bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron hole as an antenna radiating plasma waves
Authors: Singh Nagendra , Loo S. M. , Wells B. E.
Published: February 2004

Recent observations of electron holes (e‐holes) in space plasma have led to theoretical and numerical studies which show that e‐holes in a magnetized plasma are unstable nonlinear structures. Their decay generates plasma waves in the frequency bands of lower hybrid (LH) and electrostatic whistler (EW) waves. An analysis is presented demonstrating that the e‐holes are an effective radiator of plasma waves in the above frequency bands critically depending on their scalelength (ℓ⊥) transverse to the ambient magnetic field. In this sense, an e‐hole acts like a radiating antenna. The results from 3‐D numerical simulations are presented to examine the nonlinear consequences of the radiation from e‐holes. When e‐holes have long ℓ⊥ during the initial stage of their existence, they undergo a beading process. This involves radiation of spatial Fourier components corresponding to long scalelength in the structure of e‐holes, leaving behind smaller structures. This divides the initially large e‐hole structure into several fragments. The resulting smaller structures with ℓ⊥∼ ℓ∥ eventually dissipate by radiating transversely structured lower hybrid waves.
Influence of oceanic whitecaps on the Global Radiation Budget
Authors: Frouin R. , Iacobellis S. F. , Deschamps P.‐Y.
Published: February 2004

Oceanic whitecaps may exert a cooling influence on the planet by increasing surface albedo. The direct, globally averaged radiative forcing due to whitecaps lies in the range 0–0.14 Wm−2 with a probable value of 0.03 Wm−2. Though small, this global value is not negligible compared with the forcing due to some greenhouse gases and anthropogenic aerosols since preindustrial times. The relative importance of whitecaps may be greater on regional and seasonal scales, with radiative forcing values reaching 0.7 Wm−2 in the Indian Ocean during summer. Whitecap effects on surface albedo should be taken into account explicitly in the numerical modeling and analysis of climate change.
Scattering of seismic waves in arbitrarily heterogeneous and acoustic media: A general solution and simulations
Authors: Li Xiaofan
Published: February 2004

The question of strong scattering of seismic waves in arbitrarily heterogeneous media is one of extremely difficult problems in the research into seismic scattering. For developing methods of seismic inversion and imaging with high resolving power, however, the above‐mentioned problem has to be solved. In the past tens' years, some nice results on the problem of strong scattering of seismic waves have been obtained. These results, however, are valid only for some special cases. In order to treat more general problems of scattering of seismic waves, a general solution of wave equation for arbitrarily heterogeneous acoustic media is given by the method of Green's function in the research described in this paper. This Green function not only is available for arbitrarily heterogeneous acoustic media, but also can be written as a simple and convenient series. Also, some numerical results are shown in this paper.
Influence of channelling on heating in ice‐sheet flows
Authors: Hindmarsh Richard C. A.
Published: February 2004

Ice‐sheet flows can be channelled by perturbations in the basal topography or in the sliding coefficient. These lead to spatial variation in the steady profile, the flux and the dissipative heating. This paper examines the linearized theory of heating variations, showing that the map plane aspect ratio of the basal perturbation has a dominating effect on the qualitative behaviour. For ribbing transverse to the direction of flow, maximum heating occurs over bedrock and sliding viscosity highs. When flow‐parallel channelling occurs maximum heating occurs over bedrock lows and sliding viscosity lows. These results are used to examine symmetry‐breaking behaviour of numerical thermoviscous ice‐sheet models in terms of a dissipation‐driven creep instability.
Anticyclonic eddies and Kuroshio Meander Formation
Authors: Mitsudera Humio , Waseda Takuji , Yoshikawa Yasushi , Taguchi Bunmei
Published: February 2004

A meander‐formation mechanism of the Kuroshio that involves anticyclonic eddies propagating from the Kuroshio Extension, is presented using the analysis of observations of the TOPEX/POSEIDON (T/P) altimeter data and in‐situ data. Support of the mechanism comes also from a numerical simulation. In October 1997, a current meter mooring over the Izu Ridge at 500‐m‐depth captured large velocity fluctuations of about 50 cm s−1 that were associated with a strong anticyclonic eddy. The observations from T/P show that the anticyclonic eddy propagated westward and collided with the Kuroshio off Kyushu. At collision, the anticyclonic eddy coupled with a cyclonic circulation accompanied by a small meander and formed a vortex pair. They were then advected downstream and finally formed a large‐meander‐like path off the south coast of Honshu. The meander lasted for a few months. Subsequently, the anticyclonic eddy was detached, and the meander grew smaller in amplitude. Numerical experiments successfully simulate this interaction between the Kuroshio and anticyclonic eddies.
Visible/near‐infrared spectra and two‐layer modeling of palagonite‐coated basalts
Authors: Johnson Jeffrey R. , Grundy William M.
Published: February 2004

Fine‐grained dust coatings on Martian rocks and soils obscure underlying surfaces and hinder mineralogic interpretations of both remote sensing and in‐situ observations. We investigate laboratory visible/near‐infrared spectra of various thicknesses of palagonite coatings on basalt substrates. We develop a two‐layer Hapke scattering model incorporating porosity, grain size, and derived absorption coefficients of palagonite and basalt that reproduces the observed spectra only when the single scattering particle phase function is varied with wavelength.
First direct magnetic field measurements of an asteroidal magnetic field: DS1 at Braille
Authors: Richter I. , Brinza D. E. , Cassel M. , Glassmeier K.‐H. , Kuhnke F. , Musmann G. , Othmer C. , Schwingenschuh K. , Tsurutani B. T.
Published: February 2004

