bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport theoretic solutions for the beam‐spreading effect in the proton‐hydrogen aurora
Authors: Jasperse John R.
Published: February 2004

In this paper, we give matched asymptotic solutions for the particle fluxes in the Earth's proton‐hydrogen aurora. The proton (ΦP) and hydrogen atom (ΦH) fluxes are functions of two spatial and three velocity variables. These results are new and are given in closed form to the lowest order in the expansion parameter, which is the ratio of the proton gyroradius to the atmospheric scale height, and show a pronounced lateral, beam‐spreading effect. Numerical calculations for ΦP and ΦH where no approximations are made are also given and found to agree reasonably well with the matched asymptotic solutions.
Integrated IR band intensities of the v5 and v1 bands of ClOOCl
Authors: Brust A. S. , Zabel F. , Becker K. H.
Published: February 2004

ClOOCl was prepared in situ in two static reactors and in a flow tube by photolyzing OClO or by the reaction of Cl with O3, at temperatures ≤253 K. IR and UV spectra were monitored simultaneously, and concentrations of ClOOCl were determined from the known UV absorption cross sections. Based on these concentrations, absorption coefficients and integrated band intensities of the v5 and v1 bands of ClOOCl near 650 cm−1 and 750 cm−1 were derived for spectral resolutions between 1 and 0.125 cm−1 using a FTIR spectrometer. Diode laser spectra of several regions of the v5 band demonstrate that the rotational structure of this band can be resolved at total pressures of several mbar. The low line intensities of the 650 cm−1 band, however, do not allow to detect ClOOCl by airborne diode laser absorption at today's detection sensitivities.
First polar and 1995‐034 observations of the midaltitude cusp during a persistent northward IMF condition
Authors: Grande M. , Fennell J. , Livi S. , Kellett B. , Perry C. , Anderson P. , Roeder J. , Spence H. , Fritz T. , Wilken B.
Published: February 2004

We present the first observations by Polar and 1995‐034 of the mid‐altitude cusp. On May 29, 1996, the Polar and 1995‐034 spacecraft crossed into an extended cusp region. The region was characterized by intense fluxes of solar wind like ions in the energy range 1–10 keV that had angular distributions that showed evidence of flows and trapping. The ion composition data are combined with energetic proton observations from Polar and plasma observations from 1995‐034 and DMSP satellites to examine the spatial and temporal extent and plasma characteristics of the cusp during a persistent northward IMF condition. The composition data is consistent with expected solar wind composition with a source temperature of ∼1.25 × 106 K. The combined spacecraft observations show an extended cusp‐like region, probably produced by northward IMF.
The closure of region‐1 field‐aligned current in MHD simulation
Authors: Janhunen P. , Koskinen H. E. J.
Published: February 2004

We have studied the closure path of Region‐1 field‐aligned current system in our global MHD simulation and found some interesting results. After leaving the ionosphere on the eveningside the current deviates from the field‐aligned direction rather early and bends towards the Sun. After passing through the velocity shear region near the magnetopause, which is a generator region, it climbs up along the magnetopause, being more or less field‐aligned. Because of this it again bends sunward. When approaching the noon‐midnight meridian plane (Y=0 plane in GSM coordinates), however, the current becomes more perpendicular to the magnetic field. It passes through the Y=0 plane at about X=2±1, Z=11±1. On the morningside the closure path is a mirror reflection of that on the evening side. Thus the closure path seems to reside more on the dayside than perhaps usually thought. We give a simple physical explanation for the dayside bending, which is based on the MHD pressure balance equation.
Ground‐based measurements of solar ultraviolet radiation in Tibet: Preliminary results
Authors: Ren Pu Bu Ci , Sigernes Fred , Gjessing Yngvar
Published: February 2004

Measurements were carried out on Tibetan Plateau (Lhasa, 3648 m above sea level) with a multi‐channel moderate bandwidth filter instrument during the period from June 24. to November 30., 1996. The analysis of preliminary data shows that hourly mean CIE‐weighted biologically effective UV dose rate at local noon can reach to as high as 390.5 mW/m² . The corresponding average value was 225.4 mW/m²; Due to the combined effect of cloud cover variation with ozone variation, the increasing trend of this UV dose rate exists during this period of measurements. The relation between the ratio of irradiance close to noon at 340nm to that at 305nm and total ozone column shows that the variation of total ozone column may also cause the variation of UV radiation. In addition, the UV dose rate in the morning is slightly higher than that at afternoon with same solar zenith angle.
Aspects of layer electrodynamics inferred from high‐resolution ISR observations of the 80–270 km ionosphere
Authors: Mathews John D. , Sulzer Michael P. , Perillat Phil
Published: February 2004

The Arecibo 430 MHz Incoherent Scatter Radar (ISR) has been used to observe vertical ionospheric electron concentration profiles in the 80–280 km altitude region at the highest sustained resolutions (150 m, 10 s) thus far reported for “ion‐line” measurements. We present results that reveal layers and wave‐like features in unprecedented detail and likely point to electrodynamic processes linking the E and F regions. Tidal Ion Layers (TILs) and sporadic E (Es) layers in the 100–110 km altitude region often display significant peaks and edges that appear in only one range gate (150 m). Also, previously unreported wave‐like plasma structures—termed “ion rain”—with ∼12 minutes apparent period, normalized amplitudes of 1–3%, and vertical wavelengths in excess of 30 km have been observed extending from base of the F‐layer to the evening intermediate TIL with indications of coupling into the 90–110 km region below.
Spatial variations in the rate of sea level rise caused by the present‐day melting of glaciers and ice sheets
Authors: Conrad Clinton P. , Hager Bradford H.
Published: February 2004

