bluuebunny/crossref_metadata_2025 huggingface dataset:
Association of Low‐Charge‐State Heavy Ions up to 200 Re upstream of the Earth's bow shock with geomagnetic disturbances
Authors: Posner Arik , Schwadron Nathan A. , Zurbuchen Thomas H. , Kozyra Janet U. , Liemohn Michael W. , Gloeckler George
Published: October 2002

We present the first study of Low‐Charge‐State Heavy Ion (LCSHI) events covering a region from Earth's bow shock to the L1 point, obtained with the Suprathermal Ion Composition Spectrometer onboard Wind. STICS is capable of distinguishing charge states of suprathermal ions. In 1995–2000 we found a large number of particle events revealing species of magnetospheric origin. LCSHI events tend to occur in series and in connection with geomagnetic activity. The occurrence rate is found to increase towards solar maximum. The spatial region covered by this particle population ranges from the bow shock to beyond distances of 130 Re, where one of the strongest events occurred. Based on the characterization of LCSHI events we discuss mechanisms for their formation. We conclude that the most probable sources of these ion events are substorms in association with Alfvén waves in high‐speed solar wind streams and the magnetic storm recovery ring current.
The impact of land cover change and increasing carbon dioxide on the extreme and frequency of maximum temperature and convective precipitation
Authors: Zhao Mei , Pitman Andrew J.
Published: October 2002

The impact on the extreme and frequency distribution of maximum temperature and convective precipitation resulting from a change in land cover is compared to the impact of an increase in CO2. Simulations using estimates of natural and current land cover at 280, 355, 430 and 505 ppmv were performed to explore the relationship between land cover change and CO2 level. We analyzed the return values of the annual daily maximum temperature and the seasonal changes of frequency in daily maximum temperature and convective precipitation over Europe and China. Our results confirm that increasing CO2 leads to increases in maximum temperatures and changes in rainfall intensity. We show that land cover change can cause similar impacts. Depending on the nature of the land cover changes, rainfall intensity and maximum temperatures can changed by amounts similar to those caused by increased CO2. In effect, the distribution of land cover can affect the climate's sensitivity to increasing CO2.
Simulations of Heinrich Events in a coupled ocean‐atmosphere‐sea ice model
Authors: Meissner K. J. , Schmittner A. , Wiebe E. C. , Weaver A. J.
Published: October 2002

Between 20 and 80 kyr ago several cooling cycles occurred in the Northern Hemisphere which culminated in a discharge of icebergs into the North Atlantic. These so called “Heinrich Events” (HEs) were followed by an abrupt shift to a warmer climate. Here we use a coupled ocean‐atmosphere‐sea ice model to study the response of the climate system under glacial conditions to a hypothetical HE. The HE is simulated by meltwater discharges and combined changes in land albedo and ice sheet topography mimicking a break‐up of a considerable part of the Laurentide ice sheet. Despite very different initial strengths of the overturning circulation in the Northern Hemisphere, the model response to the HEs is qualitatively similar. A warming of ocean and atmosphere temperatures due to the topography/albedo changes is simulated after the iceberg discharge. North Atlantic Deep Water (NADW) formation drops and reestablishes due to the meltwater event.
Characteristics of seismic radiation during the 1994 Bolivian earthquake and implications for rupture mechanisms
Authors: Huang Bor‐Shouh
Published: October 2002

The PKP waves of the 1994 deep Bolivian earthquake (Mw = 8.3) recorded by the dense short‐period seismic array in Taiwan were used to make direct measurements of seismic source radiation. Employing array stacking technique, those data were used to reconstruct the time function of the source rupture. The well‐resolved frequency content of this source time function was from the period of 1 to 10 seconds and, to resolve the rupture properties, it provided source information at higher frequencies than that in previous studies from global seismic network data. Rupture time analysis identifies four asperities in the array observations, and the initial rupture time of each asperity correlates well with results from previous studies using global network data. The analysed results of this study also indicate that, unlike other asperities, the two major ones did not release as much high frequency energy. However, based on the limited broadband observations in Taiwan, the long‐period energy was normally released. This study concludes that this can be well explained by the lubrication of fault during the great earthquake. Several deep earthquake mechanisms have been discussed for this special rupture characteristic, and none may be fully ruled out.
Mesospheric potassium layer over the Arecibo Observatory, 18.3°N 66.75°W
Authors: Friedman Jonathan S. , Collins Stephen C. , Delgado Rubén , Castleberg Paul A.
Published: October 2002

A resonance lidar has made regular measurements of mesospheric potassium at the Arecibo Observatory (18.3°N, 66.75°W) since July 1999. Through July 2001 a total of 65 nights of density measurements were carried out, amounting to several nights each month over most of the period. The layer shows considerable nightly and seasonal variation: Spring and early summer nights had frequent sporadic layer activity; nightly variability in the layer width was large due to sporadic layer activity, but the seasonal variation was small; the altitude of the layer centroid was fairly constant throughout the year; and the column abundance showed semi‐annual variation. These results are compared with a similar set of potassium measurements from a mid‐latitude site, and the latitudinal implications are discussed.
Multiyear La Niña events and persistent drought in the contiguous United States
Authors: Cole Julia E. , Overpeck Jonathan T. , Cook Edward R.
Published: October 2002

