bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat exchange during snow ablation in plains and mountains of Eurasia
Authors: Aizen Elena M. , Aizen Vladimir B. , Melack J. M. , Krenke Alexander N.
Published: February 2004

Rates of snow water equivalent (SWE) decrease were obtained as a difference between two successive values of SWE at 189 stations in the former Soviet Union (FSU). The required distribution of duration of snow ablation (snowmelt plus sublimation) was obtained from longterm data on average dates of maximum SWE and dates of snow disappearance. Stations were grouped by dates of snow disappearance and beginning of ablation. The amount of ablated snow for the 10‐day periods, normalized by the maximum mean SWE at a station, was averaged throughout stations with the same dates of snow disappearance and beginning of snow ablation. On plains and foothills, up to 80% of snow ablated during the last 10 days of snow cover. At high altitudes in mountains, about 40% of snow ablated during the penultimate 10 days of snow cover. During the ablation season, the amount of energy used to melt snow was of the same order as the combination of other components of the heat budget (e.g‥ heat associated with atmospheric advection, radiation balance, and turbulent heat exchange). Heating of the air would have been 3 times higher if snowmelt had not occurred. Over the continental plains of the FSU, maximum energy used to melt snow occurred in the foothills of the Urals and the northwest portion of the Srednerusskaya upland. Over the mountains, maximum energy to melt snow per unit area was observed in the northern and western Tien Shan where most snow accumulation occurred. A maximum mean energy used to melt snow was observed in the beginning of April over the plains and in June over the mountains.
Synoptic‐scale Rossby waves and the geographic distribution of lateral transport routes between the tropics and the extratropics in the lower stratosphere
Authors: Horinouchi Takeshi , Sassi Fabrizio , Boville Byron A.
Published: February 2004

Atmospheric transport between the tropics and the extratropics, in the lowest part of the stratosphere during Northern Hemisphere winter, is investigated. The role of synoptic‐scale disturbances that propagate laterally into the tropics is examined using the middle atmosphere version of the National Center for Atmospheric Research Community Climate Model Version 3 general circulation model. In the lower stratosphere, synoptic‐scale Rossby waves propagate vigorously from the northern (i.e., winter) extratropics through two “westerly ducts,” where the westerly zonal mean winds near the equator are favorable to Rossby wave propagation. The waves break in the westerly ducts and modify the mean potential vorticity (PV) structure to connect subtropical and equatorial regions of sharp PV gradients. Frequent wave breaking and the wave‐induced PV structure create distinct routes where transport occurs vigorously between the tropics and the northern extratropics. Interhemispheric transport also occurs through regions associated with the westerly ducts. In the Southern (summer) Hemisphere lower stratosphere, synoptic‐scale disturbances propagate mainly as “tongues” of PV elongated from extratropical disturbances. The transport between the tropics and the southern extratropics has a strong geographic preference but is dominated by the monsoon circulation, as was shown for the upper troposphere by Chen [1995]. PV tongues and other transient anomalies are of secondary importance.
A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements
Authors: Dubovik Oleg , King Michael D.
Published: February 2004

The problem of deriving a complete set of aerosol optical properties from Sun and sky radiance measurements is discussed. Algorithm development is focused on improving aerosol retrievals by means of including a detailed statistical optimization of the influence of noise in the inversion procedure. The methodological aspects of such an optimization are discussed in detail and revised according to both modern findings in inversion theory and practical experience in remote sensing. Accordingly, the proposed inversion algorithm is built on the principles of statistical estimation: the spectral radiances and various a priori constraints on aerosol characteristics are considered as multisource data that are known with predetermined accuracy. The inversion is designed as a search for the best fit of all input data by a theoretical model that takes into account the different levels of accuracy of the fitted data. The algorithm allows a choice of normal or lognormal noise assumptions. The multivariable fitting is implemented by a stable numerical procedure combining matrix inversion and univariant relaxation. The theoretical inversion scheme has been realized in the advanced algorithm retrieving aerosol size distribution together with complex refractive index from the spectral measurements of direct and diffuse radiation. The aerosol particles are modeled as homogeneous spheres. The atmospheric radiative transfer modeling is implemented with well‐established publicly available radiative transfer codes. The retrieved refractive indices can be wavelength dependent; however, the extended smoothness constraints are applied to its spectral dependence (and indirectly through smoothness constraints on retrieved size distributions). The positive effects of statistical optimization on the retrieval results as well as the importance of applying a priori constraints are discussed in detail for the retrieval of both aerosol size distribution and complex refractive index. The developed algorithm is adapted for the retrieval of aerosol properties from measurements made by ground‐based Sun‐sky scanning radiometers used in the Aerosol Robotic Network (AERONET). The results of numerical tests together with examples of experimental data inversions are presented.
Aircraft measurements of tracer correlations in the Arctic subvortex region during the Polar Stratospheric Aerosol Experiment (POLSTAR)
Authors: Ziereis H. , Schlager H. , Fischer H. , Feigl C. , Hoor P. , Marquardt R. , Wagner V.
Published: February 2004

