bluuebunny/crossref_metadata_2025 huggingface dataset:
The 11 December, 1995 earthquake (Mw=6.4): Implications for the present‐day relative motion on the Rivera‐Cocos Plate Boundary
Authors: Suárez Gerardo , Escobedo David , Bandy William , Pacheco Javier F.
Published: September 2002

The 11 December, 1995 earthquake is the largest and best constrained instrumentally recorded event which has occurred on the Rivera‐Cocos plate boundary. The reported focal mechanism for this event indicates almost pure strike‐slip faulting with nodal planes oriented north‐south and east‐west. A visual inspection shows that the seismograms recorded world‐wide strongly suggest a directivity effect indicative of a rupture propagating eastward from the epicenter. This observation is confirmed by a directivity analysis which shows a sharp reduction in the difference between observed and synthetic seismograms when the rupture direction is at an azimuth of approximately 90°. These results indicate that the east‐west trending nodal plane of the earthquake of 11 December, 1995 is the actual fault plane. Considering that this is the largest instrumentally recorded earthquake in the region, it strongly suggests that the relative motion of the Rivera plate with respect to the Cocos plate takes place along east‐west oriented faults, and that the sense of motion is right‐lateral, strike‐slip.
Constraints on ocean volume change since the Archean
Authors: Harrison C. G. A.
Published: September 2002

Water may be added to Earth's surface by the bombardment of large numbers of small comets, increasing free water on Earth's surface & deepening the oceans. Continental freeboard is tied to the ocean surface, because of the balance between erosion & mountain building. Addition of water will also affect continental thickness & area. I calculate the effect of increasing ocean volume on the balance between continental & oceanic area. One model also includes crustal volume growth. Significant oceanic depths are known to exist during the Archean, because sulphide deposits requiring deep oceans occur in greenstone belts. These observations prohibit the constant addition of large quantities of water (comparable to the present day ocean volume) throughout Earth history, but smaller quantities could be added.
Evidence for slow slip following a moderate‐size earthquake (Mw=5.7) in a subducting plate
Authors: Takai Kaori , Kumagai Hiroyuki , Fujii Naoyuki
Published: September 2002

Postseismic deformation following the Aichiken‐Tobu earthquake (Mw =5.7), which occurred on March 16, 1997 in central Japan, was detected by strainmeter networks. We show that this deformation can be consistently explained by slow slip on the fault, total amount of which is comparable to the high‐speed (coseismic) slip. The time constant of the slow after‐slip fitted to a logarithmic function is estimated to be roughly 0.25 hour. Comparison of this feature with that of Sanriku‐Haruka‐Oki earthquake (Mw=7.6), in which significant slow slip was detected by a GPS network, suggests a direct proportionality of the time constant and seismic moment of coseismic slip. We could detect very small signals (strain between 10−7 and 10−8) associated with this moderate‐size earthquake due to the high sensitivity of strainmeters. Strainmeters are especially useful in detecting afterslip from smaller earthquakes.
Deformation across the Alaska‐Aleutian Subduction Zone near Kodiak
Authors: Savage J. C. , Svarc J. L. , Prescott W. H.
Published: September 2002

The Kodiak‐Katmai geodetic array, nine monuments distributed along a profile trending north‐northwestward across Kodiak Island and the Alaska Peninsula, was surveyed in 1993, 1995 and 1997 to determine the deformation at the Alaska‐Aleutian subduction zone. Velocities on Kodiak island measured relative to the stable North American plate decrease with distance from the Alaska‐Aleutian trench (distance range 106 to 250 km), whereas no appreciable deformation was measured on the Alaska Peninsula (distances 250 to 370 km from the trench). The measured deformation is reasonably well predicted by the conventional dislocation representation of subduction with the model parameters determined independently (i.e., not simply by fitting the observations). The deformation of Kodiak Island is in striking contrast to the very minor deformation measured in the similarly situated Shumagin Islands, 450 km southwest of Kodiak along the Alaska‐Aleutian trench.
Influence of Asian emissions on the composition of air reaching the north western United States
Authors: Berntsen Terje K. , Karlsdóttir Sigrún , Jaffe Daniel A.
Published: September 2002

A global 3‐D CTM has been used to study the impact of current and future emissions from Asia on CO, PAN and O3 across the North Pacific. Recent measurements from Washington State have been used to verify the model results with respect to average concentrations as well as amplitude of perturbations during episodic events of strong Asian influence. By performing CTM experiments with and without anthropogenic emissions from Asia, we find that there is a significant contribution from Asian sources in the air arriving to the North Western United States, especially during spring. The mean contribution, which can not easily be inferred from the available measurements, during spring are 34 ppbv, 26 pptv and 4 ppbv for CO, PAN and O3, respectively. The maximum enhancements caused by Asian sources during episodes are 42 ppbv, 75 pptv, and 7.5 ppbv, respectively. The amplitude of the perturbations during short term (2–5 days) episodes of strong Asian influence are quite similar to springtime Asian pollution events which have recently been observed on the west coast of Washington state. A doubling of the current Asian emissions in the model yields significant enhancements in all species, though not necessarily in a linear manner.
Mirror mode structures observed in the dawn‐side magnetosheath by Equator‐S
Authors: Lucek E. A. , Dunlop M. W. , Balogh A. , Cargill P. , Baumjohann W. , Georgescu E. , Haerendel G. , Fornacon K. ‐H.
Published: September 2002

