bluuebunny/crossref_metadata_2025 huggingface dataset:
Conditions for the formation of hot flow anomalies at Earth's bow shock
Authors: Schwartz Steven J. , Paschmann Götz , Sckopke Norbert , Bauer Thomas M. , Dunlop Malcolm , Fazakerley Andrew N. , Thomsen Michelle F.
Published: September 2002

Hot flow anomalies (HFAs) result from the interaction of an interplanetary current sheet with Earth's bow shock and were discovered over a decade and a half ago. The deflected flow and hot interior of an HFA are consequences of ions reflected at the bow shock being channeled along the current sheet. Previous studies have shown that this requires a solar wind motional electric field pointing toward the current sheet on at least one side and that the current sheet must be a tangential discontinuity. Recent reports of a rapid displacement of the magnetopause by 5 Re as the result of an HFA have led us to explore the interplanetary conditions surrounding all reported HFAs. The kinetic aspects of HFA formation suggest that current sheets should pass relatively slowly along the bow shock; that is, their normals should have large cone angles. This hypothesis is confirmed. Individual multispacecraft case studies confirm that the underlying current sheets are tangential discontinuities, but most HFAs have relatively small jumps in field magnitude from before to after and thus would fail traditional identification tests as definite tangential discontinuities. The combination of our results suggests that HFAs should occur at a rate of several per day, and thus they may play a significant role in the solar‐terrestrial dynamics.
Electron temperature anisotropy instabilities: Computer simulations
Authors: Gary S. Peter , Winske Dan , Hesse Michael
Published: September 2002

An electron temperature anisotropy T⊥e/T‖e > 1 leads to excitation of three distinct modes, the whistler, the electrostatic, and the Z‐mode instabilities, in collisionless plasmas at frequencies below the electron cyclotron frequency |Ωe|. (Here perpendicular and parallel subscripts denote directions relative to the background magnetic field.) Two‐and‐one‐half‐dimensional particle‐in‐cell simulations are used to study the nonlinear consequences of the growth of these modes in homogeneous plasmas with ωe ∼ |Ωe|, where ωe is the electron plasma frequency. The simulations show that wave‐particle scattering by enhanced fluctuations from the whistler and electrostatic anisotropy instabilities imposes a β‐dependent upper bound on the electron temperature anisotropy at β‖e ≤ 0.10. The simulations also demonstrate that the maximum value of the dimensionless fluctuating magnetic fields increases with β‖e and that at sufficiently low β the electrostatic instability leads to non‐Maxwellian suprathermal enhancements on the reduced electron velocity distribution fe(v‖).
Velocity and magnetic field fluctuations in Alfvénic regions of the inner solar wind: Three‐fluid observations
Authors: Bavassano B. , Bruno R.
Published: September 2002

A three‐fluid analysis of Alfvénic fluctuations in the solar wind is done using Helios 2 data. We focus on the relationship between velocity and magnetic field fluctuations, in particular, on the factor relating their amplitudes. As well known, the ratio of velocity to magnetic fluctuation amplitudes decreases with increasing heliocentric distance. However, this result comes from analyses that almost completely disregard the multifluid nature of the solar wind plasma. In the present study we reexamine some observations of Alfvénic fluctuations done by Helios 2 at 0.29 and 0.88 AU within the trailing edge of a high‐speed stream, stimulated by the fact that in the investigated regions, and especially at 0.88 AU, an isotropic plasma approach appears to be too crude. In our analysis all effects of total mass density, total thermal anisotropy, and ion differential streamings for a plasma of protons, alpha particles, and electrons are taken into account. The results clearly indicate that the amplitude imbalance in favor of the magnetic fluctuations can only in part be accounted for by multifluid effects.
Detection of coronal mass ejection associated shock waves in the outer corona
Authors: Sheeley N. R. , Hakala W. N. , Wang Y.‐M.
Published: September 2002

White light coronal images from the Large‐Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) spacecraft show disturbances propagating away from high‐speed coronal mass ejections (CMEs). The disturbances are faintly visible ahead of the ejected material at the noses of the CMEs but are strongly visible along the flanks and rear ends, where they produce kinks in the streamers and other raylike features that extend in all directions from the Sun at this phase of the sunspot cycle. The kinks decelerate as they move radially outward along the rays, apparently indicating the slowing of the entire wave front as it passes by. For a fast CME seen head on (or tail on) the deceleration occurs at virtually all position angles around the occulting disk. However, for a CME seen obliquely the speed varies strongly with position angle, being fast and uniform near the nose but slower and decelerating at the sides and rear where the deflected rays are more inclined from the sky plane and farther from the Sun. The initial speeds (≳800–1400 km/s) are faster than the nominal MHD speed (∼600 km/s) at these heights, implying that these disturbances are shock waves, made visible like “amber waves of grain” [Bates, 1895] in the field of coronal rays around the Sun.
A scenario covering all phases of nightside convection with the roles of ion drifts and reconnection determined from the observed field‐aligned currents
Authors: Atkinson Gerry
Published: September 2002