Total reactive nitrogen (NOy), ozone (O3), the tracer nitrous oxide (N2O), and carbon monoxide (CO) were measured in situ as part of the Polar Stratosphere Aerosol Experiment (POLSTAR 1 and 2). In total, 14 missions were performed in January and February 1997 and 1998 in the Arctic subvortex region, by using the Deutsches Zentrum für Luft‐und Raumfahrt research aircraft Falcon. During the two campaigns, no signatures of nitrification events in the lowermost stratosphere, due to sedimentation and evaporation of aerosol particles containing HNO3, were found. Compact correlations were observed between NOy and O3, between NOy and N2O, and between O3 and N2O. Mean NOy/O3 ratios observed in the lowermost Arctic stratosphere in 1997 and 1998 were 0.0046 and 0.0030, respectively. During POLSTAR 1, NOy‐N2O and O3‐N2O slopes compare quite well with results of previous measurements in the lowermost stratosphere. However, indications for a nonstratospheric NOy source, possibly aircraft emissions, were found. During POLSTAR 2, inferred NOy‐N2O and O3‐N2O slopes were significantly lower than those previously observed in this region. This might indicate transport from lower latitudes to the Arctic subvortex region.
Reactive and nonreactive uptake on hydrocarbon soot: HNO3, O3, and N2O5
Authors: Longfellow C. A. , Ravishankara A. R. , Hanson D. R.
Published: February 2004

The reactive and physical uptakes of HNO3, O3, and N2O5 were examined on hydrocarbon soot by using a flow tube equipped with a chemical ionization mass spectrometer. The uptake of HNO3 at 298 K was found to be reversible, and it did not produce NO2 or NO; i.e., HNO3 was not reduced. The uptake of O3 on to soot was measured at 298 and 253 K and found to be small when the surface area of the soot was taken into account. We conclude that neither the HNO3 nor the O3 reaction on soot has much impact on the atmosphere. We observed the production of gas phase NO2 from the uptake of N2O5 on the soot surface with an efficiency of close to unity. It was concluded that the uptake of N2O5 on soot is reactive. The implications of the N2O5 reaction on soot to the atmosphere are not clear, because not all the products of this reactive uptake have been identified
On the evolution of aerosol properties at a mountain site above Mexico City
Authors: Baumgardner D. , Raga G. B. , Kok G. , Ogren J. , Rosas I. , Báez A. , Novakov T.
Published: February 2004

Size distributions, scattering and absorption coefficients, and the bulk chemical composition of aerosols have been measured at a mountain site 400 m above the southwest sector of the Mexico City basin during a two‐week period in November 1997. Variations in these properties are primarily related to local meteorology, i.e., wind direction and relative humidity; however, a link was found between carbon monoxide and ozone and the partitioning of aerosols between Aitken and accumulation mode sizes. Relative humidity was also found to affect this partitioning of aerosol size and volume. In addition, the fraction of sulfate in the aerosols was much higher on a high‐humidity day than on a very low humidity day; however, the fraction of the mass contained in organic and elemental carbon was the same regardless of humidity levels. The daily variations of aerosol properties are associated with the arrival of new particles at the research site transported from the city basin and their subsequent mixture with aged aerosols that remain in the residual layer from the night before.
How coupling of the atmosphere to ocean and land helps determine the timescales of interannual variability of climate
Authors: Dickinson Robert E.
Published: February 2004

The key to understanding the link between climate variability and the biosphere are feedbacks of the ocean and land surfaces to atmospheric variability. Generalizations of the Hasselman random forcing model continue to provide a framework for much of the observed climate variability. Zero dimension ocean‐atmosphere and land‐atmosphere coupled models reveal the timescales of mutual adjustment and hence the amplitude of variability for a given forcing. The coupling in both models introduces longer timescales than in any uncoupled model and hence illustrates how the coupled systems act to amplify climate variability. The common feature of both models is a quantity that is conserved between the surface and the atmosphere. For the atmosphere‐ocean model, this is energy, whereas for the atmosphere‐land model, the conserved quantity is water. These conservative quantities represent the projection of climate variability onto the slowest system mode, an inference that readily generalizes to modes of climate variability with spatial structure and hence they provide a useful focus for diagnosis of observations and complex model simulations.
Applications of SHEBA/FIRE data to evaluation of snow/ice albedo parameterizations
Authors: Curry J. A. , Schramm J. L. , Perovich D. K. , Pinto J. O.
Published: February 2004

Climate models use a wide variety of parameterizations for surface albedos of the ice‐covered ocean. These range from simple broadband albedo parameterizations that distinguish among snow‐covered and bare ice to more sophisticated parameterizations that include dependence on ice and snow depth, solar zenith angle, and spectral resolution. Several sophisticated parameterizations have also been developed for thermodynamic sea ice models that additionally include dependence on ice and snow age, and melt pond characteristics. Observations obtained in the Arctic Ocean during 1997–1998 in conjunction with the Surface Heat Budget of the Arctic Ocean (SHEBA) and FIRE Arctic Clouds Experiment provide a unique data set against which to evaluate parameterizations of sea ice surface albedo. We apply eight different surface albedo parameterizations to the SHEBA/FIRE data set and evaluate the parameterized albedos against the observed albedos. Results show that these parameterizations yield very different representations of the annual cycle of sea ice albedo. The importance of details and functional relationships of the albedo parameterizations is assessed by incorporating into a single‐column sea ice model two different albedo parameterizations, one complex and one simple, that have the same annually averaged surface albedo. The baseline sea ice characteristics and strength of the ice‐albedo feedback are compared for the simulations of the different surface albedos.
Errant inferences of gravity wave momentum and heat fluxes using airglow and lidar instrumentation: Corrections and cautions
Authors: Fritts David C.
Published: February 2004

