bluuebunny/crossref_metadata_2025 huggingface dataset:
The radial temperature profile of the solar wind
Authors: Richardson John D. , Smith Charles W.
Published: May 2003

The Voyager data show a decrease in temperature in the inner heliosphere, an increase in temperature from 30–50 AU, a decrease from 50–63 AU, followed by another increase from 63–68 AU. Models of pickup proton heating predict a monotonic temperature rise beyond about 30 AU but do not account for the smaller scale (few AU) temperature variations. At 1 AU, the solar wind temperature is a strong function of the solar wind speed. We find that incorporating a temperature dependence on speed into the pickup proton heating results can reproduce much of the smaller‐scale temperature variation observed out to 68 AU. The same speed‐temperature dependence provides good fits to data from both the outer heliosphere and from near Earth. Since a large fraction of the proton energy results from heating, this work implies that the heating rate is a function of the speed.
Use of a two‐mode soil pore size distribution to estimate soil water transport in a land surface model
Authors: Liu Q. , Dickinson R. E.
Published: May 2003

Hydraulic properties determine the soil water content and its transport in the soil. They are provided in most current climate models as empirical formulas by functions of the soil texture. Such is not realistic if the soil contains a substantial amount of macropores. A two‐mode soil pore size distribution is incorporated into a land surface model to provide more accurate estimation of hydraulic properties of well‐aggregated soils. The pore‐size distribution for soils with heterogeneous pore systems is regarded as a linear combination of two simple (uni‐mode) distributions, thus the macropores can be isolated as an component of the size distribution. The matric potential and the unsaturated hydraulic conductivity are derived from this distribution. Using an observational dataset at a tropical forest site with aggregated soils, the treatment is found to significantly improve the simulation of its soil moisture and surface water fluxes.
On continuous versus discontinuous neutral lines at the dayside magnetopause for southward interplanetary magnetic field
Authors: Petrinec S. M. , Fuselier S. A.
Published: May 2003

During intervals of southward interplanetary magnetic field (IMF), it is thought that magnetic reconnection occurs along an extended region of the dayside magnetopause. The reconnected magnetic field lines are believed to transport solar wind plasma into the magnetosphere and into the high‐latitude ionosphere. The precipitation pattern therefore provides information on the location and extent of reconnection at the magnetopause. This study uses observations of the energy and local time distribution of energetic proton precipitation into the dayside ionosphere during periods of southward IMF from the Far UltraViolet (FUV) imager on board the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft. These precipitation patterns suggest that the magnetic neutral line can be discontinuous across the dayside magnetopause.
High‐resolution profiling of layered structures in the lower stratosphere by GPS occultation
Authors: Hocke Klemens , Igarashi Kiyoshi , Tsuda Toshitaka
Published: May 2003

The back propagation method is applied to GPS occultation measurements of the lower stratosphere in order to reduce diffraction effects and to enhance the vertical resolution of the derived temperature profiles. The ionospheric bending angle correction should not be applied to small‐scale bending angle fluctuations (λz < 1 km) of the GPS L1 and L2 signal, otherwise the retrieved profiles have enhanced artificial noise. Temperature profiles of two occultation events near to Japan on 4 and 5 February 1997 are discussed as examples for two different states of the lower stratosphere. One time the small‐scale fluctuations appear as sinusoidal wave trains. The other time the high‐resolution temperature profile has stairs which may result from atmospheric wave energy dissipation within a turbulence layer at each stair. The spectral energy distribution of the retrieved temperature fluctuations of both examples are well explained by the theoretical power spectra of saturated gravity waves at vertical wavelengths 0.1–2 km.
Observational evidence that soil moisture variations affect precipitation
Authors: Koster Randal D. , Suarez Max J. , Higgins R. Wayne , Van den Dool Huug M.
Published: May 2003

Land‐atmosphere feedback, by which precipitation‐induced soil moisture anomalies affect subsequent precipitation, may be an important element of Earth's climate system, but its very existence has never been demonstrated conclusively at regional to continental scales. Evidence for the feedback is sought in a 50‐yearobservational precipitation dataset covering the United States. The precipitation variance and autocorrelation fields are characterized by features that agree (in structure, though not in magnitude) with those produced by an atmospheric general circulation model (AGCM). Because the model‐generated features are known to result from land‐atmosphere feedback alone, the observed features are suggestive of the existence of feedback in nature.
Effects of plasma sheet variability on the fast initial ring current decay
Authors: Jordanova V. K. , Kistler L. M. , Thomsen M. F. , Mouikis C. G.
Published: May 2003

We study the effects of plasma sheet variations on the fast initial ring current (RC) decay during the March 31, 2001 storm. Previous studies have focused on the effects of enhanced plasma sheet density on RC buildup during the main phase of the storms. Using model simulations and energetic particle data from the instruments on CLUSTER and LANL, we demonstrate that the drop of plasma sheet density during the early recovery phase is important for the fast RC decay. In fact, an additional ∼50 nT decrease in Dst index occurs if this drop is not taken into account. We also demonstrate that there is no preconditioning of the RC during this storm period. The second enhancement in the convection electric field is not more effective in building the RC than the first in the case of the same magnetospheric plasma inflow on the nightside. This study shows that the fast initial RC decay is controlled not only by the decreased convection electric field, dayside outflow through the magnetopause, and internal loss processes, but also by the time‐varying nightside inflow of plasma from the magnetotail. All factors should be considered for accurate predictions of RC decay timescales and Dst index.
Crustal loading near Great Salt Lake, Utah
Authors: Elósegui P. , Davis J. L. , Mitrovica J. X. , Bennett R. A. , Wernicke B. P.
Published: May 2003

