bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐altitude polar cap electric field responses to southward turnings of the interplanetary magnetic field
Authors: Turner N. E. , Baker D. N. , Pulkkinen T. I. , Singer H. J. , Mozer F. , Lepping R. P.
Published: February 2004

Interplanetary electric field coupling with the magnetosphere has been analyzed predominantly using data from the Wind magnetometer and the Polar electric field instrument. The coupling was investigated using the Polar Electric Field Instrument (EFI) to measure the electric field in the northern polar cap immediately following sharp southward turnings of the IMF as observed by Wind. Southward turnings were chosen which exhibited a sudden change of the IMF north–south component from BZ > 0 to BZ < 0 (GSM coordinates) after an hour or more of relatively stable conditions, and for which Polar was in the northern polar cap. These BZ changes correspond to EY changes in the interplanetary electric field. For each of the 30 identified events, a time was estimated for the arrival of the IMF change at the magnetopause using the solar wind speed observed by the Wind Solar Wind Experiment (SWE), and Polar electric field data were examined to identify responses. For many of the selected events (about one third), abrupt changes of state in the magnetospheric electric field were evident with timing that matched the expected solar wind arrival time at Earth. For events for which additional data were available, we conducted in‐depth examination of the individual events using IMP 8, Geotail, and GOES 9. In one such event, GOES 9 data showed a substorm growth phase and onset which also corresponded to features in the solar wind observed by Wind, Geotail, and IMP 8. In addition to the individual event studies, a superposed epoch analysis of all available events revealed a consistent rise in the mean polar cap electric field about 15 min following sharp IMF southward turnings.
Short‐duration convection bays and localized interplanetary magnetic field structures on November 28, 1995
Authors: Sergeev V. A. , Kamide Y. , Kokubun S. , Nakamura R. , Deehr C. S. , Hughes T. J. , Lepping R. P. , Mukai T. , Petrukovich A. A. , Shue J.‐H. , Shiokawa K. , Troshichev O. A. , Yumoto K.
Published: February 2004

We present ground‐based, plasma sheet, and magnetosheath observations of two subsequent short‐duration (10–20 min) increases of the postmidnight westward electrojet on November 28, 1995. Appearing as though small (150–200 nT) substorms, they were not accompanied by any substorm expansion onset signatures. Auroral breakup, worldwide Pi2 pulsations, and the corresponding plasma sheet activity, such as fast flows, current disruption, and plasmoid generation, were all observed only at the recovery of the second electrojet increase. These convection bays were associated with the equatorward expansion of the auroras and simultaneous magnetic variations in the polar cap and middle latitudes. Growth phase signatures of the lobe field increase and tailward stretching of magnetic field were also observed in the plasma sheet. Bursty bulk flows in the plasma sheet seem to be quenched at the onset of first convection bay and did not resume until the auroral breakup which concluded the second convection bay. A point of interest of this event was the “incomplete” convection/current system with a well‐developed dawn vortex in the absence of well‐defined dusk vortex; instead, a complicated transient activity dominated over the afternoon‐dusk local time sector. We interpret this asymmetry either in terms of the magnetopause encounter with the edge of the solar wind driver, i.e., strong southward IMF, which hits only the dawn part of the magnetosphere, or with an extremely slant interplanetary discontinuity. This unique configuration was inferred from observations of uncorrelated strong southward Bz events by the Wind and IMP 8 spacecraft in the dusk and dawn magnetosheath, respectively, as well as from the directional analysis of the interplanetary discontinuities which form the edges of these structures. We suggest that interaction of the magnetosphere with very slant solar wind discontinuities may bring various specific features to magnetospheric and ionospheric dynamics that have not been reported.
Magnetospheric plasma regimes identified using Geotail measurements: 1. Regime identification and distant tail variability
Authors: Eastman T. E. , Christon S. P. , Doke T. , Frank L. A. , Gloeckler G. , Kojima H. , Kokubun S. , Lui A. T. Y. , Matsumoto H. , McEntire R. W. , Mukai T. , Paterson W. R. , Roelof E. C. , Saito Y. , Tsuruda K. , Williams D. J. , Yamamoto T.
Published: February 2004