The redistribution of surface water mass associated with the melting of glacial ice causes uplift near areas of mass depletion, depression of the seafloors, and changes in the earth's gravitational field which perturb the ocean surface. As a result, local spatial variations exist in the rate of sea level rise. Tide gauges on continental coastlines measure a sea level rise 5% smaller than the global average. Tide gauges in the hemisphere opposite a source of continental mass depletion measure sea level rise 10 to 20% greater than the global average produced by that source while satellites make measurements 10% too low. Because most long duration tide gauges are in the northern hemisphere, if the sources of sea level rise are unbalanced between the two hemispheres, estimates of global sea level rise could be in error by 10 to 20%. Individual tide gauges could be more seriously unrepresentative if they are near regions of significant present‐day mass depletion.
Foundering of the lithosphere at the onset of subduction
Authors: Schubert Gerald , Zhang Keke
Published: February 2004

An analytic theory is presented for the foundering of the lithosphere at the onset of subduction. The two‐dimensional cartesian model calculates the instantaneous response of a viscous half‐space to a surface load that corresponds to the negative buoyancy of a semi‐infinite plate. In the early stages of foundering, just after the mantle floods onto the top of the lithosphere, the edge of the slab sinks into the mantle with a downward velocity uz given by (1/6e) (Δρ/ρ)4 (ρgd²/μ) (d/xn)², where ρ is the density of the mantle, Δρ is the density of the lithosphere minus the density of the mantle, d is the thickness of the lithosphere, g is the acceleration of gravity, μ is the viscosity of the mantle, and xn is the flexural length scale of the lithosphere. Alternatively, uz is given by (3/e) (Δρ/ρ)³ (d/xn)² uz (Stokes), where uz (Stokes) is the Stokes velocity of fall of a sphere of radius d/2 with excess density Δρ through a fluid of viscosity μ and density ρ. The initial subsidence velocity of the edge of a lithospheric slab is much slower than the sinking velocity of a similar‐sized and negatively buoyant sphere. For typical values of the above parameters, the edge of the plate sinks into a mantle of viscosity 1018 P as at a rate of about 7.5 mm yr−1. Lithospheric foundering is facilitated by low mantle viscosity and old, thick plates.
The effect of foreshock on the motion of the dayside magnetopause
Authors: Russell C. T. , Petrinec S. M. , Zhang T. L. , Song P. , Kawano H.
Published: February 2004

The role of the foreshock or quasi parallel shock in causing motions of the magnetopause is studied using both the number of crossings of the magnetopause found as ISEE 1 and 2 passed through the expected region of the magnetopause on each orbit and by determining the minimum and maximum distances to the magnetopause on each pass. Downstream of the afternoon magnetosheath and bow shock, a region free from foreshock effects for typical interplanetary magnetic field (IMF) directions, the north‐south component of the IMF controls these motions. On the morning side additional oscillation in the magnetopause position is found for both northward and southward IMF. We interpret these increased motions as driven by the pressure variations in and behind the foreshock region or quasi‐parallel shock. These results are consistent with other studies of foreshock effects on the magnetosphere which show little effect on erosion of the magnetopause or flux transfer event occurrence.
Two‐dimensional seismic image of the San Andreas Fault in the Northern Gabilan Range, central California: Evidence for fluids in the fault zone
Authors: Thurber C. , Roecker S. , Ellsworth W. , Chen Y. , Lutter W. , Sessions R.
Published: February 2004

A joint inversion for two‐dimensional P‐wave velocity (Vp), P‐to‐S velocity ratio (Vp/Vs), and earthquake locations along the San Andreas fault (SAF) in central California reveals a complex relationship among seismicity, fault zone structure, and the surface fault trace. A zone of low Vp and high Vp/Vs lies beneath the SAF surface trace (SAFST), extending to a depth of about 6 km. Most of the seismic activity along the SAF occurs at depths of 3 to 7 km in a southwest‐dipping zone that roughly intersects the SAFST, and lies near the southwest edge of the low Vp and high Vp/Vs zones. Tests indicate that models in which this seismic zone is significantly closer to vertical can be confidently rejected. A second high Vp/Vs zone extends to the northeast, apparently dipping beneath the Diablo Range. Another zone of seismicity underlies the northeast portion of this Vp/Vs high. The high Vp/Vs zones cut across areas of very different Vp values, indicating that the high Vp/Vs values are due to the presence of fluids, not just lithology. The close association between the zones of high Vp/Vs and seismicity suggests a direct involvement of fluids in the faulting process.
Coda wave imaging of the Long Valley Caldera using a spatial stacking technique
Authors: O'Doherty Kathryn B. , Bean Christopher J. , Mc Closkey John
Published: February 2004

Numerous geological and seismological studies of the Long Valley caldera, eastern California, suggest that it is at present an active magmatic system. Tomographic measurements utilising local and regional earthquake data have traditionally been made on the principle ‘direct' arrivals. This paper presents the results from a technique developed to image the S‐wave attenuation structure. We measure the attenuation value of the S‐wave coda from almost 17,000 vertical‐component seismograms. A more stable estimate of Q is determined from coda waves which are less sensitive to local path effects than direct waves as they sample a volume. We find that the resultant tomograms produced from spatial stacking show a high attenuation anomaly (Qs ∼ 125) centred within the caldera compared with Qs ∼ 220 outside the caldera.
Observations of altitudinal and latitudinal E‐region neutral wind gradients near sunset at the magnetic equator
Authors: Larsen M. F. , Odom C. D.
Published: February 2004