The rate of transfer of magnetic flux into the nightside dipole‐like region is a function of the field‐aligned current (FAC) intensity and Nt–Nd, where Nt and Nd are the total number of plasma sheet ions on flux tubes in the near‐Earth tail and just inside the dipole‐like region. In addition, for slowly varying convection, the FAC intensity is a function of the magnetic flux in the tail. The above two relationships provide the basis for a scenario for convection. Convection bays and steady state occur if there is an ample supply of flux tubes with a small value of Nt in the near‐Earth tail. The growth phase occurs when a major increase in dayside reconnection leads to an increase in the amount of tail flux, which in turn causes increased convection into the nightside dipolar region. The plasma sheet thins until the predipolarization phase starts (reconnection or some similar process). The reconnection provides magnetic flux with reduced Nt, and also produces a change in the field‐aligned currents, both of which increase the dipolarization rate after electrical coupling with the ionosphere is established. At that time, either a pseudobreakup or a substorm onset will occur. The recovery phase is a convection toward a steady state, in which the plasma undergoes redistribution in latitude, local time, radial distance, and energy. It can be either fairly localized or magnetosphere‐wide, depending on the changes that have occurred in the dayside reconnection rate.
Variations of Saturn's radio rotation period measured at kilometer wavelengths
Authors: Galopeau Patrick H. M. , Lecacheux Alain
Published: September 2002

The Unified Radio and Plasma Wave (URAP) experiment on the interplanetary spacecraft Ulysses is able to detect the Saturnian kilometric radiation (SKR) thanks to the high sensitivity of the receiver and in spite of the remoteness of the planet (8–13 AU). Our knowledge about Saturn comes essentially from the observations by the two Voyager spacecraft. Ulysses allows us to reassess the main properties of the SKR as they had been observed by Voyager 1 and 2: average flux density, spectrum, periodicity, and polarization. A striking difference between the results obtained from Voyager and those obtained from Ulysses is the periodicity of the radio emission linked to the planetary rotation (10 hours 39 min 24 s): The period deduced from Ulysses' observations is not constant and may differ by 1% from that of Voyager. The northern and southern sources of SKR are distributed along magnetic field lines which are fixed in local time. We interpret the source location by a Kelvin‐Helmholtz instability developing on the flanks of Saturn's magnetopause, in the morningside. This instability could be at the origin of the acceleration of the particles responsible for the radio emission. Because of the solar wind fluctuations, the position of the magnetopause and the magnetohydrodynamic flow around it are modified so that the zone of Kelvin‐Helmholtz instability slowly moves, implying a drift of the radio sources in local time. We examine and discuss the possibility for this drift to be the cause of the variations observed for the SKR period.
Two‐dimensional coherent structures in the magnetopause: Recovery of static equilibria from single‐spacecraft data
Authors: Hau L.‐N. , Sonnerup Bengt U. Ö.
Published: September 2002

A new technique for recovering magnetic field maps that describe two‐dimensional, coherent field structures observed in space is documented, benchmarked, and then applied to four magnetopause crossings by the spacecraft AMPTE/IRM (Active Magnetospheric Particle Tracer Explorers/Ion Release Module) in which the basic observed signatures were those associated with a tangential discontinuity. The calculations required for the recovery consist of the numerical solution of the Grad‐Shafranov equation, using as initial values magnetic field and plasma data collected by a single spacecraft along a straight‐line trajectory, produced when structures are convected past it. The integration proceeds in small spatial steps in both directions away from the trajectory. The integration domain, which is rectangular, is limited in the transverse direction by the appearance of numerically generated singularities. Nevertheless, the method offers a substantial field of view of the region surrounding the trajectory, within which the accuracy is a few percent. For the magnetopause events examined, it is found that the simple tangential‐discontinuity structure is modified by embedded strings of magnetic islands, separated by X‐type nulls in the transverse field. These configurations are interpreted as being the result of the tearing mode after it has reached its saturated state. Two or more islands contained within larger islands are observed, indicating that, during the active phase of the tearing mode, the reconnection rate was not the same at all X points. The possibility exists that one dominant X point produces a pair of narrow channels of open flux, connecting the magnetosphere to the magnetosheath. Even without such open flux, the presence of the islands should allow flow of plasma along magnetic field lines, from the outermost (magnetosheath) to the innermost (magnetosphere) parts of the magnetopause current layer, thus facilitating the overall plasma transport across the layer.
A search for Langmuir solitons in the Earth's foreshock
Authors: Kellogg Paul J. , Goetz Keith , Monson Steven J. , Bale Stuart D.
Published: September 2002

The Earth's foreshock region, the region which is magnetically connected to the bow shock, is a region of intense Langmuir waves. Some of these waves have an envelope similar to that expected for one‐dimensional Langmuir solitons. A computer search for such waveforms has identified a number sufficient for statistical investigation. It is concluded that there is no evidence for stable waveforms like one‐dimensional Langmuir solitons.
HF radar observations of the high‐latitude ionospheric convection pattern in the morning sector for northward IMF and motion of the convection reversal boundary
Authors: Rash J. P. S. , Rodger A. S. , Pinnock M.
Published: September 2002