Two sites of the BARGEN GPS network are located ∼30 km south of Great Salt Lake (GSL). Lake‐level records since mid‐1996 indicate seasonal water elevation variations of ∼0.3 m amplitude superimposed on a roughly “decadal” feature of amplitude ∼0.6 m. Using an elastic Green's function and a simplified load geometry for GSL, we calculate that these variations translate into radial crustal loading signals of ±0.5 mm (seasonal) and ±1 mm (decadal). The horizontal loading signals are a factor of ∼2 smaller. Despite the small size of the expected loading signals, we conclude that we can observe them using GPS time series for the coordinates of these two sites. The observed amplitudes of the variations agree with the predicted decadal variations to <0.5 mm. The observed annual variations, however, disagree; this difference may be caused by some combination of local precipitation‐induced site motion, unmodeled loading from other nearby sources, errors in the GSL model, and atmospheric errors.
Two components in major solar particle events
Authors: Cane H. V. , von Rosenvinge T. T. , Cohen C. M. S. , Mewaldt R. A.
Published: May 2003

A study has been made of 29 intense, solar particle events observed in the energy range 25–80 MeV/nuc near Earth in the years 1997 through 2001. It is found that the majority of the events (19/29) had Fe/O ratios that were reasonably constant with time and energy, and with values above coronal. These all originated on the Sun's western hemisphere and most had intensities that rose rapidly at the time of an associated flare (and coronal mass ejection). Interplanetary shocks observed near Earth had little effect on particle intensities during these events. The remaining 10 events had different intensity‐time profiles and Fe/O ratios that varied with time and energy with event‐averaged values at or below coronal. Most of these originated near central meridian and 6 had strong interplanetary shocks that were observed near Earth. There were four events with two peaks in the intensity‐time profiles, the first near the time of the associated flare (with high Fe/O) and the other at shock passage (with a lower Fe/O) suggesting that solar particle events have two components. At high rigidities the first component (probably flare generated) usually dominates and interplanetary shock‐accelerated particles (forming the second component) make a minor contribution except in the case of unusually fast shocks.
Production of methyl bromide in a temperate forest soil
Authors: Varner Ruth K. , White Marguerite L. , Mosedale Cindy H. , Crill Patrick M.
Published: May 2003

Field enclosure measurements of a temperate forest soil show net uptake of ambient methyl bromide (CH3Br), an important trace gas in both tropospheric and stratospheric ozone cycling. The net flux for 1999 was estimated to be −168 ± 72 μg CH3Br m−2 (negative indicates loss from the atmosphere). Individual enclosure flux measurements ranged from −4.0 to +3.3 μg CH3Br m−2 d−1. Soil consumption of CH3Br was estimated from laboratory soil incubations. Production of CH3Br was calculated as the difference between net flux and predicted consumption. Fungi could be responsible for the production of CH3Br in this temperate forest soil.
Site‐to‐bedrock over 1D transfer function ratio: An indicator of the proportion of edge‐generated surface waves?
Authors: Cornou Cécile , Bard Pierre‐Yves
Published: May 2003

We study multi‐dimensional site effects in the small‐size deep sediment filled basin of Grenoble (French Alps). A very dense array composed of 3‐component seismometers over a 1 km aperture is used to investigate propagation parameters of waves propagating across the array. We present results for 6 teleseismic events for which we had a reference rock site. For the frequency range 0.1 to 1 Hz, records are clearly dominated by edge‐generated surface waves. Quantification of energy carried by each identified wave train allows interpreting the difference between site‐to‐bedrock and 1D transfer function estimates in terms of laterally propagating basin‐edge induced waves only above the fundamental resonance frequency of the basin. A simple ratio between site‐to‐bedrock and 1D transfer function curves should thus provide an estimation of the relative contribution of 1D and 2D/3D effects in ground motion on the condition that all the time signal length is taken into account.
Cyclic ridge subduction at an inter‐plate locked zone off central Japan
Authors: Kodaira Shuichi , Nakanishi Ayako , Park Jin‐Oh , Ito Aki , Tsuru Tetsuro , Kaneda Yoshiyuki
Published: May 2003

There are significant variations in the size, especially lateral extent, of the co‐seismic rupture zones and inter‐plate locked zones for an inter‐plate mega‐thrust earthquake. Obvious factors controlling those variations have been still unsolved questions. We designed integrated seismic profiles, including a wide‐angle seismic profile and a multichannel reflection seismic profile, at the eastern Nankai trough in central Japan. Refraction tomography and pre‐stack depth migration of wide‐angle seismic data successfully image a trough‐parallel cyclic ridge subduction, with thickness of 13–20 km and wavelength of 35–50 km, at a geodetically determined inter‐plate locked zone in a non‐rupture zone during the 1944 Tonankai mega‐thrust earthquake. This result suggests a first direct evidence for the “subducted seamount = strongly locked” hypothesis.
On correlations between the North Atlantic Oscillation, geopotential heights, and geomagnetic activity
Authors: Thejll Peter , Christiansen Bo , Gleisner Hans
Published: May 2003