Sounding rocket chemical release measurements of the E‐region neutral wind profiles were carried out at the magnetic equator at dusk on two consecutive days in September 1994 when a strong prereversal enhancement of the F‐region vertical plasma drift was present. Wind profiles were obtained at the equator and ∼450–480 km further north. The profiles show wind speeds of 80–100 m s−1 in the lower E‐region and reversals of the wind direction over vertical scales of 10–15 km. On both days, the wind direction in the lower E region changed consistently between the northern and equatorial releases, with a strong southward wind evident at the northern position and a stronger eastward wind at the equator.
A comparison between short term (Co‐Seismic) and long term (one year) slip for the Landers Earthquake: Measurements from strong motion and SAR interferometry
Authors: Hernandez Bruno , Cotton Fabrice , Campillo Michel , Massonnet Didier
Published: February 2004

The long term relative displacements in the region of the Landers earthquake were measured over a time interval of about one year using SAR interferometry. We have also evaluated the co‐seismic slip distribution through a strong motion inversion [Cotton and Campillo, 1995] and these results are used to compute the static displacement field associated with the co‐seismic slip. We show that the synthetic static and the interferometry measurements are in very good agreement. To give an evaluation of the magnitude of the pre‐ and post‐seismic slip, a residual interferogram between data and synthetic co‐seismic slip has been computed. A simple analysis of the residual displacements gives a limiting value of the amplitude of pre‐ and post‐seismic slip integrated over a period of one year and suggests that it is on the order of a few decimeters.
The sensitivity of a global ocean model to wind forcing: A test using sea level and wind observations from satellites and operational wind analysis
Authors: Fu Lee‐Lueng , Chao Yi
Published: February 2004

Investigated in this study is the response of a global ocean general circulation model to forcing provided by two wind products: operational analysis at 1000 mb from the National Center for Environmental Prediction (NCEP); observations made by the ERS‐1 radar scatterometer. The sea level simulated by the model using the two wind fields is compared to the observations made by the TOPEX/POSEIDON radar altimeter for a period of two years. The focus of the analysis is placed on the large‐scale ocean variabilities at mid and high latitudes. The sea level simulations resulting from the ERS‐1 wind are found to be closer to the TOPEX/POSEIDON observations over most of the global oceans. However, after being scaled down in wind stress by 50%, the NCEP wind becomes consistent with the ERS‐1 wind in driving the ocean model to simulate the seasonal and intraseasonal sea level variabilities. The sensitivity of the model to wind forcing at the investigated scales is particularly pronounced in the Southern Ocean, where the sea level variabilities are primarily caused by large‐scale barotropic motions driven by wind. Other areas of appreciable sensitivity to wind forcing include the western and central North Pacific, the western subtropical South Pacific and the South Indian Ocean. The result of the study has demonstrated the sensitivity of a widely‐used ocean model to the quality of wind forcing, as well as the synergistic use of two satellite sensors in the study of ocean dynamics.
High resolution TEC monitoring method using permanent ground GPS receivers
Authors: Hernández‐Pajares M. , Juan J. M. , Sanz J.
Published: February 2004

In this paper we propose a new and simple method for obtaining the ionospheric Total Electron Content (TEC) variations from GPS permanent station data, in a very precise manner and with high temporal and spatial resolution.

The key idea is to use of the resonant period of 1 sidereal day between the Earth's rotation and the GPS satellite orbit periods, in order to obtain one TEC variation estimate directly from each ionospheric observation.

This new strategy can be applied on both global and local scales, for instance to one single station. Its capabilities are shown in the application performed with the data gathered on 17, 18 and 19 October 1995 from 95 GPS permanent stations and 9 and 10 January 1997 (180 stations), coinciding with two major geomagnetic storms.
On ELF pulses from remote lightnings triggering sprites
Authors: Sukhorukov A. I. , Stubbe P.
Published: February 2004

ELF waveforms at large distances from strong CG (cloud‐to‐ground) discharges are evaluated in the framework of Greifinger's night‐time propagation model. It is shown that if the CG discharges triggering red sprites involve, as now generally accepted, ≳10² C of charge, then they should generate remote ELF atmospherics with considerably larger magnitudes than measured in the upper ELF (> 300 Hz) range.
Crustal feeding in the Oman ophiolite: From the top and from the bottom? A thermal and mass balance model
Authors: Chenevez Jérôme , Nicolas Adolphe
Published: February 2004

The stability of the basalt melt lens identified below fast spreading ridges has been tested by a thermal and mass balance model in order to investigate how the generation of the crust by basaltic melt can be affected by spreading rate. The mpdel is constrained using field information from the Oman ophiolite, the main piece of evidence dealing with the nature and structure of the root zone of sheeted dikes which acts as a thermal boundary layer between the melt lens below, and the hydrothermally cooled sheeted dike unit above. For a mass balance calculation we first assume that the gabbro unit is entirely created by the melt issued from the lens. We examine how the heat generated by crystallization of this mass can be evacuated through the boundary layer on top of the melt lens. A steady‐state situation is found for a given spreading rate and ratio of the Nusselt number to the field‐deduced thickness of the boundary layer. If, as suggested by geophysical data, the melt lens exists only for spreading rates larger than 6 cm/yr, the boundary layer needs to be essentially conductive. With increasing spreading rates and increasing heat supply the system thermally adjusts itself until it must work in a new mode. Geological evidence suggests that this could be achieved by developing an additional feeding of the gabbro unit by a large number of sills being emplaced below the melt lens into the lower gabbros.
The Ulysses north polar pass: Latitudinal gradients of anomalous cosmic ray O, N And Ne
Authors: Trattner K. J. , Marsden R. G. , Sanderson T. R.
Published: February 2004