Observations of plasma convection in the morning sector (0000 to 0600 magnetic local time (MLT)) during a period of northward IMF (Bz = +5 to +10 nT) on September 11, 1991, made with the conjugate HF radars at Goose Bay and Halley and supplemented by DMSP plasma flow data, are described. There are several interesting features of the data: the period over which large (>500 m/s) plasma flow velocities are maintained while the IMF is northward; the range of latitudes over which the convection is observed; and the short timescale responses to changes in IMF conditions. The period was characterized by several strong (±10 nT) reversals of IMF By and an absence of substorm activity, as seen in geostationary satellite particle data. The effects of these By reversals and the motion of the convection reversal boundary (CRB, the boundary between eastward flow at lower latitudes and westward flow at higher latitudes) are examined. A significant crosscorrelation is found between IMF By and the latitude of the CRB. The observed short time delays and other features are consistent with convection driven by lobe cell merging.
A comparison of ground‐based and spacecraft observations of coronal mass ejections from 1980–1989
Authors: St. Cyr O. C. , Burkepile J. T. , Hundhausen A. J. , Lecinski A. R.
Published: September 2002

We report here an analysis of observations of solar coronal mass ejections (CMEs) acquired in white light by the Mark III (MK3) K coronameter at Mauna Loa Solar Observatory between 1980 and 1989. Statistical properties of the locations, sizes, and speeds of these events are described. These properties are compared to those in the two other white light CME catalogs from the 1980s, the CMEs observed by the Solwind and SMM spaceborne coronagraphs, and relatively good statistical agreement is found between the three data sets taken over the entire period of observation. A detailed examination was performed for the 141 MK3 CMEs that were also observed by SMM. Virtually all (93%) of the CMEs detected low in the corona by the MK3 instrument were observed to travel out of the SMM field of view, into interplanetary space. The average width of CMEs in the MK3 field of view was 12° smaller than that measured in SMM, and we interpret this statistic as an indication of some increase in size as CMEs move outward through the corona. For a subset of 55 of those mass ejections we were able to combine detailed observations from both MK3 and SMM. Using the combined measurements, we were able to detect and to quantify the initial period of acceleration in a much larger fraction (61%) of the features than was possible from either MK3 alone (9%) or SMM alone (21%). The acceleration was positive for 87% of those features, with an average (median) value of +0.264 km s−2 (+0.044 km s−2). A distinction in terms of association with other forms of solar activity was also evident in this analysis: 55% of the CMEs associated with active regions moved with constant speed, but 82% of the features associated with the eruption of solitary prominences moved with constant acceleration. Also, the average speed for CMEs associated with active regions was significantly faster than those with prominence association (955 versus 411 km s−1). The detection of positive acceleration demonstrates that the forces propelling the CME continue to dominate these events, at least through the altitudes covered by the MK3 and SMM fields of view.
A density and current plasma wave antenna
Authors: Kellogg Paul J. , Goetz Keith , Monson Steven J. , Wygant John R.
Published: September 2002

The theoretical limits of the sensitivity of a pair of back‐to‐back electron retarding potential analyzers for the detection of the density fluctuations and currents of plasma waves, particularly in the solar wind, are considered. Such an instrument might replace or augment electric antennas for the detection of waves. It is shown that such an instrument, of sufficiently small size to be hidden behind a heat shield, can have sufficient sensitivity to detect most known phenomena, and to detect all waves whose power would be of interest in energizing the solar wind. It is capable of measuring electrostatic waves in a frequency range which has been little studied. An added advantage is that in certain cases, possibly in conjunction with electric antennas, it can provide a measure of the wave vector k.
Storm‐like dynamics of Jupiter's inner and middle magnetosphere
Authors: Mauk B. H. , Williams D. J. , McEntire R. W. , Khurana K. K. , Roederer J. G.
Published: September 2002

The discovery of energy‐time dispersed, charged particle signatures of dynamic, longitudinally confined charged particle injections within Jupiter's inner magnetosphere has been reported previously as measured in >20‐keV particle intensities by the Galileo energetic particles detector (EPD). While these events have similarities to so‐called substorm injections observed within the Earth's magnetosphere, it is unknown whether the driving mechanisms are similar. Over 100 Jovian injection events have now been documented between radial distances of ∼9 RJ (the inner boundary of most of the observations) and 27 RJ Injections occur at all System III longitudes and local time positions. Similar to Earth magnetospheric injections, the Jovian injections occur throughout the broad radial region of transition between the quasi‐dipolar and neutral sheet magnetic field configurations, and where the charged particle energy densities are competitive with the magnetic energy densities. The Jovian injections can be clustered in time, analogous to what often happens during well‐known magnetic storms that occur in the Earth's magnetosphere. During one particular periapsis of Galileo's orbital trajectory, the magnetosphere was observed by EPD to become suddenly very disturbed with multiple injections following a prolonged period (>24 Earth hours) of relative quiescence. Because of the prestorm coincidence of a signature of an apparent Earth‐like global magnetospheric disturbance, we hypothesize that this Jovian storm occurred when the inner and middle magnetosphere were triggered out of marginal stability by the passage of a magnetohydrodynamic fast mode wave launched at the magnetopause by a pressure variation in the interplanetary (solar wind) environment.
Particle simulation of the auroral zone showing parallel electric fields, waves, and plasma acceleration
Authors: Schriver David
Published: September 2002

