bluuebunny/crossref_metadata_2025 huggingface dataset:
Program for Arctic Regional Climate Assessment (PARCA): Goals, key findings, and future directions
Authors: Thomas Robert H.
Published: February 2004

The NASA Program for Arctic Regional Climate Assessment (PARCA) has the prime objectives of measuring and understanding the mass balance of the Greenland ice sheet. It includes measurement of changes in ice sheet volume using different approaches, analysis of satellite and aircraft data to investigate various characteristics of the ice sheet, and in situ measurements aimed at understanding observed changes. The most important result from PARCA is the first accurate assessment of the mass balance of a polar ice sheet. Higher‐elevation parts of the ice sheet are in overall balance, with local areas of quite rapid thickening or thinning, most of which could represent the effects of temporal variability in snow accumulation rates. Many coastal regions thinned considerably during the 1990s, with net losses from the ice sheet sufficient to raise global sea level by almost 10% of the total increase. There was coastal warming during this period, and a network of automatic weather stations (AWS) on the ice sheet measured a 2° warming for 1995–1999 compared to the 1950s. Nevertheless, observed ice‐thinning rates of up to several meters per year cannot be explained by increased melting, indicating that discharge velocities must also have increased. In addition to the scientific results, major advances have been made in the use of satellite data for ice sheet research, particularly application of synthetic aperture radar (SAR) data to the measurement of ice velocity and identification and monitoring of glacier grounding lines. On the basis of these observations, PARCA focus has shifted to the coastal regions, with emphasis on surface ablation and its sensitivity to summer warming and possible albedo feedback, and on the dynamics of the glaciers that are observed to be changing rapidly.
Aerosol radiative, physical, and chemical properties in Beijing during June 1999
Authors: Bergin M. H. , Cass G. R. , Xu J. , Fang C. , Zeng L. M. , Yu T. , Salmon L. G. , Kiang C. S. , Tang X. Y. , Zhang Y. H. , Chameides W. L.
Published: February 2004

Beijing experiences air pollution such that the sky overhead is gray much of the time even on cloudless days. In order to understand the cause of this problem, the aerosol light scattering coefficient σsp and absorption coefficient σap were measured under dry conditions (instrumental relative humidity <40%) during a 1‐week intensive field sampling period in June 1999 in Beijing, China. Additional measurements included the aerosol mass size distribution, chemical composition of the aerosol mass having particle diameters less than 2.5 μm (PM2.5) as well as the chemical composition of the total suspended particulate matter. The mean (and standard deviation) for hourly averages of σsp, σap, and the single‐scattering albedo ω were 488 Mm−1 (370 Mm−1), 83 Mm−1 (40 Mm−1), and 0.81 (0.08), respectively, which is significantly higher than values reported in urban regions of the United States. The relatively high values of σsp were accompanied by a daily mean value for the PM2.5 mass concentration of 136 μg m−3 (48 μg m−3), which is significantly higher than the proposed U.S. 24‐hour average mean National Ambient Air Quality Standard of 65 μg m−3. The visual range during the field study, based on measurements of σsp and σap, was typically less than 6 km. For several days that did not have rain or fog, there was a clear diurnal trend in σsp, σap, and ω, with peak values in the early morning and minima that occur in the evenings. The peaks correspond to minima in ambient temperature and maxima in relative humidity. Mass size distribution measurements indicate that although ∼80% of the aerosol mass was located in the coarse particle mode (Dp > 1.0 μm), the submicron aerosol was responsible for ∼80% of the light scattering at 530 nm. The largest contribution to the PM2.5 aerosol mass was due to organic compounds, which accounted for ∼30% of the mass. The contributions of sulfate, ammonium, and nitrate to the PM2.5 mass concentration were ∼15%, 5%, and 8%, respectively. Mineral aerosol contributed ∼16% to the PM2.5 aerosol mass. These data show that combustion‐related particles rather than wind‐blown dust dominated the light extinction budget during June 1999.
A 420,000 year deuterium excess record from East Antarctica: Information on past changes in the origin of precipitation at Vostok
Authors: Vimeux F. , Masson V. , Delaygue G. , Jouzel J. , Petit J. R. , Stievenard M.
Published: February 2004

Here we present and analyze the complete Vostok ice cores deuterium excess record which spans the last four climatic cycles, back to ∼420,000 years B.P. To extract paleoclimate information from this record, we use isotopic modeling showing that changes in deuterium excess (d = δD‐8δ18O) of Vostok precipitation reflect changes in the average temperature of oceanic moisture sources. Over the last 250,000 years the deuterium excess is strongly anticorrelated with changes in Earth's obliquity. This reflects changes in the relative contribution of low and high latitudes to the Vostok precipitation, resulting from changes in the latitudinal annual mean insolation gradient governed by the obliquity. However, this modulation by obliquity is not observed prior to 250,000 years B.P. We attribute this difference to the ice flow, the deeper ice under Vostok station having accumulated in a location upstream Vostok, receiving precipitation from different oceanic origins. Despite this difference between the earlier and the later portions of the record, the deuterium excess changes during all the glacial inceptions are similar in amplitude and timing relative to the deuterium decrease. The glacial inceptions are characterized by high deuterium excess, indicating the significant role of the tropics in supplying moisture to the already cold poles.
Chemical composition and source signature of spring aerosol in Seoul, Korea
Authors: Choi Jae C. , Lee Meehye , Chun Youngsin , Kim Jiyoung , Oh Sungnam
Published: February 2004

