bluuebunny/crossref_metadata_2025 huggingface dataset:
Large‐scale hydro‐climatology of the terrestrial Arctic drainage system
Authors: Serreze Mark C. , Bromwich David H. , Clark Martyn P. , Etringer Andrew J. , Zhang Tingjun , Lammers Richard
Published: December 2002

The large‐scale hydro‐climatology of the terrestrial Arctic drainage system is examined, focusing on the period 1960 onward. Special attention is paid to the Ob, Yenisey, Lena, and Mackenzie watersheds, which provide the bulk of freshwater discharge to the Arctic Ocean. Station data are used to compile monthly gridded time series of gauge‐corrected precipitation (P). Gridded time series of precipitation minus evapotranspiration (P−ET) are calculated from the moisture flux convergence using NCEP reanalysis data. Estimates of ET are obtained as a residual. Runoff (R) is obtained from available discharge records. For long‐term water‐year means, P−ET for the Yenisey, Lena, and Mackenzie watersheds is 16–20% lower than the observed runoff. In the Ob watershed, the two values agree within 9%. Given the uncertainties in P−ET, we consider the atmospheric and surface water budgets to be reasonably closed. Compared to the other three basins, the mean runoff ratio (R/P) is lower in the Ob watershed, consistent with the high fraction of annual precipitation lost through ET. All basins exhibit summer maxima in P and minima in P−ET. Summer P−ET in the Ob watershed is negative due to high ET rates. For large domains in northern Eurasia, about 25% of July precipitation is associated with the recycling of water vapor evapotranspirated within each domain. This points to a significant effect of the land surface on the hydrologic regime. Variability in P and P−ET has generally clear associations with the regional atmospheric circulation. A strong link with the Urals trough is documented for the Ob. Relationships with indices of the Arctic Oscillation and other teleconnections are generally weak. Water‐year time series of runoff and P−ET are strongly correlated in the Lena watershed only, reflecting extensive permafrost. Cold‐season runoff has increased in the Yenisey and Lena watersheds. This is most pronounced in the Yenisey watershed, where runoff has also increased sharply in spring, decreased in summer, but has increased for the year as a whole. The mechanisms for these changes are not entirely clear. While they fundamentally relate to higher air temperatures, increased winter precipitation, and strong summer drying, we speculate links with changes in active layer thickness and thawing permafrost.
Ground‐based measurements of peroxycarboxylic nitric anhydrides (PANs) during the 1999 Southern Oxidants Study Nashville Intensive
Authors: Roberts James M. , Flocke Frank , Stroud Craig A. , Hereid Daniel , Williams Eric , Fehsenfeld Fred , Brune William , Martinez Monica , Harder Hartwig
Published: December 2002

Peroxycarboxylic nitric anhydrides (PANs) were measured at Cornelia Fort Airpark during the 1999 Nashville Intensive of the Southern Oxidants Study. The observed concentrations were similar to those measured in the 1994 and 1995 Nashville Intensives. The average daytime ratio of peroxypropionic nitric anhydride (PPN) to peroxyacetic nitric anhydride (PAN) was 13.7%. Extensive measurements were also made of peroxyisobutyric nitric anhydride (PiBN), which confirm the anthropogenic origin of this compound, and its ratio to PAN was 2.4% on average. The daytime ratio of peroxymethacrylic nitric anhydride (MPAN) to PAN was as high as 25% during periods of high biogenic hydrocarbon (BHC) impact. A simple linear combination model was used to estimate anthropogenic hydrocarbon (AHC) and BHC contributions to O3 production. On average, 80% of the O3 observed over 80 ppbv was attributed to AHC chemistry and 20% to BHC chemistry. An exception to this was a plume derived from a combination of power plant NOx and isoprene emissions from west of the city, in which the BHC contribution was at least 50 to 75%.
Impact of vegetation and preferential source areas on global dust aerosol: Results from a model study
Authors: Tegen Ina , Harrison Sandy P. , Kohfeld Karen , Prentice I. Colin , Coe Michael , Heimann Martin
Published: December 2002

We present a model of the dust cycle that successfully predicts dust emissions as determined by land surface properties, monthly vegetation and snow cover, and 6‐hourly surface wind speeds for the years 1982–1993. The model takes account of the role of dry lake beds as preferential source areas for dust emission. The occurrence of these preferential sources is determined by a water routing and storage model. The dust source scheme also explicitly takes into account the role of vegetation type as well as monthly vegetation cover. Dust transport is computed using assimilated winds for the years 1987–1990. Deposition of dust occurs through dry and wet deposition, where subcloud scavenging is calculated using assimilated precipitation fields. Comparison of simulated patterns of atmospheric dust loading with the Total Ozone Mapping Spectrometer satellite absorbing aerosol index shows that the model produces realistic results from daily to interannual timescales. The magnitude of dust deposition agrees well with sediment flux data from marine sites. Emission of submicron dust from preferential source areas are required for the computation of a realistic dust optical thickness. Sensitivity studies show that Asian dust source strengths are particularly sensitive to the seasonality of vegetation cover.
Simulation of stratospheric sulfate aerosols using a Center for Climate System Research/National Institute for Environmental Studies atmospheric GCM with coupled chemistry 1. Nonvolcanic simulation
Authors: Takigawa Masayuki , Takahashi Masaaki , Akiyoshi Hideharu
Published: December 2002