This paper examines the self‐consistent generation of the large‐scale quasi‐static, parallel electric fields that are formed in the auroral zone and how these fields affect local plasma distributions. A one‐dimensional electrostatic particle‐in‐cell simulation is employed in this study with its axis aligned along a dipolar magnetic field line that includes the magnetic mirror force as well as a cold dense ionosphere at low altitudes. Earthward drifting plasma from the magnetotail is injected into the system at the high‐altitude end of the simulation. Simulation results show that injection of magnetotail plasma leads to the mirroring of ions at lower altitudes than electrons, thereby creating a large‐scale, quasi‐static, parallel potential drop. In addition, the results show that the magnitude of the large‐scale potential drop depends on the earthward directed drift speed; the drop can be as large as 2 kV over a distance of a few thousand kilometers for inflowing ion beam energies of 10 to 25 keV. The potential gradient corresponds to a parallel electric field that is directed away from the Earth. The field accelerates ionospheric ions away from the Earth, and the accelerated ions form up welling beams with drift speeds that are in approximate agreement with observed high‐altitude auroral ion beams. Electrons are accelerated earthward and appear as a precipitating high‐energy tail in low‐altitude ionospheric distribution functions. A broadband plasma wave spectrum is generated where the magnetotail and ionospheric plasma interact, and it plays an important role in auroral dynamics by modifying local plasma distributions. Not only do these modifications of the local distributions affect plasma flow in the region, they also decrease the magnitude of the large‐scale potential drop by drawing off energy from the inflowing distributions that otherwise would support the potential drop.
Interstellar dust filtration at the heliospheric interface
Authors: Linde Timur J. , Gombosi Tamas I.
Published: September 2002

In recent years, interstellar dust has been detected by spacecraft within a few AU from the Sun. The first analysis of observed data revealed that certain properties such as size distribution and average mass of interstellar dust grains found close to the Sun differ from those of classical interstellar grains. In particular, detected grains seem to be heavier at small distances from the Sun than in the interstellar space. It was concluded that the characteristics of interstellar dust grains are modified by some process as they approach the vicinity of the Sun. In this paper for the first time we simulate the dynamics of dust grains in the interstellar medium and the heliosphere and demonstrate that they experience a filtration process in the region of the heliopause. The main result of this process is the exclusion of small submicron‐sized grains from the incoming stream. We estimate the cutoff range for the process to lie between 0.1 and 0.2 μm, which corresponds to 10−16 – 10−17 kg dust grains. Although this result is consistent with satellite observations, we show that it alone does not explain interstellar grain data that were collected in situ in the interplanetary space.
Escape of H and D from Mars and Venus by energization with hot oxygen
Authors: Shizgal Bernie D.
Published: September 2002

A kinetic theory collisional production model is used to determine the product velocity distributions of H and D resulting from collisional energy transfer with hot oxygen. The energetic oxygen atoms are the products of the dissociative recombination of O2+. Quantum mechanical cross sections for O‐H and O‐D collisions are used to determine the production distributions. The distributions of the particles entering a collision are assumed to be Maxwellian functions. The fraction of atoms with speeds above the escape speed is determined for Venus and Mars. For Venus, available density and temperature profiles are used to obtain estimates of the H and D escape fluxes and fractionation ratios.
Signatures of the ionospheric cusp in digital ionosonde measurements of plasma drift above Casey, Antarctica
Authors: Parkinson M. L. , Breed A. M. , Dyson P. L. , Morris R. J.
Published: September 2002

Signatures of the ionospheric cusp in HF digital ionosonde measurements of plasma drift made at the polar cap station Casey, Antarctica (−80.8° geomagnetic latitude), are investigated. Measurements recorded during the campaign interval February 13–17, 1996, are considered in this case study because the summer dipole tilt effect, and an interplanetary magnetic field (IMF) northward condition on February 16, were favorable for the detection of the cusp at a higher than usual latitude. On February 14 and 15 the magnitude of the IMF was about 4–6 nT, and the station probably passed just poleward of the cusp. The most general signatures of the cusp were enhanced electric field and electric field turbulence shown by increased drift velocity and velocity scatter in the convection throat, respectively. Broadband, unstructured fluctuations in the geomagnetic field measured by magnetometers near to noon are well known to be a signature of cusp currents and were associated with the intervals of enhanced convection turbulence. A major cusp event occurred above Casey on February 16, when the magnitude of the IMF increased from about 5 to > 10 nT. Cusp signatures during this event included the drift velocity surging to large values just before and after an interval during which the F region echoes were lost because of an absence of F region ionization and the formation of electron density patches. The loss of echoes was only partly explained by increased absorption and scatter of the transmitted radio waves. Although the spectral width of Doppler peaks increased, this, by itself, was not a unique signature of the cusp because the obliquity of echoes also controlled the spectral width in our near‐vertical interferometry. However, signatures of the cusp were easily recognized in digisonde data, and the cusp's location and dynamics can be monitored using digisondes.
On relative timing in substorm onset signatures
Authors: Liou K. , Meng C.‐I , Lui T. Y. , Newell P. T. , Brittnacher M. , Parks G. , Reeves G. D. , Anderson R. R. , Yumoto K.
Published: September 2002