Optical techniques are increasingly being used to measure the dynamics and influences of gravity waves in the mesosphere and lower thermosphere because of their unique spatial sensitivity and their potential for high‐resolution measurements of winds and temperatures at these altitudes. Such systems, however, also exhibit measurement biases which can, if uncorrected, cause significant errors in inferences of dynamical quantities. Inappropriate assumptions about the character of the motion field can likewise lead to errors in data analyses. Estimates of momentum and heat fluxes due to gravity waves are particularly sensitive to such errors because of their dependence on correlations among wave quantities and the character of the wave motions. The purpose of this paper is to identify such errors in previous applications of lidar and airglow data collected at the Starfire Optical Range and in Hawaii in order that subsequent data analyses will yield useful estimates of gravity wave fluxes, mean flow influences, and guidance for modeling studies in the future.
Calibration of laser‐light scattering measurements of dust concentration for Wisconsinan GISP2 ice using instrumental neutron activation analysis of aluminum: Results and discussion
Authors: Ram Michael , Donarummo John , Stolz Michael R. , Koenig Gerson
Published: February 2004

In past work we used laser‐light scattering (LLS) from bubble‐free ice to measure how the dust concentration varied along the Wisconsinan (glacial) section of the Greenland Ice Sheet Project 2 (GISP2) ice core from central Greenland. In this paper we show how we calibrated this dust profile using instrumental neutron activation analysis (INAA) of aluminum. In the course of the calibration, we found that excluding NO3−, all the major impurities (soluble and insoluble) present in the ice covaried linearly. With respect to the dust concentration, we find that the LLS signal from ice below a depth of 2600 m follows a different linear trend than the LLS signal from shallow ice. We attribute this to the presence of numerous microbubbles (diameter <0.3 mm) that emerged in the deeper ice following core extraction.
Supply‐limited horizontal sand drift at an ephemerally crusted, unvegetated saline playa
Authors: Gillette Dale A. , Niemeyer Tezz C. , Helm Paula J.
Published: February 2004

A site at Owens Dry Lake was observed for more than 4 years. The site was a vegetation‐free saline playa where the surface formed “ephemeral crusts,” crusts that form after rainfall. Sometimes these crusts were destroyed and often a layer of particles on the crust would engage in vigorous aeolian activity. Three “phases” of active sand drifting are defined as almost no movement (extreme supply limitation), loose particles on crust with some degree of sand drift (moderate supply limitation), and unlimited source movement corresponding to a destroyed surface crust (unlimited supply). These “phases” occurred 45, 49, and 6% of the time, respectively. The accumulation of loose particles on the crust was mostly the result of in situ formation. Crusted sediments with loose particles on top can exhibit mass flux rates about the same as for noncrusted sediments. Crusted sediments limit or eliminate sand drift in two conditions: for rough crusts that effect a sufficiently high threshold friction velocity (above the wind friction velocity) and for limited amounts of loose particles on the crust where particle supply is less than would be transported in normal saltation for a thick sandy surface. These “supply‐limited” cases are similar to wind erosion of limited spilled material on a hard concrete surface. We quantified “supply limitation” by defining a “potential” or “supply unlimited” sand drift function Q = AG where A represents supply limitation that decreases as the particle source is depleted. Here Q is the mass of sand transported through a surface perpendicular to the ground and to the wind and having unit width during time period t, and G = ∫ u*(u2* − u2*t) dt for u* > u*t. G is integrated for the same time period t as for Q, u* is the friction velocity of the wind, and u*t is the threshold friction velocity of the wind. Hard crusts (usually formed in the summer) tended to show almost no change of threshold friction velocity with time and often gave total protection from wind erosion. Rough crusts provided sufficient protection expressed as high threshold friction velocities. For these high threshold friction velocities, aeolian activity was greatly reduced or practically prevented. The softest crusts, usually formed in the winter, provided much less protection and sometimes were destroyed by the wind. Following this destruction the “potential” or “supply unlimited” sand drift would be observed.
Path histories and timescales in stratospheric transport: Analysis of an idealized model
Authors: Hall Timothy M.
Published: February 2004