A new middle‐atmosphere general circulation model (GCM) that includes the photochemistry for Ox‐HOx‐NOx‐ClOx‐SOx species has been developed. The dynamical, radiative, and chemical processes of the model are fully interactive. The model is based on the Center for Climate System Research/National Institute for Environmental Studies atmospheric GCM (CCSR/NIES AGCM). The chemical process predicts the concentration of 37 chemically reactive gases and includes 26 photolysis and 71 homogeneous reactions. It also includes four heterogeneous reactions on the surface of sulfate aerosols. Gaseous sulfuric acid is produced by the photolysis of carbonyl sulfide (OCS) and SO2 oxidation, and saturated sulfuric acid is condensed into aerosols. The aerosol size distribution is assumed to be unimodal and lognormal, and the aerosol composition is assumed to be 75% sulfuric acid droplets. The model considers washout, surface deposition, and sedimentation of sulfate aerosols. The parameterized updraft and downdraft of tracers by deep convection is also taken into consideration. In order to investigate the chemical effect of nonvolcanic sulfate aerosols, an 8‐year integration has been done. A net flux of gaseous sulfate precursors from the troposphere to the stratosphere is estimated to be 0.067 TgS/yr. The transport of SO2 from the troposphere to the stratosphere contributes about 48% of the net flux.
Evolution of ozone and ozone‐related species over Kiruna during the SOLVE/THESEO 2000 campaign retrieved from ground‐based millimeter‐wave and infrared observations
Authors: Kopp Gerhard , Berg Hermann , Blumenstock Thomas , Fischer Herbert , Hase Frank , Hochschild Gerd , Höpfner Michael , Kouker Wolfgang , Reddmann Thomas , Ruhnke Roland , Raffalski Uwe , Kondo Yutaka
Published: December 2002

Vertical profiles of stratospheric ozone and ozone‐related trace gases were measured in winter 1999/2000 using the ground‐based millimeter‐wave radiometer MIRA 2 and a Fourier‐transform infrared spectrometer (FTIR) located at the Swedish Institute of Space Physics at Kiruna. The MIRA 2 measurements covered all three SOLVE/THESEO 2000 flight phases. An almost complete time series of O3 profiles and complementary profiles of ClO, HNO3, and N2O were achieved. Profiles of O3, HCl, HNO3, and N2O, as well as stratospheric column amounts of NO2, ClONO2, and ClO, were obtained from the continuous ground‐based FTIR measurements between January and March 2000. From the measurements of N2O and HF, a diabatic subsidence inside the polar vortex of about 1.2 km between January and March for altitudes of about 20 km was deduced. On 26 and 28 January, an uptake of about 25% of stratospheric HNO3 by polar stratospheric clouds (PSCs) could be measured and between January and March, an significant denitrification of the lower stratosphere was derived from the measurements. Strong chlorine activation was detected by both instruments in January and March, resulting in an ozone loss of more than 1 ppmv in a layer below 23 km. In comparison to recent cold winters, this layer was found to be quite thin. Therefore the total loss measured in column amount of (1.2–1.4) × 1022 molec/m2 was smaller than the losses in previous cold winters.
Assessment of volatile organic compound emissions from ecosystems of China
Authors: Klinger L. F. , Li Q.‐J. , Guenther A. B. , Greenberg J. P. , Baker B. , Bai J.‐H.
Published: December 2002

Isoprene, monoterpene, and other volatile organic compound (VOC) emissions from grasslands, shrublands, forests, and peatlands in China were characterized to estimate their regional magnitudes and to compare these emissions with those from landscapes of North America, Europe, and Africa. Ecological and VOC emission sampling was conducted at 52 sites centered in and around major research stations located in seven different regions of China: Inner Mongolia (temperate), Changbai Mountain (boreal‐temperate), Beijing Mountain (temperate), Dinghu Mountain (subtropical), Ailao Mountain (subtropical), Kunming (subtropical), and Xishuangbanna (tropical). Transects were used to sample plant species and growth form composition, leafy (green) biomass, and leaf area in forests representing nearly all the major forest types of China. Leafy biomass was determined using generic algorithms based on tree diameter, canopy structure, and absolute cover. Measurements of VOC emissions were made on 386 of the 541 recorded species using a portable photo‐ionization detector method. For 105 species, VOC emissions were also measured using a flow‐through leaf cuvette sampling/gas chromatography analysis method. Results indicate that isoprene and monoterpene emissions, as well as leafy biomass, vary systematically along gradients of ecological succession in the same manner found in previous studies in the United States, Canada, and Africa. Applying these results to a regional VOC emissions model, we arrive at a value of 21 Tg C for total annual biogenic VOC emissions from China, compared to 5 Tg C of VOCs released annually from anthropogenic sources there. The isoprene and monoterpene emissions are nearly the same as those reported for Europe, which is comparable in size to China.
Airborne spectroscopic observations of chlorine activation and denitrification of the 1999/2000 winter Arctic stratosphere during SOLVE
Authors: Coffey M. T. , Mankin William G. , Hannigan James W. , Toon G. C.
Published: December 2002