Deep Space 1 (DS1) is the first interplanetary spacecraft (s/c) using ion propulsion and aims at investigating the compatibility of innovative technology with scientific measurements. DS1 performed a successful flyby at the asteroid Braille on July 29th, 1999. This closest‐ever encounter allowed for the first time a direct measurement of an asteroidal magnetic field. The manifold magnetic disturbances caused by the ion propulsion onboard DS1, however, required an elaborate data processing scheme in order to extract the magnetic signature of Braille. Its successful application to the magnetometer data of the asteroid flyby reveals a magnetic moment of 2.1 · 1011Am² for Braille.
Quantitative prediction of radiation belt electrons at geostationary orbit based on solar wind measurements
Authors: Li Xinlin , Temerin M. , Baker D. N. , Reeves G. D. , Larson D.
Published: February 2004

Solar wind measurements are used to predict the MeV electron radiation belt flux at the position of geostationary orbit. Using a model based on the standard radial diffusion equation, a prediction efficiency of 0.81 and a linear correlation of 0.90 were achieved for the years 1995–1996 for the logarithm of average daily flux. Model parameters based on the years 1995‐1996 gave a prediction efficiency and a linear correlation for the years 1995–1999 of 0.59 and 0.80, respectively. The radial diffusion equation is solved after making the diffusion coefficient a function of the solar wind velocity and interplanetary magnetic field. The solar wind velocity is the most important parameter governing relativistic electron fluxes at geostationary orbit. The model also provides a physical explanation to several long standing mysteries of the variation of the MeV electrons.
Determination of cloud top amount and altitude at high latitudes
Authors: Cawkwell Fiona G. L. , Bamber J. L. , Muller J.‐P.
Published: February 2004

Cloud identification over snow and ice has proved to be a difficult process to automate due to the similarity in their visible and thermal properties. A method is described here which utilises the nadir and forward views of the Along Track Scanning Radiometer to determine the height of the surface observed to a nominal accuracy of ±1000 m (pixel resolution). A digital elevation model allows the surface topography to be ascertained, with the remainder of high elevation features classed as cloud. Visual verification of the resulting cloud masks indicates that the stereo‐matcher identifies 10–20% more cloud than is recognised by the human eye, but nearly 100 % of cloud‐free land identified by stereo‐matching was confirmed by examination of the images. Further validation of the cloud top heights using radiosonde data, indicates 73% of the stereo‐matched heights to be within 500 m of the radiosonde predicted cloud tops.
Mantle deformation beneath southern Africa
Authors: Silver Paul G. , Gao Stephen S. , Liu Kelly H. ,   Kaapvaal Seismic Group
Published: February 2004

Seismic anisotropy from the southern African mantle has been inferred from shear‐wave splitting measured at 79 sites of the Southern African Seismic Experiment. These data provide the most dramatic support to date that Archean mantle deformation is preserved as fossil mantle anisotropy. Fast polarization directions systematically follow the trend of Archean structures and splitting delay times exhibit geologic control. The most anisotropic regions are Late‐Archean in age (Zimbabwe craton, Limpopo belt, western Kaapvaal craton), with delay times reduced dramatically in off‐craton regions to the southwest and Early‐Archean regions to the southeast. While thin lithosphere can account for weak off‐craton splitting, small or vertically incoherent anisotropy is a more likely explanation for the Early‐Archean region. We speculate that this difference in on‐craton anisotropic structure is the result of two different continent‐forming processes operating.
Centurial‐millenial ice‐rafted debris pulses from ablating marine ice sheets
Authors: Hindmarsh Richard C. A. , Jenkins Adrian
Published: February 2004

We use an ice‐sheet model to show that (i) margins of marine ice‐sheets can be expected to be frozen to the bed, except where ice‐streams discharge; (ii) 20–50km retreats induced by ablation rates of 2 m/yr provide sufficient debris flux through the grounding line to produce large sedimentation events. Such ablation would reduce ice‐shelf extent markedly, permitting debris to reach the calving front and be transported by icebergs leading to ice‐rafted debris (IRD) events. Ice shelf break‐up takes around a century (start of IRD pulse), while the creation of warm‐based conditions (end of IRD pulse) due to upwards motion of warm ice takes a few more centuries. Such IRD pulses are unlikely to explain Heinrich events, which are associated with relatively cold periods within glaciations. Surges are not necessary conditions for the production of large IRD events.
Singular spectrum analysis for time series with missing data
Authors: Schoellhamer David H.
Published: February 2004

Geophysical time series often contain missing data, which prevents analysis with many signal processing and multivariate tools. A modification of singular spectrum analysis for time series with missing data is developed and successfully tested with synthetic and actual incomplete time series of suspended‐sediment concentration from San Francisco Bay. This method also can be used to low pass filter incomplete time series.
Impact of the leakage of liquefied petroleum gas (LPG) on Santiago Air Quality
Authors: Chen Tai‐Yih , Simpson Isobel J. , Blake Donald R. , Rowland F. Sherwood
Published: February 2004