Mean age and the age spectrum, transport diagnostics independent of photochemistry, have been put to good use diagnosing stratospheric circulation and evaluating models. These diagnostics reveal how long air took to reach a stratospheric location from the troposphere, but they provide no direct information about where the air traveled en route. I define a complement to the age spectrum to explore how stratospheric transport timescales are related to path histories. Just as one constructs the age spectrum by distributing components of an air parcel according to transit time since last tropospheric contact, one can distribute the components according to the maximum height achieved en route to the parcel. Combining the age spectrum and the “maximum path height” distribution, one has a “joint distribution” of transit time and maximum path height. These ideas are illustrated with an idealized model of stratospheric transport, as well as a general circulation model. Transport features in the idealized model that strongly affect mean age affect the distribution of maximum path heights relatively weakly, especially in midlatitudes. The mass fraction of an air parcel at r that passed above some specified height z above r is strongly constrained by the mass continuity of stratospheric regions and is only more weakly affected by the circulation. This represents a limit on the relationship between mean age and trace gases of predominantly upper stratospheric photochemistry.
New model for the vapor growth of hexagonal ice crystals in the atmosphere
Authors: Wood Stephen E. , Baker Marcia B. , Calhoun Donna
Published: February 2004

We present a new microphysical model for the vapor growth and aspect ratio evolution of faceted, hexagonal ice crystals in the atmosphere. Our model is based on a novel, efficient numerical method for solving Laplace's equation for steady state diffusion on the surface of a three‐dimensional hexagonal prism, and also takes into account the surface kinetic processes of crystal growth. We do not include ventilation, so our model is limited to stationary crystals or falling crystals smaller than 100 μm. We calculate a self‐consistent solution for the distribution of the supersaturation and the condensation coefficient on each crystal face, for several different assumptions regarding the crystal growth mechanism and ice surface properties. We use this model to predict the aspect ratios expected for faceted ice crystals over a range of temperatures and supersaturations, as well as to estimate the conditions for which faceted growth becomes unstable and the crystals become hollowed or dendritic. We compare these predictions to observed features of ice cloud crystals to infer some microphysical characteristics of ice crystals and their temperature dependence. We also compare our predicted mass growth rates with those of the capacitance model for spheres and ellipsoids to look at the effects of shape and surface kinetics. Finally, we insert the single‐particle code into a simple parcel cloud model to investigate the feedbacks between crystal surface kinetics, shape, and the thermodynamic properties of clouds.
Ice‐supersaturated regions and subvisible cirrus in the northern midlatitude upper troposphere
Authors: Gierens Klaus , Schumann Ulrich , Helten Manfred , Smit Herman , Wang Pi‐Huan
Published: February 2004

Humidity and temperature data from the Measurement of Ozone by Airbus in‐service Aircraft (MOZAIC) project have been used to produce maps of probability for ice supersaturation in two 50 hPa thick layers centered around 200 and 250 hPa. As the MOZAIC data cover only international air routes, the resulting maps cover mainly the northern midlatitudes. The data of ice supersaturation have then been correlated with data of frequency of occurrence of subvisible cirrus from the Stratospheric Aerosol and Gas Experiment (SAGE II) satellite instrument. The correlation analysis provided strong indications that subvisible cirrus (SVC) is associated to ice‐supersaturated regions (ISSRs), although processes are possible that can decouple SVC from ISSRs. A first trial to derive a global picture of ice supersaturation near the tropopause was performed using a measure of cirrus fractional coverage constructed from meteorological analyses of European Centre for Medium‐Range Weather Forecasts and to correlate this with the supersaturation data. The correlation was only moderate (although significant), leading to the tentative conjecture that regions of frequent ice supersaturation are to be expected over the Indonesian archipelago, over the Amazonas basin, and over the northern Pacific between Japan and Canada. A final correlation analysis between the meteorological analysis data and the SVC data indicated that the formation of SVC is generally thermodynamically controlled, with the exception of the northern midlatitude SVC. The composition of the aerosol at the northern midlatitude tropopause is probably variable due to industrial emissions and air traffic. Hence the freezing properties of these particles may become important, which results in a weaker thermodynamic control of SVC formation in the northern midlatitudes.
A study of the aerosol radiative properties needed to compute direct aerosol forcing in the southeastern United States
Authors: Yu Shaocai , Saxena V. K. , Wenny B. N. , DeLuisi J. J. , Yue G. K. , Petropavlovskikh I. V.
Published: February 2004