A key finding of the Ulysses mission has been the absence of large latitudinal gradients in the Anomalous Cosmic Ray (ACR) component. Studies using data from several satellites have consistently shown a small (∼ 2%/deg.) positive latitudinal gradient for anomalous O, N and Ne in the energy range 4 to 30 MeV/n, and even smaller gradients for ACR He. In this paper we use data from the COSPIN/LET experiment on board Ulysses to investigate (a) the behaviour of the ACR latitudinal gradients during the passage over the northern polar regions, and (b) possible north‐south asymmetries. The descent from the north pole has taken place under solar minimum conditions, providing a unique opportunity to study fully developed latitudinal effects. Our data survey covers three ACR species, O (4 to 20 MeV/n), N (4 to 20 MeV/n) and Ne (4 to 30 MeV/n). ACR gradients have been calculated for three different regions: 0°–20° (∼ 5%/deg.), 20°–60° (∼ 3%/deg.) and 60°–80.2° (∼ 1%/deg.). Comparison of data from the northern and southern hemishere at a given latitude shows an asymmetry with higher fluxes in the north than in the south at a given latitude.
Galileo evidence for rapid interchange transport in the Io torus
Authors: Thorne R. M. , Armstrong T. P. , Stone S. , Williams D. J. , McEntire R. W. , Bolton S. J. , Gurnett D. A. , Kivelson M. G.
Published: February 2004

Anomalous plasma signatures were detected by the Galileo particles and fields instruments during the initial transit through the Io torus. These unusual events are characterized by abrupt changes in the magnetic field, enhanced levels of broadband low frequency electromagnetic waves and a pronounced change in both the flux and pitch angle anisotropy of energetic particles. Here we present a coordinated study of one of the events which occurred near 6.03RJ just after 17:34 UT on December 7, 1995. The available data are consistent with the concept of rapid inward transport, and this is interpreted as the first evidence for the predicted interchange motions in the region exterior to the orbit of Io. Theoretical arguments indicate that the interchanging flux tube is characterized by substantially reduced plasma density, a spatial scale comparable to 10³ km, and an inward radial velocity comparable to 10² km/s.
Seamount abundances and Abyssal Hill Morphology on the eastern flank of the East Pacific Rise at 14°S
Authors: Grevemeyer Ingo , Renard Vincent , Jennrich Claudia , Weigel Wilfried
Published: February 2004

Bathymetric data from a Hydrosweep multibeam sonar survey of a 720 km long tectonic corridor on the east flank of the southern EPR at 14° 14′S covered about 25,000 km² of zero‐age to 8.5 m.y. old crust (magnetic anomaly 4A). In this corridor we document a strong correlation of robust along flowline changes in abyssal hill morphology and seamount size distribution with spreading rate changes deduced from our magnetic data. Indeed, we find that both rms height of abyssal hills and abundance and height of seamounts increase significantly as spreading rate changes from ∼ 75 mm/yr to over 85 mm/yr (half rate). Moreover, we identified 46 seamounts taller than 100 m. Previous studies on the southern EPR reported a larger density of seamounts, organized primarily in chains. Our investigation, however, revealed seamounts not associated with major chains, leading us to the conclusion that different forms of off‐axis volcanism occur along the spreading center.
Complex scattering within D″ observed on the very dense Los Angeles Region Seismic Experiment Passive Array
Authors: Kohler M. D. , Vidale J. E. , Davis P. M.
Published: February 2004

Several seismic phases that scattered within a few hundred kilometers of the base of the mantle are observed in a very dense seismic section. The Los Angeles Region Seismic Experiment passive phase array was composed of 88 seismometers placed along a 175 km profile. Records from two deep earthquakes in Tonga and one earthquake near Honshu, Japan show a secondary arrival between clear P and PcP arrivals. Modeling with layered structures shows that the Tonga and Honshu seismic sections are consistent with an increase in seismic velocity 140 and 240 km above the core‐mantle boundary, respectively, and a ≃10‐km thick low‐velocity zone at the base of the mantle beneath a region in the mid Pacific. Several of these arrivals are not coherent enough to appear in higher resolution stacks from the much larger Southern California Seismic Network. This experiment illustrates that fine‐scale passive array data can reveal small‐scale deep Earth structure invisible to larger‐scale seismic networks.
Aftershocks of the Andreanof Islands Earthquake of June 10, 1996, and local seismotectonics
Authors: Kisslinger Carl , Kikuchi Masayuki
Published: February 2004