La Niña events typically bring dry conditions to the southwestern United States. Recent La Niñas rarely exceed 2 years duration, but a new record of ENSO from a central Pacific coral reveals much longer La Niña anomalies in the 1800s. A La Niña event between 1855–63 coincides with prolonged drought across the western U.S. The spatial pattern of this drought correlates with that expected from La Niña during most of the La Niña event; land‐surface feedbacks are implied by drought persistence and expansion. Earlier periods also show persistent La Niña‐like drought patterns, further implicating Pacific anomalies and surface feedbacks in driving prolonged drought. An extended index of the Pacific Decadal Oscillation suggests that extratropical influences would have reinforced drought in the 1860s and 1890s but weakened it during the La Niña of the 1880s.
Deserts: Can they be the potential suppliers of bioavailable iron?
Authors: Saydam A. C. , Senyuva H. Z.
Published: October 2002

The temporal and spatial variability of bioavailable iron delivered to the ocean may be controlled via in‐cloud photochemical reduction of desert dust, assisted by the impact of oxalate released by fungi in the desert soil. The basic process in the photochemical production of bioavailable iron through decarboxylation reaction involves simultaneous action of oxalate released by the fungus encapsulated in a cloud droplet, above some threshold solar radiation. Therefore, diurnal and latitudinal variations in solar irradiation and the sporadic nature of rain along the path of the synoptic‐scale atmospheric depressions are the governing factors that determine spatial and temporal distribution of phytoplankton growth and especially that of coccolithophorid blooms on the ocean surface.
Model mismatch between global and regional simulations
Authors: Chen Shyh‐Chin
Published: October 2002

A method to identify and to correct the large‐scale biases in regional climate simulations is proposed. This bias is caused by the mismatch of the regional and the driving global models' physical parameterizations. It is suggested that simulations at spatial resolution similar to the driving global model should be used to estimate the possible bias in the higher resolution simulations. This correction is shown for a climate downscaling experiment over Southeast Asia. The global model is the NCAR community climate model (CCM3), and the regional model is the regional spectral model (RSM) of NCEP. The bias is estimated by taking the difference between a RSM0 (RSM run with similar CCM3 resolution) and the CCM3 solution. Once this bias is removed, the resulting seasonal‐mean at higher resolution simulation shows a large‐scale pattern more similar to that of the driving CCM3, but still retains additional realistic regional details.
Solar EUV flux, exospheric temperature and thermospheric wind inferred from incoherent scatter measurements of the electron density profile at Millstone Hill and Shigaraki
Authors: Zhang Shun‐Rong , Oliver William L. , Holt John M. , Fukao Shoichiro
Published: October 2002

We explore a method for inferring solar EUV flux, atmospheric composition and wind using ionospheric electron density Ne profile measurements. Incoherent scatter radar data from Millstone Hill and Shigaraki measured on October 5, 1989 are assimilated into a theoretical model whose driving forces, solar EUV flux, exosphere temperature Tex, and meridional wind, are adjustable. Adjustments are made to give best match between the model Ne profile and the data. The derived Tex values, found to be low near noon at Millstone and high in the afternoon at Shigaraki, are essentially those required to give the [O]/[N2] ratio necessary to fit the data. Our inferred EUV fluxes for the two sites are similar. Our technique of using profile data may resolve the ambiguity in deriving EUV and [O]/[N2] from electron‐density measurements.
Morphology and origin of the Challenger Deep in the Southern Mariana Trench
Authors: Fujioka Kantaro , Okino Kyoko , Kanamatsu Toshiya , Ohara Yasuhiko
Published: October 2002

A high resolution bathymetry survey reveals the detailed morphology of the Southern Mariana Trench. Distinct right stepping, N80°E trending en echelon deeps were found on the trench bottom within the Challenger Deep. Horst and graben structures were revealed on the outer swell of the Southern Mariana Trench. These structures, as well as slope‐failure on the inner and outer slopes of the trench are similar to features observed in other deep sea trenches. We propose here that the Southern Mariana Trench is a transform fault based on swath mapping, morphological analysis and tectonic interpretation. The en echelon deeps formed in a right‐lateral strike‐slip stress regime related to oblique Pacific/Caroline Plate subduction under the Southern Mariana Trench combined with the Mariana Trough backarc spreading. We confirm that the world's deepest point lies in the western portion of the Challenger Deep, among the en echelon deeps.
Hall‐induced inductive shielding effect on geomagnetic pulsations
Authors: Yoshikawa Akimasa , Obana Yuki , Shinohara Manabu , Itonaga Masahiro , Yumoto Kiyohumi
Published: October 2002

A new formula describing the inductive response of the magnetosphere‐ionosphere‐atmosphere‐Earth electromagnetic coupled system to the time development of the field‐aligned current (FAC) source‐field is developed. Using this new formula, the Hall‐induced inductive shielding effect (ISE) on geomagnetic pulsation is investigated. The ISE is caused by the reduction of the amplitude of total rotational current because of the generation of “inductive” rotational current by the inductive part of ionospheric divergent electric field, which originates the existence of divergent Hall current. It will be shown that the ISE is more efficient for high‐frequency pulsations, large horizontal scale phenomena and high‐conducting ionospheric conditions. Quantitative analysis strongly suggests that the ionospheric conductivity in the dayside hemisphere can easily reach and sometimes exceed the turning point of geomagnetic pulsations of which frequencies are in the Pc 3 ∼ 4 pulsations range.
First observational evidence of the modulation of gravity wave activity in the low latitude middle atmosphere by equatorial waves
Authors: Parameswaran K. , Rajeev K. , Sasi M. N. , Ramkumar Geetha , Krishna Murthy B. V.
Published: October 2002