The leakage of unburned liquefied petroleum gas (LPG) is a major source of urban nonmethane hydrocarbons (NMHCs) in the air of Santiago, Chile. Roughly 5% of the LPG that is sold in Santiago leaks in its unburned form to the atmosphere. Because of the leakage, propane is the most abundant NMHC in Santiago's air, even under heavy traffic conditions. NMHCs are an important precursor to the formation of ground‐level ozone, and the LPG leakage may contribute as much as 15% to the excess ozone levels in Santiago. Improvement to the local air quality may be obtained by lowering the rates of LPG leakage, and by minimizing the use of alkene‐rich LPG formulations.
Mercury in smoke from biomass fires
Authors: Friedli Hans R. , Radke Lawrence F. , Lu Julia Y.
Published: February 2004

Litter and green vegetation were collected in 7 locations in the contiguous United States, analyzed for mercury, and burned under controlled conditions at the US Forest Service Fire Science laboratory in Missoula, MT. Among fuels, leaf and 3needle litter contained the highest concentration (up to 71ng/g on dry weight) of mercury. The combustion of litter and green vegetation resulted in essentially complete release of mercury stored in the fuel. Mercury is emitted primarily as elemental mercury, >95% for most burns, with particulate mercury (TPM) accounting for the remainder. From the laboratory experiments we project that mercury emitted from temperate/boreal forest fires and from all biomass burning is an important source components for the atmospheric mercury budget.
Stochastic growth theory of spatially‐averaged distributions of Langmuir Fields in Earth's foreshock
Authors: Boshuizen Christopher R. , Cairns Iver H. , Robinson P. A.
Published: February 2004

Langmuir‐like waves in the foreshock of Earth are characteristically bursty and irregular, and are the subject of a number of recent studies. Averaged over the foreshock, it is observed that the probability distribution (log E) is power‐law in the wave field E, with the bar denoting this averaging over position. In this paper it is shown that stochastic growth theory (SGT) can explain power‐law spatially‐averaged distributions (log E), when the observed power‐law variations of the mean and standard deviation of log E with position are combined with the log normal statistics predicted by SGT at each location.
Measurements of OH, H2SO4, and MSA at the South Pole during ISCAT
Authors: Mauldin R. L. , Eisele F. L. , Tanner D. J. , Kosciuch E. , Shetter R. , Lefer B. , Hall S. R. , Nowak J. B. , Buhr M. , Chen G. , Wang P. , Davis D.
Published: February 2004

The first measurements of OH, H2SO4, and MSA performed at the South Pole as part of the Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) study are presented. OH concentrations were found to be quite elevated for such a dry environment, with average values of 2x106 molecule cm−3. Model simulations suggest that much of the observed OH is a result of unexpectedly high NO concentrations. Concentrations of H2SO4 and MSA were generally low with average values of 2.5x105 and 1x105 molecule cm−3, respectively. Major variations in the concentration levels of the above species were found to have a high correlation with changes in the polar mixing layer as estimated from the measured temperature difference from 22 to 2m above the snow surface. Chemical details are discussed.
The production of Barberton komatiites in an Archean Subduction Zone
Authors: Parman S. W. , Grove T. L. , Dann J. C.
Published: February 2004

Based upon their geochemical similarity, we propose that the 3.5 Ga Barberton basaltic komatiites (BK) are the Archean equivalents of modern boninites, and were produced by the same melting processes (i.e. hydrous melting in a subduction zone). The Barberton komatiites also share some geochemical characteristics with boninites, including petrologic evidence for high magmatic H2O contents. Experimental data indicates that the Archean sub‐arc mantle need only be 1500–1600°C to produce hydrous komatiitic melts. This is considerably cooler than estimates of mantle temperatures assuming an anhydrous, plume origin for komatiites (up to 1900°C). The depleted mantle residue that generates the Barberton komatiites and BK will be cooled and metasomatised as it resides beneath the fore‐arc, and may represent part of the material that formed the Kaapvaal cratonic keel.
Non‐sea salt sulfate and other aerosol constituents at the South Pole during ISCAT
Authors: Arimoto R. , Nottingham A. S. , Webb J. , Schloesslin C. A. , Davis D. D.
Published: February 2004

Bulk aerosol samples collected at the South Pole were analyzed for Na, SO42−, Cl−, NO3−, methanesulfonate (MSA), 210Pb and 210Po. Sea salt concentrations were relatively high compared with previous reports, with Na, averaging 45 ng m−3 Chloride was depleted by ∼65% compared with its ratio to Na in seawater. Non‐sea salt sulfate (NSS) averaged 212 ng m−3, and less than 5% of the sulfate was from sea salt. The mean concentration of MSA (an indicator of marine biogenic sulfur) was 12 ng m−3, and the MSA/NSS mass ratio (0.059) was similar to that in Antarctic ice. Although MSA and NSS were correlated, the data set is not sufficiently robust to draw a quantitative conclusion concerning the fraction of NSS that is biogenic. Data for 210Po and 210Pb showed no evidence for strong volcanic influences on sulfate, and NSS also was not correlated with NO3−, a possible tracer of continental emissions.
Kinetics of the reaction OH + CO under atmospheric conditions
Authors: McCabe David C. , Gierczak Tomasz , Talukdar Ranajit K. , Ravishankara A. R.
Published: February 2004