To assess the direct radiative forcing due to aerosols in southeastern United States where a mild cooling is under way, an accurate set of data describing the aerosol radiative properties are needed. We report here aerosol optical depth (AOD) and diffuse to‐direct solar irradiance ratio (DDR) at three operational wavelengths (415, 500, 673 nm) determined by using Multifilter Rotating Shadowband Radiometers (MFRSR) at two sites (a mountain top site: Mount Gibbes, 35.78°N, 82.29°W, 2006 m mean sea level (msl); a valley site: Black Mountain, 35.66°N, 82.38°W, 951 m msl), which are separated horizontally by 10 km and vertically by 1 km. The characteristics AOD and DDR were determined from the field measurements obtained during 1995. It was found that the representative total AOD values at 500 nm at the valley site for highly polluted (HP), marine (M) and continental (C) air masses were 0.68±0.33, 0.29±0.19, and 0.10±0.04, respectively. The fact that the ratio of the mean 1 km layer optical depth to total mean optical depth at 500 nm from the valley site was 71% indicates that the major portion of the atmospheric aerosol was located in the lowest 1 km surface boundary layer (SBL). There was a significant linear correlation between the DDR and the total AOD at both sites. A simple, fast, and operative search‐graph method was used to retrieve the columnar size distribution (number concentration N effective radius reff, and geometric standard deviation σg) from the optical depth observations at the three operational wavelengths. The ground albedo, single‐scattering albedo, and imaginary part of the refractive index are calculated using a mathematically unique procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, AOD, and DDR. It was found that N, reff, and σg were in the range of 1.9×10 to 1.7×104 cm−3, 0.09–0.68 μm, and 1.12–2.70, respectively. The asymmetry factor and single‐scattering albedo were in the ranges of 0.63–0.75 and 0.74–0.99 respectively. The ground albedo over the forested terrain and the imaginary part of refractive index were found to be in the range of 0.08–0.29 and 0.005–0.051, respectively.
Use of Doppler radar to assess ice cloud particle fall velocity‐size relations for remote sensing and climate studies
Authors: Matrosov Sergey Y. , Heymsfield Andrew J.
Published: February 2004

Knowledge of ice crystal terminal velocities, both for individual crystals and for size distributions, is important for an adequate representation of ice particle sedimentation in climate models. While the terminal velocities (υt) of individual crystals of simple shapes have been measured, theoretical relations of the form υt = ADB (where D is the maximum particle dimension), obtained using expressions for the aerodynamic drag force, are often more useful because they can be applied to a wide range of particle sizes and heights and temperatures in the atmosphere. For high tropospheric ice clouds the coefficient A has been found to vary over 1 order of magnitude; the exponent B is generally within the range 0.7–1.4. Aerodynamic drag force calculations show that A and B are related. A and B can also be used to characterize terminal‐velocity‐particle characteristic size relations for size distributions. In this study we use collocated, vertically pointing measurements of ice cloud radar reflectivity, Doppler velocity, and IR brightness temperatures to estimate the vertical profiles of cloud particle characteristic size, cloud ice water content, and vertically averaged value of the coefficient A, emphasizing cirrus clouds. We analyze variations in terminal‐velocity‐size relations for individual particles and corresponding variations for ensembles of particles: for example, in relations between the reflectivity‐weighted terminal velocity and the median volume size and between the mass‐weighted terminal velocity and the median volume size. The retrievals indicate that A ranges from ∼250 to almost 4000 (cgs units), similar to the range found from the theoretical calculations. The coefficient A tends to decrease as a characteristic particle size (e.g., median size) increases. As a simplification for climate modeling efforts, we present an empirical relation between median size and A, although there is a fair amount of variability about this relation. Using the Doppler measurements and retrieval data, we also derive relations between the mass‐weighted terminal velocity and cloud ice water content. Such relations are useful for representing fallout of ice particles in climate and cloud‐resolving models.
Comparisons of GPS‐derived precipitable water vapors with radiosonde observations in Japan
Authors: Ohtani Ryu , Naito Isao
Published: February 2004

We investigated the accuracy and features of precipitable water vapor (PWV) obtained from the Japanese Global Positioning System (GPS) network. We compared PWVs estimated from the Geographical Survey Institute (GSI) routine geodetic analysis using the Bernese software with those derived from the nearest 10 radiosonde stations over the Japanese islands. The comparisons for a half year showed that the agreement of the GPS‐derived PWV was 3.7 mm in terms of rms difference, with a standard deviation of 2.6 mm and a mean bias of −2.7 mm, which is less precise than those obtained in central North America. This may reflect the high temporal and spatial variability of water vapor over the Japanese islands, causing differences between PWVs if GPS and radiosonde launch stations are not colocated. We also found systematic biases in the GPS‐derived PWV. The absolute value of the mean bias at 1200 UT was systematically larger than that at 0000 UT. Their difference reached as much as 2 mm. Moreover, the mean biases tended to increase as PWV increased. We also confirmed that there were similar systematic biases in the PWV obtained from our GPS analysis using the GIPSY software with high temporal resolution. This fact indicates that the systematic biases depend neither on analysis software nor on temporal resolution of PWV estimation. We analyzed GPS data collected at the Tsukuba station using GIPSY for 2 years and showed a possibility that the systematic biases also found at the Tsukuba station were attributed to ocean tidal loading and seasonal variation of the mapping function both of which were not taken into account in the GPS analysis with the routine analysis using Bernese and our analysis using GIPSY. These results suggest the importance of implementing them in the analysis for accurate estimates of absolute value of PWV from the Japanese GPS network.
Uptake of gas‐phase SO2 in aqueous sulfuric acid: Oxidation by H2O2, O3, and HONO
Authors: Rattigan O. V. , Boniface J. , Swartz E. , Davidovits P. , Jayne J. T. , Kolb C. E. , Worsnop D. R.
Published: February 2004