Evidence for the modulation of the gravity wave activity by the equatorial waves in the tropical middle atmosphere is presented using the Rayleigh lidar observations of the temperature over Gadanki (13.5°N, 79.2°E) and the rocketborne measurements of winds over Shriharikota Range (13.7°N, 80.2°E) during the period of 29 February to 31 March, 2000. The potential energy per unit mass associated with the gravity wave activity in the upper stratosphere and mesosphere is found to undergo periodic fluctuations, which is well correlated with the zonal and meridional wind oscillations in the stratosphere produced by the equatorial waves. The most dominant modulation of the gravity wave activity due to equatorial waves is found to occur at periods around 4‐days and 12‐days. Minimum gravity wave activity in the mesosphere is observed during the southward phase of meridional wind and the westward phase of zonal wind oscillations in the lower stratosphere.
Forecasting the geomagnetic field at 2005 using Ørsted and observatory data
Authors: Cain J. C. , Ajayi O. , Ferguson B. B. , Mozzoni D. T.
Published: October 2002

Spherical harmonic models were derived using observatory data taken since 1995 and Ørsted vector data. Such models were used to predict both the field in 2005 and estimated error surfaces. Using only satellite data taken over the 2‐year interval produced unsatisfactory predictions of the field. It was essential to include longer period observations at fixed observatories and other surface data, such as ship‐towed data. To accurately determine the field for past epochs it is necessary to use parabolic terms in time to degree n = 12 as well as annual terms to allow for external contributions. However, using only linear terms provided the best accuracy for projections to 2005. Reduction of the complexity of the model to n = 8 tends to smooth over areas devoid of a long period of observation though slightly decreasing the accuracy elsewhere. The best estimates for 2005 using these techniques cannot be more accurate than a few hundred nT at the Earth's surface.
Evidence for rapid fault healing derived from temporal changes in S wave splitting
Authors: Tadokoro Keiichi , Ando Masataka
Published: October 2002

Tadokoro et al. [1999] had made an S wave splitting analysis on the Nojima fault zone that ruptured during the 1995 Hyogo‐ken Nanbu earthquake for a period 9–12 months after the mainshock. The direction of faster shear wave polarization φ had been parallel to the fault strike, suggesting fractures of shear fault origin. In this study, we made an additional S wave splitting analysis for a period 33–45 months after the mainshock and detected the rotation of φ, that is, the direction φ was parallel to the regional maximum horizontal compressional stress which is oblique to the fault strike. This temporal change suggests that all the fractures of shear fault origin had completely healed and cracks of tectonic stress origin recovered between the two periods. This is strong evidence for rapid fault healing which completed within 33 months after the mainshock.
Assessing the depth resolution of tomographic models of upper mantle structure beneath Iceland
Authors: Wolfe Cecily J. , Bjarnason Ingi Th. , VanDecar John C. , Solomon Sean C.
Published: October 2002

Earlier inversions of body wave delay‐time data recorded during the ICEMELT portable broadband experiment imaged a cylindrical plume‐like low‐velocity anomaly extending to at least 400 km depth beneath Iceland, but the depth extent of the anomaly resolvable by tomography has recently been called into question. We have performed several additional resolution tests to evaluate the depth resolution of tomographic models of the Icelandic upper mantle. The distribution of paths of body waves recorded by ICEMELT can distinguish among three different types of models: (a) a wide and shallow anomaly, (b) a narrow and deep anomaly, and (c) a narrow and shallow anomaly. While tomographic models contain an element of nonuniqueness, these tests illustrate that the depth resolution of passive seismic experiments spanning subaerial Iceland is adequate for distinguishing among alternative geodynamic models.
Evaluation of solar Type II radio burst estimates of initial solar wind shock speed using a kinematic model of the solar wind on the April 2001 solar event swarm
Authors: Sun W. , Dryer M. , Fry C. D. , Deehr C. S. , Smith Z. , Akasofu S.‐I. , Kartalev M. D. , Grigorov K. G.
Published: October 2002

We compare simulation results of real time shock arrival time prediction with observations by the ACE satellite for a series of solar flares/coronal mass ejections which took place between 28 March and 18 April, 2001 on the basis of the Hakamada‐Akasofu‐Fry, version 2 (HAFv.2) model. It is found, via an ex post facto calculation, that the initial speed of shock waves as an input parameter of the modeling is crucial for the agreement between the observation and the simulation. The initial speed determined by metric Type II radio burst observations must be substantially reduced (30 percent in average) for most high‐speed shock waves.
Ørsted verifies regional magnetic anomalies of the Antarctic lithosphere
Authors: Kim Hyung Rae , von Frese Ralph R. B. , Kim Jeong Woo , Taylor Patrick T. , Neubert Torsten
Published: October 2002