We investigate correlations between geomagnetic activity indices, the North Atlantic Oscillation (NAO), and stratospheric geopotential heights. It is shown that the correlation between the geomagnetic index Ap and the NAO index is high and significant since about 1970, that it is significant during winter only, that it was not significant before about 1970, and that the correlations are dominated by quasi‐decadal scales of variability. Analysis of the spatial pattern of correlations, restricted to the Northern Hemisphere and wintertime, shows that significant correlations between Ap and sea‐level pressures and between Ap and stratospheric geopotential heights are found for the period 1973–2000. However, for the period 1949–1972 no significant correlations are found at the surface while significant correlations still are found in the stratosphere. This might indicate that a solar forcing, primarily acting in the stratosphere, is propagating its influence downward in the later period but not in the earlier.
Optical and meteorological properties of smoke‐dominated haze at the ARM Southern Great Plains Central Facility
Authors: Iziomon Moses G. , Lohmann Ulrike
Published: May 2003

The optical and meteorological properties of smoke‐dominated haze at the Southern Great Plains Central Facility of the Atmospheric Radiation Measurement (ARM) Program from 1997 to 2001 are presented. Aerosol optical properties for smoke‐dominated haze vary with season at the ARM site, with an inter‐seasonal mean single scattering albedo, Ångström exponent, hemispheric backscatter fraction and hygroscopic growth factor of 0.91 ± 0.03, 2.0 ± 0.1, 0.14 ± 0.02 and 1.6 ± 0.2, respectively. In addition, the local seasonal direct radiative forcing for smoke haze ranges from −0.25 to −3.14 Wm−2. Relative to smoke‐free periods, months with enhanced smoke are characterised by reduced cloud cover, increased shortwave radiation, lower liquid water path and precipitation.
Zeta potential measured for an intact granite sample at temperatures to 200°C
Authors: Tosha T. , Matsushima N. , Ishido T.
Published: May 2003

Streaming potential was measured in an intact granite sample, saturated with aqueous KCl solutions at three different concentrations, at temperatures between 25° and 200°C. The magnitudes of the streaming potential coefficient and of the surface conductance (which dominates the sample conductivity) both increase with increasing temperature. Using a capillary model, we found that the magnitude of the zeta potential also increases with increasing temperature.
Buttressing and fractional spreading of Tenerife, an experimental approach on the formation of rift zones
Authors: Walter Thomas R.
Published: May 2003

The island of Tenerife is composed of three Miocene shields, which are centered by the Cañadas volcano since the Pliocene. Tenerife sits on more than 2 km thick oceanic sediments. Quaternary volcanism of the Cañadas series and giant landslides were principally confined to triaxial rift zones. The mechanism of triaxial rifting, however, has remained unclear. Physical analog models show that these rift zones may have formed by gravity‐driven lateral escape of island segments, induced by loading of the deformable substratum. For experiments scaled to Tenerife, three adjacent sand cones were mounted onto viscous PDMS substratum. Gravitational spreading caused circumferential expansion of each cone, until a large edifice (Cañadas) was constructed in their center. The older cones now acted each as a buttress; radial fractures were overprinted by fractional spreading of the Cañadas edifice. This resulted in formation of three main extensional zones, resembling the triaxial rifting configuration of Tenerife.
Improved global maps and 54‐year history of wind‐work on ocean inertial motions
Authors: Alford Matthew H.
Published: May 2003

The global distribution and 54‐year time dependence of the energy‐flux from the wind to near‐inertial motions is computed by driving a slab mixed‐layer model with NCEP/NCAR Reanalysis winds, improving upon previous estimates [Alford, 2001; Watanabe and Hibiya, 2002]. The slab model is solved spectrally with frequency‐dependent damping. The resulting solutions are more physically sensible than the previous, and more skillful at high latitudes, where the inertial frequency approaches the 4×‐daily sampling of the Reanalysis winds. This enables Alford's calculation, whose domain was limited to ±50°, to be extended to the poles. The high‐latitude reliability is demonstrated by direct comparison with a high‐resolution regional model (REMO) in the NE Atlantic. The total power input, 0.47 TW, has increased by 25% since 1948, paralleling observed increases in extratropical cyclone frequency and intensity. If believable, the trend may have important consequences for modulation of the meridional overturning circulation.
Coastal upwelling air‐sea fluxes revealed in atmospheric observations of O2/N2, CO2 and N2O
Authors: Lueker Timothy J. , Walker Stephen J. , Vollmer Martin K. , Keeling Ralph F. , Nevison Cynthia D. , Weiss Ray F. , Garcia Hernan E.
Published: May 2003

We capture water column ventilation resulting from coastal upwelling in continuous records of O2/N2, CO2, and N2O at Trinidad, California. Our records reveal the gas exchange response time of the ocean to the upwelling and ensuing biological production. Satellite and buoy wind data allow extrapolation of our records to assess coastal upwelling air‐sea fluxes of O2 and N2O. We improve on previous regional estimates of N2O flux in coastal and continental shelf region of the western U.S. We characterize the source of N2O as being predominately from nitrification based on the O2/N2O emissions ratio observed in our atmospheric records.
The influence of the interplanetary magnetic field on the entry of solar wind ions into the magnetosphere
Authors: Peroomian Vahé
Published: May 2003