We investigate the timing of popular substorm onset signatures to understand their temporal relationship. Proxies for substorm onsets include auroral breakups, high‐latitude magnetic bays, low‐latitude Pi2 bursts, dispersionless injections at geostationary orbits, and auroral kilometric radiation. We use the auroral breakup, identified with Polar UVI images, as a common reference time frame to calibrate the others. Results, illustrated by two well‐defined auroral substorms, unambiguously indicate that none of the four frequently used substorm onset proxies can provide a consistent timing of substorm onset. This inconsistency in substorm onset timing is attributed as a consequence of temporal and spatial limitations on each observational technique. A delay between the proxy identifiers and the auroral breakup is found to be typical. It is therefore strongly suggested from this study result that a common reference time frame for substorm onset is necessary, and we propose it should be auroral breakups. We argue that there is a need for an intercalibration of magnetospheric substorm phenomenology by using a unified definition of the substorm onset.
Modeling the ionospheric effects of ion and electron precipitation in the cusp
Authors: Millward G. H. , Moffett R. J. , Balmforth H. F. , Rodger A. S.
Published: September 2002

The effect of increased ion production due to the precipitation of both ions and electrons in the cusp region has been studied using a computational model of the high‐latitude ionosphere. The modeling assumes that the cusp region is subject to fluxes of precipitating electrons which have a Maxwellian energy distribution at a temperature of 50 eV. In addition to the electrons the modeled cusp ionosphere is also subjected to precipitating ions with a Maxwellian energy distribution, at a temperature of 500 eV and a “low energy cutoff” for ions with an energy less than 900 eV. The results reveal both ion and electron precipitation to be important production sources in the cusp region, but at markedly different altitudes. Electron precipitation produces dominant effects at F2 peak altitudes of around 300 km while the ions, at higher energies, are capable of creating a precipitation “F1 ledge” at altitudes of around 150 km. A simulation of the ion dispersion with latitude, known as the “velocity filter effect,” reveals that this leads to large enhancements in lower‐altitude electron concentration on the equatorward edge of the cusp, the enhancement tailing off sharply in latitude.
Modeling the OI 630.0 and 557.7 nm thermospheric dayglow during EISCAT‐WINDII coordinated measurements
Authors: Witasse O. , Lilensten J. , Lathuillère C. , Blelly P.‐L.
Published: September 2002

The 630.0 and 557.7 nm thermospheric dayglow was modeled at high‐latitude using an eight‐moment fluid model, from measurements coordinated between the European Incoherent Scatter (EISCAT) radar and the Wind Imaging Interferometer (WINDII). The emission computation in particular included the electron (suprathermal and thermal) impact whose cross sections have been updated, the dissociative recombination of O2+ ion described for the first time by a theoretical rate coefficient, the photodissociation of molecular oxygen, and some relevant chemical reactions. The neutral atmosphere was adjusted by calibrating the ionospheric model outputs to EISCAT data. Slight adjustments were needed in order to reach a good agreement. The results were successfully compared to WINDII observations. Our present study shows that simultaneous EISCAT‐WINDII measurements can be used to reduce uncertainties due to the neutral composition and that new observations of the EUV solar spectrum are still needed.
First attempt at assimilating data to constrain a magnetospheric model
Authors: Garner T. W. , Wolf R. A. , Spiro R. W. , Thomsen M. F.
Published: September 2002

We have developed a direct insertion scheme for assimilating observed electron fluxes into a large‐scale model of the inner magnetosphere. This data assimilation scheme is being developed for the Integrated Space Weather Prediction Model, but a simpler test model is used for the initial tests. The test model is a particle drift code that allows locally inserted electron flux measurements to propagate east along electron drift paths. Fluxes of ∼40 keV electrons measured by geosynchronous satellites are used to constrain model electron fluxes as the model steps along in time, while similar measurements from separate spacecraft are used to test the procedure's effectiveness. In testing this scheme, two periods are used, April 21–23, 1988 (with three spacecraft about 120° apart in longitude), and March 28–April 4, 1996 (two spacecraft separated by 34°). In these tests our data assimilation procedure modestly improved electron flux specification. The test results indicate that the data insertion scheme generally improved the electron flux specification within a region extending ∼30° longitude east of the data‐supplying satellite. However, only for quiet conditions does this direct insertion procedure improve the electron flux specification when the spacecraft are ∼ 120° apart.
Solar cycle variations in the storm‐substorm relationship
Authors: Nakai H. , Kamide Y.
Published: September 2002