Initial magnetic measurements from the Ørsted satellite reveal lithospheric anomalies over the Antarctic that are similar to those obtained by Magsat. Accordingly, lithospheric anomalies can be extracted from the Ørsted data, despite the much greater operational altitude of Ørsted (650–865 km) relative to Magsat (350–550 km). Furthermore, these correspondences confirm the lithospheric origins for the resulting small‐amplitude anomalies in the satellite data. In studies of the Antarctic lithosphere, the Magsat data particularly were limited by the large relative uncertainties of their lithospheric components. These uncertainties occurred because the short nearly seven‐month mission more than 20 years ago collected data over austral high summer and early fall when the contaminating large‐amplitude external field effects were at a maximum. Therefore, the recent and more numerous Ørsted measurements greatly facilitate our efforts to separate effectively the core, lithospheric, and external field components for enhanced studies of the Antarctic lithosphere.
Propagation of auroral hiss at high altitudes
Authors: Santolík O. , Gurnett D. A.
Published: October 2002

Using multicomponent wave measurements of the Polar spacecraft, we provide direct evidence of the propagation pattern of funnel‐shaped auroral hiss at a radial distance of 5 Earth radii. The waves propagate upward and the Poynting flux is directed toward higher latitudes in the high‐latitude part of the emission and to lower latitudes in the low‐latitude part. The wave vectors are found to be close to the whistler mode resonance angle. Consistent with the theory, the latitudinal component of the wave vector is opposite compared to that of the Poynting flux in the low‐latitude and high‐latitude parts of the funnel‐shaped emission. In the central part of the emission we observe a very broad distribution of the wave energy with respect to the azimuth angle. The waves thus simultaneously come from different directions with different wave vectors. This leads us to the conclusion that hiss is more likely generated in an extended sheet source rather than in a vertical line source or a point source. In this case the observed propagation pattern suggests that the sheet source is oriented roughly in the longitudinal direction, consistent with the region where we can expect presence of upgoing or counterstreaming electron beams.
Determination of tropical cyclone center by using TRMM Microwave Imager data
Authors: Ahn Myoung‐Hwan , Seo Young‐Kyung , Park Hye‐Sook , Suh Ae‐Sook , Kwon H. Joe
Published: October 2002

Two new parameters helpful in determining the center position of tropical cyclones (TC) using the TRMM (Tropical Rainfall Measurement Mission) Microwave Imager (TMI) data have been devised. The new parameters utilize the differential responses of the center and surrounding eye‐wall of a tropical cyclone to the upwelling microwave radiation in two different channels in terms of intensity and polarization. One uses the intensity difference between 37 and 85 GHz and another uses different characteristics of polarization at 37 GHz. Case studies show advantages of the derived parameters over the single channel microwave or optical imagery, especially when high clouds cover the center. When the TC center determined with the two parameters is compared with the best track position reported by JTWC (Joint Typhoon Warning Center) and RSMC (Regional Specialized Meteorological Center) Tokyo, the mean differences are about 39 km and 41 km, respectively, for 91cases detected in the east Asia region by TMI during 1999 and 2000. For the same cases, the mean difference of the center position between RSMC and JTWC is about 23 km.
A high resolution AGCM study of the El Niño impact on the North Atlantic/European sector
Authors: Merkel Ute , Latif Mojib
Published: October 2002

An atmospheric general circulation model (AGCM) sensitivity study has been performed with the ECHAM4 model forced by anomalous sea surface temperatures to investigate the role of the horizontal resolution (T42 versus T106) in determining the El Niño/Southern Oscillation (ENSO) response in the North Atlantic/European region. The higher resolution has been chosen in order to represent more realistically the transient eddy activity that is supposed to play a crucial role in the signal communication to regions remote from the tropical Pacific. In contrast to the T42 experiments, the T106 experiments reveal significant changes both in the mean of selected atmospheric variables (sea level pressure, temperature, precipitation) over Europe and in the transient and stationary wave activity. A cyclone tracking analysis reveals a southward shift of the North Atlantic low pressure systems in the winter season during El Niño events.
Search for the origins of Pacific decadal climate variability
Authors: Liu Z. , Wu L. , Gallimore R. , Jacob R.
Published: October 2002

The origin of Pacific decadal climate variability is investigated in a coupled ocean‐atmosphere general circulation model. The impact of regional ocean‐atmosphere coupling and oceanic teleconnection on decadal variability is evaluated by performing a set of specifically designed experiments. It is found that decadal variability in the tropical and North Pacific originates predominantly from local coupled ocean‐atmosphere processes within the tropical and North Pacific region, respectively. Furthermore, tropical Pacific decadal variability appears to be associated with higher baroclinic modes and can be enhanced substantially by extratropical‐tropical oceanic teleconnection.
A simple “geometric” mapping function for the hydrostatic delay at radio frequencies and assessment of its performance
Authors: Foelsche Ulrich , Kirchengast Gottfried
Published: October 2002