This study investigated the entry of solar wind ions into the magnetosphere by following particle orbits from the solar wind through the magnetopause boundary in time‐dependent electric and magnetic fields obtained from a 3D global magnetohydrodynamic (MHD) simulation of the magnetosphere; five different orientations of the interplanetary magnetic field (IMF) were considered. We found the region of the upstream solar wind that mapped to the magnetopause entry regions to be parallel to the y‐z orientation of the IMF. However, significant asymmetries were caused by the history of the IMF, the orientation of the interplanetary electric field (IEF), the nonadiabatic acceleration of ions at the magnetopause reconnection region, and acceleration by the magnetopause electric fields. Ions generally entered the magnetosphere through extended dayside regions corresponding to the reconnection region for each IMF and were accelerated by that region's electric fields. Entry also occurred along high‐latitude open field lines convecting into the magnetotail.
Synthesis of Rayleigh‐wave envelope on the spherical Earth: Analytic solution of the single isotropic‐scattering model for a circular source radiation
Authors: Maeda Takuto , Sato Haruo , Ohtake Masakazu
Published: May 2003

Surface waves propagating around the spherical Earth are scattered by medium heterogeneities and topographical variations. Wave trains appearing between the multiple arrivals of surface waves are interpreted as scattered waves. Mean‐Squared (MS) envelopes of vertical‐component seismograms in long periods can be explained by the single isotropic scattering process of Rayleigh waves of the fundamental mode based on the radiative transfer theory on the spherical Earth. For the case of circular radiation from a point source on the sphere, we can analytically solve the single scattering approximation of the radiative transfer equation. The resultant MS envelope is written by using an elliptic integral of the first kind.
First measurements of the Twomey indirect effect using ground‐based remote sensors
Authors: Feingold Graham , Eberhard Wynn L. , Veron Dana E. , Previdi Michael
Published: May 2003

We demonstrate first measurements of the aerosol indirect effect using ground‐based remote sensors at a continental US site. The response of nonprecipitating, ice‐free clouds to changes in aerosol loading is quantified in terms of a relative change in cloud‐drop effective radius for a relative change in aerosol extinction under conditions of equivalent cloud liquid water path. This is done in a single column of air at a temporal resolution of 20 s (spatial resolution of ∼100 m). Cloud‐drop effective radius is derived from a cloud radar and microwave radiometer. Aerosol extinction is measured below cloud base by a Raman lidar. Results suggest that aerosols associated with maritime or northerly air trajectories tend to have a stronger effect on clouds than aerosols associated with northwesterly trajectories that also have local influence. There is good correlation (0.67) between the cloud response and a measure of cloud turbulence.
Detection of volcanic, solar and greenhouse gas signals in paleo‐reconstructions of Northern Hemispheric temperature
Authors: Hegerl Gabriele C. , Crowley Thomas J. , Baum Steven K. , Kim Kwang‐Yul , Hyde William T.
Published: May 2003

We apply a multiple regression method to estimate the response to anthropogenic and natural climate forcings simultaneously from a number of paleo‐reconstructions of Northern Hemispheric average temperature. These long records (600 to 1000 years) provide a unique opportunity to distinguish between different external influences on climate. The response to volcanic forcing is reliably detected in all reconstructions, and the simulated temperature response to volcanic eruptions compares favorably with observations. The response to solar forcing is detected in Hemispheric mean data only over some periods in some records, and appears weak. Although most records can be used only to the middle of the 20th century, the temperature response to CO2 can be detected by this time in most records.
Holocene climate instability during the termination of the African Humid Period
Authors: Renssen H. , Brovkin V. , Fichefet T. , Goosse H.
Published: May 2003

The termination of the Holocene African Humid Period (∼9 to ∼6 kyr BP) is simulated with a three‐dimensional global coupled climate model that resolves synoptic variability associated with weather patterns. In the simulation, the potential for “green” and “desert” Sahara states becomes equal between 7.5 and 5.5 thousand years ago, causing the climate system to fluctuate between these states at decadal‐to‐centennial time‐scales. This model result is supported by paleoevidence from the Western Sahara region, showing similar paleohydrological fluctuations around that time. For the present‐day, only the desert Sahara state is stable in the model.
Multiple energy‐dispersed ion signatures in the near‐Earth magnetotail: Geotail observation
Authors: Kazama Yoichi , Mukai Toshifumi
Published: May 2003

Multiple energy‐dispersed ion signatures were observed by the Geotail spacecraft in the plasma sheet at ∼10 Re down the tail and ∼4 Re on the duskside, corresponding to a small and localized auroral intensification recorded by Polar/UVI. They were also accompanied by magnetic field dipolarization and enhancement of electron parallel pressure. All the dispersed signatures are interpreted as due to a time‐of‐flight effect of ion clusters produced in remote regions magnetically connected to the observation site. They can be categorized into two types in terms of energies and pitch angles. One is the higher‐energy components having crescent‐shaped distributions in the phase space and counterstreaming in the magnetic field direction. The other, of which the energy was dispersed from 2 keV down to 60 eV, was a collimated beam along the magnetic field line and unidirectionally streaming away from the Earth. The former is interpreted as bouncing ion clusters which are produced in a mid‐tail region with a similar process to the convection surge model, while the latter is most likely to be protons upflowing from the ionosphere. An interesting point in terms of the magnetosphere‐ionosphere coupling is nearly the simultaneous occurrence of ion accelerations in the mid‐tail region and above the ionosphere along the same field tube.
Biogeochemical evidence of vigorous mixing in the abyssal ocean
Authors: Lampitt Richard S. , Popova Ekaterina E. , Tyrrell Toby
Published: May 2003