The rate coefficients for the reaction of OH with CO, k1 at pressures of 50–750 Torr from 220 K to 400 K, in He, N2, and air, are reported to be k1=(1.57 × 10−13 + 3.54 × 10−33 × [M]) cm³ molecule−1 s−1, with [M] in molecule cm−3. k1 increases linearly with the bath gas number density; this increase is independent of temperature. k1, at a given temperature and number density, is the same in N2, dry air, and mixtures of O2 (up to 49%) and N2. The presence of water vapor does not significantly alter k1 under atmospheric conditions. The uncertainty in our value of k1 is ±15%, at the 95% confidence level, at any given [M] and temperature, which is smaller than the currently recommended uncertainty by a factor of four or more. Our k1 values are compared with previous data and their atmospheric implications are discussed.
Estimation of global field aligned currents using the iridium® System magnetometer data
Authors: Waters C. L. , Anderson B. J. , Liou K.
Published: February 2004

The Iridium® System satellite constellation consists of 66 satellites in circular, polar, 780 km altitude orbits in six equally spaced planes. Each satellite carries an engineering magnetometer which has sufficient resolution to sense the Birkeland currents. This paper presents a spherical harmonic fitting (SHF) technique for estimating field aligned currents (FACs) using the cross track component of the magnetic field measurements from the Iridium satellites. The SHF magnetic field perturbations along with Ampere's law are used to derive the global FACs from 40° MLAT to the pole in either hemisphere. Data for 10–11 UT, 23 August, 1999 were obtained from Iridium, Defense Meteorology Satellite Program (DMSP) Fl3 and the Ultraviolet Imager (UVI) onboard the POLAR satellite. The SHF data were evaluated along the DMSP F13 track. The range of east‐west component, SHF magnetic perturbations from Iridium was (−530,465) nT compared with ( −630,634) nT from DMSP F13. The derived upward FACs ranged from −0.8 to 0.9 µAm−2. Upward FACs were co‐located with bright dayside UVI emissions.
A simple explanation for the occurrence of the 1911 Morgan Hill Earthquake in the stress shadow of the 1906 San Francisco Earthquake
Authors: Hori Takane , Kaneda Yoshiyuki
Published: February 2004

We propose a new model to overcome an apparent stress shadow paradox. The stress shadow of the 1906 San Francisco earthquake was so effective in inhibiting earthquake activity that no M > 6 earthquakes occurred in the San Francisco Bay area for more than 70 years after the 1906 earthquake, with one exception: the 1911 Morgan Hill earthquake. How could this earthquake occur only 5 years after the 1906 earthquake in an area where earthquake activity should have been inhibited? Our model is characterized by localized locked patches on the Morgan Hill segment of the Calaveras fault surrounded by steadily creeping patches. According to this model, the tectonic stressing rate on the Morgan Hill segment is so high that the stress shadow caused by the 1906 earthquake can be dissipated within several years. This simple model is consistent with both the surface deformation data and the apparent earthquake recurrence at Morgan Hill, in contrast to two previous models which are either poorly constrained or have difficulty explaining such observations.
Rapid climate shifts in the southern African interior throughout the Mid to Late Holocene
Authors: Lee‐Thorp J. A. , Holmgren K. , Lauritzen S. ‐E. , Linge H. , Moberg A. , Partridge T. C. , Stevenson C. , Tyson P. D.
Published: February 2004

A detailed climate proxy record based on δ18O, δ13O, and grey index of a well‐dated stalagmite from Cold Air Cave in the Makapansgat Valley of north‐eastern South Africa suggests that regional precipitation, temperatures and vegetation oscillated markedly and rapidly over the last ∼6500 years on centennial and multi‐decadal scales. The mid‐Holocene prior to 5200 years ago was humid and warm. A fundamental transition occurred 3200 years ago, leading to drier and cooler conditions that culminated at 1750 AD. Comparisons with ice core records suggest synchronous changes implicating rapid global teleconnections.
Subtropical Indian Ocean SST dipole events and southern African rainfall
Authors: Reason C. J. C.
Published: February 2004

An atmospheric general circulation model (AGCM) is used to examine how the regional atmospheric circulation and rainfall over southern Africa respond to a recently observed dipole in subtropical sea surface temperature (SST) over the South Indian Ocean. Observations suggest that when SST is warm to the south of Madagascar and cool off Western Australia, increased summer rains occur over large areas of southeastern Africa. The model results suggest that this SST pattern leads to increased rainfall via enhanced convergence of moister than average air over the region. Increased evaporation occurs over the warm pole in the South West Indian Ocean and this moist air is advected towards Mozambique and eastern South Africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow.
Stability of the boundary separating Antarctic Bottom Water from North Atlantic Deep Water in the western South Atlantic
Authors: Sutherland Stewart C. , Broecker Wallace S. , Takahashi Taro
Published: February 2004

A comparison of data collected between 1911 and 1937 with those obtained during SAVE (1987–89) and AJAX (1984) expeditions reveals no significant change in the position of the boundary separating Antarctic Bottom Water and North Atlantic Deep Water in the western South Atlantic Ocean.
The Atlantic Multidecadal Oscillation and its relation to rainfall and river flows in the continental U.S.
Authors: Enfield David B. , Mestas‐Nuñez Alberto M. , Trimble Paul J.
Published: February 2004

North Atlantic sea surface temperatures for 1856–1999 contain a 65–80 year cycle with a 0.4 °C range, referred to as the Atlantic Multidecadal Oscillation (AMO) by Kerr [2000]. AMO warm phases occurred during 1860–1880 and 1940–1960, and cool phases during 1905–1925 and 1970–1990. The signal is global in scope, with a positively correlated co‐oscillation in parts of the North Pacific, but it is most intense in the North Atlantic and covers the entire basin there. During AMO warmings most of the United States sees less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Between AMO warm and cool phases, Mississippi River outflow varies by 10% while the inflow to Lake Okeechobee, Florida varies by 40%. The geographical pattern of variability is influenced mainly by changes in summer rainfall. The winter patterns of interannual rainfall variability associated with El Niño‐Southern Oscillation are also significantly changed between AMO phases.
Stratospheric NOx enhancements in the Southern Hemisphere Vortex in winter/spring of 2000
Authors: Randall C. E. , Siskind D. E. , Bevilacqua R. M.
Published: February 2004