For many important scientific objectives, the analysis and interpretation of magnetospheric data sets require a sorting by primary plasma regimes. This sorting process is much more difficult in the distant magnetotail than for data sets sampled close to Earth. We have carried out systematic regime identifications for the entire deep‐tail portion of Geotail data at timescales down to ∼l min. Criteria were developed for selection of five basic plasma regimes: plasma sheet, lobe, magnetospheric boundary layer, magnetosheath, and solar wind. In addition to low‐energy plasma data central to the identification process, critical supplementary information derives from magnetic field and plasma wave data. We find that all basic plasma regimes remain physically distinct populations at all downtail distances sampled by the Geotail spacecraft. Preliminary automated separation of subregimes using a B versus δB method shows that plasma mantle intervals increase in probability of occurrence from 18% near Earth to about 50% near 205 RE. In contrast, plasma sheet intervals decrease overall with increasing tailward distance. Beyond about X = −100 RE, the frequency of short regime intervals steadily increases, overall variability increases, and the lobe and plasma sheet are progressively displaced by the boundary layer, here mostly plasma mantle. Our plasma regime identifications provide a critical baseline for the development of automated identification and a key resource for both Geotail data analysis and correlative studies between Geotail and other International Solar Terrestrial Physics mission data sets.
Multi‐instrument analysis of the ionospheric signatures of a hot flow anomaly occurring on July 24, 1996
Authors: Sitar R. J. , Baker J. B. , Clauer C. R. , Ridley A. J. , Cumnock J. A. , Papitashvili V. O. , Spann J. , Brittnacher M. J. , Parks G. K.
Published: February 2004

We present the analysis of a coordinated set of observations from the POLAR ultraviolet imager (UVI), ground magnetometers, incoherent scatter radar, solar wind monitors, and the DMSP satellite, focused on a traveling convection vortex (TCV) event on July 24, 1996. Starting at approximately 1036 UT, ground magnetometers in Greenland and eastern Canada observe pulsations consistent with the passing overhead of a series of TCV field‐aligned current pairs. Azimuthal scans by the Sondrestrom incoherent scatter radar located near Kangerlussuaq (formerly Sondrestrom), Greenland, at this time show strong modulation in the strength and direction of ionospheric plasma flow. The magnetometer pulsations grow in magnitude over the next hour, peaking in intensity at 1137 UT. Images from the UVI instrument show a localized intensification of auroral emissions over central and western Greenland at 1139 UT. Subsequent images show the intensification grow in strength and propagate westward (tailward) until approximately 1158 UT, at which time the intensification fades. These observations are consistent with the westward passage of four pairs of TCVs over central Greenland. The intensification of auroral emissions at 1139 UT is associated with the leading vortex of the fourth TCV pair, thought to be the result of an upward field‐aligned current. The modulated flow observed by the radar is the result of the strong electric fields associated with the field‐aligned current systems responsible for the impulsive TCV as they pass through the field of view of the radar. Measurements taken in the solar wind by the Wind spacecraft suggest that a pressure change triggers the onset of TCV activity. A subsequent sudden change in the orientation of the interplanetary magnetic field produces a hot flow anomaly which forms at the bow shock. We believe that the interaction of the hot flow anomaly with the magnetopause intensified the fourth TCV pair and produced the associated auroral brightening. DMSP particle data indicate that the TCVs occur on field lines which map to the boundary plasma sheet‐low latitude boundary layer interface. The ground observations associated with the hot flow anomaly are the first of their kind and provide a mechanism to tie an interplanetary magnetic field orientation change into the existing theory that TCVs result from a deformation of the magnetopause.
Pi1 magnetic pulsations in space and at high latitudes on the ground
Authors: Arnoldy R. L. , Posch J. L. , Engebretson M. J. , Fukunishi H. , Singer H. J.
Published: February 2004