We have used Fourier transform spectrometers aboard the NASA DC‐8 and on balloons as part of the SAGE III Ozone Loss and Validation Experiment (SOLVE) to record infrared absorption spectra of the polar stratosphere. From the high‐resolution aircraft spectra we derived vertical column amounts of HCl, HF, NO2, HNO3, and a number of other gases for 11 flights in the region of the northern polar vortex. Vertical mixing ratio profiles are derived for a number of gases from two balloon flights. Within the vortex, where low values of total ozone are observed during the latter part of the observation period, we observed markedly reduced columns of HCl and NO2 and elevated columns of HF and HNO3 relative to columns outside the vortex. The low value for the ratio of HCl to HF indicates that HCl had been chemically or physically removed, probably providing a source for active chlorine. High values of HNO3 inside the vortex indicate that nitrogen oxides, which might otherwise mitigate chlorine‐catalyzed ozone destruction, have been converted into more stable reservoirs. Because of incorporation into particles, some nitric acid may be removed from the stratosphere altogether.
CHASER: A global chemical model of the troposphere 2. Model results and evaluation
Authors: Sudo Kengo , Takahashi Masaaki , Akimoto Hajime
Published: December 2002

We present results from a global three‐dimensional chemical model for the troposphere, named Chemical AGCM for Study of Atmospheric Environment and Radiative Forcing (CHASER). This model has been developed to simulate the tropospheric photochemistry involving the O3‐HOx‐NOx‐CH4‐CO photochemical system and oxidation of nonmethane hydrocarbons (NMHCs), based on an atmospheric general circulation model (AGCM). In this paper, we present results from a climatological run of the model, and evaluate them with observational data. The simulation was conducted at the model horizontal resolution of T21 (5.6° × 5.6°) with 32 vertical layers from the surface to about 40 km altitude. The model reproduces well the observed vertical profiles of CO and NMHCs as ethane, propane, and acetone in almost all cases. The simulated seasonal cycle of surface CO in the biomass‐burning region (South America) shows a good agreement with observation. In the case of nitric oxide (NO), the model generally reproduces the observed vertical profiles well, though it appears to somewhat underestimate NO in the upper troposphere in the low latitudes. Although the model overestimates nitric acid (HNO3) in some cases like other model studies, the calculated HNO3 is generally within the range of observations. Peroxyacetyl nitrate (PAN) appears to be generally simulated well, but overestimated by the model in some remote regions. In the simulation of O3, the vertical profiles and seasonal variations observed in polluted and remote sites are well reproduced. The ozone distributions calculated in the biomass‐burning‐related regions as South America, Africa, and the South Atlantic show good agreements with observations. However, in the midlatitudes, the model tends to overestimate O3 in the upper troposphere in winter‐springtime, maybe indicating the need of improving the model's horizontal resolution. The model calculates a net chemical ozone production of 397 TgO3/yr in the global troposphere (4895 TgO3/yr production and 4498 TgO3/yr destruction). The estimated net O3 flux from the stratosphere is 593 TgO3/yr, well within the range suggested by recent studies. The calculated global OH concentration leads to a global mean CH4 lifetime of 7.9 years in this simulation.
A study of an INDOEX period with aerosol transport to the eastern Mediterranean area
Authors: Krichak Simon O. , Tsidulko Marina , Alpert Pinhas
Published: December 2002

Forward trajectories of the air masses from the Arabian Sea area were computed for each day from February 1 to April 10, 1999. This allowed the determination of the episodes characterized by the air mass transport to Africa and the Mediterranean region. Numerical simulation of one of such episodes, also characterized by intense cyclone and dust plume development, was performed using the Eta weather and dust predicting system. The simulation allowed an evaluation of the vertical distribution of the pollutants in the cyclone. Backward trajectories, ending in the area of the cyclone development point to the origin of a part of its air masses over the Arabian Sea. Potential role of the eastern Mediterranean weather systems in the transport to Europe of the polluted air masses from the INDOEX area is discussed.
A new model of spongy icing from first principles
Authors: Blackmore R. Z. , Makkonen L. , Lozowski E. P.
Published: December 2002

A new icing model has been developed to predict the sponginess (liquid fraction) and growth rate of freshwater ice accretions growing under a surface film of unfrozen water. This model is developed from first principles and does not require experimental sponginess data to tune the model parameters. The model identifies icing conditions that include no accretion, dry accretion, glaze accretion, spongy nonshedding, and spongy shedding regimes. It is a steady state model for a stationary vertical cylinder intercepting horizontally directed spray. The model predicts both the accretion mass growth flux and the accretion sponginess. The model results suggest that spongy shedding and spongy nonshedding regimes are common under the high liquid flux conditions typical of freshwater ship icing. Moreover, the unfrozen liquid incorporated into the spongy ice matrix can substantially increase the ice accretion load over that which would be predicted purely thermodynamically. Despite differences in the experimental setup, the model's performance compares well with two independent freshwater experimental data sets for icing on horizontal rotating cylinders. The model performs well in its prediction of both accretion sponginess and growth rate. The model predicts sponginess with a variation in liquid mass fraction of about 0.2–0.5, over the range of air temperature of 0°C to −30°C, in agreement with observations.
Constraining tropospheric ozone column through data assimilation
Authors: Lamarque J.‐F. , Khattatov B. V. , Gille J. C.
Published: December 2002