The measurement of atmospheric aerosol was made in Seoul during the spring of 1998. The objective of this study was to investigate the chemical characteristics of atmospheric aerosol with an emphasis on the effect of Asian dust. Total suspended particles (TSP) and particles smaller than 10 μm (PM10) were collected during March‐May 1998. For PM10, water‐soluble ions and trace elements were analyzed: NO3−, SO42−, Na+, NH4+, K+, Mg2+, Ca2+, Na, Mg, Al, Ca, Fe, Mn, Cr, Co, Cu, Zn, Cd, and Pb. All data were sorted into three groups on the basis of the intensity of Asian dust observed in Seoul: nondust, regular dust, and heavy dust. Chemical characteristics of aerosol were distinct for the heavy dust incidence compared to the other two cases. The average mass concentration of TSP and PM10 increased substantially during the heavy dust period. For water‐soluble ions, concentrations of SO42− and NO3− were the lowest, whereas Ca2+ and Mg2+ concentrations were remarkably enhanced. Concentrations and mass fraction of crustal elements such as Na, Mg, Ca, Fe, and Mn were highly elevated, but those of pollution‐derived heavy metals were appreciably decreased. Enrichment ratios of metallic components indicated that soil dust was the primary source of spring aerosols over Seoul. This was also confirmed by factor analysis. Trajectory analysis provided a convincing evidence for the air mass coming from the Asian desert areas, which are the source region of mineral dust. In contrast, the anthropogenic influence was more pronounced for the regular dust period: concentrations of heavy metals, NO3−, and SO42− were the highest. It could be associated with the transport of air mass over the industrialized regions of China, which is demonstrated by backward trajectory analysis. The result of factor analysis with high factor loadings in SO42− and NO3− implied the considerable influence of industrial emission on the composition of all spring aerosols over Korea.
Possible solar modulation of the equatorial quasi‐biennial oscillation: Additional statistical evidence
Authors: Soukharev Boris E. , Hood Lon L.
Published: February 2004

Although the quasi‐biennial oscillation (QBO) in the equatorial zonal wind is dominantly driven by wave forcing originating in the troposphere, a recent study suggests that certain properties of the QBO may vary slightly on the 11‐year solar cycle timescale [Salby and Callaghan, 2000]. Here we report further statistical investigation using both equatorial wind data for levels from 50 to 1 hPa and longterm proxy solar ultraviolet flux time series (10.7‐cm solar radio flux and sunspot numbers). Spectral analysis of the solar time series yields evidence for a significant spectral peak at periods between 25 and 30 months, approximately equivalent to the mean QBO period, as had also been noted by earlier authors [Shapiro and Ward, 1962]. Cross‐spectral analysis of the 10.7‐cm solar radio flux and equatorial zonal wind time series shows significant coherency at the QBO period at all available pressure levels. The phase lag of the wind data relative to the solar flux at the QBO period ranges from 0–1 months near the stratopause (1 hPa) to 20–24 months in the lower stratosphere (50 hPa). The nearly inphase relationship near the stratopause suggests a possible modulation of the QBO at this level by the radiative and photochemical effects of solar ultraviolet variations. The amplitudes of the solar variations at the QBO period tend to be larger under solar maximum than under solar minimum conditions. Composite analysis of the westerly and easterly phases of the equatorial zonal wind shows subtle but consistent differences in the durations of the westerlies and easterlies between solar maximum and minimum conditions.
Design, calibration, and performance of MICROTOPS II handheld ozone monitor and Sun photometer
Authors: Morys Marian , Mims Forrest M. , Hagerup Scott , Anderson Stanley E. , Baker Aaron , Kia Jesse , Walkup Travis
Published: February 2004

MICROTOPS II is a five‐channel, handheld Sun photometer that can be configured to measure total ozone, total water vapor, or aerosol optical thickness at various wavelengths. The instrument measures 10×20×4.3 cm and weighs 600 g. A principal design goal was the measurement of total ozone to within 1% of ozone measurements made by much larger, heavier, and more expensive Dobson and Brewer spectrophotometers. This goal has been met for a maximum air mass of up to ∼2.5, as demonstrated by comparisons of MICROTOPS II and its immediate predecessor, Supertops, with Dobson and Brewer instruments at various locations. Conventional interference filters are subject to gradual and unpredictable degradation. MICROTOPS II avoids these problems by using highly stable ultraviolet filters manufactured with an ion deposition process. The 2.4 nm (FWHM) band pass of the UV filters was selected to balance noise and ozone measurement performance. The optical collimators and electronics of the instrument were carefully designed to optimize pointing accuracy, stray light rejection, thermal and long‐term stability, signal‐to‐noise ratio, and data analysis. An internal microcomputer automatically calculates the total ozone column based on measurements at three UV wavelengths, the site's geographic coordinates, and universal time, altitude, and pressure. The coordinates can be entered manually or by a Global Positioning System (GPS) receiver. A built‐in pressure transducer automatically measures pressure. MICROTOPS II saves in nonvolatile memory up to 800 scans of the raw and calculated data. Measurements can be read from a liquid crystal display or transferred to an external computer.
The close lightning electromagnetic environment: Dart‐leader electric field change versus distance
Authors: Crawford David E. , Rakov Vladimir A. , Uman Martin A. , Schnetzer George H. , Rambo Keith J. , Stapleton Michael V. , Fisher Richard J.
Published: February 2004