Three questions have been addressed in connection with an Mw = 7.7 earthquake that occurred in the Andreanof Islands, Alaska, on June 10, 1996. First, was there any variation in seismic activity rate during the previous five years that might have been diagnostic of the imminent occurrence of this event? The answer, based on the USGS PDE catalog, is “No.” Second, though there were abundant pre‐event earthquakes and aftershocks on both sides of Adak Canyon, why was there very little activity under the canyon itself, a property that has been observed previously?. It is not possible to resolve the cause of the behavior with existing seismological data. Finally, how does one explain the eastern group of aftershocks, which fell within the zone of abundant aftershocks of the 1986 Mw = 8 Andreanof Islands earthquake, when very little of the 1996 mainshock moment was released under or to the east of Adak Canyon? One explanation of these aftershocks is that the recent aftershocks are late aftershocks of 1986 whose occurrence within a short time was induced by the stress pulse, but not seismic slip, from the 1996 earthquake. Though large earthquakes in the Aleutians occur in distinct tectonic blocks, the boundaries of these blocks may not always be defined reliably by aftershock zones.
Galileo ultraviolet spectrometer observations of atomic hydrogen in the atmosphere of Ganymede
Authors: Barth C. A. , Hord C. W. , Stewart A. I. F. , Pryor W. R. , Simmons K. E. , McClintock W. E. , Ajello J. M. , Naviaux K. L. , Aiello J. J.
Published: February 2004

Atomic hydrogen Lyman alpha radiation (121.6 nm) has been measured in emission from the atmosphere of Ganymede with the Galileo ultraviolet spectrometer. An exospheric model with the following parameters has been fit to the observational data: atomic hydrogen density directly above the surface (radius 2634 km) equal to 1.5 × 104 atoms cm−3 scale height 2634 km, exospheric temperature 450 K. A model calculation of the photodissociation of water vapor from surface ice at 146 K is used to obtain the photodissociation rate necessary to supply the hydrogen atoms that are escaping from the exosphere of Ganymede. The calculated escape flux of atomic hydrogen is 7 × 108 atoms/cm² sec. Two alternate but speculative sources of the atomic hydrogen escaping from Ganymede are photodesorption of water ice by ultraviolet photons in the wavelength range 120.5–186.0 nm and sputtering of water ice by Jupiter's magnetospheric ion plasma.
Slab detachment in continental collision zones: An analysis of controlling parameters
Authors: Wong A Ton S. Y. M. , Wortel M. J. R.
Published: February 2004

During the early stages of continental collision when continental lithosphere is subducted after a prolonged period of normal oceanic subduction, changes in the temperature distribution and stress field of the subducting lithosphere can lead to failure within the lithosphere, and result in detachment of the deeper portion of subducted lithosphere (slab detachment or slab breakoff). We use a 2D time‐dependent numerical model to identify the parameters controlling slab detachment and to estimate breakoff depths and time lengths. Temperature and rheology of subducting continental lithosphere are found to control slab detachment.
Retrieval of aerosol properties from boundary layer extinction measurements with a DOAS System
Authors: Flentje H. , Dubois R. , Heintzenberg J. , Karbach H.‐J.
Published: February 2004

Boundary layer trace gas and particulate extinction measurements in the wavelength region from 320 nm to 680 nm have been performed by means of a differential optical absorption spectroscopy (DOAS) system at Cape Arkona (Island Rügen/Germany). The wavelength‐dependent extinction coefficient σe(λ) is determined from the attenuation of radiation along two paths of different lengths. Nearly simultaneous recording of the concentrations of O3 and NO2 within the same air mass allows a correction of their contribution to σe(λ). The extinction coefficients are compared with volume scattering coefficients measured by an open integrating nephelometer. Differences between the measurements can be attributed to atmospheric inhomogeneities. A simplified model involving monomodal log‐normal distributions is applied to approximate the total particle surface area concentration and an upper limit of the accumulation mode radius. This allows a rough estimate of the particle number concentration. During the summer of 1995 the mean (median) surface area concentration was about 350 (250) µm²/cm³, and the particle number concentration ranged from about 100 cm−3 to some 1000 cm−3.
Source mechanisms of the 1944 Tonankai and 1946 Nankaido earthquakes: Spatial heterogeneity of rise times
Authors: Kato Tetsuro , Ando Masataka
Published: February 2004

The most recent great earthquakes that occurred along the Nankai trough are the 1944 Tonankai and 1946 Nankaido earthquakes. The aftershock areas of both events are smaller than the tsunami source areas, and the seismic moments estimated from geodetic or tsunami data are much larger than those estimated from seismic data. Until now these discrepancies have not been reconciled. We propose a model based on analysis of tsunami waveform data. We find that the rise time is very short on the portion of the fault plane corresponding to the aftershock area, while rupture lasts for 3–9 min. on the rest of the fault where aftershocks were absent. Since the easternmost portion of the 1944 fault slipped slowly and acted as a relaxation barrier, the 1944 rupture might have stopped here. The seismic moments of the 1944 and 1946 events on the basis of both tsunami and geodetic data are 2.8×1021 Nm and 4.0×1021 N m, respectively; the moments of the portions with short rise time are consistent with the previous seismic estimates by Kanamori [1972].
Volumetric imaging of aperture distributions in connected fracture networks
Authors: Pyrak‐Nolte Laura J. , Montemagno Carlo D. , Nolte David D.
Published: February 2004

We use x‐ray computerized tomographic (CT) imaging to present quantitative aperture data for three‐dimensional interconnected fracture networks imbedded in intact opaque rock samples several centimeters in length. X‐ray images are obtained by injecting a high‐density liquid metal into the fractured rock specimen under lithostatic conditions. The combination of tomographic reconstruction with gravimetric analysis makes it possible for the first time to obtain effective fracture aperture sizes to an accuracy of only several microns, located spatially within 300 microns. The apertures in the fracture network are spatially correlated over distances of 10 mm to 30 mm. The apertures of the intersections of the fractures were not found to be statistically larger in size than for the complete fracture network
An eastern Indian Ocean ³He section from Australia to Bali: Evidence for a Deep Pacific‐Indian Throughflow
Authors: Jean‐Baptiste P. , Fieux M. , Ilahude A. G.
Published: February 2004