The Equator‐S satellite was ideally positioned to make magnetic field observations in the dawn‐side magnetosheath, relatively close to the magnetopause. The magnetosheath data were particularly rich in compressional signatures, consistent with mirror mode structures, which occurred during ∼30% of orbits crossing into the magnetosheath. In most, although not all cases, strongly compressive signatures extended up to the magnetopause boundary, with no increase in the underlying magnetic field magnitude on the time scale of ten to thirty minutes. The proximity and character of mirror‐like fluctuations near the magnetopause suggest that in the dawn‐side magnetosheath the plasma depletion layer (PDL) is of narrower extent than is generally observed closer to the subsolar point, or is absent.
Simulation of an abrupt change in Saharan vegetation in the Mid‐Holocene
Authors: Claussen Martin , Kubatzki Claudia , Brovkin Victor , Ganopolski Andrey , Hoelzmann Philipp , Pachur Hans‐Joachim
Published: September 2002

Climate variability during the present interglacial, the Holocene, has been rather smooth in comparison with the last glacial. Nevertheless, there were some rather abrupt climate changes. One of these changes, the desertification of the Saharan and Arabian region some 4–6 thousand years ago, was presumably quite important for human society. It could have been the stimulus leading to the foundation of civilizations along the Nile, Euphrat and Tigris rivers. Here we argue that Saharan and Arabian desertification was triggered by subtle variations in the Earth's orbit which were strongly amplified by atmosphere‐ vegetation feedbacks in the subtropics. The timing of this transition, however, was mainly governed by a global interplay between atmosphere, ocean, sea ice, and vegetation.
An improvement of June–September rainfall forecasting in the Sahel based upon region April–May moist static energy content (1968–1997)
Authors: Fontaine Bernard , Philippon Nathalie , Camberlin Pierre
Published: September 2002

This study provides statistical evidence that June–September Sahelian rainfall hindcasts currently based on oceanic thermal predictors apprehend more the negative trend than the interannual rainfall variations. Four physically meaningful predictors of June–September Sahel rainfall are first selected through the near‐surface April–May information and several experimental hindcasts provided. We then discuss the skills achieved using regression techniques and cross‐validated discriminant functions. In that context, 8/11 of the driest seasons and 8/10 of the wettest are correctly predicted. Finally using completely independent training and working periods we show that better and significant hindcast skills are obtained by adding regional moist static energy predictors to the large‐scale sea surface temperature information.
The climatological annual cycle of satellite‐derived phytoplankton pigments in the Alboran Sea
Authors: Garcia‐Gorriz Elisa , Carr Mary‐Elena
Published: September 2002

The circulation and upwelling processes that control the phytoplankton distribution in the Alboran Sea (western Mediterranean) are examined from a climatological perspective for the first time. To characterize the annual cycle of the near‐surface phytoplankton patterns, we analyze the monthly distributions of pigments from the Coastal Zone Color Scanner (CZCS). Two regimes occur: a fall‐to‐winter bloom (November–March) and a non‐bloom period (May–September). These regimes differentiate the basin from other parts of the western Mediterranean, where a significant spring bloom occurs. The newest ocean color data sets available today from the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) and the Ocean Color and Temperature Scanner (OCTS) fall within this annual progression. The combined interaction of seasonal stratification, coastal and gyre‐induced upwelling, and horizontal advection control the near‐surface pigment distribution in Alboran, while light availability does not determine the seasonal cycle of pigments.
OH and HO2 chemistry in the North Atlantic free troposphere
Authors: Brune W. H. , Tan D. , Faloona I. F. , Jaeglé L. , Jacob D. J. , Heikes B. G. , Snow J. , Kondo Y. , Shetter R. , Sachse G. W. , Anderson B. , Gregory G. L. , Vay S. , Singh H. B. , Davis D. D. , Crawford J. H. , Blake D. R.
Published: September 2002

Interactions between atmospheric hydrogen oxides and aircraft nitrogen oxides determine the impact of aircraft exhaust on atmospheric chemistry. To study these interactions, the Subsonic Assessment: Ozone and Nitrogen Oxide Experiment (SONEX) assembled the most complete measurement complement to date for studying HOx (OH and HO2) chemistry in the free troposphere. Observed and modeled HOx agree on average to within experimental uncertainties (±40%). However, significant discrepancies occur as a function of NO and at solar zenith angles >70°. Some discrepancies appear to be removed by model adjustments to HOx‐NOx chemistry, particularly by reducing HO2NO2 (PNA) and by including heterogeneous reactions on aerosols and cirrus clouds.
Ion layer separation and equilibrium zonal winds in midlatitude sporadic E
Authors: Earle G. D. , Kane T. J. , Pfaff R. F. , Bounds S. R.
Published: September 2002