The metabolic activities of biological communities living at the abyssal seabed create a strong source of nutrients and a sink for oxygen. If the published estimates of vertical mixing based on instantaneous microstructure measurements are correct, near to the abyssal seabed away from rough topographic features there should be enhanced concentrations of nitrate and phosphate and depletion of oxygen. Recent data on the vertical concentration profiles of inorganic nutrients and oxygen over the bottom 1000 m of the water column (World Ocean Circulation Experiment ‐ WOCE) provide no such evidence. It is concluded that the effective vertical mixing rates are much more vigorous than previously indicated and may even be higher than estimates of average basin scale rates based on temperature and salinity distributions. We propose that the enhanced mixing associated with rough topography influences the entire volume of the abyssal ocean on short time scales (e.g., one month ‐ one year).
Assessing climate forcings of the Earth system for the past millennium
Authors: Bauer Eva , Claussen Martin , Brovkin Victor , Huenerbein Anja
Published: May 2003

The effects of natural and anthropogenic forcings (solar activity, volcanism, atmospheric CO2 concentration, deforestation) on climate changes are estimated with the Earth system model of intermediate complexity, CLIMBER‐2, for the past millennium. Simulated surface air temperatures for the Northern Hemisphere from the combined forcing correlate reasonably well with paleoclimatic data (r = 0.70). The largest negative anomalies occur when insolation minima coincide with volcanic eruptions. Anthropogenic forcings impose additional climate changes after 1850. The increasing warming from increasing CO2 concentrations is attenuated by the cooling effect from deforestation. Results from differently combined forcings suggest that the relatively cool climate in the second half of 19th century is largely attributable to cooling from deforestation.
EOF analysis of three records of sea‐ice concentration spanning the last 30 years
Authors: Singarayer Joy S. , Bamber Jonathan L.
Published: May 2003

Several continuous observational datasets of Artic sea‐ice concentration are currently available that cover the period since the advent of routine satellite observations. We report on a comparison of three sea‐ice concentration datasets. These are the National Ice Center charts, and two passive microwave radiometer datasets derived using different approaches: the NASA team and Bootstrap algorithms. Empirical orthogonal function (EOF) analyses were employed to compare modes of variability and their consistency between the datasets. The analysis was motivated by the need for a reliable, realistic sea ice climatology for use in climate model simulations, for which both the variability and absolute values of extent and concentration are important. We found that, while there are significant discrepancies in absolute concentrations, the major modes of variability derived from all records were essentially the same.
Possible deposit of soil dust from the 1930's U.S. dust bowl identified in Greenland ice
Authors: Donarummo J. , Ram M. , Stoermer E. F.
Published: May 2003

We have identified a dust storm deposit in the GISP2 ice core that most likely originated from the Great Plains region of the United States during the 1930's ‘Dust Bowl’ era. These results indicate that the Central U.S. can be a significant source of dust to the Greenland ice sheet, especially when the source area is affected by intense drought conditions.
Accuracy and resolution of shuttle radar topography mission data
Authors: Smith Bridget , Sandwell David
Published: May 2003

We assess the accuracy and resolution of topography data provided by the Shuttle Radar Topography Mission (SRTM) through spectral comparisons with the National Elevation Dataset (NED) and a high‐resolution laser data set of the 1999 Hector Mine earthquake rupture. We find that SRTM and the NED are coherent for wavelengths greater than 200 m, however the spatial resolution of the NED data is superior to the SRTM data for wavelengths shorter than 350 m, likely due to the application of a boxcar filter applied during final SRTM processing stages. From these results, a low‐pass filter/decimation algorithm can be designed in order to expedite large‐area SRTM applications.
Atmospheric input of mineral dust to the western North Pacific region based on direct measurements and a regional chemical transport model
Authors: Uematsu Mitsuo , Wang Zifa , Uno Itsushi
Published: May 2003

The spatial and temporal variation of the mineral aerosol concentration and its total deposition flux over the western North Pacific region were analyzed with a regional chemical transport model (AQPMS) for the period March 1994 through May 1995. Dry deposition accounted for more than 60% of the total deposition of Asian mineral dust throughout the period. The annual deposition flux was found to decrease rapidly from the coastal area (21 g m−2 yr−1) to the open ocean (0.8 g m−2 yr−1) over the study region. Sporadic dust deposition events over the HNLC region may increase the dissolved iron concentration in seawater and hence stimulate marine biological activity. The main eastward flow of mineral dust is located in the free troposphere between 30 and 40°N, above the layer of maximum concentration. These results support the intercontinental transport of Asian mineral dust across the North Pacific as background aerosol.
Outer core density heterogeneity and the discrepancy between PKP and PcP travel time observations
Authors: Soldati G. , Boschi L. , Piersanti A.
Published: May 2003