The distribution of ³He has been measured on an Australia‐Bali transect, across the Pacific‐Indian throughflow region of the Eastern Indian Ocean, in SE and NW monsoonal regimes. Additional samples were also collected directly on the main sills over which water is exchanged between the Indonesian Seas and the Indian Ocean. The ³He data show that the South Banda Sea deep waters, between 800 and 1400 m, leave the Banda basin over the sills in the straits of Sumba, Savu, Roti and Timor and enter the equatorial Indian Ocean. The permanence of the ³He in both opposite monsoonal regimes, and the only weak dilution of the ³He signal between the straits and the Australia‐Bali section hundreds of kilometers apart, suggest that this deep outflow is not negligible.
Polar stratospheric clouds observed at Eureka (80°N, 86°W) in the Canadian Arctic during the 1994/1995 winter
Authors: Nagai T. , Uchino O. , Itabe T. , Shibata T. , Mizutani K. , Fujimoto T.
Published: February 2004

A lidar system was installed at Eureka (80°N, 86°W) in January 1993 to monitor stratospheric aerosols and polar stratospheric clouds (PSCs). In the winter of 1994/1995, PSCs were found at altitudes of around 20km in the middle of December. In early January 1995, PSCs were observed at altitudes from 14.3 km to 16 km, where the temperature ranged from 199K to 202K. Since this range is higher than the frost point of nitric acid trihydrate (NAT), the particles in these PSCs may have consisted of sulfuric acid tetrahydrate (SAT).
A preliminary comparison between TOVS and GOME level 2 ozone data
Authors: Rathman William , Monks Paul S. , Llewellyn‐Jones David , Burrows John P.
Published: February 2004

A preliminary comparison between total column ozone concentration values derived from TIROS Operational Vertical Sounder (TOVS) and Global Ozone Monitoring Experiment (GOME) has been carried out. Two comparisons of ozone datasets have been made: a) TOVS ozone analysis maps vs. GOME level 2 data; b) TOVS data located at Northern Hemisphere Ground Ozone Stations (NHGOS) vs. GOME data. Both analyses consistently showed an offset in the value of the total column ozone between the datasets [for analyses a) 35 Dobson Units (DU); and for analyses b) 10 DU], despite a good correlation between the spatial and temporal features of the datasets. A noticeably poor correlation in the latitudinal bands 10°/20° North and 10°/20° South was observed—the reasons for which are discussed. The smallest region which was statistically representative of the ozone value correlation dataset of TOVS data at NHGOS and GOME level‐2 data was determined to be a region that was enclosed by effective radius of 0.75 arc‐degrees (83.5km).
Geotail observations of ion velocity distributions with multi‐beam structures in the post‐plasmoid current sheet
Authors: Tu J.‐N. , Mukai T. , Hoshino M. , Saito Y. , Matsuno Y. , Yamamoto T. , Kokubun S.
Published: February 2004

Two unusual ion velocity distributions were observed by the Geotail LEP instrument in the distant current sheet just after the passage of plasmoids. These ion distributions are particular in that in each case there are two or three well‐ordered, cold and dense beams embedded in a hot, tenuous component. The beams are roughly aligned in the convection direction and flow duskward and tailward with large velocities. When those distributions were observed, the spacecraft was very close to the middle plane of the current sheet, where the Bx and Bz components of the magnetic field were quite small and at the same time Bx was the dominant component. The present observations reveal much more complicated pattern of the ion velocity distributions in the current sheet during the course of substorm than as expected.
Long‐term variation in TOMS ozone over 60–70°S
Authors: Zou Han , Gao Yongqi
Published: February 2004

This article discusses the long‐term variations, seasonal cycle, trends, Quasi‐biennial Oscillation (QBO) and El Niño‐Southern Oscillation (ENSO), in total ozone over 60–70°S latitude zone, using data from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus 7 (version 7). The study is focused on the zonal distribution of the above long‐term variations in this latitude zone. Recognizably different characteristics are revealed in the ozone variations over the West Antarctic from those over the East Antarctic. The discussion of these differences notes the possible impact of the land‐sea contrast in the West Antarctic on the ozone variations.
Estimation of lateral hydrothermal flow distance from spatial variations in oceanic heat flow
Authors: Stein Carol A. , Stein Seth
Published: February 2004

Measured heat flow in young oceanic crust is generally less than predicted by lithospheric cooling models, even where thick sediments had been expected to isolate the crust from the ocean and hence eliminate hydrothermal heat transfer. At isolated sites with basement outcrops or topographic highs, however, heat flow sometimes exceeds the model predictions. It thus appears that water migrates and upwells at distant sites, hence transferring heat laterally. Simple estimates of the lateral flow distance can be made when heat flow data have adequate areal sampling. The data can be parametrized by distance from the presumed upwelling site, and integrated to estimate the area from which heat must be transferred. Along the Juan de Fuca ridge, the minimum effective lateral flow distances are 8 km for 3–5 Ma crust, and 2 km for younger (< 1 Ma) crust.
Possible change in climate parameters with zero net radiative forcing
Authors: Sinha Ashok , Harries John E.
Published: February 2004