In‐situ observations of a moderately strong midlatitude sporadic‐E layer show a separation in altitude between distinct sublayers composed of Fe+, Mg+, and NO+. From these observations it is possible to estimate the zonal wind field consistent with diffusive equilibrium near the altitude of the layer. The amplitude of the zonal wind necessary to sustain the layer against diffusive effects is less than 10 m/s, and the vertical wavelength is less than 10 km.
Perspectives on NO, NOy, and fine aerosol sources and variability during SONEX
Authors: Thompson Anne M. , Sparling Lynn C. , Kondo Yutaka , Anderson Bruce E. , Gregory Gerald L. , Sachse Glen W.
Published: September 2002

Distributions of upper tropospheric tracer data on each of the 14 science flights of SONEX (SASS [Subsonics Assessment] Ozone and Nitrogen Oxides Experiment) provide a statistical overview of NO, NOy and fine aerosol variability during SONEX (an aircraft mission conducted in October and November 1997). The wide range of variability of NO from all sources provides a perspective on the aircraft perturbation. Background distributions of NOy are somewhat elevated inside flight corridors relative to outside; fine aerosol and NO/NOy in and out of corridors are similar. The potential vorticity of air sampled during SONEX is low relative to the NAFC (North Atlantic Flight Corridor) as a whole, due either to advection of lower latitude air into the corridor or biases in sampling to avoid the stratosphere. High NO/NOy (>0.4) from fresh lightning and aircraft sources was usually associated with pv much lower than the NAFC as a whole. Air masses identified as tropospheric by a low ozone criterion nevertheless have high pv, a marker for stratospheric air. Thus, stratospheric and surface sources also contribute to overall variability. A statistically robust assessment of the relative aircraft NO contribution during SONEX, based on data alone, is unlikely, given the mixture of other NO sources within which the aircraft signal is embedded. This underscores the need for more data and modeling studies.
Multiple‐point electron measurements in a nightside auroral arc: Auroral turbulence II particle observations
Authors: Lynch K. A. , Pietrowski D. , Torbert R. B. , Ivchenko N. , Marklund G. , Primdahl F.
Published: September 2002

We report here three‐point measurements of bursty, velocity‐dispersed, field‐aligned electron precipitation at the poleward edge of a northward‐moving, post‐breakup, nightside auroral arc. The three‐point measurement allows detection of the proper motion of the inverted‐V arc, which is shown to be 550 m/sec northward. The velocity dispersion patterns are fitted to find the source altitude of the precipitation bursts as a function of distance from the poleward edge of the arc. These source points are interpreted to trace out the low‐altitude boundary of the inverted‐V potential drop, which is seen to rise both in time, and in the northward direction. The precipitation bursts under the inverted‐V are seen to have an arc‐aligned velocity which varies with time, and which is consistent with the measured E × B local drift speed.
On overestimation of tropical precipitation by an atmospheric GCM with prescribed SST
Authors: Kitoh Akio , Arakawa Osamu
Published: September 2002

We investigate how an atmospheric general circulation model (AGCM) can reproduce atmospheric aspects of climate, when the boundary conditions are prescribed. The AGCM is integrated with sea surface temperature (SST) specified from an integration of a coupled general circulation model (CGCM). A systematic difference in the mean climate is found between the AGCM and the CGCM in the tropical Pacific. This difference is apparent when and where local SST is warmest. In the CGCM, precipitation does not last long due to SST and cloud‐radiation feedback. Precipitation in the AGCM, however, tends to persist longer. Results of this experiment imply that caution is needed when using an AGCM with boundary conditions derived from a CGCM for climate change studies.
Self‐consistent model of the solar wind interaction with three‐component circumsolar interstellar cloud: Mutual influence of thermal plasma, galactic cosmic rays, and H atoms
Authors: Myasnikov Artyom V. , Alexashov Dmitrii B. , Izmodenov Vladislav V. , Chalov Sergei V.
Published: September 2002

In this paper we continue our study of the galactic cosmic ray (GCR) influence on the structure of the heliospheric interface plasma flow [Myasnikov et al., this issue]. The model presented here is more realistic and takes the mutual influence of plasma, neutral, and cosmic ray components into account self‐consistently. In the model, GCRs are described hydrodynamically under the assumption that their mass density is negligible; while neutrals are described kinetically. We explore the GCR influence on the heliospheric interface plasma structure by varying the diffusion coefficient, cosmic ray pressure, and adiabatic index. The problem is studied numerically, using the global iterations that couple the soft fitting technique for describing the plasma and GCR components and Monte Carlo simulations for H atoms. A strong GCR modulation is found in the heliospheric interface. At the same time, the GCR influence on the plasma flow is negligible as compared with the influence of H atoms. The exception is the bow shock, a structure which can be strongly modified by the cosmic rays. The Baranov‐Malama model is therefore acceptable for interpretation of the physical processes in the heliosphere as long as the processes are not related to the bow shock structure. Although the simplest model of the cosmic ray transport is good enough to estimate GCR influence on the plasma and atom distributions in the heliospheric interface, more advanced models should be used to interpret the observed GCR spectra.
Findings concerning the positions of substorm onsets with auroral images from the Polar spacecraft
Authors: Frank L. A. , Sigwarth J. B.
Published: September 2002