Global distributions of the tropospheric ozone column (TOC) and its error are estimated by assimilating satellite observations of total ozone column and stratospheric ozone profiles in a global chemistry‐transport model. A quantitative comparison of the calculated TOC with collocated ozonesondes observations shows good agreement over a wide range of latitudes for the period studied (July–September 1992), even at the daily timescale. In most cases, the difference with the ozonesonde‐based TOC is within the calculated error estimate. Comparison with the TOC distribution by Thompson and Hudson [1999] does not lead to any quantitative conclusion due to a mix of similarities and differences, even in the geographical distribution of the TOC. A positive TOC bias with respect to ozonesondes is found in this study over Hilo and Irene, probably due to a misrepresentation of the transport of ozone in a region of strong TOC gradients. In September 1992 the LIDAR observations from the TRACE‐A campaign are also assimilated. This is shown to provide a constraint on the TOC that significantly propagates across the Atlantic Ocean, indicating the importance of point measurements of ozone for constraining its large‐scale distribution.
Role of temperature history in polar stratospheric cloud sightings
Authors: Steele H. M. , Lumpe J. D. , Bevilacqua R. M. , Hoppel K. W. , Turco R. P.
Published: December 2002

In this paper, aerosol data from the Polar Ozone and Aerosol Measurement (POAM) satellites between 1994 and 1998 are used to explore the existence of polar stratospheric clouds (PSCs) in the Antarctic winter stratosphere. Multiwavelength aerosol extinction data are combined to yield aerosol volume density which is compared with that generated from theoretical equilibrium models for nitric acid trihydrate (NAT) particles and supercooled ternary solution (STS) droplets at 30 mb. As winter progresses, PSC volume falls, a strong indication of stratospheric denitrification or dehydration. Six‐day isentropic back trajectories are generated from each of the POAM observation locations and are used to examine the recent temperature history of the aerosols. Statistical studies are carried out using multiple regression to determine whether temperature history plays a role in NAT cloud formation. We are unable to identify any factors which unquestionably affect the formation of PSCs at and just below the NAT condensation temperature, although the probability of PSC occurrence at this temperature is higher in air that had previously been colder. There is no significant evidence found for preferential cloud occurrence based upon the length of time that the aerosols were below the NAT condensation point. We conclude from this study that factors, other than temperature and temperature history, are partially responsible for the formation of NAT PSCs.
Sensitivity of photooxidant production in the Milan Basin: An overview of results from a EUROTRAC‐2 Limitation of Oxidant Production field experiment
Authors: Neftel Albrecht , Spirig Christoph , Prévôt André S. H. , Furger Markus , Stutz Jochen , Vogel Bernhard , Hjorth Jens
Published: December 2002

The international field experiment Pianura Padana Produzione di Ozono (PIPAPO) studying the volatile organic compounds (VOC)/NOxozone production sensitivity took place in May and June 1998 downwind of the metropolitan area of Milan. The project was embedded in the framework of the EUROTRAC‐2 Limitation of Oxidant Production (LOOP) subproject. Several ground stations between the city of Milan and the Alps north of Milan combined with airborne measurements delivered a comprehensive data set suitable for observation‐based analysis and validation of chemical transport models. The special section devoted to the PIPAPO project contains 10 contributions on the characterization of secondary aerosol formation, and radical precursors, and the characterization of ozone production sensitivity based on field measurements and numerical model simulations. In this paper the scientific background and the major objectives of PIPAPO are described. An overview of the field measurement program, the study site, and the meteorological conditions prevailing during the experiment are given. A general conclusion of the combined results is that under typical summer conditions in the Milan area with clear skies, low wind speeds and high temperatures, the transition from VOC‐ to NOx‐sensitive ozone production occurs a few tens of kilometers downwind of the strongest emission sources in the city of Milan.
Multiple regimes and low‐frequency oscillations in the Southern Hemisphere's zonal‐mean flow
Authors: Koo Seongjoon , Robertson Andrew W. , Ghil Michael
Published: December 2002

Multiple regimes in the atmospheric zonal‐mean flow of the Southern Hemisphere are examined using 53 years of daily observational data. Estimates of the probability density function in the reduced‐phase space spanned by the two leading empirical orthogonal functions (EOFs) exhibit significant deviations from bivariate Gaussianity. Two major regimes are identified, which describe the extreme phases of atmospheric zonal‐flow vacillation: in the high‐latitude regime the jet is displaced poleward from its climatological mean position, while in the low‐latitude regime it is displaced equatorward. The two zonal‐flow regimes are maintained by the forcing due to transient eddies against surface friction. Significant low‐frequency oscillatory components, with peaks near 135 and 70 days, are found in the EOF mode associated with zonal‐flow vacillation. These oscillations are described using both the multitaper method and singular spectrum analysis. Close examination of the relationship between the regimes and the oscillations suggests that the high‐ and low‐latitude regimes tend to be associated with the extremes of either low‐frequency oscillation. We illustrate how the phase information of either low‐frequency oscillation could be used as a predictor for the high‐ and low‐latitude regime.
Chlorine activation and chemical ozone loss deduced from HALOE and balloon measurements in the Arctic during the winter of 1999–2000
Authors: Müller Rolf , Tilmes Simone , Grooß Jens‐Uwe , McKenna Daniel S. , Müller Melanie , Schmidt Ulrich , Toon Geoffrey C. , Stachnik Robert A. , Margitan James J. , Elkins James W. , Arvelius Johan , Russell James M.
Published: December 2002