We derive 3‐D tomographic maps of the Earth's mantle, CMB and outer core, from seismic P, PcP, PKPbc, PKPdf travel time data, based on the bulletins of the International Seismological Centre (1964–1995), after source relocation by Antolik et al. [2001] and phase re‐identification by Engdahl et al. [1998]. Maps of the CMB derived independently from core‐reflected (PcP) or core‐refracted (PKP) phases are not well correlated. We attempt to explain this discrepancy, and study the radial coherence of whole‐Earth tomographic images, to identify possible trade‐offs between CMB undulations and velocity anomalies in the mantle or outer core. Imaged velocity anomalies in the lowermost mantle are anticorrelated with the topography of the CMB; likewise, imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the study of Piersanti et al. [2001], suggests that the core anomalies might not be entirely fictitious.
A fast and accurate operational model of ionospheric electron density
Authors: Schoendorf J. , Rabitz H. , Li G.
Published: May 2003

High dimensional model representation (HDMR), a technique useful for reducing the computational burden of complex geophysical models, is applied to a global first principles model of the ionosphere/thermosphere system. HDMR captures the input‐output relationship of a model with a series of correlation functions that accurately represents the original model. The resulting Fully Equivalent Operational Model (FEOM) of ionospheric electron density ([e]) described herein is derived from the Integrated Space Weather Prediction Model (ISM). It reproduces ISM [e] with errors of less than 3% over 97% of the three‐dimensional ISM grid. The observed factor of 103speed up in CPU time demonstrates the feasibility of using HDMR to construct a fast and accurate ionospheric model based on first principles model output.
Double flux‐rope magnetic cloud in the solar wind at 1 AU
Authors: Hu Qiang , Smith Charles W. , Ness Norman F. , Skoug Ruth M.
Published: May 2003

We present a study of a magnetic cloud observed by Advanced Composition Explorer (ACE) in the solar wind at 1 AU on August 12, 2000. Its cross‐section is obtained from magnetic field and plasma measurements by using a Grad‐Shafranov reconstruction technique. This shows a configuration of asymmetric double flux ropes with a single‐X point in between. Overall magnetic field and current density distributions are obtained numerically in a 2D domain. The boundary confining the flux ropes is defined in consistency with two‐dimensional, magnetohydrostatic theory. Several parameters characterizing the flux ropes are derived. A benchmark case is illustrated to validate the approach.
Distribution of crustal magnetic fields on Mars: Shock effects of basin‐forming impacts
Authors: Hood L. L. , Richmond N. C. , Pierazzo E. , Rochette P.
Published: May 2003

Crustal magnetic fields on Mars are inhomogeneously distributed with the strongest fields occurring over the southern highlands in a longitude sector between approximately 130°E and 240°E. Using analytic approximations and empirical scaling laws, it is estimated that much of the weakly magnetized southern highlands (i.e., that between 110°W and 130°E) was shocked to pressures exceeding 1–2 GPa during the Hellas and Argyre impacts. Possible primary remanence carriers in the martian crust include iron oxides and iron sulfides (pyrrhotite). If pyrrhotite is the main remanence carrier, extensive demagnetization of crustal regions (∼90%) may occur at shock pressures of 2 GPa or more. Thus, at least for this remanence carrier, impact shock demagnetization can potentially explain the distribution of crustal fields in the southern highlands.
Methane escape from gas hydrate systems in marine environment, and methane‐driven oceanic eruptions
Authors: Zhang Youxue
Published: May 2003

Huge quantities of CH4 are stored in marine sediment in the form of methane hydrate, bubbles, and dissolved CH4 in pore water. Here I discuss the various pathways for methane to enter the ocean and atmosphere, including: (i) Methane hydrate dissolution or dissociation as it rises through seawater. The dissociation rate can be 2 to 3 orders of magnitude greater than the dissolution rate. (ii) The dissolution and expansion of a bubble with or without a hydrate shell as it rises through seawater. There is a critical radius (which depends on depth), above which a bubble would reach the surface or even become larger as it rises. I also propose and model the dynamics of a new type of terrestrial gas‐driven eruptions: methane‐driven oceanic eruptions. Such eruptions not only represent a yet unrecognized geohazard, but also provide a pathway for CH4 to rapidly enter the atmosphere as a greenhouse gas.
Benzene and Haze Formation in the Polar Atmosphere of Jupiter
Authors: Wong Ah‐San , Yung Yuk L. , Friedson A. James
Published: May 2003

Jupiter has a large magnetosphere that episodically precipitates large amounts of energy into the polar atmosphere, giving rise to intense auroras [Clarke et al., 1996; Grodent et al., 2000]. An important consequence of this energy influx is the production of a dark haze [Pryor and Hord, 1991], the formation mechanism of which was hitherto poorly known. Recent observations of benzene on Jupiter [Bézard et al., 2001; Flasar, 2002] provide new clues for a chemical and aerosol model for the formation of heavy hydrocarbon aerosols. The chemistry begins with the destruction of methane by energetic particles, followed by neutral and ion reactions, ultimately leading to the formation of benzene and other complex hydrocarbons, including multi‐ring compounds which subsequently condense. High temperatures and effective eddy mixing engendered by the auroras enhance the formation of heavy hydrocarbons and aerosols. This mechanism may be relevant in the atmospheres of Saturn and extrasolar giant planets, and is an example of how a planetary magnetosphere may influence the chemical composition and climate forcing of the upper atmosphere.
Cold halocline in the northern California Current: An invasion of subarctic water
Authors: Freeland Howard J. , Gatien Germaine , Huyer Adriana , Smith Robert L.
Published: May 2003