High‐resolution global images of Earth's auroras in the visible emissions of atomic oxygen at 557.7 nm with a camera on board the Polar spacecraft were used to determine the magnetic latitude of the auroral arc which brightens at the onset of a substorm. Six events were analyzed: an intensification and an onset on December 17, 1997, three substorms on January 6, 1998, and a substorm on March 1, 1999. The Tsyganenko [1989] model for the global magnetic field was used to map the field lines threading the center of the auroral arc to equatorial distances. During the period of relative magnetic quiescence on December 17 the equatorial distances were ∼9 RE. During the magnetically disturbed periods of January 6 and March 1 the magnetic field lines for the auroral onset brightenings were mapped to equatorial distances in the range of 5–7 RE, and thus in the region of the extraterrestrial ring current. The equatorial position of the field lines was independently verified for the substorm on March 1 by observing the atmospheric footprint of proton precipitation from the ring current. This footprint was seen in the emissions of atomic hydrogen at 656.3 nm. The onset arc was located near the earthward edge of the ring current at magnetic shell parameter L = 4 RE and within 1 RE of the equatorial position computed with the global magnetic field model. The equatorial distance of the elusive substorm onset is important in establishing plasma parameters for quantitative evaluation of candidate mechanisms for the explosive instability that initiates substorms.
Temperature dependence of the reaction N2(A 3∑u+)+O in the terrestrial thermosphere
Authors: Hill Steven M. , Solomon Stanley C. , Cleary David D. , Broadfoot A. Lyle
Published: September 2002

Previous models for dayglow and auroral emissions of the N2(A 3∑u+→X 1∑g+) Vegard‐Kaplan (VK) bands and O(1S) lines, when based on laboratory rate coefficients, disagree with observations. The problem has two parts: the overall rate of N2(A)+O and the state‐specific yield of O(1S). Resolving these discrepancies should yield more accurate determinations of atomic oxygen density by remote sensing of the 2972 and 5577 Å lines. To solve the problem, the sources and sinks Of O(1S) are considered using dayglow observations from 105 to 315 km and a numerical model. Line and band intensities are extracted from the data using a multiple regression fit to synthetic spectra. A photoelectron and photochemical model is used to analyze the resulting vertical emission profiles. N2 Second Positive (2P) altitude profiles indicate that photoelectron excitation of the N2 triplet system is modeled with an absolute uncertainty of ±23%. The VK/2P intensity ratio suggests that laboratory rate coefficients for the reaction N2(A; v'=0,1,2) + O should be increased by a factor of 1.74 to 2.34. However, the laboratory rates were measured at room temperature. When the effect of high thermospheric temperatures on collision frequency is accounted for, the rate coefficients for v' =0, 1, and 2 are found to be (3.4±0.8)×10−11(T/298)1/2, (5.6±1.3)×10−11(T/298)1/2, and (4.8±1.2)×10−11(T/298)1/2 cm3S−1. At 298 K, the v'=0 and 2 values are within 5% of the laboratory values, but for v' =1 the value is 40% larger than the laboratory value. The effective quantum yield of O(1S) by N2(A)+O is found to be 0.47+0.17. The observations support a photoelectron cross section for O(1S) that is consistent with laboratory measurements, but about 2.0 times larger than theoretical calculations.
Thin current sheet embedded within a thicker plasma sheet: Self‐consistent kinetic theory
Authors: Sitnov M. I. , Zelenyi L. M. , Malova H. V. , Sharma A. S.
Published: September 2002

A self‐consistent theory of thin current sheets, where the magnetic field line tension is balanced by the ion inertia rather than by the pressure gradient, is presented. Assuming that ions are the main current carriers and their dynamics is quasi‐adiabatic, the Maxwell‐Vlasov equations are reduced to the nonlocal analogue of the Grad‐Shafranov equation using a new set of integrals of motion, namely, the particle energy and the sheet invariant of the quasi‐adiabatic motion. It is shown that for a drifting Maxwellian distribution of ions outside the sheet the equilibrium equation can be reduced in the limits of strong and weak anisotropy to universal equations that determine families of equilibria with similar profiles of the magnetic field. In the region Bn/B0 < vT/vD ≪ 1 (B0, Bn, vD, and vT are the magnetic fields outside the sheet and close to its central plane, the ion drift velocity outside the sheet, and the ion thermal velocity, respectively) the thickness of such similar profiles is of the order of (vT/vD)1/3 ρ0, where ρ0 is the thermal ion gyroradius outside the sheet. In the limit of weak anisotropy (vT/vD ≫ 1) the self‐consistent current sheet equilibrium may also exist with no indications of the catastrophe reported earlier by Burkhart et al. [1992a]. On the contrary, it is found that in this limit the magnetic field profiles again become similar to each other with the characteristic thickness ∼ ρ0. The profiles of plasma and current densities as well as the components of the pressure tensor are calculated for arbitrary ion anisotropy outside the sheet. It is shown that the thin current sheet for the equilibrium considered here is usually embedded into a much thicker plasma sheet. Moreover, in the case of weak anisotropy the perturbation of the plasma density inside the sheet is shown to be proportional to the parameter vD/vT, and as a result the electrostatic effects should be small, consistent with observations. This model of the thin current sheet satisfies the basic force balance equations including the marginal fire‐hose condition and preserves the nonguiding center effects including the pressure nongyrotropy.
Field patterns of Alfven wave resonance cones
Authors: Singh Nagendra
Published: September 2002