There has been much debate over the possibility that radiative cooling due to anthropogenic aerosols may substantially offset global warming from the enhanced greenhouse effect of raised atmospheric carbon dioxide levels. It is accepted that regional climates may alter if the net local forcing is non‐zero. However, recent studies have alluded to the possibility of climate change even when the net radiative forcing from aerosols and carbon dioxide is very small. We present calculations demonstrating that even when the net radiative forcing of climate from simultaneous aerosol and CO2 perturbations at all locations is zero, heating rates within the atmosphere and surface radiation characteristics may still be substantially altered. Given the effect of radiative heating on atmospheric motions, and the dependence of biological systems on insolation, we conclude that the effects of possible climate change even when the mean radiative forcing at all locations is unchanged need to be quantified. Although an important quantity, the radiative forcing of climate should not be used as the sole indicator of possible climate change.
A model for lower hybrid wave excitation compared with observations by Viking
Authors: Khazanov G. V. , Liemohn M. W. , Krivorutsky E. N. , Horwitz J. L.
Published: February 2004

The mechanism of lower hybrid wave (LHW) excitation due to the O+ relative drift in a plasma subjected to low‐frequency waves (LFWs) is used for analysis of Viking satellite data for events in the cusp/cleft region. In some cases, such a mechanism leads to LHW energy densities and ion distribution functions close to those observed, suggesting the proposed mechanism is a plausible candidate to explain certain classes of LHW generation events in space plasmas.
Structural evolution of Western Fortuna Tessera, Venus
Authors: Pritchard M. E. , Hansen V. L. , Willis J. J.
Published: February 2004

Western Fortuna Tessera, Ishtar Terra, records polyphase deformation. Structures include: ribbons forming long, narrow, steep‐sided troughs that reflect surface layer extension; N‐trending folds related to Maxwell Montes deformation; short, wide, NW‐trending graben that reflect late local extension; and, within the southwestern map area, gentle, E‐trending warps, which postdate ribbon structures. Flood lava flows postdate deformation. Ribbon structures change orientation radially from NNE to WNW. These observations caution against the correlation of Fortuna Tessera with tessera elsewhere on Venus and against the proposal that tessera forms a global stratigraphic layer.
Eleven year cycle of dust concentration variability observed in the dust profile of the GISP2 Ice core from central Greenland: Possible solar cycle connection
Authors: Ram Michael , Stolz Michael , Koenig Gerson
Published: February 2004

We have re‐examined the dust record from the GISP2 ice core retrieved from central Greenland and found that the background dust concentration is modulated with a period of 11 years all the way back to ice from at least 100,000 yrs BP. The only known, relevant, naturally occurring phenomenon with such a period is the well‐known solar cycle. We believe that the background modulation we observe is related to the solar cycle and discuss this hypothesis.
Effect of frictional healing on the scaling of seismicity
Authors: Wang Jeen‐Hwa
Published: February 2004

A 1D Burridge‐Knopoff model, with velocity‐dependent friction, is used to study the effect of frictional healing on the scaling of seismicity. When a mass element stops motion, the frictional sliding strength in the model is considered to be linearly increased at a healing rate, h, from dynamic friction to static friction. The ratio of the frictional healing rate to the tectonic loading rate, LV, is considered to be a factor. Results show that when h/LV>1, the frequency‐magnitude (FM) distributions of model events exhibit a Gutenberg‐Richter‐type scaling, and the related b‐value is relatively insensitive to h/LV. When h/LV=1, the pattern of the FM relation and the related b‐value somewhat change. However, the ratio h/LV is only a minor factor in affecting the FM scaling.
Whistler triplets, bands, and fine structures observed in a low latitude ground station
Authors: Singh Birbal , Singh Raghuraj , Singh Rajvir
Published: February 2004

Whistler triplets, banded whistlers, and temporal fine structure in whistlers observed for the first time in a low latitude ground station at Agra (geomag. lat. 17° 1′ N , L = 1.15) are reported here. We show that the whistler triplets recorded by us are the one hop multipath whistlers which propagated to the ground under the influence of the equatorial anomaly in the dayside of the earth and reached our station in the earth‐ionosphere waveguide mode of propagation. The similar time intervals between the successive triplets are due to similar time intervals between the causative lightning discharges. The banded structure (showing frequency‐ fine structure) and temporal fine structure obseved in groups of high dispersion whistlers are interpreted in terms of the effects of multistroke lightning.
The Lyman‐α line from the solar wind acceleration region: Results from an eight‐moment approximation two‐fluid solar wind model
Authors: Olsen Espen Lyngdal
Published: February 2004

We investigate neutral hydrogen in an eight‐moment, two‐fluid, high speed solar wind model. In this model the proton heat flux decreases rapidly in the solar wind acceleration region, and extended coronal heating of the proton gas leads to high coronal proton temperatures and large solar wind flow speeds. The properties of the Lyman‐α line from the neutral hydrogen in two such models are studied. We show that the temperature maximum in the corona inferred from the observed Lyman‐α line may be more than 20% lower than the proton temperature maximum.
Heterogeneous PSC ozone loss during an ozone mini‐hole
Authors: Grewe Volker , Dameris Martin
Published: February 2004

