emission conditions, confirm these findings. The impact of heterogeneous hydrolysis on ozone is small, but it causes remarkable changes in the nocturnal concentrations of nitrogen‐containing species and on aerosol properties such as surface area density and nitrate content.
Properties of midlatitude mesosphere summer echoes after three seasons of VHF radar observations at 54°N
Authors: Zecha M. , Bremer J. , Latteck R. , Singer W. , Hoffmann P.
Published: May 2003

During the three summer seasons of the years 1998, 2000 and 2001 mid‐latitude mesosphere summer echoes (MSE) were observed with the OSWIN VHF radar. The radar is located at Kühlungsborn (54.1°N, 11.8°E). Based on nearly continuous operation of the radar a large data set with altogether more than 200 hours of MSE observations with signal‐to‐noise ratios greater than 0 dB has been obtained. We present and discuss the results of the three years observation. Mid‐latitude mesosphere summer echoes occur much more seldom than their corresponding polar mesosphere summer echoes (PMSE) in polar regions. Both phenomena are characterized by very strong radar returns with a high aspect sensitivity and a restriction to the summer mesosphere. But beside these analogies their main differences will be discussed also. MSE occur in a shorter time interval in the summer months and normally only during daytime. They are still observable although the low temperatures and the sufficient degree of saturation necessary for the existence of ice particles cannot be reached at all times. Furthermore we show MSE distribution, scattering characteristics, aspect sensitivity, and turbulence characteristics as functions of height.
Soil moisture and plant stress dynamics along the Kalahari precipitation gradient
Authors: Porporato Amilcare , Laio Francesco , Ridolfi Luca , Caylor Kelly K. , Rodriguez‐Iturbe Ignacio
Published: May 2003

We present an analysis of water balance and plant water stress along the Kalahari precipitation gradient using a probabilistic model of soil moisture. The rainfall statistical characteristics, obtained from daily data of four stations along the transect, show that the rainfall gradient (from 950 to 300 mm/year) is mostly due to a decrease in the mean rate of storm arrivals (from 0.38 to 0.09 1/day) rather than to a change in the mean storm depth (practically constant at 10 mm). Using this information and typical vegetation and soil parameters, the analysis relates the vegetation properties along the transect with those of climate and soil. It is shown that differences in water balance and plant water stress between trees and grasses generate varying preferences for vegetation types along the transect, with deeper‐rooted trees favored in the more mesic regions of the northern Kalahari and grasses favored in the drier zones of the southern Kalahari. The point of equal plant water stress is found at about 420 mm of rainfall during the growing season (October–April), indicating the possibility of tree‐grass coexistence in the central sector of the Kalahari. These findings are consistent with patterns of vegetation distribution across the Kalahari transect.
Effects of polar ice sheets on global sea level in high‐resolution greenhouse scenarios
Authors: Wild Martin , Calanca Pierluigi , Scherrer Simon C. , Ohmura Atsumu
Published: May 2003

Projections of future global sea level critically depend on reliable estimates of mass balance changes on the polar ice sheets. The most sophisticated tools allowing for such estimates are General Circulation Models (GCM). A major impediment until recently has been their coarse grid resolution (3°–6°) causing substantial uncertainties in the mass balance calculations on the poorly resolved ice sheets. The present study is based on a climate change experiment of highest resolution currently feasible (T106, 1.1°). The precipitation distribution significantly benefits from the more realistic orographic forcing in the high‐resolution experiment and is very accurately reproduced. A greenhouse warming experiment with doubled carbon‐dioxide concentration based on the same high‐resolution model suggests an increase in accumulation on both Greenland and Antarctic ice sheets. On the other hand, even a T106 resolution is still too coarse for the simulation of ablation on the narrow ice sheet margins, where most of the melting takes place. A simple method is presented to improve ablation diagnostics from GCMs, based on the interpolation of the reference temperature and temperature anomaly fields onto a fine mesh topography of 2 km horizontal resolution. The increase in ablation on Greenland in the greenhouse scenario is thereby smaller than the increase directly inferred from the GCM grid. As for Antarctica, it is still too cold at the time of doubled carbon‐dioxide concentration for significant ablation. The results from the greenhouse experiment with doubled carbon‐dioxide concentration thus suggest not only a mass gain in Antarctica due to the increase in accumulation, but also a mass gain in Greenland, since the enhanced ablation in the warmer climate does not fully compensate for the increased accumulation. In terms of global sea level change, these mass balance shifts correspond to a net sea level decrease of 1.2 mm y−1 at the time of doubled carbon‐dioxide. This may compensate for a substantial fraction of the melt‐induced sea level rise from smaller glaciers and ice caps, leaving thermal expansion as the dominant factor for sea level rise over the coming decades. The compensating effect, however, could fade if carbon‐dioxide concentrations in the atmosphere cannot be stabilized and continue to rise above double the present values, since the associated greenhouse warming could then become large enough to induce significant melting also on the Antarctic ice sheet.
A localized structure in OH airglow images near the mesopause region
Authors: Shiokawa K. , Ejiri M. K. , Ogawa T. , Yamada Y. , Fukunishi H. , Igarashi K. , Nakamura T.
Published: May 2003