One of the fascinating observations from recent rocket and satellite experiments is on the solitary Alfven waves (SAW). SAWs are electromagnetic structures with a spatial width ∼1 km across the Earth's magnetic field B0. The measurements from Freja have revealed that the SAWs are not simply the product of an obliquely propagating plane Alfven wave; instead, they are the radiation (field) patterns of distant Alfven wave sources (AWS) oscillating at frequencies ω < Ωi, the ion cyclotron frequency. The field pattern of an AWS is highly directional in the form of a cone aligned with B0, and with half‐cone angle θc, less than a milliradian or so when ω ≪ Ωi Such radiation patterns are known as resonance cones (RC) or more specifically Alfven wave RC (AWRC), and they are intimately determined by the allowable directions of the group‐velocity vector in the anisotropic plasma. We have studied here the group‐velocity pattern of shear Alfven waves including both warm plasma and inertial effects. It is found that both the kinetic and the inertial Alfven waves show group‐velocity resonance‐cone patterns. Along any direction within the cone there are two group‐velocity vectors having wave vectors with different directions and magnitudes, giving rise to a slow and a fast wave contributing to the propagation. The RC field pattern of a filamentary field‐aligned current source oscillating at frequencies ω < Ωi, is studied. The far‐field pattern shows that within the cone there are two waves propagating at any angle θ < θc as determined by the group‐velocity directions; these waves produce an interference pattern. Near RC surface the interference pattern is given by the Airy function. The scaling laws for the interference pattern and nonlinear effects arising from the pondermotive force are analyzed. Possible applications of the AWRC field pattern, its scaling laws, and the associated nonlinear effects to SAWs are discussed.
Modeling energetic electron precipitation near the South Atlantic anomaly
Authors: Abel Bob , Thorne Richard M.
Published: September 2002

A numerical simulation of electron pitch angle scattering in an asymmetric magnetic field environment has been applied to the Earth's inner radiation belt to obtain a global pattern of energetic electron precipitation. Under conditions of weak pitch angle scattering, which characterize the region L ≤ 2, the flux of electrons precipitated into the atmosphere is strongly localized to a longitudinal range (±15°) centered near the South Atlantic anomaly (SAA), where the surface magnetic field intensity is weakest and the bounce loss cones are exceptionally large. For realistic average rates of pitch angle scattering, the energy deposition rates, obtained from the modeled precipitation flux patterns, yield peak ionization rates in the middle mesosphere (near 75 km) between 0.1 to 1 ions cm−3 s−1 over the L range 1.35–1.95, respectively. This indicates that precipitating electrons should be a prominent mesospheric ionization source near the SAA but relatively insignificant elsewhere.
A technique to investigate plasma mass density in the topside ionosphere using ULF waves
Authors: Price I. A. , Waters C. L. , Menk F. W. , Bailey G. J. , Fraser B. J.
Published: September 2002

The relatively cold core plasma density in the region where the ionosphere mixes with the plasmasphere is difficult to probe experimentally. It is shown that resonances of ULF magnetohydrodynamic waves can provide unique information on plasma mass density in the region where the ionosphere and plasmasphere merge. The technique depends on the detection of harmonics of ULF field line resonances and allows the determination of plasma mass densities at discrete locations along a magnetic field line without assuming any function for plasma distribution along the field. The plasma mass densities obtained from ULF harmonics at L=1.8 are compared with several plasma mass density models of this region. In addition to describing and illustrating the technique, the method is critically examined for its limitations. These include the finite number of ULF harmonics that can be detected, the complexity of the nonlinear solving scheme, the consequences of using the method at larger L values, and approximating the system of equations with a finite difference scheme. It is shown that the technique can provide independent estimates of plasma mass densities at discrete, magnetic field‐aligned altitudes, which gives an additional experimental check on theoretical models that predict the dynamics of plasma from the topside ionosphere to the inner plasmasphere.
Simulation of the heliosphere: Generalized charge‐exchange cross sections
Authors: McNutt Ralph L. , Lyon John , Goodrich Charles C.
Published: September 2002

The interaction of the solar wind with the very local interstellar medium depends strongly on charge exchange between the neutral and ionized hydrogen outside of the heliopause. While the protons are diverted by the heliosphere obstacle, the neutral atomic hydrogen sees no immediate change in environment and continues its free streaming. The ensuing difference in flow velocities results in resonant charge exchange that tends to divert the neutral flow around the heliosphere as well. Large mean free paths strictly require a kinetic approach, yet some idea of the interaction can be gleaned from a much less computationally complex fluid treatment. We show that the momentum‐ and energy‐exchange operators between the charge and neutral fluids can be evaluated in a near‐exact fashion for the charge‐exchange cross section. This new formulation can be used both to provide a better fluid description and to test how robust the fluid picture is.
Electrostatic oscillations due to filamentary structures in the magnetic‐field‐aligned flow: The ion‐acoustic branch
Authors: Gavrishchaka Valeriy V. , Ganguli Supriya B. , Ganguli Gurudas I.
Published: September 2002