Uptake of SO2(g) was measured as a function of sulfuric acid concentration in the range pH = 1 to 70 wt% H2SO4 at 293 K. Uptake studies were carried out in the presence of solvated H2O2, O3, HONO, NO2, and HNO3. The studies yielded Henry's law coefficients for SO2 which were in accord with previous measurements. The results provided first time determinations at high acidities of rate coefficients for the reaction of SO2 with H2O2, O3, and HONO in the solvated state. The observed SO2(g) uptake was consistent with bulk phase oxidation processes. The measured rate coefficients were used to evaluate the role of heterogeneous interactions with the selected species for aerosol formation in aircraft plumes. Calculations show that these interactions are insignificant compared to gas phase oxidation by the OH radical.
High‐resolution regional climate model validation and permafrost simulation for the East European Russian Arctic
Authors: Christensen Jens Hesselbjerg , Kuhry Peter
Published: February 2004

A 15‐year‐long, 16 km horizontal resolution, present‐day climate simulation has been conducted with the HIRHAM4 regional climate model. The model has been forced by the European Centre for Medium‐Range Weather Forecasts reanalyses at the lateral boundary and over sea by sea surface temperature and sea ice concentrations from the same source. The model domain is centered over the European part of Arctic Russia focusing on the Usa River basin near the Ural Mountains. It is demonstrated that with this fine mesh, the model simulates the annual course and interannual variability in temperature and precipitation quite realistically. Furthermore the model captures the timing of permanent snow cover very accurately with less than 1‐week discrepancy in both autumn and spring. An interpretation of modeled subsurface layer temperatures in terms of mean annual temperature and a “frost index” reveals that the model captures presentday regional permafrost patterns to a high degree of accuracy.
Changes in surface solar UV irradiances and total ozone during the solar eclipse of August 11, 1999
Authors: Zerefos C. S. , Balis D. S. , Meleti C. , Bais A. F. , Tourpali K. , Kourtidis K. , Vanicek K. , Cappellani F. , Kaminski U. , Colombo T. , Stübi R. , Manea L. , Formenti P. , Andreae M. O.
Published: February 2004

During the solar eclipse of August 11, 1999, intensive measurements of UV solar irradiance and total ozone were performed at a number of observatories located near the path of the Moon's shadow. At the Laboratory of Atmospheric Physics (LAP) of the Aristotle University of Thessaloniki, Greece, global and direct spectra of UV solar irradiances (285–365 nm) were recorded with a double monochromator, and erythemal irradiances were measured with broadband pyranometers. In addition, higher‐frequency measurements of global and direct irradiances at six UV wavelengths were performed with a single Brewer spectrophotometer. Total ozone measurements were also performed with Dobson and Brewer spectrophotometers at Hradec Kralove (Czech Republic), Ispra (Italy), Sestola (Italy), Hohenpeissenberg (Germany), Bucharest (Romania), Arosa (Switzerland), and Thessaloniki (Greece). From the spectral UV measurements the limb darkening effect of the solar disk was tentatively quantified from differences of measured solar spectral irradiances at the peak of the eclipse (near to limb conditions) and before the eclipse. Two blackbody curves were fit to the preeclipse and peak eclipse spectra, which have shown a difference in effective temperatures of about 165°K between the limb and the whole of the solar disk. The limb darkening effect is larger at the shorter UV wavelengths. The ratio of the diffuse to direct solar irradiances during the eclipse shows that the diffuse component is reduced much less compared to the decline of the direct solar irradiance at the shorter wavelengths. Moreover, a 20‐min oscillation of erythemal UV‐B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20‐min fluctuation in total ozone, presumably caused by the eclipse‐induced gravity waves. This work also shows that routine total ozone measurements with a Brewer or a Dobson spectrophotometer should be used with caution during a solar eclipse. This is because the diffuse light increases by more than 30% with respect to the direct solar radiation, increasing more at the shorter wavelength side of the UV spectrum. This plausible mechanism introduces an artificial decrease in total ozone during solar eclipse of more than 30 Dobson units (DU), which is confirmed by all Brewer and Dobson measurements. Changes in total ozone cited earlier in the refereed literature have not been confirmed in the present study.
The use of long‐duration balloon data to determine the accuracy of stratospheric analyses and forecasts
Authors: Keil Michael , Heun Matt , Austin John , Lahoz William , Lou Guang Ping , O'Neill Alan
Published: February 2004

Wind velocity data from seven high‐altitude long‐duration balloon flights are compared with stratospheric analyses and forecasts produced by the U.K. Meteorological Office (UKMO) and the Data Assimilation Office (DAO). The results suggest that biases in both the UKMO and DAO analyses arise from the displacement of the polar night jet to higher latitudes in the winter and from a cold bias in the stratosphere in the summer. At high latitudes the DAO analysis performs better than the UKMO analyses, with the use of a rotated pole in the DAO system the most likely cause of the improvement. The trajectories for each flight were simulated using UKMO and DAO 5‐day forecasts and by using simple persistence techniques. It is shown that UKMO and DAO forecasts based on better initial analyses produced trajectories that were more accurate. On the 1‐day forecast timescale there is little difference between the techniques, but on the 2‐ to 5‐day range the trajectories based on forecasts generally performed significantly better than persistence. The results demonstrate the usefulness of stratospheric balloon data for validating both analyses and forecasts.
Changes in the Earth's UV reflectivity from the surface, clouds, and aerosols
Authors: Herman J. R. , Larko D. , Celarier E. , Ziemke J.
Published: February 2004