We employ Halogen Occultation Experiment (HALOE) observations and balloon‐borne measurements (on the large Observations of the Middle Stratosphere [OMS] and Triple balloons, as well as on two small balloons) to investigate ozone loss in the stratospheric vortex in the 1999–2000 Arctic winter. Using HF and CH4 as long‐lived tracers, we identify chlorine activation and chemical ozone destruction in the polar vortex. Reference relations, representative of chemically undisturbed “early vortex” conditions, are derived from the OMS remote and in situ balloon measurements on 19 November and 3 December 1999, respectively. Deviations from this “early vortex” reference are interpreted as chemical ozone loss and heterogeneous chlorine activation. The observations show an extensive activation of chlorine; in late February 2000, the activation extends to altitudes of 600 K. Between 360 and 450 K chlorine was almost completely activated. At that time, about 70% of the HCl column between 380 and 550 K was converted to active chlorine. Furthermore, the measurements indicate severe chemical ozone loss, with a maximum loss of over 60% in the lower stratosphere (415–465 K) by mid‐March 2000. Substantial ozone loss was still observable in vortex remnants in late April 2000 (80 ± 10 Dobson units [DU] between 380 and 550 K). The average loss in column ozone between 380 and 550 K, inside the vortex core, in mid‐March amounted to 84 ± 13 DU.
An examination of the convective charging hypothesis: Charge structure, electric fields, and Maxwell currents
Authors: Helsdon John H. , Gattaleeradapan Sirin , Farley Richard D. , Waits C. Christopher
Published: December 2002

An examination of the convective charging hypothesis is undertaken using our three‐dimensional (3D) storm electrification model (SEM). In an attempt to cover the range of storm conditions over which the convective mechanism might be expected to operate, two storms are simulated: a small, weak storm and a larger, severe storm. Elements of the model relevant to the convective hypothesis are the full treatment of small ions, including attachment to hydrometeors, the inclusion of field‐dependent surface point discharge, and the components of the Maxwell current. For comparison purposes, each storm is also simulated using a noninductive mechanism. Results from both the small and large storm simulations using convective‐only charging indicate disorganized, weak electrical structures during the mature and dissipating stages. Conversely, the use of noninductive charging produces strong electrification in both storms. Maxwell current analysis shows that, for the most part, currents within the storm are dissipative and that the cloud acts as a barrier to the external conduction current when convective‐only charging is considered. For the noninductive simulations, the Maxwell current is that of a generator. The treatment of small ions and their attachment to hydrometeors accounts for the formation of screening layers; thus this aspect of the convective charging mechanism still plays an important role in the modeling of thunderstorm charge structures. However, since the convective charging hypothesis, by itself, is unable to produce significant charging or strong electric fields in either simulated cloud, we conclude that it is not a viable mechanism for thunderstorm electrification.
Impact of aerosol size representation on modeling aerosol‐cloud interactions
Authors: Zhang Y. , Easter R. C. , Ghan S. J. , Abdul‐Razzak H.
Published: December 2002

We use a one‐dimensional version of a climate‐aerosol‐chemistry model with both modal and sectional aerosol size representations to evaluate the impact of aerosol size representation on modeling aerosol‐cloud interactions in shallow stratiform clouds observed during the second Aerosol Characterization Experiment. Both the modal (with prognostic aerosol number and mass or prognostic aerosol number, surface area and mass, referred to as the Modal‐NM and Modal‐NSM) and the sectional approaches (with 12 and 36 sections) predict total number and mass for interstitial and activated particles that are generally within several percent of references from a high‐resolution 108‐section approach. The modal approach with prognostic aerosol mass but diagnostic number (referred to as the Modal‐M) cannot accurately predict the total particle number and surface areas, with deviations from the references ranging from 7 to 161%. The particle size distributions are sensitive to size representations, with normalized absolute differences of up to 12% and 37% for the 36‐ and 12‐section approaches, and 30%, 39%, and 179% for the Modal‐NSM, Modal‐NM, and Modal‐M, respectively. For the Modal‐NSM and Modal‐NM, differences from the references are primarily due to the inherent assumptions and limitations of the modal approach. In particular, they cannot resolve the abrupt size transition between the interstitial and activated aerosol fractions. For the 12‐ and 36‐section approaches, differences are largely due to limitations of the parameterized activation for nonlognormal size distributions, plus the coarse resolution for the 12‐section case. Differences are larger both with higher aerosol (i.e., less complete activation) and higher SO2 concentrations (i.e., greater modification of the initial aerosol distribution).
Aerosol optical properties during INDOEX based on measured aerosol particle size and composition
Authors: Eldering A. , Ogren J. A. , Chowdhury Z. , Hughes L. S. , Cass G. R.
Published: December 2002