Recent space missions such as FAST and Freja report highly structured plasma flows along the magnetic field. Electrostatic fluctuations that can be supported by such inhomogeneous parallel flows are investigated. It is found that even a small transverse gradient in parallel flow can significantly reduce the critical value of the relative ion‐electron field‐aligned drift for the current‐driven electrostatic ion acoustic modes. It is also shown that the shear‐modified ion acoustic mode can be excited without any relative field‐aligned drift provided that the flow gradient is sufficiently strong. The instability mechanism can be described in a local limit. The new shear‐modified ion‐acoustic modes considered in this paper are shown to be different from both the nonresonant mode due to a velocity shear in the parallel flow [D'Angelo, 1965] and the resonant classical current‐driven ion‐acoustic mode [Fried and Gould, 1961]. The new modes discussed in this paper can be excited for typical ionospheric conditions and a wide range of ion‐electron temperature ratios. The reported results may explain ionospheric observations of low‐frequency ion‐acoustic‐like waves, especially for ion‐electron temperature ratios of the order of unity and larger when the critical current for the homogeneous current‐driven ion acoustic mode is significantly above the observed values. Other possible applications of our results to space plasmas are also discussed.
Electrostatic solitary waves carried by diffused electron beams observed by the Geotail spacecraft
Authors: Omura Y. , Kojima H. , Miki N. , Mukai T. , Matsumoto H. , Anderson R.
Published: September 2002

We study waveforms of electrostatic solitary waves (ESW) and corresponding electron velocity distribution functions observed by the Geotail spacecraft. When we observe a series of ESW in the plasma sheet boundary layer of the Earth's magnetotail, we find enhanced fluxes of high‐energy electrons flowing along the ambient magnetic field. We find good correlation between the propagation direction of the ESW and the direction of the enhanced high‐energy electron flux. This supports the model proposed by computer simulations that ESW are formed by the electrons modulated through the bump‐on‐tail instability. The enhanced electron flux is regarded as the diffused electron beam after the saturation of the instability. From comparison between the variation of waveforms and the velocity of the electron beams, the spatial scales and depths of the ESW potentials and their propagation directions are estimated. We found both tailward and earthward ESW in the plasma sheet boundary layer, even in the deep magnetotail.
On the dynamic cusp aurora and IMF By
Authors: Sandholt Per Even , Farrugia Charles J.
Published: September 2002

Using a new form of presentation of optical data from meridian scanning photometers, we demonstrate two important aspects of cusp dynamics concerning transients called midday auroral breakups or poleward moving auroral forms (PMAFs). Many previous studies have associated PMAFs with pulsed (in time) reconnection at the magnetopause, where these transients are thought to represent the auroral footprint of reconnected magnetic flux tubes (flux transfer events) and their motion is thought to reflect the motion of the corresponding flux tubes. Some studies have indicated that there is a prenoon‐postnoon asymmetry in the occurrence and motion pattern of PMAFs related to the east‐west component of the interplanetary magnetic field (IMF) By. In two case studies we point out the strong modulation in intensity that exists between the PMAF and the surrounding cusp emission, evident in both the red and green lines. We then show cases where the local occurrence of PMAFs is dependent on IMF By in the sense that PMAF activity at ∼1100 magnetic local time ceases when IMF By changes from positive to negative values. This is explained by reconfigurations of the magnetopause reconnection geometry and ionospheric convection pattern causing PMAFs to disappear from the field of view of the optical instruments, an interpretation which is supported by local ground magnetic field observations.
A Pc5 ULF wave with large azimuthal wavenumber observed within the morning sector plasmasphere by Sub‐Auroral Magnetometer Network
Authors: Chisham G. , Mann I. R.
Published: September 2002

In this paper we present details of an unusual Pc5 ULF wave with a large azimuthal wavenumber (m) which is observed within the plasmasphere by ground‐based magnetometers. In a previous statistical study, 129 Pc5 events were identified at midlatitudes by the U.K. Sub‐Auroral Magnetometer Network (SAMNET), but only three displayed large azimuthal wavenumbers (m > 10). Analysis of the variation of wave parameters during one of these events using a novel complex demodulation technique is presented. The technique reveals the temporal variation of wave characteristics, including the azimuthal wavenumber and wave frequency, and allows us to study the azimuthal dispersion characteristics of the wave and estimate the azimuthal phase and group speeds. The method used to estimate the azimuthal wavenumbers resolves the ambiguity resulting from aliasing, which can occur for large‐m waves observed at stations more than one azimuthal wavelength apart. The drift‐bounce resonance mechanism is discussed as a possible wave excitation mechanism for this event, and resonance with H+ and/or O+ ions at the inner edge of the ring current is presented as a possible excitation scenario.
Variations on solar condensation: Sources of interstellar dust nuclei
Authors: Ebel Denton S.
Published: September 2002