POAM III data show unusually large increases in stratospheric NO2 throughout the late winter and spring at high southern latitudes during 2000. Using HALOE CH4 data as a tracer of vertical descent, we conclude that excess NOx was created by particle impacts in the upper atmosphere and descended in the polar vortex during the winter. We speculate that these NOx enhancements were due to the solar proton event that occurred on 14–15 July 2000, and show that they caused reductions of up to ∼45% in middle stratospheric ozone mixing ratios. Comparison of HALOE and POAM data in 2000 to data from 1991–1999 suggests that the 2000 NOx enhancements were the largest ever documented by satellite in the southern hemisphere middle stratosphere. Also, based on H2O data, we conclude that NOx‐enriched air observed in the south polar vortex from 1991–1999 originated in the mesosphere, not the thermosphere as is often assumed.
Seismological in situ estimation of density jumps across the transition zone discontinuities beneath Japan
Authors: Kato Mamoru , Kawakatsu Hitoshi
Published: February 2004

We investigate the magnitude of shear‐wave velocity and density jumps across the 410‐km and 660‐km discontinuities in the Earth's mantle. We estimate SS reflection and PS conversion coefficients from ScS reverberations and receiver‐side P‐S converted phases, respectively, using broadband seismograms recorded at stations in western Japan. Fractional changes of model parameters that satisfy our observations in the northwest Pacific are (ΔVs, Δρ)=(8.5%, 5.4%) for the 660‐km discontinuity, and (4.9%, 1.9%) for the 410‐km discontinuity.
InSAR analysis of natural recharge to define structure of a ground‐water basin, San Bernardino, California
Authors: Lu Zhong , Danskin Wesley R.
Published: February 2004

Using interferometric synthetic aperture radar (InSAR) analysis of ERS‐1 and ERS‐2 images, we detect several centimeters of uplift during the first half of 1993 in two areas of the San Bernardino ground‐water basin of southern California. This uplift correlates with unusually high runoff from the surrounding mountains and increased ground‐water levels in nearby wells. The deformation of the land surface identifies the location of faults that restrict ground‐water flow, maps the location of recharge, and suggests the areal distribution of fine‐grained aquifer materials. Our preliminary results demonstrate that naturally occurring runoff and resultant recharge can be used with interferometric deformation mapping to help define the structure and important hydrogeologic features of a ground‐water basin. This approach may be particularly useful in investigations of remote areas with scant ground‐based hydrogeologic data.
Intercomparison of aerosol optical depth measurements in the UVB using Brewer Spectrophotometers and a Li‐Cor Spectrophotometer
Authors: Gröbner J. , Vergaz R. , Cachorro V. E. , Henriques D. V. , Lamb K. , Redondas A. , Vilaplana J. M. , Rembges D.
Published: February 2004

The first Iberian UV radiation intercomparison was held at “El Arenosillo”‐Huelva station of the Instituto Nacional de Técnica Aeroespatial (INTA) from September 1 to 10, 1999. During this campaign, seven Brewer spectrophotometers and one Li‐Cor spectrophotometer measured the total column aerosol optical depth (AOD) at 306, 310, 313.5, 316.75 and 320 nm. The AOD calibration of one Brewer was transferred to all other Brewers using one day of intensive measurements. The remaining days were used to observe the stability and reproducibility of the AOD measurements by the different instruments. All Brewer spectrophotometers agreed to within an AOD of 0.03 during the whole measurement campaign. The differences in AOD between the Li‐Cor spectrophotometer and the Brewer spectrophotometers were between −0.07 and +0.02 at 313.5, 316.75, and 320 nm. This investigation demonstrates the possibility of using the existing worldwide Brewer network as a global UV aerosol network for AOD monitoring.
Sea level rise in the Arctic Ocean
Authors: Proshutinsky Andrey , Pavlov Vladimir , Bourke Robert H.
Published: February 2004

About 60 tide‐gauge stations in the Kara, Laptev, East‐Siberian and Chukchi Seas have recorded the sea level change from the 1950s through 1990s. Over this 40‐year period, most of these stations show a significant sea level rise (SLR). In light of global change, this SLR could be a manifestation of warming in the Arctic coupled with a decrease of sea ice extent, warming of Atlantic waters, changes in the Arctic Ocean circulation, and an increase in coastal erosion and thawing of permafrost.