The light scattering and light absorption as a function of wavelength and relative humidity due to aerosols measured at the Kaashidhoo Climate Observatory in the Republic of the Maldives during the INDOEX field campaign has been calculated. Using size‐segregated measurements of aerosol chemical composition, calculated light scattering and absorption has been evaluated against measurements of light scattering and absorption. Light scattering coefficients are predicted to within a few percent over relative humidities of 20–90%. Single scattering albedos calculated from the measured elemental carbon size distributions and concentrations in conjunction with other aerosol species have a relative error of 4.0% when compared to measured values. The single scattering albedo for the aerosols measured during INDOEX is both predicted and observed to be about 0.86 at an ambient relative humidity of 80%. These results demonstrate that the light scattering, light absorption, and hence climate forcing due to aerosols over the Indian Ocean are consistent with the chemical and physical properties of the aerosol at that location.
Remote sensing from the infrared atmospheric sounding interferometer instrument 2. Simultaneous retrieval of temperature, water vapor, and ozone atmospheric profiles
Authors: Aires F. , Rossow W. B. , Scott N. A. , Chédin A.
Published: December 2002

A fast algorithm is developed to retrieve temperature, water vapor, and ozone atmospheric profile from the high spectral resolution Infrared Atmospheric Sounding Interferometer spaceborne instrument. Compression, denoising, and pattern recognition algorithms have been developed in a companion paper [Aires et al., 2002b]. A principal component analysis neural network using this a guess information is developed here to retrieve simultaneously temperature, water vapor and ozone atmospheric profiles. The performance of the resulting fast and accurate inverse model is evaluated with a climatological data set including rare events: temperature is retrieved with an error ≤1 K, and total amount of water vapor has a mean percentage error between 5 and 7%. Atmospheric water vapor layers are retrieved with an error between 10 and 15% most of the time. The statistics of the ozone retrieval are too optimistic due to a lack of representation of ozone variability in our test data set.
Sources of tropospheric ozone along the Asian Pacific Rim: An analysis of ozonesonde observations
Authors: Liu Hongyu , Jacob Daniel J. , Chan Lo Yin , Oltmans Samuel J. , Bey Isabelle , Yantosca Robert M. , Harris Joyce M. , Duncan Bryan N. , Martin Randall V.
Published: December 2002

The sources contributing to tropospheric ozone over the Asian Pacific Rim in different seasons are quantified by analysis of Hong Kong and Japanese ozonesonde observations with a global three‐dimensional (3‐D) chemical transport model (GEOS‐CHEM) driven by assimilated meteorological observations. Particular focus is placed on the extensive observations available from Hong Kong in 1996. In the middle‐upper troposphere (MT‐UT), maximum Asian pollution influence along the Pacific Rim occurs in summer, reflecting rapid convective transport of surface pollution. In the lower troposphere (LT) the season of maximum Asian pollution influence shifts to summer at midlatitudes from fall at low latitudes due to monsoonal influence. The UT ozone minimum and high variability observed over Hong Kong in winter reflects frequent tropical intrusions alternating with stratospheric intrusions. Asian biomass burning makes a major contribution to ozone at <32°N in spring. Maximum European pollution influence (<5 ppbv) occurs in spring in the LT. North American pollution influence exceeds European influence in the UT‐MT, reflecting the uplift from convection and the warm conveyor belts over the eastern seaboard of North America. African outflow makes a major contribution to ozone in the low‐latitude MT‐UT over the Pacific Rim during November–April. Lightning influence over the Pacific Rim is minimum in summer due to westward UT transport at low latitudes associated with the Tibetan anticyclone. The Asian outflow flux of ozone to the Pacific is maximum in spring and fall and includes a major contribution from Asian anthropogenic sources year‐round.
Diurnal and seasonal cycles of trends of surface air temperature
Authors: Vinnikov Konstantin Y. , Robock Alan , Basist Alan
Published: December 2002

A new technique was recently developed to study seasonal cycles of climatic trends of expected values, variance, skewness, and other statistical moments of climatic variables. Here we apply that technique to analyze the diurnal and seasonal cycles of trends of surface air temperature and its variability using hourly observations from nine geographically distributed meteorological stations in the United States for the period 1951–1999. The analysis reveals a complex pattern of trends in temperature and its variance at different times of the seasonal and diurnal cycle, showing warming trends for all stations during most times of the year and times of day, but with diurnal asymmetry of warming only in the warm half of the year. We found no correspondence between the trends in temperature and the trends in temperature variability. This analysis may be used as a prototype for developing the next generation of climate services that will be able to supply customers with detailed information about the first few moments of the statistical distribution of any meteorological variable for every day and hour of the period of observation.
Long‐range tracking of thunderstorms using sferic measurements
Authors: Wood T. G. , Inan U. S.
Published: December 2002