Net electric field changes due to dart leaders in triggered lightning from experiments conducted in 1997, 1998, and 1999 at the International Center for Lightning Research and Testing at Camp Blanding, Florida, are analyzed and compared with similar data obtained in 1993 at Camp Blanding and at Fort McClellan, Alabama. In 1997–1999 the fields were measured at 2–10 stations with distances from the lightning channel ranging from 10 to 621 m, while in 1993 the fields were measured at three distances, 30, 50, and 110 m, in Florida and at two distances, about 10 and 20 m, in Alabama. With a few exceptions, the 1997–1999 data indicate that the distance dependence of the leader electric field change is close to an inverse proportionality (r−1), in contrast to the 1993 data in which a somewhat weaker distance dependence was observed. The typically observedr−1dependence is consistent with a uniform distribution of leader charge along the bottom kilometer or so of the channel.
Hemispheric roles of climate forcings during glacial‐interglacial transitions as deduced from the Vostok record and LLN‐2D model experiments
Authors: Pépin L. , Raynaud D. , Barnola J.‐M. , Loutre M. F.
Published: February 2004

The Vostok ice contains fingerprints of atmospheric greenhouse trace gases, Antarctic temperature, Northern Hemisphere temperature, and global ice volume/sea level changes during the last glacial‐interglacial cycles and thus allows us to investigate the sequences of these climatic events, in particular during the transitions from full glacial to interglacial conditions. The use of the updated CO2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at Vostok. Antarctic air temperature and CO2 increase in parallel and almost synchronously, while the rapid warmings over Greenland take place during the last half of their change and coincide with the marked decay in continental ice volume. The Vostok results thus emphasize a fundamental difference between South and North in terms of climate dynamics. Our results confirm the role of CO2 as an important amplifier of the glacial‐interglacial warming in the South. It appears also that the marked warming observed at high northern latitudes (lagging behind the CO2 increase by several thousand years) is roughly synchronous with the decay of the northern ice sheets, suggesting a major role of climatic feedback due to this decay. Such a climatic scenario is supported by sensitivity experiments performed with the LLN 2‐D model forced by the Northern Hemisphere insolation and CO2. Model results indicate that the decay of the northern ice sheets and the Northern Hemisphere temperature depend primarily on the northern summer insolation. These results, nevertheless, could be affected if mechanisms specific to the Southern Hemisphere appear to play a major role in driving the Northern Hemisphere climate. The model also helps to constrain the time response of ice volume to insolation and CO2 changes.
Numerical simulations of the July 10, 1996, Stratospheric‐Tropospheric Experiment: Radiation, Aerosols, and Ozone (STERAO)‐Deep Convection experiment storm: Redistribution of soluble tracers
Authors: Barth M. C. , Stuart A. L. , Skamarock W. C.
Published: February 2004

By using a three‐dimensional convective cloud model to simulate the July 10, 1996, Stratospheric‐Tropospheric Experiment: Radiation, Aerosols, and Ozone‐Deep Convection experiment storm, we investigate the fate of tracers of varying solubilities in midlatitude convection. The tracer distribution resulting from the interactions of the soluble tracers with the cloud hydrometeors is illustrated for two cases. The first case assumes that the dissolved tracer in the cloud water or rain completely degasses when the parent hydrometeor is converted to ice, snow, or hail through microphysical processes. The second case assumes that the dissolved tracer is retained in the ice, snow, or hail. We find that when soluble tracers are degassed, both low‐ and high‐solubility tracers are transported to the upper troposphere. When tracers are retained in ice hydrometeors, the highly soluble tracers are not ultimately transported to the upper troposphere but, instead, are precipitated out of the upper troposphere by snow and hail. Tracers of low solubility are transported upward, similar to passive tracer transport. The key microphysical processes that control these results are the accretion of cloud water by snow and hail. For the simulation in which retention of tracers in ice was considered, highly soluble scalars (105 M atm−1) have a scavenging efficiency >55% and have a mass change in the upper troposphere (8–15 km mean sea level) of −0.5×105 kg to 0 for a 3‐hour period, while a passive scalar has a mass change of 2.3×105 kg.
Three‐dimensional solar radiative transfer in small tropical cumulus fields derived from high‐resolution imagery
Authors: Benner Timothy C. , Evans K. Franklin
Published: February 2004