An upper tropospheric high pressure system resulting in large scale ascent even in the stratosphere, is investigated by means of simulations using the coupled dynamic‐chemical general circulation model ECHAM3/CHEM. These simulations show two kinds of impact on stratospheric ozone. Dynamic redistribution caused by ascent leads to a rapid decrease of total ozone, i.e. an ozone mini‐hole. The formation of polar stratospheric clouds caused by adiabatic cooling leads to a chlorine activation at the location of the ozone mini‐hole. The resulting chemical ozone depletion occurs downstream of the ozone mini‐hole, due to the stratospheric circulation.
The frequency and size of ozone “mini‐hole” events at northern midlatitudes in February
Authors: McCormack John P. , Hood Lon L.
Published: February 2004

Ozone “mini‐holes” represent regions of low total ozone (<300 D U) that persist for several days over extratropical latitudes in winter. These events are usually associated with breaking Rossby waves in the upper troposphere that allow poleward injections of ozone‐poor, low potential vorticity (PV) tropospheric air into the lower stratosphere. Using daily TOMS total ozone data together with daily PV maps derived from reanalyzed NCEP data, the interannual variability of ozone mini‐hole events in the northern hemisphere is investigated for one winter month (February) during the 1979–1993 period. For this purpose, the total area of anomalously low total ozone and PV between 40°N and 50°N and between 90°W and 90°E is computed for February of each year. The low‐ozone and low‐PV areas both peak during February of 1988, 1989, and 1990, coincident with the lowest monthly zonal mean total ozone values observed at northern midlatitudes prior to the Pinatubo eruption.
Evidence for sulfuric acid coated particles in the Arctic air mass
Authors: Cantrell Will , Shaw Glenn , Benner Richard , Veazey David
Published: February 2004

In this paper, we discuss results from an experiment conducted on natural aerosol in a clean Arctic environment during the spring. The aerosol behaved as though coated with a volatile film, possibly of sulfuric acid. The thermography of the aerosol observed is consistent with a small fraction of the sulfate being neutralized by ammonium as evidenced by an ammonium to sulfate ratio of 0.14. The volatility behavior of the aerosol is also consistent with an increase in the ammonium to sulfate ratio to 0.39 over one day. The change in the ammonium to sulfate ratio and aerosol volume is consistent with 10 pptv of ammonia in the atmosphere being lost to the aerosol during the period. These values are consistent with others observed in the Arctic winter.
Quantifying the Pinatubo volcanic signal in south polar snow
Authors: Cole‐Dai Jihong , Mosley‐Thompson Ellen , Thompson Lonnie G.
Published: February 2004

Recent snow and firn core samples from South Pole contain increased sulfate (SO42−) concentrations during 1992–1994 as a result of the June 1991 Pinatubo eruption and the August 1991 Cerro Hudson eruption in Chile. Traces of Pinatubo tephra (volcanic ash) were identified in the 1993 and 1994 snow layers, supporting the conclusion that increased SO42− in 1993–1994 is from the Pinatubo eruption. Although the Pinatubo eruption preceded Hudson, its SO42− signal in south polar snow follows and is resolved from that of Hudson. The deposition of the Pinatubo SO42− aerosol was delayed due to the long transport to the high southern latitudes and its initial existence at high altitudes in the Antarctic atmosphere. Multi‐year, multi‐site sampling demonstrates that the volcanic signals are well preserved and spatially consistent. Measurements on 2 firn cores show that the South Pole SO SO42− flux from Pinatubo is 10.9±1.2 kg km−2 over 2.2 years, while the Hudson flux is 3.2±0.6 kg km−2 in 1.1 years. These results, when combined with satellite‐determined Pinatubo sulfur dioxide (SO2) emission, make it possible to link quantitatively the atmospheric aerosol mass loading from a low‐latitude volcanic eruption to its signal in polar ice cores.
GRL Special Section: WOCE Indian Ocean Expedition
Authors: Ffield Amy
Published: February 2004

The World Ocean Circulation Experiment (WOCE) is the most ambitious global oceanographic program ever undertaken. The program combines in situ measurements of unprecedented quality and coverage with state‐of‐the‐art satellite observations and modeling. The Indian Ocean expedition is one part of the WOCE field endeavor, with other expeditions covering the Pacific, Atlantic, and Southern Oceans. Focusing on 1995, the Indian Ocean was intensively sampled by the international oceanographic community using a fleet of oceanographic research vessels and relying on the cooperation and resources of many countries (Figure 1). In technique and scope the expedition far surpasses the last great coordinated Indian Ocean effort, the International Indian Ocean Expedition of the 1960s [Wyrtki, 1971].
Infrared glow above thunderstorms?
Authors: Picard R. H. , Inan U. S. , Pasko V. P. , Winick J. R. , Wintersteiner P. P.
Published: February 2004

Sustained heating of lower ionospheric electrons by thundercloud fields, as recently suggested by Inan et al. [1996], may lead to the production of enhanced infrared (IR) emissions, in particular 4.3‐µm CO2 emission. The excitation rate for N2(v) via electron collisions is calculated using a new steady‐state two‐dimensional electrostatic‐heating (ESH) model of the upward coupling of the thundercloud (TC) electric fields. The vibrational energy transfer to CO2 and 4.3‐µm radiative transfer are then computed using a line‐by‐line non‐LTE (non‐local thermodynamic equilibrium) radiation model. Limb‐viewing radiance profiles at 4.3‐µm and typical radiance spectra are estimated for five different TC charge distributions and ambient ionic conductivities. Broadband 4.3‐µm enhancements of greater than a factor of two above ambient nighttime levels are predicted for tangent heights (TH) in the range ∼80 to >130 km for the most perturbed case, with larger enhancements in selected narrower spectral regions. The predicted IR enhancements should be observable to an orbiting IR sensor.