Each lightning stroke launches an electromagnetic pulse, known as a radio atmospheric or sferic that propagates in the waveguide between the Earth and the ionosphere. Sferics, with most of their energy contained in the frequency band from 3 Hz to 30 kHz, can propagate with low loss to distances of tens of megameters. Using very low frequency (VLF) magnetic field measurements at Palmer Station, Antarctica, the azimuths of sferics originating in North America (∼10,000 km range) are found to be measurable to less than 1 degree accuracy. Analysis of the arrival azimuths at Palmer Station allows the assessment of lightning flash rates of storms occurring in diverse regions of the globe including North America and Africa. Arrival azimuths are compared with flash level data from the National Lightning Detection Network (NLDN) and 83.6% of the sferics that could be matched to NLDN flashes were within 2 degrees of the predicted azimuths for those flashes. Results are also compared with data from the satellite‐based Optical Transient Detector (OTD), and the arrival azimuths of sferics detected at Palmer Station are consistent with the location of lightning occurring elsewhere around the world. The relative distribution of and the relationship between ground flashes and cloud flashes are discussed for a specific localized thunderstorm. Evidence that sferics generated by intracloud discharges were detected at Palmer Station is also presented.
Desert aerosol transport in the Mediterranean region as inferred from the TOMS aerosol index
Authors: Israelevich P. L. , Levin Z. , Joseph J. H. , Ganor E.
Published: December 2002

We proposed to identify the sources of desert dust aerosols with local maxima of the TOMS aerosol index distribution averaged for the long period. Being simpler than the approach based on a dusty days occurrence, our method gives the same results. It was first shown that in spring‐summer, the flux of dust from the sources located at latitude ∼16°N and longitude ∼16°E and around latitude ∼19°N and longitude ∼6°W exceed the sinks due to settling and transport. As a result the atmosphere over North Africa is almost permanently loaded with a significant amount of mineral desert dust in spring and in summer. It is also shown that the Chad basin source located around latitude 16°N and longitude 16°E is relatively more stable with a maximum activity around April. The region around latitude 19°N and longitude 6°W appears as a more variable source with maximum in July. Low pressure systems, called Sharav cyclones, mobilize the already suspended mineral dust and transport it eastward and northward along the Mediterranean basin. A new method for description of dust plumes propagation was applied to the study of dust events in the Mediterranean Sea and enabled us to follow their dynamics. Identifiable dust plumes appear first in the western sector of the sea and then move eastward with a speed of about 7 to 8 degrees per day. In spring, this motion continues at least up to the eastern coast of the Mediterranean. In summer the dustplume is prevented from penetrating further east of about 15°E.
Chronology of the formation process of Venusian novae and the associated coronae
Authors: Aittola M. , Kostama V.‐P.
Published: December 2002

Venusian radial features (novae) have been interpreted to represent the initial stage of the corona evolution. Thus they are hypothesized to be older than the corona rim structure. However, based on recent studies, the majority of novae that are located in the inner part of the coronae seem to postdate corona formation. The topography, as well as the mutual age relationships of coexisting coronae and novae, indicates that nova formation may have taken place during different corona evolution phases. In this study we present a chronology for nova formation that offers an explanation of both age and location relations of the novae inside the coronae. Due to the proven age differences between coronae and novae located within them, we conceive most of the novae within the corona annulus as representations of reactivation of the corona location. We believe that the morphology, the topography, and the age relations of corona annulus and nova radial features depend on the stage of corona evolution during the reactivation period or event, when the nova is formed. Our model explains the observed regularity between nova location and age relations of the corona‐nova joint structure better than the assumed movement of the lithosphere or migrating mantle plumes.
A model for formation of dust, soil, and rock coatings on Mars: Physical and chemical processes on the Martian surface
Authors: Bishop Janice L. , Murchie Scott L. , Pieters Carlé M. , Zent Aaron P.
Published: December 2002

A model is presented here to explain the generation of surface material on Mars using chemical, magnetic, and spectroscopic data from Mars and geologic analogs from terrestrial sites. One basic premise is that the dust/soil units are not derived exclusively from local rocks, but are rather a product of global, and possibly remote, weathering processes. Another assumption in this model is that there are both physical and chemical interactions of the atmosphere with dust particles and that these two processes create distinctly different products. Physical processes distribute dust particles on rocks and drift units, forming physically aggregated layers; these are reversible processes. Chemical reactions of the dust/soil particles create alteration rinds on rock surfaces and cohesive, crusted surface units between rocks, both of which are relatively permanent materials. According to this model the dominant components of the dust/soil particles are derived from alteration of volcanic ash and tephra and contain primarily nanophase and poorly crystalline ferric oxide/oxyhydroxide phases as well as silicates. These phases are the alteration products that formed in a low‐moisture environment. These dust/soil particles also contain a smaller amount of material that was exposed to more water and contains crystalline ferric oxides/oxyhydroxides, sulfates, and clay silicates. These components could have formed through hydrothermal alteration at steam vents or fumeroles, thermal fluids, or through evaporite deposits. Wet/dry cycling experiments are presented here on Mars soil analogue mixtures containing poorly crystalline and crystalline components dominated by nanophase to ∼2 μm diameter particles. Cemented products of these soil mixtures are formed in these experiments, and variation in the surface texture was observed for samples containing smectites, nonhydrated silicates, or sulfates. Reflectance spectra were measured of the initial particulate mixtures, the cemented products, and ground versions of the cemented material. The spectral contrast in the visible/near‐infrared and midinfrared regions is significantly reduced for the cemented material compared to the initial soil and somewhat reduced for the ground, cemented soil compared to the initial soil. The results of this study suggest that transient fluvial activity on Mars will have a profound effect on the texture and spectral properties of the dust/soil particles on the surface. The model developed in this study provides an explanation for the generation of cemented or crusted soil units and rock coatings on Mars and may explain albedo variations on the surface observed near large rocks or crater rims.
Nonmigrating tides in the thermosphere of Mars
Authors: Forbes Jeffrey M. , Bridger Alison F. C. , Bougher Stephen W. , Hagan Maura E. , Hollingsworth Jeffery L. , Keating Gerald M. , Murphy James
Published: December 2002