Since three‐dimensional (3‐D) radiative transfer in cloudy atmospheres is too expensive for large‐scale atmospheric models, approximate radiative transfer methods are used. The accuracy of these approximations for a large sample of realistic cloud fields has not been determined. This study examines 150 fields of small marine tropical cumulus to assess the magnitude of 3‐D effects on domain average solar fluxes and to evaluate the accuracy of these approximations in actual cumulus fields. The cloud fields are derived from Moderate‐Resolution Imaging Spectroradiometer Airborne Simulator (MAS) visible and thermal infrared imagery. Domain average broadband solar fluxes in these fields are simulated with a Monte Carlo radiative transfer model using four radiative transfer methods: full three‐dimensional, the independent pixel approximation (IPA), the tilted IPA, and the plane‐parallel approximation. The average 3‐D radiative effects of these cumulus cloud fields are small, with mean reflected flux errors up to 3 W/m2 for overhead Sun and less than 1 W/m2 for the daytime average. The mean errors for column‐absorbed fluxes are less than 0.3 W/m2 for all Sun angles. The small absolute flux errors are a result of the average field having small cloud fraction (10%), low cloud optical depth (4.4), and shallow clouds. Some individual fields have large 3‐D absolute reflected flux effects, and the normalized reflected flux errors are significant. The errors correlate well with the cloud fraction; so it may be possible to make corrections to the approximations.
Impact of cumulus cloud spacing on Landsat atmospheric correction and aerosol retrieval
Authors: Wen Guoyong , Cahalan Robert F. , Tsay Si‐Chee , Oreopoulos Lazaros
Published: February 2004

A Landsat 7 Enhanced Thematic Mapper Plus (ETM+) image acquired over the Southern Great Plains site of Department of Energy's Atmospheric Radiation Measurement Program during the Atmospheric Radiation Measurement Enhanced Shortwave Experiment II is used to study the effect of clouds on reflected radiation in clear gaps in a cumulus cloud field. A technique using the spectral information of background and clouds is applied to identify clouds. The path radiance technique is used to extract the apparent path radiance in a clear region of the cumulus cloud field. The result shows that the apparent path radiance is enhanced by nearby clouds in both band 1 (blue) and band 3 (red) of ETM+. More importantly, the magnitude of the enhancement depends on the mean cloud‐free distance in the clear patches. For cloud‐free distances <0.5 km the enhancement of apparent path radiance is more than 0.025 and 0.015 (reflectance units) in band 1 and band 3, respectively, which corresponds to an enhancement of apparent aerosol optical thickness of ∼0.25 and ∼0.15. Neglecting of the three‐dimensional cloud effect would lead to underestimates of surface reflectance of ∼0.025 and ∼0.015 in the blue and red band, respectively, if the true aerosol optical thickness is 0.2 and the surface reflectance is 0.05. The enhancement decreases exponentially with mean cloud‐free distance, reaching asymptotic values of 0.09 for band 1 and 0.027 for band 3 at a mean cloud‐free distance about 2 km. The asymptotic values are slightly larger than the mean path radiances retrieved from a completely clear region: 0.086 and 0.024 for the blue and red bands, respectively.
High‐resolution radar mapping of internal layers at the North Greenland Ice Core Project
Authors: Kanagaratnam P. , Gogineni S. P. , Gundestrup Niels , Larsen Lars
Published: February 2004

Existing accumulation maps with reported errors of about 20% are determined from sparsely distributed ice cores and pits. A more accurate accumulation rate might be obtained by generating continuous profiles of dated layers from high‐resolution radar mapping of near‐surface internal layers in the ice sheet (isochrones). To generate such profiles we designed and developed an ultrawideband radar for high‐resolution mapping of internal layers in the top 200 m of ice and tested it at the North Greenland Ice Core Project drill site. Reflection profiles of 2‐ and 10‐km length reveal horizons that we correlate with electrical conductivity measurement (ECM) recordings. Our results show that the radar‐determined depth of internal layers is within ±2 m of that in an ice core collected at a nearby location. Preliminary frequency analyses of layer reflections reveal that the reflections are strongest at the 500–1000 MHz frequency range. Long‐term accumulation rate computed from radar data is within 5% of that obtained from snow pits.
A modeling study of the direct effect of aerosols over the tropical Indian Ocean
Authors: Podgorny I. A. , Ramanathan V.
Published: February 2004

The microphysical, chemical, optical, and lidar data collected during the Indian Ocean Experiment (INDOEX) resulted in a self‐consistent aerosol formulation for a multiple‐scattering Monte Carlo radiation model. The model was used to simulate the direct aerosol radiative forcing, cloud radiative forcing, and heating rates for typical winter monsoon conditions over the tropical Indian Ocean. The focus of the study is to understand how the anthropogenic and natural aerosols partition the incoming solar energy between the ocean mixed layer and the overlying cloudy atmosphere. The observed aerosol single‐scattering albedo, ϖ, was in the range 0.8–0.9 at 500 nm, mean aerosol visible optical thickness, τA, was in the range 0.1–0.8 at 500 nm, and the low‐level clouds had horizontal scales of few kilometers and a cloud fraction of about 25%, typical of low‐level clouds in the tropical oceans. The aerosol layer extended well above the low‐level clouds in many instances, which has a significant impact on the radiative forcing. Although contributing only about 10% to the aerosol optical thickness, the soot transported from Asia and the Indian subcontinent significantly affects the aerosol direct forcing of the cloudy atmosphere. For monthly mean conditions (τA = 0.4, ϖ = 0.9 and 25% low‐cloud fraction), the diurnal mean surface radiative forcing is about −25 W m−2 and the atmospheric forcing ranges from +22 to +25 W m−2. The top‐of‐the‐atmosphere direct aerosol forcing is in the range of zero to −3 W m−2. The aerosol enhances the cloud atmospheric forcing by 0.5 and by 2.5 W m−2 when aerosol is mostly below and above the clouds, respectively. Furthermore, the trade wind boundary layer is subject to a heating of about 1 to 1.5 K/d which might burn off the trade cumulus themselves. Thus the major impact of the predominantly anthropogenic aerosol over the tropical Indian Ocean is a substantial redistribution of the solar energy between the atmosphere and the ocean mixed layer.
Global ozone trends in potential vorticity coordinates using TOMS and GOME intercompared against the Dobson network: 1978–1998
Authors: Bodeker G. E. , Scott J. C. , Kreher K. , McKenzie R. L.
Published: February 2004