We have analyzed monthly mean sea level data and assessed the role that different factors may play in influencing the process of sea level change in the Arctic Ocean. Analysis of the observational data and model results shows that changes in the patterns of wind‐driven and thermohaline circulation may account for most of the increase of sea level in the Arctic Ocean and their cumulative action can explain more than 80% of the sea level variability during 1950–1990.
Fault geometry and slip distribution of the 1999 Chi‐Chi, Taiwan Earthquake imaged from inversion of GPS data
Authors: Johnson Kaj M. , Hsu Ya‐Ju , Segall Paul , Yu Shui‐Beih
Published: February 2004

GPS measurements of coseismic displacements from the 1999, Chi‐Chi, Taiwan earthquake are modeled using elastic dislocation theory. We find that a single fault plane cannot fit the data, but rather a curved fault surface consisting of multiple segments dipping 20–25° best fits the observations. The model fault exhibits reverse and left‐lateral slip on a 75 km long N‐S trending segment and reverse and right‐lateral slip on a 25 km E‐W trending segment at the northern end of the rupture. The 21° dipping E‐W segment is inconsistent with previous interpretations of high angle tear faulting.
Reconfiguration timescales of ionospheric convection
Authors: Murr D. L. , Hughes W. J.
Published: February 2004

Changes in ionospheric flow patterns provide direct observations of how the magnetosphere‐ionosphere system is coupled to the IMF. The nature and location of reconnection on the magnetopause is communicated to the ionosphere, which responds by reconfiguring global convection patterns. We investigate the dynamics of the changing global ionospheric convection patterns using a large two‐dimensional array of ground magnetometers. We have found that for sharp north to south transitions of the IMF, dayside ionospheric convection patterns globally reconfigure themselves in timescales as short as 8 minutes. We find that all local times initially respond within 1‐2 minutes of the first detectable response in the ionosphere. The length of time (after the initial onset) required for the ionosphere to transition from its initial state to its new state, which we refer to as the reconfiguration time, is measured. IMF Bz northward to southward transitions have reconfiguration times near local noon of approximately 5 minutes and lengthen approximately 2 minutes for every 3 hours of local time away from noon.
Probing an ultra‐low velocity zone at the core mantle boundary with P and S waves
Authors: Ni Sidao , Helmberger Don V.
Published: February 2004

Recent studies of the core‐mantle boundary (CMB) have revealed some very anomalous structures interpreted in terms of ultra low velocity zones (ULVZ). However, there remains considerable uncertainties about their physical descriptions or even if they occur above or below the CMB. They have only been detected in isolated situations using rather special techniques; these includes: distortions in SKS with the development of SKPdS and SPdKS, broadband PKP precursors, distinct ScS and S beyond 100 degree, and rapid changes in differential travel times of neighboring phases. Here we report on a situation where ray paths associated with PKP precursors and SKPdS sample the same ULVZ structure. The structure lies beneath central Africa and has been detected from WWSSN analog data (SKPdS) discussed previously. This data set has been enhanced with a collection of digital records sampling an elongated North‐South zone roughly 800 km long. The entire SKPdS data set can be modeled with a ridge‐shaped cross section with widths of 250 to 400 km and drops in P and S velocity of 10 and 30 percent. Fortunately, a new IRIS station (MSKU) located in Western Africa provided excellent PKP data from the New Britain Region events sampling the above structure. The PKP and strong precursors can be modeled by 2D synthetics generated from the same structure (used in modeling SKP dS) which provides a strong constraint on the definition characteristics of this particular ULVZ.
The solar wind helium abundance: Variation with wind speed and the solar cycle
Authors: Aellig Matthias R. , Lazarus Alan J. , Steinberg John T.
Published: February 2004

We investigate the helium abundance in the solar wind and variations thereof on a time scale of years. Data from the WIND‐SWE experiment gathered between the end of 1994 and early 2000 are analyzed. In agreement with similar work for previous solar cycles, we find a clear dependency of the He/H ratio in the solar wind on the solar cycle. In the slow solar wind, the average He/H rises from a minimum of less than two percent around solar minimum to about 4.5% in early 2000. The solar cycle dependency is stronger the lower the speed that is used to sort the data. We observe the strongest dependency of the He/H ratio on the solar wind speed around solar minimum and it weakens as the solar activity increases. We speculate that the expansion factor of the magnetic field close to the Sun changes over the solar cycle and thereby changes the efficiency of the Coulomb drag. Inefficient Coulomb drag leads to a low helium abundance in the solar wind.
High‐resolution radon monitoring and hydrodynamics at Mount Vesuvius
Authors: Cigolini Corrado , Salierno Francesco , Gervino Gianpiero , Bergese Paolo , Marino Ciro , Russo Massimo , Prati Paolo , Ariola Vincenzo , Bonetti Roberto , Begnini Stefania
Published: February 2004

A yearlong high‐resolution radon survey has been carried on at Mount Vesuvius, starting in May 1998. Radon activities were acquired by exposing charcoal canisters and track‐etch detectors. Sampling stations were deployed along two major summit faults and around the caldera bottom. Volcanically‐related earthquakes, with MD ≥ 2.5, may be discriminated from regional seismic events since their cumulative radon anomalies are recorded from stations located along all the above structural features. On the contrary, radon anomalies correlated to regional earthquakes, with MD ≥ 4, are essentially recorded by the sampling sites located along the two summit faults (whose roots extend deeper into the Tertiary basement rocks that underlay the volcano). Radon migration to the surface is ruled by convection within a porous medium of relatively low porosity (ϕ ≈ 10−5), suggesting that fluid motion is strongly localised along fractures. It is suggested that fluid pressure build up, followed by fluid release and migration during incipient fracturing of the porous medium, precede the onset of volcanically‐induced earthquakes.
Resolution of the discrepancy between experiment and theory of midlatitude F‐region structures
Authors: Kelley Michael C. , Makela Jonathan J.
Published: February 2004