The vertical propagation of nonmigrating (i.e., longitude‐dependent or non–Sun‐synchronous) solar diurnal and semidiurnal tides into the thermosphere of Mars is investigated through numerical simulation. The waves are generated in the NASA Ames Mars general circulation model (MGCM) through solar radiative, topographic, and nonlinear processes using a comprehensive physics package and including a diurnal cycle. At an altitude near 70 km, zonal wave number decompositions of the diurnal and semidiurnal tidal fields are performed, and each wave component is extended from 70 to 250 km using a linear steady state global scale wave model for Mars (Mars GSWM). Conditions representative of aerocentric longitudes Ls = 30 (near equinox) and Ls = 270 (Southern Hemisphere summer solstice) are considered. Modeled total relative density variations of order ±10–40% near 125 km are analyzed in terms of the zonal wave numbers (ks) seen from the Sun‐synchronous perspective of the Mars Global Surveyor (MGS) accelerometer experiment, and yield reasonable agreement in amplitude and phase with the density measurements. The model indicates the two most important waves responsible for ks = 3 to be the eastward‐propagating diurnal and semidiurnal oscillations with zonal wave numbers s = 2 (∼15–40%) and s = 1 (∼8%), respectively. The eastward‐propagating diurnal component with s = 1 (∼15%) and the semidiurnal standing (s = 0) oscillation (∼4–23%) are concluded to be the main contributors to the ks = 2 longitudinal density variation seen from the Mars Global Surveyor (MGS). The standing (s = 0) diurnal oscillation (∼4–5%) and the westward‐propagating semidiurnal component with s = 1 (∼5–8%) emerge as the most likely contributors to ks = 1. Other waves that may make important secondary contributions include the westward‐propagating semidiurnal oscillations with s = 3 (∼4–6%) and s = 4 (∼3–9%). In addition, above 100 km the wind and temperature fields associated with the above waves represent ∼15–30% perturbations on the Sun‐synchronous wind and temperature fields driven in situ by EUV and near‐IR solar radiation absorption. Nonmigrating tides primarily arise from zonal asymmetries in wave forcing associated with Mars' topography; our results show for the first time that the dynamical effects of Mars' topography extend throughout the atmospheric column to Mars' exobase (∼200–250 km).
Impact glasses from the Apollo 14 landing site and implications for regional geology
Authors: Zellner N. E. B. , Spudis P. D. , Delano J. W. , Whittet D. C. B.
Published: December 2002

Lunar impact glasses possess the unmodified refractory element ratios of the original fused target materials at the sites of impacts. These target materials are regolith developed on different terrains and local rock types. Almost 800 glasses from the Apollo 14 landing site have been analyzed by electron microprobe in this study. These glasses show significant variation and hint at the existence of multiple terrains of differing compositions near the landing site. To test this idea, we have used Clementine color image data to construct iron and titanium maps from which a petrologic map in an elemental system analogous to the sample database was made. This map shows the regional provenance of Apollo 14 samples and suggests that the highlands in the Fra Mauro region of the Moon consist of a potassium, rare Earth element, and phosphorus (KREEP)‐rich, basaltic debris layer that overlies a more feldspathic terrain in some areas. This mapping effort demonstrates the efficacy of using Clementine image data to place lunar sample information into a regional, and ultimately global, context. Lunar impact glasses and orbital data can provide geochemical constraints on the local and regional geology of the Moon.
Characterization and formation of polygonal fractures on Venus
Authors: Smrekar Suzanne E. , Moreels Pierre , Franklin Brenda J.
Published: December 2002

Fracture theory predicts that polygonal cracks will form in the presence of an isotropic, extensional stress field. On Venus, polygonal fractures are observed on scales several orders of magnitude larger than on Earth, with an average diameter of 1.8 ± 0.9 km. Proposed formation mechanisms include cooling following lava flow emplacement, lithospheric heating, and climate change. Here we examine the characteristics and geologic setting of 204 regions of polygons. Some regions display two spatially overlapping size ranges, with the larger spacing typically 10–25 km. Most polygonal fractures appear to be extensional, but some have the morphology of compressional ridges. Polygons are confined to plains regions and occur in association with shield fields (49%), coronae and coronae‐like features (21.3%), tessera (17.5%), and wrinkle ridges (20%). In locations where polygons occur with shield fields, coronae, or both, they appear to have formed contemporaneously. Formation in conjunction with local heating events is consistent with the lithospheric cooling hypothesis. However, there is almost never the predicted decrease in size away from the center of coronae or shield fields. Only a small percentage of coronae and shield fields contain polygons, indicating that they are not typical of the formation process. The climate change‐induced scenario is consistent with many characteristics of the polygons, including the small and large size ranges, the compressional ridges, and their occurrence with and without evidence of local heating. Although polygons may have diverse origins, including formation by multiple deformation events, overall polygon characteristics support the climate change hypothesis.