Nightside, high‐latitude (68°–80° magnetic) Pi1 waves, measured with a ground array of induction magnetometers, are studied and compared with magnetic field measurements made at synchronous orbit near the meridian of the ground measurements. The objectives of the study are to relate the ground signatures of Pi1B and PiC to the auroral substorm and its manifestation at synchronous orbit in an attempt to understand the origin of the Pi1 waves. Pi1 waves are measured in the equatorial plane by the GOES spacecraft and appear to be initiated by the dipolarization process of the nightside tail magnetic field at the onset of substorms. Across two meridional arrays of ground stations the earliest onset of Pi1B generally occurred at the lowest‐latitude station and, in many instances, this burst was superimposed on a ground signature of a sudden onset of the westward electrojet. In one instance, where good coverage of ground optical data was available, this sudden onset Pi1B was time related to the overhead passage of a westward traveling auroral surge. The timing of maximum Pi1B across the array in both longitude and latitude agrees with the westward motion of the local auroral surge and the poleward motion of the aurora after the surge has arrived at a given site, suggesting a local ionospheric source for some of the Pi1 waves. However, across the entire array, extending about 12° in latitude and 20° in longitude, there often was nearly simultaneous Pi1B wave power at all sites which occurred before the maximum signal at a given site (and presumably local aurora), suggesting horizontal ducting of wave power from the onset of PiIB seen earlier at the auroral zone latitude. Prompt turn‐on of PiC waves across the array also indicates ducting of these waves. The narrow bandwidth of the PiC waves themselves suggests a resonant cavity source for them which would indicate that some wave power enters the ionosphere from space (consistent with the GOES in situ data) as the trigger wave for this resonant source mechanism. In conclusion, this study finds evidence for local ionospheric currents, magnetospheric waves, and resonant cavity modes as sources for Pi1 ground waves.
Interplanetary Lyman α observations from Pioneer Venus over a solar cycle from 1978 to 1992
Authors: Pryor Wayne R. , Lasica Scott J. , Stewart A. Ian F. , Hall Doyle T. , Lineaweaver Sean , Colwell William B. , Ajello Joseph M. , White Oran R. , Tobiska W. Kent
Published: February 2004

The Pioneer Venus Orbiter ultraviolet spectrometer (PVOUVS) routinely obtained interplanetary hydrogen Lyman α data while viewing ecliptic latitudes near 30°S from 1978 to 1992 (during solar cycles 21 and 22). We describe “hot” models for this interplanetary Lyman α data that include the solar cycle variation of (1) the solar flux, as a function of latitude and longitude; (2) the radiation pressure on hydrogen atoms; (3) the solar wind flux; (4) the solar EUV flux; and (5) the multiple scattering correction to an optically thin radiative transfer model. These models make use of solar radiation flux parameters (solar wind, solar EUV, and solar Lyman α) from spacecraft and ground‐based solar proxy observations. Comparison of the upwind data and model indicates that the ratio of the solar Lyman α line center flux (responsible for the interplanetary signal) to the observed solar Lyman α integrated flux is constant to within ∼20%, with an effective line width near 1.1 Å. Averaging the solar radiation pressure and hydrogen atom lifetime over 1 year before the observation reproduces the upwind intensity time variation but not the downwind. A better fit to the downwind time series is found using the 1 year average appropriate for the time that the atoms passed closest to the sun. Solar Lyman α measurements from two satellites are used in our models. Upper Atmosphere Research Satellite (UARS) solar Lyman α measurements are systematically higher than Solar Mesosphere Explorer (SME) values and have a larger solar maximum to solar minimum ratio. UARS‐based models work better than SME‐based models in fitting the PVOUVS downwind time series Lyman α data.
Source of auroral myriametric radiation observed with Geotail
Authors: Hashimoto K. , Kudo S. , Matsumoto H.
Published: February 2004

The Geotail plasma wave instrument has found the auroral myriametric radiation (AMR). Its frequency range is about 1–30 kHz similar to the trapped continuum radiation, and its occurrence shows a good correlation with auroral kilometric radiation (AKR). This suggests the source location of AMR is similar to that of AKR. Ray tracing is performed for L‐O mode waves radiated just above the local plasma frequency in the auroral plasma cavity. The waves are guided in the cavity, propagate far from the Earth, arid are observed as AMR. In the source region these guided waves are observed by the DE 1 satellite and reported as the trapped L‐O mode waves within the cavity. A limitation on initial conditions of wave normal angles for the ray tracing derived from a comparison with these observations suggests that its generation mechanism is similar to that of the nonthermal continuum. It is, however, generated in the auroral plasma cavity and it is not mode‐converted from the upper hybrid mode waves. The ray tracing results are consistent with AMR observations by Geotail.
Analysis of lightning ‐ induced ionization from VLF Trimpi events
Authors: Molchanov O. A. , Shvets A. V. , Hayakawa M.
Published: February 2004