The hydrostatic mapping function, m(ε), describes the dependence of the hydrostatic path delay on the elevation angle ε. We have developed a simple mapping function, where the only free parameter is an “effective height” of the atmosphere, Hatm, corresponding to about the first two scale heights above the surface. The value of m(ε) is given by the ratio of the straight‐line ray path length within height Hatm to height Hatm itself. We used simulated delays at GPS (Global Positioning System) frequencies derived from high resolution ECMWF (European Centre for Medium‐Range Weather Forecasts) atmospheric analysis fields to assess the performance of the “geometric” mapping function relative to well established ones (the Davis, Niell, and Herring mapping functions, respectively). At elevations >6° the new mapping function generally exhibits, based on a single parameter, a performance comparable to or better than the other mapping functions.
Temporal variation of seismic b‐values beneath northeastern Japan island arc
Authors: Cao Aimin , Gao Stephen S.
Published: October 2002

Analysis of a high quality seismic catalog reveals that the average of seismic b‐values in the crust beneath most part of northeastern Japan island arc decreased from 0.86 between 1984 and 1990, to 0.73 between 1991 and 1995. The two areas with the largest decrease are found to be in the same areas where the coupling between the North American and the Pacific plates is the highest, as suggested by a recent geodetic study. In the same time period, the annual seismic moment release increased by 10 times. In addition, there seems to be a corresponding increase in volcanic activities in the same area. One of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991. The timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity.
Interchange instability at the leading part of reconnection jets
Authors: Nakamura M. S. , Matsumoto H. , Fujimoto M.
Published: October 2002

Three‐dimensional structures of reconnection jets are investigated by hybrid simulations. Magnetic reconnection is initiated by ad‐hoc anomalous resistivity, which is uniform in the cross‐tail direction but localized within the meridian plane. At the interface between the reconnection jet and the pre‐existing plasma sheet ahead of it, the reconnected field lines are piled up and the plasma density is enhanced by compression. The interface becomes unstable to an interchange instability and deforms itself into a wavy shape. In the non‐linear growth phase, the wavy perturbations grow into magnetic bubbles into which the field lines are converged and the bubbles move faster than the other parts. It is suggested that this instability can generate localized channels with a cross‐tail extent of a few RE, in which plasma and magnetic field transports are achieved, and thus may well be related to the formation of the bursty bulk flows in the magnetotail.
Basic flow field in a tidal basin
Authors: Fagherazzi Sergio
Published: October 2002

A simplified model for tidal flow in a basin is presented. The model is based on the assumption of a flat water surface oscillating synchronously in the tidal basin. Under this hypothesis the depth‐averaged continuity equation becomes a Poisson equation that can be easily resolved at each instant of the tidal cycle. This formulation, which is particularly valid for small, deep basins, provides a simplified solution of the depth‐integrated shallow water equations and suggests a possible approach to model long‐term morphodynamic evolution of tidal basins. The model is tested in San Diego Bay, California, and the results are briefly discussed.
Impact of Soil Moisture Aggregation on Surface Energy Flux Prediction During SGP'97
Authors: Crow Wade T. , Wood Eric F.
Published: October 2002

The nonlinear nature of the point‐scale soil moisture‐transpiration relationship, combined with the highly heterogeneous spatial structure of soil moisture fields and the limited horizontal resolution of spaceborne microwave radiometers, has generated considerable interest in the soil moisture aggregation problem. Specifically, understanding the impact of aggregating soil moisture information up to regional grid‐scales (∼103 km2) on the grid‐scale prediction of surface water and energy fluxes within the land surface component of a weather prediction model. Using data from the 1997 Southern Great Plains Hydrology Experiment (SGP'97), a conceptual link is presented between the impact of soil moisture aggregation on surface energy flux prediction and the spatial scaling properties of soil moisture fields.
Earthquake modeling in the Dead Sea Basin
Authors: Gottschämmer Ellen , Wenzel Friedemann , Wust‐Bloch Hillel , Ben‐Avraham Zvi
Published: October 2002

We simulate 75 seconds of 1.5 Hz wave‐propagation of the 1927 Jericho earthquake (ML6.2) using a staggered‐grid finite‐difference (FD) method. From the time histories we compute peak ground velocities and pseudo‐acceleration responses at 1 Hz in a 3D model including the Dead Sea Basin substructure. We compare the accelerations to values computed (a) for a homogeneous model and (b) using an attenuation relation similar to the one integrated in the building code 413 of Israel. With accelerations at 1 Hz, we show that the Dead Sea Basin substructure is responsible for a significant radiation anisotropy in ground motion attenuation when the source is located within the basin. Rupture dynamics effects of strike‐slip events along faults bounding the basin enhance this behaviour. We show that both, the homogeneous model and the attenuation relation, underestimate the spectral responses on average by factors between 1.5 and 5.
Transport of water vapor in the tropical tropopause layer
Authors: Gettelman A. , Randel W. J. , Wu F. , Massie S. T.
Published: October 2002

A trajectory model coupled to a simple micro‐physical model is used to explore the observed relationship between convection, water vapor and cirrus clouds in the tropical tropopause layer (TTL). Horizontal transport associated with the local Hadley circulation leads to water vapor minima in the winter hemisphere separated from the convective regions and the region of minimum temperatures. These spatial signatures are consistent with observations of water vapor and cirrus in the TTL from the Halogen Occultation Experiment (HALOE). In the simulations, one third of observed ice is formed due to horizontal transport through cold regions. Applied variations in temperature over time scales longer than a few hours, similar to gravity wave induced perturbations, act to lower the simulated water vapor.
Relationship between N2O and CO2 emissions from the Amazon Basin
Authors: Garcia‐Montiel Diana C. , Melillo Jerry M. , Steudler Paul A. , Neill Christopher , Feigl Briget J. , Cerri Carlos C.
Published: October 2002