Global total column ozone trends were calculated by applying a least squares regression model to five homogenized satellite data sets from November 1978 to December 1998. Drifts and offsets in the satellite data were removed through comparisons of coincident satellite overpass and ground‐based Dobson spectrophotometer measurements and through intersatellite comparisons. The satellite data were remapped into a potential vorticity coordinate (equivalent latitude) before zonal means were calculated. This remapping preserves steep meridional gradients in ozone and ozone trends across the winter polar vortex boundary and thereby reveals statistically significant negative trends just poleward of the Antarctic vortex boundary (∼70°S equivalent latitude) during May (−0.51±0.42% yr−1 (2σ)), June (−0.65±0.44% yr−1) and July (−0.85±0.44% yr−1). This feature is indistinct in trends derived as a function of geographic latitude most likely as a result of the smoothing by zonal averaging across steep ozone gradients. Comparison with similar earlier analysis (November 1978 to May 1991) indicates that Antarctic ozone trends have weakened (from −3.71±1.80% yr−1 to −2.95±0.40% yr−1), most likely as a result of saturation, while Arctic ozone trends are now much larger (from −1.05±0.96%yr−1 to −1.93±0.40% yr−1) following severe wintertime Arctic ozone depletion in recent years. Midlatitude negative trends calculated over the longer time period are also slightly reduced.
Remote sensing of aerosol optical characteristics in sub‐Sahel, West Africa
Authors: Pandithurai G. , Pinker R. T. , Dubovik O. , Holben B. N. , Aro T. O.
Published: February 2004

We have determined the characteristics of sub‐Sahelian aerosols from a 2‐year record of continuous ground‐based measurements, made at the University of Ilorin, Ilorin (08°19′N, 04°20′E), Nigeria, in cooperation with the Aerosol Robotic Network. Observations of spectral aerosol optical depths during the dusty harmattan season indicate more than a twofold increase, when compared to other seasons. Retrieved columnar volume size distributions show the existence of bimodality with a dominant coarse mode. The retrieved size distributions were grouped according to different ranges of aerosol optical depths to characterize the aerosols for this particular region. Monthly means of retrieved single‐scattering albedos show a sharp decrease from ∼0.95 to ∼0.85 at 500 nm from the preharmattan to the harmattan season when biomass burning is also practiced, increasing the presence of absorbing aerosols. On the basis of these comprehensive observations, we propose to augment existing desert aerosol models, as presented in the literature, to better characterize the dust outbreak season in West Africa, which is quite prolonged and overlaps with the biomass burning season.
Cloud effective particle size and water content profile retrievals using combined lidar and radar observations: 2. Comparison with IR radiometer and in situ measurements of ice clouds
Authors: Donovan D. P. , van Lammeren A. C. A. P. , Hogan R. J. , Russchenberg H. W. J. , Apituley A. , Francis P. , Testud J. , Pelon J. , Quante M. , Goddard J.
Published: February 2004

A new combined iidar/radar inversion procedure has been developed for cloud effective radius and water content retrievals. The algorithm treats the lidar extinction, derived effective particle size, and multiple‐scattering effects together in a consistent fashion. This procedure has been applied to data taken during the Netherlands Cloud and Radiation (CLARA) campaign and the Cloud Lidar and Radar Experiment (CLARE'98) multisensor cloud measurement campaign. The results of the algorithm compare well with simultaneous IR radiometer cloud measurements as well as with measurements made by using aircraft‐mounted two‐dimensional probe particle‐sizing instruments.
Cloud effective particle size and water content profile retrievals using combined lidar and radar observations: 1. Theory and examples
Authors: Donovan D. P. , van Lammeren A. C. A. P.
Published: February 2004

In this paper, a novel lidar/radar method for simultaneously determining cloud particle effective size profiles (for water and ice clouds) and the lidar attenuation profile is described. Simulations and application to real data show that this procedure can be quite robust even in cases where significant lidar attenuation is present. In addition, the concept of a suitable lidar/radar effective particle size is introduced, and the determination of water contents for both water and ice clouds using this effective size together with the radar reflectivity profile is discussed. This paper concludes by presenting examples of effective size profiles and water content profiles inferred from measurements made during the Dutch Clouds and Radiation (CLARA) campaign. In a companion paper, it is demonstrated that the results of the inversion procedure compare favorably with infrared radiometer measurements as well as with in‐situ measurement results.
Introduction to the special section: The Mars Global Surveyor mission
Authors: Albee Arden
Published: February 2004