Subsurface upper ocean waters off Oregon and Vancouver Island were about 1°C cooler in July 2002 than in July 2001. The anomalously cool layer coincides with the permanent halocline which has salinities of 32.2 to 33.8, suggesting an invasion of nutrient‐rich Subarctic waters. The anomalously cool layer lies at 30–150 m. The cool anomaly is likely caused by stronger southward flow in the California Current and weaker northward flow in the Alaska and Davidson Currents during spring 2002. Other factors may include reduced coastal downwelling in late winter and early spring 2002, enhanced eastward flow in the Subarctic Current, and enhanced winter mixing offshore.
Measurements of aerosol optical depth over Arabian Sea during summer monsoon season
Authors: Vinoj V. , Satheesh S. K.
Published: May 2003

Aerosol spectral optical depths were measured over Arabian Sea as a part of the Arabian Sea Monsoon Experiment (ARMEX). These are the first measurements of aerosols over northern and central Arabian Sea during Indian summer monsoon season. Aerosol visible optical depths were in the range of 0.4 to 0.7 with Angstrom wavelength exponent of ∼0.35 and single scattering albedo of ∼0.97 indicating the dominance of large non‐absorbing aerosols. Aerosol optical depth increases exponentially with sea‐surface wind speed. Our estimates show that sea‐salt contributes ∼60% to the composite aerosol optical depth. The presence of aerosols over Arabian Sea during summer monsoon season decreases the short wave radiation arriving at the surface by as much as 21 W m−2 and increases top of the atmosphere reflected radiation by 18 W m−2.
Characteristic silent earthquakes in the eastern part of the Boso peninsula, Central Japan
Authors: Ozawa Shinzaburo , Miyazaki Shinichi , Hatanaka Yuki , Imakiire Tetsuo , Kaidzu Masaru , Murakami Makoto
Published: May 2003

Analysis of Global Positioning System (GPS) data shows transient crustal deformation in the Boso peninsula, central Japan, for about fifty days from October 2002. The southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the Philippine Sea plate and the North American plate, six years after a similar event in 1996. We estimate an area of aseismic slip with moment magnitude (Mw) 6.6 centered off the Boso peninsula, adjacent to associated seismic activity. Slip evolution of the 2002 aeismic slip started on October 4 and migrated from north to south for about ten days, followed by gradual subsidence and restarting of slip which lasted until ∼December 2, propagating more southward. Similarities in focal area and slip process between the 1996 and the 2002 events suggest the Boso aseismic slips as characteristic silent earthquakes, together with the repetitive occurrence of seismic swarm in a similar region every six to seven years. A more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude, central slip area, and duration between the 1996 and the 2002 events, if the hypothesized recurrence interval for strain accumulation is true, based on swarm seismicity.
Some aspects of the southern Pacific subtropical overturning cell (STC) during WESPALIS‐1 cruise in Oct./Nov. 1999
Authors: Ioualalen Mansour , Lukas Roger , Eldin Gerard , Gouriou Yves
Published: May 2003

Vertical distributions of salinity, temperature and currents were measured in the upper 1000 m of the tropical South Pacific Ocean along 165°E and 180° and along the equator in between, during the WESPALIS‐1 cruise (Oct./Nov. 1999). The high salinity tongue of the South Pacific subtropical overturning cell (STC) is eroded along its westward and equatorward isopycnal flow. Part of the STC is contained in the eastward flow of the EUC which is then upwelled further east. During La Niña, another, shallower, portion of the STC layer flows directly towards the equator and is upwelled but confined south of the equator. During El Niño, there is also possibly intense exchange of heat between the STC and the equatorial mixed layer.
Kelvin‐Helmholtz instability around the tropical tropopause observed with the Equatorial Atmosphere Radar
Authors: Yamamoto Masayuki K. , Fujiwara Masatomo , Horinouchi Takeshi , Hashiguchi Hiroyuki , Fukao Shoichiro
Published: May 2003

In November 2001, the Equatorial Atmosphere Radar (0.20°S, 100.32°E) observed a continuous strong eastward wind shear (10–50 m s−1 km−1), westward wind (2–27 m s−1), and the radar echo layer tilted downward to the west in the region 0–1 km above the tropopause. During the same period, the Richardson number calculated with hourly‐averaged horizontal wind and radiosonde temperature data was almost continuously <0.5 and sometimes <0.25, which seems to indicate that the Kelvin‐Helmholtz instability (KHI) frequently occurs in that region. The existence of the tilted radar echo layer can be explained by KHI billows. A spurious updraft caused by the KHI‐induced tilted echo layer and by the strong westward wind was also observed in the region.
Mineral dust sources in the surroundings of the north Indian Ocean
Authors: Léon Jean‐François , Legrand Michel
Published: May 2003