Soils of tropical forests are the most important source of atmospheric N2O from natural ecosystems, but the extant flux estimates are based on a relatively small number of field measurements and simple extrapolation procedures. We present an empirical relationship between N2O and CO2 emissions from soils of Amazon tropical forest based on seven years of field measurements in Rondônia, Brazil. This relationship can be combined with estimates of soil CO2 emissions from existing biogeochemistry models to produce estimates of N2O emissions for tropical forest regions.
Ancient lowlands on Mars
Authors: Frey Herbert V. , Roark James H. , Shockey Kelly M. , Frey Erin L. , Sakimoto Susan E. H.
Published: October 2002

Mars Orbiter Laser Altimeter (MOLA) data provide compelling evidence that the martian lowlands, below the smooth and sparsely cratered northern plains, are extremely old, far older than the plains which cover them. The evidence is in the form of a very large population of “Quasi‐Circular Depressions” (QCDs), many of which are very evident in the MOLA elevation data but generally not visible in available imagery. We interpret these “invisible” QCDs to be buried impact basins. Cumulative number versus diameter curves for lowland QCDs suggests the buried lowland surface is older than the visible highland surface and that the lowland plains are a relatively thin (1–2 km) veneer overlying this much older surface. We conclude that the martian lowlands have been low and stable for nearly all of martian history.
New observational evidence for global warming from satellite
Authors: Jin Menglin , Dickinson Robert E.
Published: October 2002

Accurate measurements of surface radiative temperature, i.e. skin temperature, would be more directly interpretable in terms of the surface response to increase of greenhouse gases than the more conventional screen temperatures. Such measurements have not previously been attempted because of the difficulties of converting existing observations into a meaningful measurement. We have developed procedures for removing the effects of changing satellite orbits and cloud contamination from skin temperatures estimated from AVHRR channels 4 and 5, and so provide a first estimate of the trends of land surface skin temperature over the last two decades. The estimated land temperature increase is not only much greater than that for the atmosphere but also apparently somewhat larger than the estimates of surface air temperature increase from in situ measurement.
Limitations in DGPS positioning accuracies at low latitudes during solar maximum
Authors: Skone Susan , Shrestha Sudhir M.
Published: October 2002

While it is possible to mitigate the impact of ionospheric effects on Global Positioning System (GPS) positioning applications through differential techniques, residual errors may persist in regions of steep TEC gradients. An enhancement of absolute TEC and large‐scale gradients is observed at low latitudes near the equatorial anomaly. This effect is significant in the equinoctial months during periods of solar maximum. In this paper, differential GPS (DGPS) positioning accuracies in the anomaly region are investigated during the period of solar maximum 1999–2000, using as data the L1 pseudoranges. TEC gradients of 30 TECU per 100 km are observed during March 2000, with corresponding horizontal and vertical position errors of approximately 25–30 m (95% confidence level) for single baseline processing. Positioning accuracies are improved by a factor of 5 for a wide area DGPS approach.
Atmospheric 210>Po anomaly as a precursor of volcano eruptions
Authors: Su Chih‐Chieh , Huh Chih‐An
Published: October 2002

Due to its high volatility, 210Po can be effectively released from active volcanoes prior to their explosions. A continuous record of the fallout rate of 210Po versus that of 210Pb in northern Taiwan reveals that most of the 210Po was derived from pre‐eruption gas emission of Philippines'Mayon volcano in the past two years. From this observation we suggest that, if a global network can be properly designed, it may be possible to employ 210Po anomaly as a precursor of volcano eruptions worldwide.
Observations of the latitude dependence of the location of the martian magnetic pileup boundary
Authors: Crider Dana H. , Acuña Mario H. , Connerney John E. P. , Vignes Didier , Ness Norman F. , Krymskii Alexander M. , Breus Tamara K. , Rème Henri , Mazelle Christian , Mitchell David L. , Lin Robert P. , Cloutier Paul A. , Winterhalter Daniel
Published: October 2002

We report observations that show the dependence of the altitude of the magnetic pileup boundary (MPB) at Mars on planetary latitude. As seen by the Mars Global Surveyor Magnetometer/Electron Reflectometer instrument, the MPB is further away from Mars on average at southern latitudes than at northern latitudes. The data are consistent with a MPB distance mapped to the terminator plane that does not vary with latitude in the northern hemisphere, but increases with increasing southern latitude in the southern hemisphere. We also report increased variability in the MPB distance within the longitude range 90–270° E. longitude in the southern hemisphere which is the region that contains the strongest crustal magnetic fields. These trends are most obvious in a planet‐fixed coordinate system, indicating a planet‐fixed driver of the MPB location. The proposed mechanism is the local diversion of shocked solar wind flow by crustal magnetic fields.
Regional bio‐optical algorithms for the Alboran Sea from a reflectance model and in situ data
Authors: Corsini Giovanni , Grasso Raffaele , Cipollini Paolo
Published: October 2002