Some portion of the interstellar dust entering the heliosphere is a refractory (Ca‐Al‐Ti‐Mg‐Si‐Fe‐Ni‐Cr‐Co‐rich) component either condensed at high temperature from stellar outflows or formed in the interstellar medium (ISM). Condensation sequences for T>1100 K, assuming chemical equilibrium, are calculated for stellar outflow gas having (1) solar composition at various Ptot; (2) compositions approaching C/O=0.9, otherwise solar; (3) metallicities reduced by Z/Zo=0.10; and (4) metallicities enhanced by added dust components. Calculated depletions are relatively insensitive to these excursions from the canonical “cosmic” abundances. The intragroup similarities of depletions observed for the element groups (Ca‐Ti), (Fe‐Ni‐Cr‐Co), and (Mg‐Si) reflect the dominant mineralogy calculated for Stardust: Ti‐ and Ca‐aluminate phases, metal alloy, and Mg2SiO4 (Mg‐olivine). This result suggests that the bulk of the refractory component of ISM dust was condensed in stellar environments.
Presolar dust grains from meteorites and their stellar sources
Authors: Hoppe Peter , Zinner Ernst
Published: September 2002

Primitive meteorites contain small concentrations (ppb to ppm) of presolar dust grains that have survived largely unaltered the processes that led to the formation of the solar system. Minerals identified to date include diamond, silicon carbide (SiC), graphite, silicon nitride (Si3N4), corundum (Al2O3), spinel (MgAl2O4), and possibly titanium oxide (TiO2). These grains exhibit large isotopic anomalies indicative of a stellar origin. Variations in the isotopic ratios of the major elements and of many trace elements contained in the grains range over more than 4 orders of magnitude. The presolar dust grains preserve memories of both nucleosynthesis in the parent stars and galactic chemical evolution. Most of the silicon carbide and corundum grains formed in the winds of red giant and asymptotic giant branch stars. Most graphite grains, some SiC and corundum grains, and all silicon nitride grains originated most likely in supernova ejecta. A few SiC and graphite grains appear to have a nova origin. The origin of the diamonds is still unknown but at least a small fraction apparently comes from supernovae. Diamonds are only 2 nm in size. The other types of presolar grains are larger and range from ≈ 0.2 to 20 μm. These sizes are larger than those inferred for dust in the interstellar medium but are comparable to the sizes of interstellar dust in the heliosphere identified by the Gallileo and Ulysses spacecraft missions.
First observations of polar mesosphere summer echoes in Antarctica
Authors: Woodman Ronald F. , Balsley Ben B. , Aquino Fredy , Flores Luis , Vazquez Edilberto , Sarango Martin , Huaman Mercedes M. , Soldi Hector
Published: September 2002

A 25‐kW peak power 50‐MHz radar was installed at the Peruvian base on King George Island, Antarctica (62°S), in early 1993. A search for polar mesospheric summer echoes (PMSEs) was made during late January and early February of the first year of operation with negative results. These results have been reported in the literature [Balsley et al., 1993; 1995]. We report here results obtained during the austral summer of the second year (1994) of operation. Observations during the second year were begun earlier, i.e., closer to the austral summer solstice. PMSEs were observed during this period, albeit the echoes were much weaker than what one would expect based on earlier Poker Flat radar results at a comparable latitude (65°N) in the Northern Hemisphere. A large and measurable asymmetry in PMSE strength in the two hemispheres therefore exists. We explain this asymmetry by postulating a difference in summer mesopause temperatures between the two hemispheres of ∼7.5 K. This difference has been estimated using an empirical relationship between the variations of the Poker Flat PMSE power as a function of temperature given by the mass spectrometer incoherent scatter extended (MSISE‐90) model.
Measurement of the directional distribution of incident particles in the Shuttle‐Mir mission orbit
Authors: Sakaguchi Takao , Doke Tadayoshi , Hasebe Nobuyuki , Kikuchi Jun , Kono Sachiko , Takagi Toru , Takahashi Kenichi , Nagaoka Shunji , Nakano Tamotsu , Takahashi Shimpei , Badhwar Gautam D.
Published: September 2002

The measurement of the directional distribution of incident particles was made by using the Real time Radiation Monitoring Device (RRMD)‐III placed inside the Space Shuttle STS‐84 cruised at an altitude of 400 km and an inclination angle of 51.6°, which are the same as the cruising orbit of the International Space Station (ISS). The directional distributions of incident particles were evaluated over the observed linear energy transfer (LET) range (1–100 keV/μm). The pitch angle distribution is also obtained using the geomagnetic model of IGRF‐95. The result is roughly in good agreement with the distribution obtained by the VF1‐MIN anisotropy model calculation within the present experimental errors, if the shielding distribution is assumed to be uniform.
Observations of slow flows in the distant plasma sheet
Authors: Mist R. T. , Owen C. J.
Published: September 2002