Since the launch of Mars Global Surveyor (MGS) in November 1996, it has returned more information about Mars than all previous missions combined. The scientific impact of MGS has been extraordinary. In many ways we now know Mars to be a very different planet than when MGS arrived in 1997. MGS has provided daily global and high resolution images, a global topographic model better than for Earth, a corresponding gravity model, and a magnetic field model, has mapped the surface composition, and has monitored the atmosphere.
Introduction to the special section: New Views of the Moon, Part 3, The Nature and Evolution of the Moon From Surface to Core, a series of papers related to the lunar science initiative “New views of the Moon enabled by combined remotely sensed and lunar sample data sets”
Authors: Neal Clive R.
Published: February 2004

The series of 12 papers that follows this brief introduction is part of the “New Views of the Moon” initiative started by NASA's Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM) in 1998 [cf. Jolliff and Ryder, 1998]. This initiative strives to integrate the various facets of lunar investigations, such as remotely sensed surface data (e.g., spectral reflectance, gamma‐ray, etc.), geophysics, sample analysis, and space weathering. The ensuing special section of 12 papers is the third that has been published in Journal of Geophysical Research (JGR)‐Planets as part of this lunar science initiative and is the result of topical sessions at the 31st Lunar and Planetary Science Conference in 2000. The first, published in 2000 (JGR, 105 (E2), 4173–4368) [Jolliff, 2000], contained 11 papers as a result of the initial “New Views” workshop that was held in Houston in 1998 [Jolliff and Ryder, 1998].
Reevaluation of the CaCO3 size index paleocarbonate ion proxy
Authors: Broecker Wallace S. , Clark Elizabeth
Published: February 2004

Measurements of the CaCO3 size index [Broecker and Clark, 1999] and of whole foraminifera shell weights [Lohmann, 1995] on glacial age sediment from a series of water depths on the Ceara Rise in the west equatorial Atlantic clearly demonstrate that the relationship between size index and pressure‐normalized carbonate ion concentration established for Holocene equatorial sediments does not apply to glacial sediments. Rather, it appears that the ratio of fine to coarse CaCO3 raining to the seafloor was greater during glacial time than during the Holocene. This finding squelches our previous enthusiasm regarding the application of the size index as a paleocarbonate ion proxy.
Role of topography‐induced gravitational stresses in basin inversion: The case study of the Pannonian basin
Authors: Bada Gábor , Horváth Frank , Cloetingh Sierd , Coblentz David D. , Tóth Tamás
Published: February 2004

Numerical stress models suggest that gravitational body forces associated with elevated topography around sedimentary basins can significantly influence the stress and strain pattern in basin interiors. In the absence of tectonic forces, basins surrounded by high‐altitude mountain ranges experience net horizontal compression. Owing to gravitational forces pointing from areas of high gravitational potential energy to subsided basin areas, further lithospheric extension can eventually terminate, leading to a gradual late stage inversion of the entire basin system. Modeling results suggest that the state of recent stress in the Pannonian basin, particularly in its western part, is controlled by the interplay of plate boundary forces, i.e., the counterclockwise rotation and northward indentation of the Adriatic microplate against the Alpine‐Dinaric belt, and buoyancy forces associated with the elevated topography and related crustal thickness variation of the Alpine‐Dinaric belt. Model calculations show that uplifted regions surrounding the basin system can exert compression on the thinned Pannonian lithosphere of ∼40–60 MPa that is of the order of the assumed far‐field tectonic stress magnitudes. The combined analysis of stress sources of tectonic and gravitational origin helps estimating the magnitude of maximum horizontal compression. High levels of compressional stresses (up to >100 MPa) are concentrated in the elastic core of the lithosphere, consistent with the ongoing structural inversion of the Pannonian basin system.
Crustal structure and tectonics of the Ninetyeast Ridge from seismic and gravity studies
Authors: Krishna K. S. , Neprochnov Y. P. , Rao D. Gopala , Grinko B. N.
Published: February 2004

Seismic reflection and refraction, gravity, and bathymetric data across and along the central part of the Ninetyeast Ridge were analyzed to determine the crustal structure of the ridge and to understand its tectonics. The ridge in the study area rises to ∼3.5 km above the seafloor of adjacent ocean basins. Basement is covered by sediments up to 0.8 km thick but exposed at some locations. Seismic refraction and gravity models of the ridge show that the crustal thickness is ∼22 km, greater than the average thickness (7 km) of oceanic crust estimated in the Central Indian and Wharton Basins. The ridge is compensated by flexure of layers 2A, 2B, and 3A to the extent of ∼2 km and by a 12 km thick deep crustal body (layer 3B) of underplated material. Upper crustal velocities (layer 2A) beneath the ridge are lower, up to 3.4 km s−1 than in adjacent basins because of weathering process and hydrothermal circulation of the waters in the tectonized blocks. While velocities in deep crustal body (layer 3B) are higher, up to 7.8 km s−1 and seem to be resulted from magmatic rocks accreted within the lithosphere. Steep down ward faulting of ∼2 km along the eastern flank of the Ninetyeast Ridge possibly originated because of compressional and extensional stresses applied along the 89°E Fracture Zone (FZ). The stresses are interpreted as resulting from multiple ridge jumps of Wharton spreading centers during the Late Cretaceous and middle Eocene. The velocity‐depth model suggests that the rocks of layers 2A and 2B and layer 3A are exposed on the eastern flank of the Ninetyeast Ridge and 90°E FZ, respectively. They are consistent with basalt, dolerite, and gabbro rocks, collected from the fault scarps. The central part of the ridge between 1°N and 11°S has uniformly deepened by ∼0.7 km and is bounded by major sublatitudinal deep‐seated fractures. We interpret that the deepened structural block and associated fractures resulted from the activity of the intense deformation of the central Indian Ocean.
Tertiary West Spitsbergen fold and thrust belt on Brøggerhalvøya, Svalbard: Structural evolution and kinematics
Authors: Saalmann K. , Thiedig F.
Published: February 2004