The Perkins instability has long been quoted as the explanation for midlatitude F‐region structure. This notion has been called into question by a number of recent experimental results using airglow and incoherent scatter radar measurements. Here we attempt to reconcile experiment and theory by invoking polarization of the Perkins structures in the direction parallel to their long axis. The resulting northwest‐directed electric field causes the observed southwestward motion, thus resolving the apparent conflict. A simple dipole polarization electric field model is proposed and compared favorably with the observations.
Imaging the Seattle Fault Zone with high‐resolution seismic tomography
Authors: Calvert Andrew J. , Fisher Michael A.
Published: February 2004

The Seattle fault, which trends east‐west through the greater Seattle metropolitan area, is a thrust fault that, around 1100 years ago, produced a major earthquake believed to have had a magnitude greater than 7. We present the first high resolution image of the shallow P wave velocity variation across the fault zone obtained by tomographic inversion of first arrivals recorded on a seismic reflection profile shot through Puget Sound adjacent to Seattle. The velocity image shows that above 500 m depth the fault zone extending beneath Seattle comprises three distinct fault splays, the northernmost of which dips to the south at around 60°. The degree of uplift of Tertiary rocks within the fault zone suggests that the slip‐rate along the northernmost splay during the Quaternary is 0.5 mm a−1, which is twice the average slip‐rate of the Seattle fault over the last 40 Ma.
Subduction of decadal North Pacific thermal anomalies in an ocean GCM
Authors: Zhang Rong‐Hua , Kagimoto Takashi , Zebiak Stephen E.
Published: February 2004

A new version of the GFDL Modular Ocean Model (MOM 3) is used to simulate interannual and interdecadal variability over the entire Pacific basin from January 1948 to April 2000, forced by NCEP reanalysis atmosphere‐ocean fluxes. The MOM 3 with high resolution and sophisticated physics realistically reproduces the subduction of temperature and salinity anomalies associated with decadal climate variability in the North Pacific. Two major decadal subduction events (one warm and salty in the 1970s, and another cold and fresh in the 1980s) are demonstrated in this paper. In the 1970s temperature anomaly signal propagates along the subduction pathway into the western boundary at 18° N. The time needed to propagate from the midlatitude outcrop sites into the western boundary is about 5 years, shorter than that suggested by previous advection‐based analyses. It is further shown that the simulated temperature and salinity variations coincide in such a way that cold (warm) anomalies tend to be accompanied by fresh (salty) anomalies along the subduction pathway, indicating that they are largely compensating in terms of density on the decadal time scales. The implication of such compensated thermal anomalies subducted from the midlatitudes are discussed with respect to the tropical variability and ocean data assimilation issues.
Extensional structure in Northern Honshu Arc as inferred from seismic refraction/wide‐angle reflection profiling
Authors: Iwasaki Takaya , Kato Wataru , Moriya Takeo , Hasemi Akiko , Umino Norihito , Okada Tomomi , Miyashita Kaoru , Mizogami Tomoko , Takeda Tetsuya , Sekine Shutaro , Matsushima Takeshi , Tashiro Katsuya , Miyamachi Hiroki
Published: February 2004

A recent extensive seismic wide‐angle experiment revealed a new image of crustal and uppermantle structure across Northern Honshu Arc, Japan. The western part of the arc recorded the crustal deformation by the Miocene back arc spreading of the Sea of Japan. The crust is composed of highly deformed Tertiary sedimentary layers, a relatively low velocity (5.75–5.9 km/s) crystalline basement and a 15‐km thick lower crust with a velocity of 6.6–7.0 km/s. Clear westward crustal thinning from 32 to 27 km represents the extensional deformation by the backarc spreading. The crust attains the maximum thickness (32–35km) east of the backbone range for which the magmatic intrusion/underplating since 10–15 Ma is a predominant factor. The eastern part of the arc has a less deformed upper crust and a reflective middle/lower crust, probably remaining a stable block since the time of the backarc spreading.
OH production from the reaction of vibrationally excited H2 in the mesosphere
Authors: Reynard Linda M. , Donaldson D. J.
Published: February 2004

We propose a novel mechanism for OH production in the mesosphere (50–100 km): the reaction of ground state oxygen atoms with vibrationally excited H2, which is formed via collisional energy transfer from
. Using published rate coefficients and altitude profiles for the chemical species involved, the contribution of this new mechanism to the total OH production rate has been estimated as a function of altitude. At altitudes above 75 km, the proposed reactions are as important as the reaction of water with excited state oxygen atoms, O(¹D). The fraction of total OH produced from the proposed mechanism is estimated to reach 16% at 100 km.
Nonkeplerian dust dynamics at Saturn
Authors: Howard J. E. , Horányi M.
Published: February 2004

We calculate the spatial location of possible stable nonequatorial halo dust grain orbits about Saturn, with surface potential determined by local photoionization and magnetospheric charging currents. Stability loci are calculated for both dielectric and conducting grains, in prograde and retrograde orbits, with the sign of the charge determined by the plasma environment. The results show that very small (<100 nm) grains in positive retrograde orbits are most likely to be found by the Cassini orbiter, while negatively charged grains are dynamically excluded.
Shape of atmospheric mineral particles collected in three Chinese arid‐regions
Authors: Okada Kikuo , Heintzenberg Jost , Kai Kenji , Qin Yu
Published: February 2004