Regional bio‐optical algorithms for SeaWiFS and MERIS over the Alboran Sea are retrieved by computational inversion of an ocean colour model. The input to the model is a set of in situ measurements of the water constituents from the OMEGA Project. The algorithms for the estimation of phytoplankton chlorophyll and dissolved organic matter are robust with respect to the variation of the internal parameters of the model. The regional chlorophyll algorithm for SeaWiFS is compared to the global one used by NASA, and an example of the application of the chlorophyll and yellow substance algorithms to SeaWiFS imagery over the study area is shown and discussed.
Velocity structure of North Brazil Current rings
Authors: Wilson W. Douglas , Johns William E. , Garzoli Silvia L.
Published: October 2002

High‐resolution shipboard surveys of four North Brazil Current rings are presented, which are the first such dedicated surveys to be made of these features. Of the four rings surveyed, three fundamentally different types of ring structures are found: (1) a shallow, surface‐trapped structure with velocities confined to the top 200 m (two rings), (2) a deep‐reaching structure with significant swirl velocities (∼0.2 m/s) extending to 2000 m (one ring), and (3) a thermocline‐intensified structure with almost no detectable surface signature (one ring). The results of this study indicate that North Brazil Current rings can have highly variable vertical structures, and that assessing their overall role in cross gyre exchange in the tropical Atlantic will require a careful combination of remote sensing and in‐situ observations.
On the observability of internal tidal waves in remotely‐sensed ocean colour data
Authors: da Silva J. C. B. , New A. L. , Srokosz M. A. , Smyth T. J.
Published: October 2002

This paper reveals bands of enhanced levels of near‐surface chlorophyll in the central Bay of Biscay in remotely‐sensed images from the SeaWiFS ocean colour sensor, and shows that these are most probably associated with the crests of internal tidal waves travelling away from the shelf break. We are able to explain this effect as likely to result from the uplifting of a subsurface chlorophyll maximum by the passing internal tides, to such a level as may be “seen” by the satellite sensor, and have quantified the effect with a simple model. We believe this is the first time that internal tidal waves have been reported as having a direct and observable effect in such remotely‐sensed ocean colour images.
Equator‐S observations of He+energization by EMIC waves in the dawnside equatorial magnetosphere
Authors: Mouikis C. G. , Kistler L. M. , Baumjohann W. , Lund E. J. , Korth A. , Klecker B. , Möbius E. , Popecki M. A. , Sauvaud J. A. , Rème H. , Di Lellis A. M. , McCarthy M. , Carlson C. W.
Published: October 2002

We present Equator‐S observations of He+energization by electromagnetic ion cyclotron (EMIC) waves in the dawn side equatorial magnetosphere at L > 7. The He+ions are transversely accelerated up to 2 keV, which is almost an order of magnitude higher than found in previous observations. The heating signatures are correlated, on short time scales (in the order of a few minutes or less), with the presence of EMIC wave emissions in the vicinity of the He+gyrofrequency (Pc1 frequency range). These events were observed during quiet magnetospheric conditions at the inner edge of the plasmasheet. At this boundary 10 to 40 keV protons, which convect on open drift paths, exhibit a pronounced pitch angle anisotropy providing the free energy for the enhancement of the Pc1 emissions.
Solar proton events and the fair weather electric field at ground
Authors: Farrell W. M. , Desch M. D.
Published: October 2002

Previous works have demonstrated the ability of solar energetic particles to affect mesospheric electric fields. In this work, we suggest that such particles can also affect the fair‐weather electric field at ground level. Our model applies previously derived changes in the high‐altitude atmospheric conductivity profile to the global electric circuit. We find that the strongest flare‐generated proton events are capable of creating a measurable change to the electric field at ground level (∼5% change), but these changes are small in comparison to those associated with passing thunderstorms.
Deep crustal structure of the Tuamotu plateau and Tahiti (French Polynesia) based on seismic refraction data
Authors: Patriat Martin , Klingelhoefer Frauke , Aslanian Daniel , Contrucci Isabelle , Gutscher Marc‐André , Talandier Jacques , Avedik Felix , Francheteau Jean , Weigel Wilfried
Published: October 2002

In French Polynesia, the young (<5Ma) Society Islands appear to result from intraplate volcanism, while the old (>50 Ma) Tuamotu plateau was likely created at or near the ridge axis. The structure of the crust between those two archipelagoes is constrained by a 300 km long refraction seismic profile. Crustal and upper mantle arrivals recorded by 6 OBHs and 3 land stations were used to provide a 2D model of the crust. Results of our study, combined with that of Grevemeyer et al. [2001] show a slight flexure below the Tahiti apron, while a deep crustal root (21 km) underlies the Tuamotu plateau. These structures reflect the different modes of load emplacement and compensation mechanisms between these two volcanic edifices, consistent with an increasing elastic thickness of the oceanic lithosphere with age.
Subsonic type earthquake dislocation moving at approximately × shear wave velocity on interface between half spaces of slightly different elastic constants
Authors: Weertman J.
Published: October 2002