The regression coefficients of the time‐weighted AL index (ALW) to the Dst index are calculated for each year from 1966 to 1994. It is found that the slope of the linear regression equation varies over a period of 11 years: The coefficient a1 in a regression equation, Dst = a0 + a1 ALW, is maximized near the sunspot maximum and is minimized near the sunspot minimum. The long‐term variations in the relationship between these indices and solar wind parameters are also examined. The dependence of Dst on the solar wind electric flux, BzV2, is nearly constant, while the values of AL for fixed values of BzV2 are greater at the solar minimum than at the solar maximum, where Bz and V denote the Z component of the interplanetary magnetic field and the solar wind speed, respectively. Possible causes that can account for these characteristics are discussed.
Monte Carlo model for electron degradation in SO2 gas: Cross sections, yield spectra, and efficiencies
Authors: Bhardwaj Anil , Michael Marykutty
Published: September 2002

A Monte Carlo model has been constructed to study the energy degradation of electrons in SO2 gas. We have reviewed all the electron‐SO2 collision cross sections and present an assembled set of cross sections along with their analytical representations. The Monte Carlo simulations are carried out in the 1–200 eV energy range to obtain the “yield spectra.” The yield spectra contain the nonspatial information about the electron degradation processes and can be employed to calculate the “yield” (or population) for any inelastic process at the required energy. The numerical yield spectra have been represented by an analytical form, generating the analytical yield spectra (AYS). The AYS can be easily applied to atmospheric and laboratory problems dealing with the electron degradation in SO2. The AYS is applied to calculate the efficiencies for various inelastic processes. The energy distribution of the secondary electrons produced per incident electron is presented at a few sample incident energies. The mean energy per ion pair for SO2 is found to be 23 eV at 200 eV. Ionization is the dominant loss channel at energies >30 eV. More than 50% of the electron energy goes into this loss channel at energies >50 eV. Excitation of SO2 bands is the major loss process in the 6–20 eV energy range, while below 5 eV all the electron energy goes to the electron attachment process. Only about 1–2% of the electron energy goes in the production of line emissions of neutral and ionized oxygen and sulfur atoms at energies greater than ∼ 100 eV and is much less at lower energies. These are the first results reported on the apportionment of the electron energy among various loss channels in SO2 gas and will be useful in the interpretation and understanding of the processes on Io from the Galileo and Hubble Space Telescope data.
On the origin of sporadic keV ion injections observed by Interball‐Auroral during the expansion phase of a substorm
Authors: Delcourt D. C. , Dubouloz N. , Sauvaud J.‐A. , Malingre M.
Published: September 2002

During the expansion phase of a substorm on October 10, 1997, the Interball‐Auroral probe traveling across the auroral zone in the midnight sector detected sporadic injections of H+ and O+ ions with energies of a few keVs. We show that these injections are of ionospheric origin and are related to the large fluxes of low‐energy (a few tens of eV) upflowing ions near the poleward boundary of the auroral oval. Using test particle trajectory simulations, we demonstrate that these low‐energy ionospheric ions may be subjected to a rapid (on the timescale of expansion phase) circulation inside the plasma sheet. After their ejection from the poleward propagating auroral bulge, these ions travel into the midtail where they behave nonadiabatically and experience energization up to the keV range. As a result of magnetic moment damping in the current sheet, some of these ionospheric ions escape from the equatorial magnetosphere and travel back toward low altitudes. Numerical calculations reveal that upon reaching Interball‐Auroral near ∼3 RE altitude, these particles give rise to the observed keV injections, the sporadic character of which is due to the chaotic nature of ion motion in the magnetotail.
On the cascade processes of Alfvén waves in the fast solar wind
Authors: Hu You Qiu , Habbal Shadia Rifai , Li Xing
Published: September 2002

We present a numerical study which explores the nonlinear cascade effect associated with Alfvén waves in the fast solar wind. The set of one‐dimensional, two‐fluid equations describing the solar wind and a power spectrum equation for Alfvén waves, as first proposed by Tu et al. [1984], are solved simultaneously in a self‐consistent manner. Both Kolmogorov and Kraichnan cascade functions, which vary as ƒ5/2P3/2 and ƒ3P2, respectively, are considered. For an Alfvén wave spectrum at the coronal base, which is flat in the low‐frequency range and has a slope of −1 in the high‐frequency range, the Kolmogorov cascade function reproduces the Alfvén wave spectrum observed beyond 0.29 AU very well. The Kraichnan cascade function, on the other hand, yields a spectrum that is within the 90% confidence level of the observed values. Both cascade functions yield a gradually accelerating fast solar wind in the inner corona, typical of wave acceleration models. The results of this first solar wind model which describes, in a self‐consistent manner, the evolution of the wave spectrum and cascade in the inner corona confirm conclusions reached by earlier studies, namely, that the Kolmogorov process produces a stronger cascade effect than the Kraichnan process and seems more relevant for Alfvén waves in the fast solar wind, at least beyond 0.29 AU. The approach shows that Alfvén waves, with periods of hours or shorter, undergo an appreciable evolution from the solar surface to 1 AU, thus implying that their spectrum; hence their total energy flux at the Sun cannot be readily predicted from that observed in interplanetary space.
Mirror instability with finite electron temperature effects
Authors: Pokhotelov Oleg A. , Balikhin M. A. , Alleyne H. St‐C. K. , Onishchenko Oleg G.
Published: September 2002