An intense localized airglow‐depletion structure was observed in OH airglow images (emission altitude ∼86 km) at Shigaraki (34.9°, 136.1°) on 19 December 1998. The structure was a single‐band airglow depletion with a small horizontal width (∼15 km) but a large amplitude (∼34% from the average intensity). Airglow rotational temperature indicated a large temperature lapse rate at this time as a result of strong semidiurnal variation. We suggest that nonlinear wave‐wave interaction is the most likely cause of this localized structure.
A modeling study of O2 and OH airglow perturbations induced by atmospheric gravity waves
Authors: Liu Alan Z. , Swenson Gary R.
Published: May 2003

A one‐dimensional model is used to investigate the relations between gravity waves and O2 and OH airglows perturbations. The amplitude and phase of the airglow perturbations induced by gravity waves (with period > 20 min) are calculated for different vertical wavelength (10–50 km) and damping rate. The model shows that for vertically propagating gravity waves, the amplitude of airglow perturbations observed from ground is larger for longer vertical wavelength, because of the smaller cancellation effect within each layer. The ratio of the amplitudes between O2 and OH is smaller for larger wave damping. For upward propagating (downward phase progression) waves, the intensity perturbation in O2 leads OH, and their phase difference (O2 minus OH) is larger for smaller vertical length and/or stronger damping. The rotational temperature perturbation leads intensity perturbation in both layers. Their phase difference is also larger for smaller vertical length but is smaller for stronger damping. Based on these relations, the vertical wavelength and damping rate of gravity waves can be derived from simultaneous measurements of airglow perturbations in O2 and OH layers.
Vertical profiles of O3, NO2, NOx, VOC, and meteorological parameters during the Berlin Ozone Experiment (BERLIOZ) campaign
Authors: Glaser K. , Vogt U. , Baumbach G. , Volz‐Thomas A. , Geiss H.
Published: May 2003

During the intensive observational periods of the BERLIOZ campaign (20 and 21 July 1998 and 3 August 1998), vertical profiles from 0 to 800 m above ground of O3, NO2, NOx, selected VOC, and meteorological parameters were measured by means of a comprehensive tethered balloon system at Papstthum, a rural site 50 north west of the city of Berlin. Every 2 hours a complete profile was obtained. The VOC were collected on charcoal tubes simultaneously at four different heights over time intervals of 3 hours. The measurement systems participated at the quality assurance measures of the BERLIOZ campaign and fully complied with the data quality objectives. The balloon data provide important information on the vertical gradients of the trace gases at Pabstthum and clearly identify the development of the boundary layer in the course of the day. This information is important for the interpretation of the radical measurements discussed in the accompanying publications. They also give insight in the vertical extent of air masses of different chemical regimes and their temporal evolution. During the morning hours of 20 July the evolution of the city plume passing the measurement site with a vertical extension of 800 m could be documented. Owing to degradation by the reaction with NO a reduced O3 concentration level was observed within the plume in the morning hours of 20 July. The highest peak concentrations of the campaign observed on ground level in the morning of 21 July could not be attributed to the Berlin city plume.
An accumulation map for the Greenland dry‐snow facies derived from spaceborne radar
Authors: Munk J. , Jezek K. C. , Forster R. R. , Gogineni S. P.
Published: May 2003