Measurements of the Earth's 380 nm UV reflectivity combine the effects of surface reflectivity, aerosols, haze, cloud optical thickness, and the fraction of the scene covered by clouds. Changes in UV cloud and aerosol reflectivity would imply similar changes over a wide range of wavelengths, UV, visible, and near infrared (at least 0.3 to 2 μm), affecting both the transmission of radiation to the Earth's surface and the reflection back to space. Using the TOMS (Total Ozone Mapping Spectrometer) 380 nm reflectivity data, the 14‐year annual mean power reflected back to space is 385.3±31 W/m2, mostly by clouds, aerosols, and snow/ice. On the basis of measured long‐term changes in global reflectivity, it is estimated that there is an additional 2.8±2.8 W/m2 per decade reflected back to space (2 standard deviation error estimate) during the TOMS observing period of 1979–1992. Since the 380 nm surface reflectivity is low (2–8%) over most surfaces, water and land, the observed reflectivity changes are mostly caused by changes in the amount of snow/ice, cloudiness, and aerosols. Time series analysis of TOMS reflectivity over the period from 1979 to 1992 shows that there were no significant changes in annually averaged zonal‐average reflectivity at latitudes within 60°S–60°N, even though there were changes at higher latitudes (e.g., 3% per decade, in reflectivity units, between 60°N and 70°N). When the effects of the 11.3‐year solar cycle and ENSO (El Niño‐Southern Oscillation) are removed from the data, statistically significant reflectivity changes are observed poleward of both 40°S and 40°N. The presence of a statistically significant 11.3‐year periodicity in the reflectivity time series correlates with the solar cycle and suggests a possible Sun‐weather relationship. There are significant regional changes in reflectivity R over land and ocean areas that affect the amount of solar radiation reaching the surface. The largest of these regions have decreases in R of 3 to 6 ± 1% per decade in central Europe, the western United States, central China, and western Russia. These decreases are offset by increases in the same latitude bands mostly over the oceans. The largest regions showing an increase in R are off the western coast of South America (near Chile and Peru), 5 to 8 ± 1%/decade and over the Weddell Sea in Antarctica of 10%/decade, but no change over the ice shelf and continent. The largest increase in R occurs over the ocean just to the north of Antarctica. This change is important because it reduces UV radiation overall (290–400 nm) and partially offsets the effect of the increased amount of UV‐B radiation (290–320 nm) caused by decreasing Antarctic ozone.
Soil moisture simulations in revised AMIP models
Authors: Srinivasan G. , Robock Alan , Entin Jared K. , Luo Lifeng , Vinnikov Konstantin Y. , Viterbo Pedro
Published: February 2004

Soil moisture is important both in its influence on climate and for assessing impacts of future climate change. It is therefore necessary to simulate it correctly in global climate models. We have used the revisit simulations contributed by six of the Atmospheric Model Intercomparison Project 1 participating modeling groups to examine the impacts of model revisions, particularly the land surface representations, on soil moisture simulations, by comparing the simulations to actual soil moisture observations. The revised models do not show any systematic improvement in their ability to simulate observed seasonal variations of soil moisture over the regions studied. Many of the revised models continue to have a strong tendency toward dry soil conditions during Northern Hemisphere summer months, both globally and regionally. There are no indications of conceptually more realistic land surface representations producing better soil moisture simulations in the revised climate models. As the revised models continue to produce incorrect simulations of the seasonal cycle of regional precipitation, it is not possible to isolate the effect of land surface schemes on the simulations. The European Centre for Medium Range Weather Forecasts and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyses, however, which are driven by observed precipitation, do capture some of the observed interannual variability of soil moisture over Illinois.
Nonhydrostatic climate simulations of precipitation over complex terrain
Authors: Grell Georg A. , Schade Lars , Knoche Richard , Pfeiffer Andreas , Egger Joseph
Published: February 2004

A climate version of the nonhydrostatic fifth‐generation Penn State/NCAR Mesoscale Model has been used to downscale a global climate scenario to cloud‐resolving scales over complex terrain (the Alps). After first describing the model and methodology, we then present comparison results from the model‐predicted and ensemble‐averaged regional‐scale winter and summer season precipitation distribution with results from the global simulation and analyzed observed precipitation climatologies. Finally, results from the cloud‐resolving simulations are compared to the regional simulations. It is shown that the degree to which the terrain is resolved in the various runs significantly alters the simulation of the precipitation climatologies. This is caused not only by the complex interaction of the flow with the topography but also by the different treatment of the convective processes (resolved versus nonresolved) in the model. Even in winter, the model‐simulated seasonally averaged precipitation patterns change drastically with every increase in horizontal resolution. Furthermore, with a horizontal grid resolution of 1km, when seen on a local scale and over complex terrain, the model‐simulated precipitation patterns are not guaranteed to converge to one solution. This behavior is still more complicated in summer. Here it is shown that parameterized convection in the regional model simulation tends to be locked to the mountains, while in the cloud‐resolving simulations the convection moves with the upper level flow, producing precipitation maxima away from the mountain tops.
The effects of gravity waves on distributions of chemically active constituents in the mesopause region
Authors: Xu Jiyao , Smith Anne K. , Brasseur Guy P.
Published: February 2004