We have used one year (1999) of Meteosat observations to monitor the dust activity in the arid and semi‐arid areas surrounding the North Indian Ocean. The method is based on the IDDI product derived from the infrared channel of the satellite. Dust sources are located according to a threshold on the IDDI and another on the surface wind speed. The global features of the dust activity in this area are in a good agreement with previous studies. Main dust sources are located in the Nubian desert, the Arabian peninsula, Iran, Pakistan and Afghanistan, and North West India. It is found that Somalia is also an area of dust emission with a maximum of activity from May to October.
Recent debris flows on Mars: Seasonal observations of the Russell Crater dune field
Authors: Reiss D. , Jaumann R.
Published: May 2003

Debris flows occur on slopes in the Russell Crater dune field. The morphology of the erosion features resembles terrestrial viscous slurry flows (mudflows) and suggests that a flow of fine‐grained material mixed with liquid water might have been responsible for their formation. Seasonal MGS‐TES and ‐MOC imagery based observations of the dune field show (1) an annual frosting and defrosting cycle and (2) that liquid H2O could be stable within a limited time period in the summer of the southern hemisphere. These observations lead to the conclusion that debris flows in the Russell Crater dune field may form under current climatic conditions by episodic or seasonal melting of small amounts of autumn/winter condensed water ice.
Changes in tropospheric ozone between 2000 and 2100 modeled in a chemistry‐climate model
Authors: Zeng Guang , Pyle John A.
Published: May 2003

We present results using a coupled chemistry/climate model to study changes in tropospheric ozone between 2000 and 2100. We assess changes first due to the increased emissions of NOx and VOCs (using the IPCC SRES scenario A2) and then due to both emission changes and the anticipated climate change with doubled CO2. In 2100, with the scenarios used, there is a substantial calculated increase in tropospheric O3, but in contrast to earlier studies, the increase is larger for doubled CO2. The increases are most pronounced in the extratropical middle and upper troposphere; changes in circulation and a chemically induced increase in lower stratospheric O3, mainly due to reduced temperatures there, both enhance stratosphere/troposphere exchange. These changes in the lower stratosphere are crucial to our results.
On the termination of the Hawaiian Lee Countercurrent
Authors: Yu Zuojun , Maximenko Nikolai , Xie Shang‐Ping , Nonaka Masami
Published: May 2003

New satellite observations reveal regions of strong island‐induced wind curl leeward of Hawaii. According to Sverdrup theory, this wind curl drives an eastward current that extends from Hawaii all the way to the Asian coast. The observed Hawaiian Lee Countercurrent (HLCC), however, terminates near the dateline. This study examines the possible role of mesoscale eddies in modifying the Sverdrup solution, using an ocean model of 0.1° horizontal resolution. The model simulates an HLCC of limited zonal extent under low horizontal viscosity that permits vigorous mesoscale eddies west of Hawaii. Preliminary analysis suggests that these eddies act to limit the westward extent of the HLCC by extracting energy from the mean flow.
The Dufek and Forrestal intrusions, Antarctica: A centre for Ferrar Large Igneous Province dike emplacement?
Authors: Ferris Julie K. , Storey Bryan C. , Vaughan Alan P. M. , Kyle Philip R. , Jones Phil C.
Published: May 2003

Newly acquired aeromagnetic data indicate the presence of a dike swarm that may have acted as a magma transport and feeder system from the plume impact site up to 3,500 km to the Ferrar Large Igneous Province (FLIP). The Dufek and Forrestal intrusions, cover approximately 6,600 km2, and may form a ponding station between a mantle superplume responsible for Gondwana breakup and the FLIP sills and lavas along the Transantarctic Mountains into Tasmania and New Zealand. Prior to this survey, no feeder dike swarms or sills connecting with the Ferrar have been found in the Pensacola Mountains. Similarities with the Mackenzie dikes and intrusions of Northwest Canada imply that Jurassic dikes may have been emplaced into the pre‐existing Ross orogeny trend during doming above a mantle plume. However, our survey area is too small to show the dikes convincingly radiating from a focal point that would indicate the plume position.
On the rate coefficient of the N(2D)+O2→NO+O reaction in the terrestrial thermosphere
Authors: Duff J. W. , Dothe H. , Sharma R. D.
Published: May 2003

The temperature dependence of the rate coefficient of the N(2D)+O2→NO+O reaction has been determined using ab initio potential energy surfaces (PES) and classical dynamics. The calculation agrees with the recommended rate coefficient at 300 K (∼110 km altitude). The rate coefficient is given by the expression k(T) = 6.2 × 10−12(T/300) cm3/s/molec. In contrast to the nearly temperature‐independent value of this rate coefficient previously recommended, the value given here increases by almost a factor of about four as the altitude increases from 110 to 200 km. It is also shown that even though N(2D) atoms in the thermosphere are produced with large translational energies, using the value of the rate coefficient at the local temperature introduces negligible error in the amount of NO produced. The new value of this rate coefficient will significantly increase the amount of NO computed in the aeronomic models causing a re‐evaluation of the heat budget and temperature and density structure of the thermosphere. In particular, implications of the larger rate coefficient for the recent observations of dramatically enhanced 5.3 μm emission from NO in the thermosphere due to solar storms are discussed.