An important component of ice sheet mass balance calculations is the snow accumulation rate, traditionally determined across the ice sheet from interpolated ice core data. We derive an accumulation rate map within the Greenland dry‐snow facies, using C‐band radar backscatter and the mean annual temperature. Values for the backscatter were obtained from the ERS‐1 synthetic aperture radar mosaic acquired during September–November 1992. An empirical equation, based on elevation and latitude, is used to determine the mean annual temperature. We examine the influence of accumulation rate, and mean annual temperature on C‐band (5.3 GHz) radar backscatter, using a forward model, which incorporates snow metamorphosis and radar backscatter components. Our model is run over a range of accumulation and temperature conditions, consistent with the Greenland dry‐snow facies. On the basis of our modeled results, a look‐up table is generated, which uniquely maps the measured radar backscatter and mean annual temperature to accumulation rate. Our results compare favorably (15.4% average difference) with 124 in situ accumulation rate measurements falling within our study area. We attribute some of the differences to (1) unreliable in situ data points, which were based on a single year's accumulation and (2) a systematic underestimate of accumulation rate by our forward model in the low‐accumulation regions associated with the northern portion of our map. With questionable data points and those above 77°N removed, the average differences were less than 10.3%, as determined from 73 ice cores.
Release of gaseous and particulate carbonaceous compounds from biomass burning during the SAFARI 2000 dry season field campaign
Authors: Hély C. , Caylor K. , Alleaume S. , Swap R. J. , Shugart H. H.
Published: May 2003

Source strengths to the atmosphere for different forms of carbon (CO2, CO, CH4, nonmethane hydrocarbons (NMHC), and PM2.5) produced by biomass burning were calculated during the Southern African Regional Science Initiative (SAFARI 2000) intensive study period (August and September 2000) for Africa south of the equator. For a given pixel burned, these calculations are a product of the aboveground biomass before a fire, the proportion of biomass that is burned by the fire, and the emission factor for a given carbon compound based on the combustion efficiency. The total emission for the region is the summation of such calculations for all the burned pixels. Products used for these calculations are a prototype satellite‐based burned area based on the SPOT‐VGT‐S1 satellite product, a fuel load map produced by a simulation model developed and applied to southern Africa at 1 km2 resolution, information from fire experiments from our own research in southern Africa to compute combustion completeness, and emission factors published for the region. Over August and September 2000, 31,067 fires detected by the SPOT satellite are calculated to have emitted 96.9 × 1012 g CO2, 4.6 × 1012 g CO, and lesser amounts of CH4, NMHC, and PM2.5. These calculations are in the range of previous estimates of the emissions of these compounds for southern Africa. Along with documenting the estimates of the emissions during the SAFARI 2000 campaign, regional emission estimates are very strongly controlled by the burned area of fires due to a correlation between the cumulative distribution of percent burned area and the cumulative distribution of percent emissions.
Measurement of deuterium isotope flux ratio from an agricultural grassland
Authors: He Hui , Smith Ronald B. , Aylor Donald E.
Published: May 2003

Atmospheric water vapor was sampled at two heights above an agricultural grassland in the summer of 1997. The cryogenic method was used for water vapor sampling. The deuterium isotope ratio, δD, and the water vapor mixing ratio, Q, were measured for 11 pairs of samples collected on three summer days. Remarkable gradients of δD and Q existed across the two sampling heights at 0.5 m and 3.0 m. The mixing line method was used to derive the deuterium isotope flux ratio, δDF, which characterizes the evapotranspiration mechanisms of the underlying surface. We found that δDF increased from days 97191 and 97193 to day 97196, indicating a continuous depletion of soil water, whereas the mean δDF falls into the range of the deuterium isotope ratio of regional summer precipitation. In addition, δD of the collected water vapor samples also increased progressively over the same period, which lacked of any significant precipitation.
Intradiurnal wind variations in the midlatitude and high‐latitude mesosphere and lower thermosphere
Authors: Kovalam Sujata , Vincent Robert A.
Published: May 2003

MF radar observations of neutral zonal and meridional wind components in the mesosphere and lower thermosphere region (78–98 km) made at Adelaide (35°S, 138°E) and Davis (68°S, 78°E) from January 1994 to December 1999 are analyzed with an emphasis on intradiurnal wind variations common to both stations. Periodograms were used to investigate the spectral content of the wave motions from 6 hours to 20 days and reveal the presence of a rich spectrum of waves. Motions due to tides and intradiurnal oscillations (6–15 hour periods) are particularly evident. Cross‐spectral analyses were used to assess the global coherence of the intradiurnal oscillations. They are found to be short‐lived (∼2–4 days) and have wave amplitudes in the range of 10–20 ms−1. The cross‐spectral analyses revealed discrete intervals during which intradiurnal oscillations showed a high degree of coherence between the two stations. The cross‐spectral phase differences suggest that oscillations with periods between 8 and 14 hours are westward propagating with zonal wave number 1. These oscillations are identified as the atmospheric manifestation of gravitational normal modes or Lamb waves.