Detailed analysis of Trimpi phenomena (Trimpis) revealed two different regimes in their temporal behavior. One time regime is the initial “nose” part of Trimpis of about 1–5 s, and the second is the “tail” of Trimpis of about 50–100 s. Using a rather simple theoretical model of VLF wave scattering from abating ion and electron density perturbations, we discovered two fitting formulas to describe the temporal evolution of Trimpis. An exponential‐hyperbolic evolution in amplitude a/a0 = (exp{−t/τ0})/[1 + b/2(1 − exp{−t/τ0})] for weak scattering and a logarithmic dependence a/a0 = [ln τ2/(t + τ1)]/(ln τ2/τ1) for strong scattering. Parameters b, τ0, τ1, τ2 were calculated for all the observed 50 Trimpi events. Maximal ion and electron density perturbation (Δnmi and Δnme) were estimated together with the background ion and electron density (ni0 and ne0) and vertical length of the perturbation column (ΔH). For the conventional model of background electron density and horizontal scale of perturbations L ≃ 5 – 10 km, we find the perturbation parameters to be as follows: Δnme ≃ 103 – 104 cm−3, Δnme/ne0 ∼ Δnmi/ni0 ≃ 10 – 100, ni0 ≃ 3 × 103 − 3 × 104 cm−3, and ΔH ∼ 10 – 15 km.
Solar wind acceleration by large‐amplitude nonlinear waves: Parametric study
Authors: Ofman L. , Davila J. M.
Published: February 2004

We investigate the parametric dependence of the solar wind acceleration by large‐amplitude nonlinear (LAN) magnetohydrodynamic waves. For this purpose we model numerically the self‐consistent problem of the solar wind with waves by solving time‐dependent, nonlinear, resistive 2.5‐dimensional (three‐dimensional with azimuthal symmetry) MHD equations driven by Alfvén waves. We find that when the Alfvén wave amplitude is above a parameter‐dependent threshold, LAN waves are generated in the model coronal hole. For typical coronal parameters the solar wind speed and density fluctuate considerably on a timescale of ∼10–40 min and with an amplitude of up to several hundred kmilometers per second near the Sun (r ≲ 10 RS) in agreement with recent interplanetary scintillation observations. The solar wind speed is inversely dependent on the driving frequency in the range 0.35–3 mHz. The amplitude of the velocity fluctuations increases with the amplitude of the magnetic field and the driving Alfvén waves at the base of the corona and decreases with the coronal temperature. We found that for the same typical solar wind and Alfvén wave parameters and an isothermal initial atmosphere, the WKB model predicts 30% higher flow velocities far from the Sun (32 RS) than our self‐consistent wave model with high‐frequency Alfvén waves (ƒ = 2.78 mHz), conforming to the WKB approximation. However, our model predicts significantly higher average flow speed near the Sun. When low‐frequency non‐WKB waves drive the wind, our model predicts 25% higher solar wind speed than the WKB model far from the Sun. This result of our model is in agreement with linear studies of solar wind acceleration by Alfvén waves that take into account Alfvén wave reflection.
Solar wind control of ultralow‐frequency wave activity at L = 3
Authors: Chi P. J. , Russell C. T. , Bloom R. M. , Singer H. J.
Published: February 2004

This study explores the statistical relationships between 2 years of solar wind data recorded by the IMP 8 spacecraft and data from the Mount Clemens magnetometer station (L = 3) to improve our understanding of possible energy sources of ULF wave activity. Within the four frequency bands, f = 4–8 mHz, 8–16 mHz, 16–32 mHz, and 32–64 mHz, that are studied, two distinct types of waves are found. One is at high frequencies corresponding to Pc3 pulsations, and the other is at low frequencies corresponding to Pc5 and low‐frequency Pc4 pulsations. The high‐frequency part clearly has an energy source in the upstream foreshock. However, our analysis shows that the magnetospheric cusps do not appear to be the conduit of energy for the wave activity in this low‐latitude region. The low‐frequency activity occurs most frequently and has greater wave power when the interplanetary magnetic field is southward. This correlation suggests that the major energy source of these low‐frequency waves is substorm‐related or is related to the reconnection on the dayside magnetopause.
The evolution of slab fluctuations in the presence of pressure‐balanced magnetic structures and velocity shears
Authors: Ghosh S. , Matthaeus W. H. , Roberts D. A. , Goldstein M. L.
Published: February 2004