The influence of a monochromatic atmospheric gravity wave of fixed amplitude on the mean vertical distribution of mesospheric minor species is studied using a dynamical‐photochemical gravity wave model. The fluctuations of winds, temperature, and species concentrations produced by the wave are calculated by a coupled linear gravity wave model. The effects of the wave on the mean mixing ratio of 19 key chemically active species is derived from a coupled system of continuity equations which accounts for full nonlinear photochemistry in a vertical column. This study focuses on the impact that gravity wave induced nonlinearities in the chemical reaction rates has on the chemical species distribution. The effects of gravity wave induced chemical transport and background diffusion are also calculated. Calculations indicate that the impacts of gravity waves on the vertical distribution (mean concentration) of atmospheric minor constituents are largest in the mesopause region, especially during nighttime. A comparison of the three effects indicates that for short lifetime chemical species such as O3 and OH, the tendency due to chemical reaction perturbations induced by gravity waves is much greater than that due to transport and diffusion. The altitude range over which these nonlinearities is important is narrowly confined to the chemically active region near the mesopause.
Global Modeling Initiative assessment model: Model description, integration, and testing of the transport shell
Authors: Rotman D. A. , Tannahill J. R. , Kinnison D. E. , Connell P. S. , Bergmann D. , Proctor D. , Rodriguez J. M. , Lin S. J. , Rood R. B. , Prather M. J. , Rasch P. J. , Considine D. B. , Ramaroson R. , Kawa S. R.
Published: February 2004

We describe the three‐dimensional global stratospheric chemistry model developed under the NASA Global Modeling Initiative (GMI) to assess the possible environmental consequences from the emissions of a fleet of proposed high‐speed civil transport aircraft. This model was developed through a unique collaboration of the members of the GMI team. Team members provided computational modules representing various physical and chemical processes, and analysis of simulation results through extensive comparison to observation. The team members' modules were integrated within a computational framework that allowed transportability and simulations on massively parallel computers. A unique aspect of this model framework is the ability to interchange and intercompare different submodules to assess the sensitivity of numerical algorithms and model assumptions to simulation results. In this paper, we discuss the important attributes of the GMI effort and describe the GMI model computational framework and the numerical modules representing physical and chemical processes. As an application of the concept, we illustrate an analysis of the impact of advection algorithms on the dispersion of a NOy‐like source in the stratosphere which mimics that of a fleet of commercial supersonic transports (high‐speed civil transport (HSCT)) flying between 17 and 20 km.
A Greenland ice core record of low molecular weight dicarboxylic acids, ketocarboxylic acids, and α‐dicarbonyls: A trend from Little Ice Age to the present (1540 to 1989 A.D.)
Authors: Kawamura K. , Yokoyama K. , Fujii Y. , Watanabe O.
Published: February 2004

A homologous series of α,ω‐dicarboxylic acids (C2‐C10), ω‐oxocarboxylic acids (C2‐C9), pyruvic acid, and α‐dicarbonyls (C2‐C3) were measured in the ice core samples (206 m long, ∼450 years old) taken from Site‐J (Greenland) using a capillary gas chromatography and mass spectrometry. The measurements have been made on a basis of discontinuous sampling (sampling frequency is roughly 8% of the total ice core length). Molecular distributions of the diacids showed a predominance of succinic acid (C4), followed by oxalic (C2) and malonic (C3) acids, whereas those of ω‐oxoacids showed a predominance of C4 or C3 species. Concentration ranges of the total diacids, ω‐oxoacids, and α‐dicarbonyls were 3.1–32.5 ng g−1, 0.13–2.8 ng g−1, and 0.09–1.7 ng g−1, respectively. Relative abundances of total diacid carbon contents in total organic carbon (TOC; 0.7–5.7 μgC g−1) ranged from 0.04% to 1.3%. The relative abundance of major diacids smoothly fluctuated with maxima at ∼1580, 1780, 1840, 1940, and 1980 years and minima at ∼1680, 1820, 1860, and 1970 years. This trend is generally in good agreement with the changes in the recorded and reconstructed air temperature in the Northern Hemisphere. Temporal trends of the diacids can be explained in terms of the past changes in the sea‐to‐air emissions of marine organic matter, which is subsequently subjected to a photochemical oxidation in the atmosphere during long‐range transport toward the Greenland ice sheet. Further, it was found that the historical trend of oxalic acid‐C/TOC correlates with the reconstructed solar irradiance since 1600, suggesting that oxalic acid is more efficiently produced in the past atmosphere by photochemical oxidation of biogenic species during periods characterized by enhanced solar radiations. Oxalic acid signals were also suggested to be modulated by the frequency of biomass burning inputs.