A linear theory of mirror instability accounting for the finite electron temperature effects is developed. Using the standard low‐frequency approach to the analysis of this instability but including some kinetic effects, we have derived an expression for the growth rate and analyzed the effects of finite electron temperature and arbitrary electron anisotropy. In comparison with earlier analyses which were limited to Isotropic electron distributions, consideration of arbitrary electron anisotropy shows that for sufficiently hot electrons an increased electron temperature enhances the growth rate of the mirror instability.
Height‐integrated conductivity in auroral substorms: 2. Modeling
Authors: Gjerloev J. W. , Hoffman R. A.
Published: September 2002

Calculations of height‐integrated conductivity from 31 individual Dynamics Explorer (DE 2) substorm crossings presented by Gjerloev and Hoffman [this issue] are used to compile empirical models of the height‐integrated Pedersen and Hall conductivities (conductances) in a bulge‐type auroral substorm. Global auroral images obtained by Dynamics Explorer 1 (DE 1) were used to select substorms displaying a typical bulge‐type emission pattern and each individual DE 2 pass was positioned with respect to key features in the observed emission pattern. The conductances were calculated for each DE 2 pass using electron precipitation data and a monoenergetic conductance model. All passes were divided into six different sectors, and average conductance profiles were carefully deduced for each of these sectors. Using a simple boxcar filter, smoothed average sector passes were calculated and from linear interpolation between these, two‐dimensional conductance models were compiled. The characteristics of our models are (1) the Hall conductance maximizes in the high‐latitude part of the surge at 48 mho with a Hall to Pedersen ratio of 2.4; (2) two channels of enhanced conductance are overlapping in local time near midnight and are fairly separated in latitude; (3) the conductance has a sharp gradient at the high‐latitude boundary in the premidnight sector while in the postmidnight sector a broad region of low conductance stretches up to 10° invariant latitude poleward of the local peak; and finally, (4) the enhanced conductance region displays a characteristic broadening toward dawn primarily owing to a poleward shift of the high‐latitude boundary.
Coupled hydromagnetic wave excitation and ion acceleration at interplanetary traveling shocks and Earth's bow shock revisited
Authors: Gordon B. E. , Lee M. A. , Möbius E. , Trattner K. J.
Published: September 2002

A revised version of the self‐consistent theory of ion diffusive shock acceleration and the associated generation of hydromagnetic waves is presented. The theory generalizes and corrects the theory of Lee [1982, 1983]. Lee assumed a linear dependence of the anisotropic part of the ion distribution function on the cosine of the ion pitch angle. Here the wave growth or damping rate is again calculated using linear theory, but a more general ion anisotropy is calculated using the pitch angle diffusion equation. The wave intensity satisfies a wave kinetic equation, and the ion omnidirectional distribution function satisfies the energetic particle transport equation. These coupled equations are solved numerically and compared with an analytical approximation similar to that derived by Lee. The analytical approximation provides an accurate representation of both the proton distribution and the wave intensity. A comparison is made between the predicted wave magnetic power spectral density adjacent to the shock as a function of frequency and the wave spectrum measured by ISEE 3 at the November 11–12, 1978, interplanetary traveling shock. There is excellent agreement between the predicted and measured power spectral density in the frequency range of 0.03–0.3 Hz. A comparison is also made between the predicted total wave energy density and that observed upstream of Earth's bow shock by the AMPTE/IRM satellite for a statistical survey of ∼400 near‐to nose events from late 1984 and 1985. This comparison revises the result presented by Trattner et al. [1994]. The correlation between the observed wave power and that predicted, based on the observed energetic proton energy density, is very good with a correlation coefficient of 0.92. However, the average observed wave magnetic energy density is ∼63% of that predicted, suggesting possible wave dissipation which is not included in the theory.
Transformation of high‐latitude ionospheric F region patches into blobs during the March 21, 1990, storm
Authors: Crowley G. , Ridley A. J. , Deist D. , Wing S. , Knipp D. J. , Emery B. A. , Foster J. , Heelis R. , Hairston M. , Reinisch B. W.
Published: September 2002