The traditional view that solar wind fluctuations are well‐described as a spectrum of parallel‐propagating Alfvén waves has been challenged many times but is still a frequently encountered perspective. Here we examine whether it remains consistent to view most of the fluctuation energy as resident in parallel‐propagating Alfvén waves in situations in which there are also present either transverse pressure‐balanced (PB) magnetic structures or transverse velocity shears. We address these questions through direct simulation of compressible magnetohydrodynamics, with expansion effects neglected. We show that parallel‐propagating Alfvén waves are redirected to large oblique angles after refractive interactions with PB structures or advective interactions with velocity shears, reflecting the nonequilibrium nature of the initial spectral distribution. The timescale for these processes ranges from 2–8 eddy‐turnover times or characteristic nonlinear times. Relatively small amounts of PB structure and/or shear energy can redirect initially parallel‐propagating Alfvén waves to highly oblique angles. Velocity microstreams appear to be particularly efficient at creating highly oblique waves. Even though the excited wave vectors are eventually primarily oblique, the magnetic variance ratios show a minimum variance in the mean magnetic field direction.
Slowing of energetic O(3P) atoms in collisions with N2
Authors: Balakrishnan N. , Kharchenko V. , Dalgarno A.
Published: February 2004

Energetic atoms influence the composition, the thermal structure and the evolution of the upper atmosphere. We investigate the slowing of energetic O(3P) atoms by elastic and inelastic collisions with N2. Results of quantum mechanical and semiclassical calculations of energy and angle‐resolved cross sections are presented for elastic and inelastic collision of O(3P) with N2. A general analytical expression is developed for the kernel of the Boltzmann equation for the energy distribution function which is valid for elastic and inelastic collisions and incorporates both the angle and the energy dependence of the cross sections. The Boltzmann kernel for the energy relaxation of fast O(3P) atoms is evaluated using the computed cross sections. We report values of the collision frequency, the average energy loss in elastic and inelastic collisions with N2, and the mean time and the number of collisions required to thermalize initially energetic O(3P) atoms. We compare the efficiencies of elastic and inelastic collisions in slowing down fast O(3P) atoms. These data are basic to the development of a reliable model of the atmospheric effects of the hot oxygen atoms produced by dissociative recombination, collisional quenching, photodissociation and photoelectron impact dissociation.
Inner magnetospheric superthermal electron transport: Photoelectron and plasma sheet electron sources
Authors: Khazanov G. V. , Liemohn M. W. , Kozyra J. U. , Moore T. E.
Published: February 2004

Two time‐dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal‐thermal intersection at a few eV, allowing for the calculation of the entire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 1010 eV cm−2 s−1 in the plasmasphere, while heating from the PSEs typically does not exceed 108 eV cm−2 s−1. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.
Recirculation of plasma sheet particles into the high‐latitude boundary layer
Authors: Delcourt D. C. , Sauvaud J.‐A.
Published: February 2004

We examine the transport of plasma sheet particles in the dayside magnetosphere using three‐dimensional single particle codes. In this region of space, whereas the equatorial plane is the locus of the field minimum at low L shells (typically, below L = 8), this field minimum is found at midlatitudes at high L shells. We show that this topological change which follows from the current system at the magnetopause, has important implications for the overall circulation of magnetospheric plasma. It is responsible for de‐trapping of plasma sheet particles originally mirroring at low latitudes. At some point during E×B transport toward the magnetopause, these particles escape from the equatorial vicinity and flow into the cusp region. Because these particles experience different energy changes in the low and high L shell field configurations, significant phasing effects are obtained between bounce and convective motions with possible violation of the second adiabatic invariant. We show that in the region adjacent to the frontside magnetopause, these phasing effects lead to characteristic energy‐latitude spectrograms with repeated streaks of enhanced flux. Most notably, we demonstrate that after their injection into the cusp, the de‐trapped particles can flow back toward the tail along the magnetopause with energies comparable to those inside the plasma sheet. Numerical calculations indicate that recirculation of these plasma sheet particles can significantly contribute to populating of the high‐latitude boundary layer, especially at high energies (a few keV up to a few tens of keV).
The relationship of HF radar backscatter to the accumulation of open magnetic flux prior to substorm onset
Authors: Lewis R. V. , Freeman M. P. , Reeves G. D.
Published: February 2004