A statistical analysis of the properties of the plasma sheet in the geomagnetic tail using the ISEE 3 deep‐tail data set is undertaken. The observed plasma sheet properties are compared to predictions of two models of reconnection. The first model [Cowley, 1980; Cowley and Southwood, 1980] is based on the balance of stress between a cold plasma inflow and the magnetic tension of reconnected field lines at the current sheet. The second [Owen et al., 1991] makes an attempt to incorporate heating of the plasma sheet population into this class of model. We find that only 60% of all plasma sheet events show densities greater than that in the adjacent lobe, as would be expected on the basis of mass conservation in the reconnection models. In addition, comparison of the distribution of the predicted velocities with the observed velocities shows that for a significant proportion of events, neither reconnection model accurately predicts the observed flows. In fact, the plasma sheet is most often seen to be in a quasi‐stagnant state. During periods of tailward convection, the heated model appears the more appropriate for describing plasma sheet flow due to reconnection. However, in the case of the heated (simple) model, at least 50% (60%) of tailward flows are observed at velocities well below the predictions. These events also have positive Bz on average and may therefore be associated with the tailward transport of closed flux tubes. They are also associated with geomagnetically quiet times. Such events are seen at all distance between −60 and −240 RE in the plasma sheet. These results strongly support previous suggestions that even at large downtail distances, the observed plasma sheet flows are often driven by processes other than reconnection. While the models correctly predict a significant proportion of the flow speeds for tailward flows, the earthward flow events are not well described by either model. In summary, 40% of the data set cannot be described by the reconnection models due to mass conservation requirements, and at most only 50% of the tailward flow speeds are in agreement with the predictions of these models. As such, only 30% of tailward flow events are well described by the models presented here.
On the processes in the terrestrial magnetosheath: 2. Case study
Authors: Song P. , Russell C. T. , Zhang X. X. , Stahara S. S. , Spreiter J. R. , Gombosi T. I.
Published: September 2002

We test a new scheme to study the magnetosheath. The scheme uses the solar wind measurements as the input into the gasdynamic convected field model, and the model output is compared with magnetosheath observations. In our four test cases there is a significant overall success in the model prediction. This scheme works better than other methods in magnetosheath studies and is potentially useful for space weather forecasts and nowcasts. The direction of the magnetic field is modeled most accurately. The prediction of the size of the magnetosphere is accurate within a few percent. The predicted thickness of the magnetosheath is accurate up to 90%. With a double‐normalization procedure developed in this study, we are able to separate the processes intrinsic in the magnetosheath from those due to large‐scale upstream temporal variations. The test cases confirm the existence of a compressional front one third of the distance from the magnetopause to the bow shock near the stagnation streamline. The magnetosheath density profile near the stagnation streamline is consistent with the models that add a compressional front between the two depletion processes described by the plasma depletion model. A major unexpected feature is that the magnetosheath flow pattern is very different from that described by the model and maybe by most other models, including MHD models. The magnetosheath flow near the stagnation streamline does not slow down gradually toward the stagnation point. It moves rapidly until reaching a very small region near the magnetopause.
On the processes in the terrestrial magnetosheath: 1. Scheme development
Authors: Song P. , Russell C. T. , Gombosi T. I. , Spreiter J. R. , Stahara S. S. , Zhang X. X.
Published: September 2002

We propose a new method to study the structure of the magnetosheath and thereby determine the underlying processes that create this structure. This method provides a systematic means of separating perturbations due to the solar wind variations from those generated within the magnetosheath. As a result, we are able to study the magnetosheath processes as well as the dynamic solar wind‐magnetopause interaction. We use the solar wind measurements from an upstream monitor as the input to the gasdynamic convected field model and then compare the model output with the in situ magnetosheath observations. We introduce three parameters to scale the model prediction to match the timings of the magnetopause crossing, bow shock crossing, and upstream variations. With this procedure the relationship between the upstream measurements and the magnetosheath observations and the location of the magnetosheath satellite relative to the magnetopause and bow shock boundaries are highly constrained. We then introduce a series of normalization procedures that provide the means to remove the effects of the solar wind variations. The systematic differences between the model prediction and observation indicate physical processes that are not included in the gasdynamic model. An application of this approach is presented in a companion paper.
The Millstone Hill ionospheric model and its application to the May 26–27, 1990, ionospheric storm
Authors: Schlesier A. C. , Buonsanto M. J.
Published: September 2002

The present study gives an overview of the Millstone Hill ionospheric model, which solves continuity and momentum equations for O+(4S), O2+, NO+, and N+. Photochemical equilibrium is assumed at the lower boundary (120km in the present study) and for estimation of the ion concentrations of N2+ and the metastable states of O+. Inputs to the model are the ion drifts, electron temperatures, and ion temperatures measured by the Millstone Hill incoherent scatter radar, the Mass Spectrometer Incoherent Scatter 1986 (MSIS‐86) neutral atmosphere, the observed electron density at the upper boundary (500km), and an empirical model for NO. The model is extremely flexible in selection of sets of cross sections, EUV flux models, and models for ionization by secondary photoelectron impact. The Millstone Hill ionospheric model is used to simulate the May 26–27, 1990, ionospheric storm, which has been previously studied by Buonsanto [1995a]. The main feature of this storm is an observed large enhancement in the F region electron density above Millstone Hill, the so‐called dusk effect. Results show that the effects of the electric fields and height variations in the neutral wind associated with a traveling atmospheric disturbance played a crucial role in the formation of the observed dusk effect. Advection of higher‐density plasma from the south apparently also contributed. Vibrationally excited N2 and O2 are found to be important in simulating the electron density during these disturbed summer solar maximum conditions. It has not been found necessary to change the MSIS‐86 neutral density in order to bring about good agreement between the observed and calculated NmF2 and HmF2.