The Tertiary fold and thrust belt on Brøggerhalvøya is characterized by a NE vergent pile of nine thrust sheets. The basal sole thrust of the pile is located in Precambrian phyllites and climbs up section to the NE. The lower thrust sheets consist predominantly of post‐Caledonian cover sediments. Two thrust sheets in the central part of the pile contain a syncline and anticline on a kilometer‐scale. The kilometer‐scale fold is cut by juxtaposed thrusts giving rise to the formation of four structurally higher basement‐dominated thrust sheets. A five‐stage kinematic model is proposed: (1) in‐sequence foreland propagating formation of the lower thrust sheets with ramp‐flat geometries in response to N‐S subhorizontal bedding‐parallel movements, (2) change in tectonic transport to more (east) northeasterly directions and first out‐of‐sequence thrusting, inversion, and uplift of the basement in the hinterland, formation of the kilometer‐scale fold structure, (3) truncation of the kilometer‐scale fold by a thrust fault and stacking of the highest basement‐dominated thrust sheets by hindward propagating mode of thrust generation, (4) N‐S extension due to extensional collaps of the stack, (5) W‐E extension. The strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheet reflecting a temporal change to a more transpressive regime. Ramping of some thrust faults is suggested to be in part controlled by reactivated Carboniferous normal faults. The basal sole thrust of the thrust sheet stack also follows the trend of the Kongsvegen fault which showed enhanced activity during late Mesozoic‐early Tertiary extension. The curvature of the West Spitsbergen Fold and thrust belt on Brøggerhalvøya is interpreted to be controlled mainly by oblique ramping on the Kongsvegen fault associated with pinning on the Nordfjorden Block as well as by along‐strike lithological and thickness variations of the post‐Caledonian strata in addition. This suggests that pre‐existing structures have controlled the Tertiary geometry. The temporal change in the kinematics during thrust tectonics can be linked with the plate tectonic framework in the Arctic during Tertiary times.
Dynamics of magma emplacement in centrifuge models of continental extension with implications for flank volcanism
Authors: Bonini Marco , Sokoutis Dimitrios , Mulugeta Genene , Boccaletti Mario , Corti Giacomo , Innocenti Fabrizio , Manetti Piero , Mazzarini Francesco
Published: February 2004

A set of experimental small‐scale models of continental extension investigated the emplacement of orthogonal and oblique magma chambers, initially underplated at the base of the crust. The models are driven by a centrifugal body force which simulates the role of gravity in nature. The models represent crustal conditions analogous to relatively mature continental rifts and consider both symmetric and asymmetric extension. The experimental results suggest that magma emplacement is controlled by the interactions between tectonics and rheology of the crustal layers. In particular, extension is mainly accommodated by lateral flow and ductile doming in the viscous layer simulating the lower crust and by listric normal faults, in the overlying brittle layer, associated with the ductile domal uplift. Stretching of the continental crust induces a “reactive” migration of viscous layers into the footwall of major normal faults, where magma accumulation at the core of the domes takes place. This behavior suggests that widespread magmatism is expected to localize in the footwall of major normal faults, a situation that is often observed in core complex structures. Although the models presented here are intended to simulate magma emplacement during extension of a two‐layer brittle‐ductile system, lateral flow and migration of magma initially underplated at the base of the crust beneath narrow rifts (e.g., the Ethiopian rift) may also provide a similar mechanism and a possible explanation for the occurrence of important volcanoes on the plateaus flanking the rift zones. In the suggested model, such volcanoes are related to large basaltic magma reservoirs, located at the base of the crust, to accommodate the space vacated by lateral flow and thinning of the ductile crust. The similarity in structure of the models with natural examples of continental extension modes (such as rift systems and core complexes) may suggest a close similarity of dynamic processes.
Crustal architecture of the southern Uralides from true amplitude processing of the Urals Seismic Experiment and Integrated Studies (URSEIS) vibroseis profile
Authors: Tryggvason A. , Brown D. , Pérez‐Estaún A.
Published: February 2004