Bouchon, Bouin, Karabulut, Toksöz, Dietrich and Rosakis reported recently that rupture appeared to propagate eastward in the 1999 Izmit and Düzce earthquakes in Turkey at a transonic velocity greater than the shear wave velocity CS and smaller than the longitudinal velocity CL. The velocity appeared to be close to the Eshelby velocity ( × shear wave velocity), a velocity at which a transonic glide edge dislocation has a subsonic (with respect to CL) type stress‐displacement field with no supersonic (with respect to CS) component. They suggest that the super shear wave velocity rupture may have been aided by a normal stress reduction in the slip process whose origin lies in the differing elastic properties of the crust on either side of the earthquake fault. They suggest that this normal stress reduction will occur if the north side of the fault has the elastically softer rock In this paper it is shown that a transonic glide edge dislocation on an interface separating material of different elastic shear moduli cannot have only a subsonic type stress field (or only a supersonic field). Moreover, the supersonic part of the displacement field is not the usual step function.
14‐day forecast of solar indices using interplanetary Lyman α background data
Authors: Quémerais Eric , Bertaux Jean‐Loup
Published: October 2002

We present a new method which can be used to forecast the variations of solar indices on the time scale of a half solar rotation. This method uses the Lyα interplanetary glow data obtained by the SWAN instrument on SOHO. We show how the maps of solar Lyα flux distributions derived from the SWAN data can be linked to the variation of activity on the solar disk. Active regions which are known to be brighter in Lyα radiation than the quiet sun illuminate more interplanetary H atoms through resonance scattering. This excess of illumination related to active regions is clearly seen in full‐sky Lyα maps recorded by the SWAN instrument on SOHO. These maps include also those excesses resulting from active regions which are on the far side of the Sun, i.e. not visible to solar disk imagers near Earth. From these data, we can derive a farside to nearside flux ratio. This ratio is then used to predict the evolution of solar indices like the solar Lyα flux seen at Earth, the 10.7cm radio flux or the MgII solar index. This technique could be used in the future to improve the quality of space weather forecast, in particular to predict atmospheric heating and increased orbital drag of sensitive spacecraft.
On the use and validation of mosaic heterogeneity in atmospheric numerical models
Authors: Bosilovich Michael G.
Published: October 2002

The mosaic land modeling approach allows for the representation of multiple surface types in a single atmospheric general circulation model grid box. Each surface type, collectively called “tiles” correspond to different sets of surface characteristics (e.g. for grass, crop or forest). Typically, the tile space data is averaged to grid space by weighting the tiles with their fractional cover. While grid space data is routinely evaluated, little attention has been given to the tile space data. The present paper explores uses of the tile space surface data in validation with station observations. The results indicate the limitations that the mosaic heterogeneity parameterization has in reproducing variations observed between stations at the Atmospheric Radiation Measurement Southern Great Plains field site.
Timing of substorm onset signatures on the ground and at geostationary orbit
Authors: Rosenqvist L. , Borälv E. , Opgenoorth H. J. , Reeves G.
Published: October 2002

In order to study the relative timing of substorm onset signatures on the ground and at geostationary orbit we have used data of simultaneous dispersionless electron and proton injections from the LANL satellite 1991–80, located slightly westward of Scandinavia. Out of 9 years of data we have identified a number of events during which such injections occurred close to local magnetic midnight. By careful inspection of ground‐based magnetograms from the Scandinavian magnetometer network, IMAGE, we then identified the location and time of the formation of a substorm current wedge (SCW) during these events. 40 clear cases of geostationary injections, which were clearly associated with the formation of SCWs, were found. A statistical study of these events reveals that there is a clear time delay of the order of several minutes in the occurrence of the substorm injection with respect to the first indication of the SCW measured on the ground.
Solar wind from high‐latitude coronal holes at solar maximum
Authors: McComas D. J. , Elliott H. A. , von Steiger R.
Published: October 2002

In this study we combine Ulysses' observations from the solar wind plasma (SWOOPS) and ion composition (SWICS) instruments to study high‐latitude coronal holes near solar maximum for the first time. While chromospheric and coronal composition signatures indicate that there is a unique type of solar wind, which flows from coronal holes, variations in the acceleration process produce a wide range of solar wind speeds from these holes. High‐speed wind (>700 km s−1) can be produced in small as well as large holes, although the very highest speed non‐transient winds do come from the centers of the largest holes. Along the edges of coronal holes, the acceleration decreases and freezing‐in temperatures increase relatively smoothly into the surrounding solar wind, indicating a transition layer around the edges of coronal holes.
Incremental approach to the optimal network design for CO2 surface source inversion
Authors: Patra Prabir K. , Maksyutov Shamil
Published: October 2002

An algorithm for observational network design to obtain maximum constraints on CO2 flux estimate uncertainty by using inverse modeling and global transport model is presented. The extension to an existing network is made by adding new station locations one by one, based on their positive impact on the flux estimate uncertainty reduction. The approach is named Incremental Optimization (IO). This extension procedure performs equally well or better compared to the well known techniques, such as the simulated annealing, used in combinatorial optimization. We could reduce the estimated total CO2 flux uncertainty by 59%, 47%, 35%, and 29% relative to a reference network by using IO with additions of 3, 5, 12, and 20 stations, respectively. IO is shown to be efficient in studying various network configurations and re‐emphasizes the need for CO2 measurements in continental Africa, South America, and Asia.