Discrete F region electron density enhancements of a factor of 2 or more have been observed in the high‐latitude ionosphere. These enhancements have been termed patches if they occur within the polar cap and blobs if they occur outside of the polar cap. It is important to understand the formation and evolution of these structures because they are associated with large phase and amplitude scintillation in transionospheric radio signals. Blobs are generally thought to result from the breakup of patches as they exit the polar cap; however, this process has not previously been observed. Detailed study of high‐latitude ionospheric plasma transport is generally difficult because of the sparseness (spatial and temporal) of electron density and velocity observations. In this paper, we present electron density enhancements measured from the Qaanaaq Digisonde, the Millstone Hill incoherent scatter radar, and the DMSP F8 satellite during a 5‐hour interval of the March 21, 1990, storm period and show definitively how a patch is transformed into a blob. We present a new trajectory analysis package that is capable of using ionospheric convection patterns to determine the motion of ionospheric plasma over a period of several hours. The new package uses convection patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique to track the motion of observed patches from one site to another and thus determines where the measured electron density enhancements originated and where they went after being observed. The trajectory analysis also establishes that there is a direct connection between the enhancements observed by the different instruments at different locations. In this case, within ∼4 hours, plasma observed by a Digisonde near the pole is convected through 35° of latitude to the northeastern United States, where it is observed by the Millstone Hill radar, then roughly equal portions are transported westward to Alaska and eastward to Scandinavia where they are observed by the DMSP satellite. This study demonstrates that the changing convection pattern can significantly distort the patch shape and trajectory, and illustrates the high degree of mixing of ionospheric plasma by convection. The changing convection pattern leads to the simultaneous existence of a boundary blob and a subauroral blob which are both observed by the Millstone Hill radar. This work is very relevant to our future ability to specify and forecast ionospheric conditions at high latitudes. It represents a critical step from a merely qualitative ability to model the evolution of patches and blobs to a quantitative ability.
Coordinated incoherent scatter radar study of the January 1997 storm
Authors: Buonsanto M. J. , González S. A. , Lu G. , Reinisch B. W. , Thayer J. P.
Published: September 2002

We describe many important features of the ionospheric F region as observed by the Sondrestrom, Millstone Hill, and Arecibo incoherent scatter radars (ISRs) and the Millstone Hill and Ramey Digisondes during January 6–10, 1997, with emphasis on the January 10, 1997 storm. Coordinated analysis of the data provides evidence for traveling atmospheric disturbances (TADs) and for two likely electric field penetration events linking these stations. Large and rapid changes in hmF2 were seen at Arecibo and nearby Ramey which are related to the TADs and penetrating electric fields. Results are compared with simulations by the thermosphere‐ionosphere electrodynamics general circulation model (TIEGCM), which utilizes high‐latitude inputs given by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. An important result of this study is that the TIEGCM is able to predict TADs similar to those observed. Exceptional features observed during this storm at Millstone Hill are a very large nighttime Te enhancement on January 10 and a larger decrease in NmF2 than predicted by the TIEGCM throughout the storm period. The latter appears to be related to an underestimation of the neutral temperature by the model.
Amplitude evolution and rigidity dependence of the 26‐day recurrent cosmic ray decreases: COSPIN/KET results
Authors: Paizis C. , Heber B. , Ferrando P. , Raviart A. , Falconi B. , Marzolla S. , Potgieter M. S. , Bothmer V. , Kunow H. , Müller‐Mellin R. , Posner A.
Published: September 2002

In the time interval extending from July 1992 to July 1994, Ulysses climbed from 10°S heliographic latitude up to over 70°S. During this time lapse, solar minimum conditions were gradually approached, which, in turn, led to stable and long‐lasting corotating interaction regions (CIRs). The corotating particle events observed during this period, associated with ∼30 registered CIRs, offer a unique opportunity to probe the three‐dimensional structures of the heliosphere. In this work we use data from the Cosmic Ray and Solar Particle Investigation Kiel Electron Telescope (COSPIN/KET) instrument on board Ulysses to study the amplitude evolution of the 26‐day recurrent cosmic ray decreases, generated by these CIRs, at different energies and derive its rigidity dependence. We find that the amplitude has a maximum around 25°–30° heliolatitude. We also find that the rigidity dependence of both the latitudinal gradient as well as the 26‐day variation amplitude show a remarkable similarity. We discuss these observations within the framework of our current understanding of heliospheric phenomena.
Ionization by energetic protons in Thermosphere‐Ionosphere Electrodynamics General Circulation Model
Authors: Galand M. , Roble R. G. , Lummerzheim D.
Published: September 2002

Originating in the magnetosphere and precipitating into the high‐latitude ionosphere, energetic protons in the keV energy range are a common auroral phenomenon and can represent an important energy source for the auroral atmosphere. In global models describing the ionosphere‐thermosphere interaction, keV protons have always been neglected or treated as if they were electrons. Here we investigate the effect of keV protons on both the ionospheric and thermospheric composition in the E region on a planetary scale. We present a parameterization of electron and ion production rates induced by an incident proton beam as a fast computational scheme for use in global models. The incident proton beam is assumed to have a Maxwellian distribution with characteristic energies between 1 and 20 keV. The parameterization is validated against a full proton transport code. By including these parameterized electron and ion production rates in a one dimension‐in‐space (1D‐in‐space) Thermosphere‐Ionosphere Global Mean Model, we show that proton precipitation can cause a significant enhancement of the electron density, the major ion (O2+ and NO+) densities, and the nitric oxide density. As a result, the conductivities in the E region are also greatly increased. Using the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM), we show that the proton precipitation, when added to the normal electron aurora, causes a large increase (up to 70%) in electron,
, and NO+ densities over much of the auroral oval. The NO density is affected in a larger area owing to the long lifetime of NO on the nightside. This first study of the influence of protons on a planetary scale clearly shows the significant impact that auroral keV protons can have on the ionospheric and thermospheric composition and the need to include proton precipitation in global models.