True amplitude processing of the Urals Seismic Experiment and Integrated Studies (URSEIS) vibroseis deep reflection seismic data acquired by the URSEIS consortium shows the southern Uralide crust to be composed of four major blocks with distinctive reflection characteristics. These blocks are juxtaposed along crustal‐scale boundaries. The foreland thrust and fold belt, developed from the East European craton crust, is imaged as subhorizontal to east dipping reflectivity that can be related to its Paleozoic and older tectonic history. The Moho beneath the foreland thrust and fold belt is not imaged in the vibroseis data set. The Main Uralian fault (the major arc‐continent suture) is unreflective, but its subsurface location can be inferred by the truncation of the reflection pattern of the East European craton and its contrast with that of the Magnitogorsk arc. The Magnitogorsk arc reflectivity is characterized by patchy, noncoherent to coherent reflections in the upper ∼10 – 15 km that are interpreted to be related to the arc volcanic rocks. Below this, reflectivity is diffuse, or the arc crust is transparent, and the Moho is not imaged. The East Magnitogorsk fault zone, which juxtaposes the arc against the East Uralian zone, is not imaged by the data. The upper 5 to 6 km of the East Uralian zone, corresponding to the Dzhabyk granite, is transparent. Below the granite the crust is characterised by east dipping patches of moderately coherent, high‐amplitude reflections that in the east become shallowly west‐dipping. A ∼10 km thick, west dipping band of coherent, high amplitude reflections between 12 and 35 km depth, corresponding to the Kartaly Reflection Sequence, extends beneath almost the entire East Uralian zone. The crust beneath the easternmost East Uralian zone reaches 53 km in thickness. The upper and middle crust of the Trans‐Uralian zone is characterized by a series of east and west dipping, concave upward, moderately coherent, high‐amplitude reflections. The lowermost middle and lower crust displays thin bands of west dipping, coherent, low‐amplitude reflectivity. The Moho is imaged as a sharp transition from reflective lower crust to transparent upper mantle at ∼49 km depth, and the lower crustal reflections appear to merge with it. The URSEIS vibroseis data are integrated with results from the explosion source reflection data, the wide‐angle reflection data, and the surface geology to place constraints on the crustal architecture of the orogen and on the timing of its assemblage.
Late Oligocene‐Neogene evolution of Europe‐Adria collision: New structural and geochronological evidence from the Giudicarie fault system (Italian Eastern Alps)
Authors: Viola Giulio , Mancktelow Neil S. , Seward Diane
Published: February 2004

The Giudicarie fault system (Giudicarie sensu stricto, Meran‐Mauls, Passeier, Thurnstein, and Jaufen faults) represents a sharp break in the generally E‐W strike direction of the orogen‐scale Periadriatic fault system and is a key element for understanding the late Oligocene‐Neogene evolution of the Alpine chain. The kinematics, timing and magnitude of movements on the Giudicarie fault system are presented here, on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples. Two main tectonic phases are established: (1) back thrusting of the Austroalpine units over the Southern Alps around 32 Ma, recorded by basement and limestone mylonites along the Giudicarie and Meran‐Mauls faults with transport directions toward 100°–110°, and (2) later sinistral transpressive displacement, characterized by structures at the ductile‐brittle transition, which overprinted the top to E/ESE thrust‐related mylonites but also partitioned into a major system of transcurrent faults in the Southalpine domain. It was during this later event that the Periadriatic fault attained its present‐day geometry. However, the amount of sinistral displacement along the Giudicarie system was only ∼15–20 km. The magnitude is established here from the ∼15 km sinistral offset of the Jaufen mylonites across the Passeier brittle fault and the ∼20 km long gap in the otherwise continuous distribution of Oligocene tonalitic lamellae along the Giudicarie fault. A direct structural connection is also established between the Brenner and the Jaufen faults. This constrains the timing of the second phase, since it must postdate the main exhumation phase of the Tauern Window at 20–18 Ma. The results of this study argue against an originally straight Periadriatic fault. The Giudicarie fault formed a restraining bend in this part of the Periadriatic fault system since at least the late Miocene and probably since the late Oligocene.
A conservative semi‐Lagrangian transport model for rivers with transient storage zones
Authors: Manson J. Russell , Wallis Steve G. , Hope Donna
Published: February 2004

A conservative, semi‐Lagrangian numerical method, domain of influence search for convective unconditional stability (DISCUS), for computing solute transport in fluvial systems with transient storage is presented. The model includes an explicit, shape‐preserving cubic interpolation update for advection and fully implicit temporal treatments of dispersion and transient storage. Numerical results with this new method are compared against exact solutions in a uniform advective‐dispersive flow with transient storage. Results from a conventional Eulerian numerical model are also shown. Both models are inherently stable and mass‐conserving. However, the semi‐Lagrangian method is shown to be accurate and free of grid‐scale oscillations over a wide range of Courant and grid Peclet numbers in contrast to the Eulerian approach whose accuracy degrades at high Courant numbers and/or large‐grid Peclet numbers. Some quantitative aspects of the comparative model efficiencies are discussed, with the semi‐Lagrangian model being particularly attractive when large time steps are used. In contrast to earlier semi‐ Lagrangian approaches, DISCUS employs the use of a cumulative solute mass variable in the advective update, and the issue of its interpolation is examined in the paper. Linear interpolation is shown to guarantee bounded solutions but can be very inaccurate, with numerical errors manifesting themselves by introducing artificially enhanced longitudinal dispersion. Higher‐order interpolation (cubic) increases accuracy but at the expense of introducing spurious maxima and minima which manifest themselves as small grid‐scale oscillations. By implementing a flux‐limiting technique, based on convexity preservation arguments, completely bounded solutions can be achieved in both spatial and temporal domains with the higher‐order interpolation.