The shape of atmospheric mineral particles of 0.1–6 µm radius was studied by electron microscopy applied to the samples collected in three arid regions in China (Qira in the Taklamakan Desert, Zhangye near the southern border of the Badain‐Jaran Desert and Hohhot in northern China). In all three regions, the mineral particles showed irregular shapes with a median aspect ratio b/a (ratio of the longest dimension b to the orthogonal width a) of 1.4. Although the aspect ratio exhibited no clear size dependence, the circularity factor (4πS/l²; S is surface area and l is periphery length) tended to decrease with increasing radius, suggesting the presence of aggregated mineral particles at larger sizes. The ratio of particle height‐to‐width h/a was also evaluated by measuring the shadow length. The median ratio h/a was 0.49 in Hohhot, 0.29 in Zhangye and 0.23 in Qira. Analytical functions were fitted to the grand total of the frequency distributions of aspect ratios, height‐to‐width ratios and circularity factors allowing parametric calculations of radiative effects and calculations of optical and sedimentation behavior of mineral particles.
Heterogeneities in D” beneath the southwestern Pacific inferred from scattered and reflected P‐waves
Authors: Kito Tadashi , Krüger Frank
Published: February 2004

We investigate the fine structure of the D” layer beneath the southwestern Pacific using short‐period data from 7 deep events in the Fiji‐Tonga region recorded at the J‐Array in Japan. We use a double array migration method which integrates source array beamforming with receiver array beamforming. The phase‐weighted stacking technique, which reduces incoherent noise by employing complex trace analysis, is also applied. This combination greatly enhances small phases common to the source and receiver beams. We present coherent phases originating from the lowermost mantle using these new array techniques. The results indicate that seismic energy is reflected at two negative discontinuities near 2550 and 2650 km. The migration shows only weak evidence for scattering objects which may be an indication that scattering in the D” layer beneath the southwestern Pacific is weak.
Variations in the onset diameter for Martian layered ejecta morphologies and their implications for subsurface volatile reservoirs
Authors: Barlow Nadine G. , Koroshetz John , Dohm James M.
Published: February 2004

We investigated regional variations in the onset diameter of craters displaying a single layer ejecta morphology within ±30° latitude using Viking imagery. Our results generally agree with those of previous studies which show onset diameters of 5 to 6 km in the equatorial region, but we have identified localized regions with unusually small onset diameters. The largest region is located in Solis and Thaumasia Planae. The 3–5 km onset diameter range in this area indicates a near‐surface ice‐rich reservoir (depth ∼110 m). This unusual concentration of near‐surface ice may have resulted from magmatic‐driven uplifts associated with the Tharsis rise, which modified parts of a regional aquifer/drainage basin system and resulted in the transfer and concentration of subsurface volatiles in this region.
Anatomy of plasma structures in an equatorial spread F event
Authors: Chen K. Y. , Yeh H. C. , Su S. Y. , Liu C. H. , Huang Norden E.
Published: February 2004

This paper investigates the small scale plasma structures observed by ROCSAT‐1 in the equatorial F region through the newly developed Hilbert‐Huang transform (HHT) method in the time (space) domain under the frozen‐in approximation. The new method allows us to decompose the non‐stationary, nonlinear data into a finite number of intrinsic scale modes. In this report the structures of vertical ion velocity and horizontal density gradient inside a plasma bubble are analyzed mode by mode anatomically without making the usual linearization assumption. We found that the intrinsic modes for velocity and density gradient of the selected event have identical wave form for structures with scales between 300 m and 50 m. This implies that the vertical velocity fluctuations induced from the electric field follows the exact Boltzmann relation in the limited regime of scale length between 300 m and 50 m. A spectral break at 50 m is clearly seen in the velocity HHT spectrum. The spectral form of velocity differs greatly from that of density gradient at scale lengths shorter than 50 m.
Viscoelastic stress‐triggering of the 1999 Hector Mine Earthquake by the 1992 Landers Earthquake
Authors: Zeng Yuehua
Published: February 2004

The 1999 Mw 7.1 Hector Mine earthquake occurred only 20 km from the 1992 Mw 7.3 Landers earthquake fault. The close spacing between the two earthquakes suggests that the Landers earthquake trigger the Hector Mine event. Based on an elastic half‐space model, scientists from the USGS, SCEC and CDMG (2000) have found a negative Coulomb stress change at the Hector Mine hypocenter due to Landers. This negative stress change is inconsistent with the hypothesis of static stress triggering. In this paper, I show evidence of stress triggering of the Hector Mine earthquake by Landers, due to a process governed by viscoelastic flow in the lower crust. This visoelastic flow has produced broad‐scale postseismic rebound observed by GPS and InSAR measurements. The result of this study is that viscoelastic flow has significantly modified the regional stress field in the Mojave Desert after the Landers earthquake. The evolving stress field, including viscoelastic flow, has gradually moved the Coulomb stress change at the Hector Mine hypocenter to a positive level. The increase in Coulomb stress exceeded 1 bar right before the Hector Mine earthquake, bringing the Hector Mine ruptures to the proximity of catastrophic failure.
The heat balance of the tropical tropopause, cirrus, and stratospheric dehydration
Authors: Hartmann Dennis L. , Holton James R. , Fu Qiang
Published: February 2004

If tropical tropopause cirrus lie above convective anvils with tops above about 13km, then net radiative cooling from the cirrus can be produced that is large enough to offset significant subsidence heating, even at the lowest temperatures observed in the tropics. Cirrus clouds near the tropopause are strongly heated by radiation unless they lie above convective anvil clouds. Radiative relaxation in the tropical troposphere is slow above about 14km unless clouds are present. Radiative cooling of tropopause cirrus may be important in processes that dehydrate air before it enters the stratosphere.