We identify a characteristic signature observed in Halley HF radar data during the substorm growth phase and investigate its relationship to magnetotail evolution leading up to substorm onset. The signature is a super‐diurnal equatorward propagation of the equatorward edge of the HF radar backscatter returns. It is found to be characteristic of a particular class of substorms, those which are the first to occur following quiet magnetospheric and ionospheric conditions. By using solar wind data, we estimate the reconnection electric field at the magnetopause for four such events. An empirical relationship is found to exist between the time integral of this electric field and the latitude of the HF radar backscatter. Relating this solely to the addition of open magnetic flux to the polar cap, we would estimate the length of the dayside reconnection X line to be 12 RE. It is likely that additional factors affect this empirical relationship.
Io‐controlled decameter arcs and Io‐Jupiter interaction
Authors: Queinnec Julien , Zarka Philippe
Published: February 2004

The motion of the satellite Io in Jupiter's magnetic field results in an electrodynamic circuit, approximately fixed in Io's frame, revealed by ultraviolet and infrared spots at the footprints of Io's flux tube (IFT) as well as prominent (so‐called “Io‐controlled”) decameter radio arcs. We analyze the frequency‐time shape of nine such arcs, corresponding to four observation geometries (A,B,C,D) and detected over their full frequency extent in joint Nançay and Wind data. We compute the radio beaming angle as a function of frequency and lag of the radio‐emitting flux tube(s) relative to the IFT. No a priori assumption is made regarding the radio source beaming, and its location is only constrained by the emission occurring near the local electron gyrofrequency. We find northern sources for A and B arcs and southern sources for C and D arcs. The shape of all Io arcs is consistent with an origin at a single flux tube (in Io's frame), shifted by an average of 10° (in the south) and 25° (in the north) with respect to the IFT. This lag must be accumulated before Io's magnetic perturbation reaches the radio emission region, at high latitudes, at altitudes ≤ 1 RJ above the Jovian surface. Radio emission is found to be beamed in a hollow cone of average half‐apex angle 70°–75° and thickness ≈1 °. Arc shapes are fully determined by the geometry of observation. Radio fringes preceding the main Io B arcs are well explained by multiple reflections of the magnetic perturbation between Jupiter's ionosphere and Io's torus. The weak trailing part of Io‐ B arcs may be accounted for through double beaming of the radio emission or through a frequency‐dependent lag of the corresponding radio source. The latter explanation suggests an emission scenario in which electron acceleration “leaks” from the magnetic perturbation on its way to Jupiter. Jovian magnetic field models are compared and evaluated in the analysis.
A new method for studying remote type II radio emissions from coronal mass ejection‐driven shocks
Authors: Reiner M. J. , Kaiser M. L. , Fainberg J. , Stone R. G.
Published: February 2004

Some interplanetary shocks associated with coronal mass ejections (CMEs) generate type II radio emissions at the local plasma frequency and/or its harmonic. These type II radio emissions provide a means of remotely studying and tracking CMEs from the solar corona to 1 AU and beyond. New analysis techniques that inherently reveal the dynamics of a CME as it propagates through the interplanetary medium are used for tracking the CME‐associated radio emissions. The techniques make use of dynamic spectra of the radio intensity plotted as a function of inverse frequency and time. When in situ measurements are also available, the analyses determine unequivocally whether the type II radio emissions occurred at the fundamental or harmonic of the local plasma frequency in the upstream or downstream regions of the CME‐driven shock. These new analysis techniques are applied to three type II radio bursts that were observed by the WAVES radio experiment on the Wind spacecraft on May 13–14, November 4–5, and November 6–7, 1997; each event corresponded to a CME observed by SOHO LASCO (large angle and spectrometric coronagraph), and each event was observed in situ by Wind. We find that the type II radio emissions for each of the three events were generated at both the fundamental and harmonic of the plasma frequency in the upstream region of the CME‐driven shock, that the type II emissions appear, in general, to originate in regions along the shock front of higher than normal densities, and that the radio emission sites along the shock front change with time. In one case, additional radio tracking, provided by the direction‐finding analysis, was used to locate the sites of the radio emission along the shock front.
A renormalization group approach to estimation of anomalous diffusion in the unstable equatorial F region
Authors: Hysell D. L. , Seyler C. E.
Published: February 2004

An expression is derived for the anomalous diffusion coefficient associated with collisional interchange turbulence in the equatorial F region ionosphere. Waves with ω ≪ Vin ≪ Ωi are considered. The calculation makes use of the renormalization group method, following closely that of Kichatinov [1985]. The calculation is applied to the problem of plasma waves in the equatorial F region ionosphere generated by the ionospheric interchange instability. Approximations appropriate for the geometry of that problem are incorporated into the calculation. Using a model spectrum of the irregularities based on in situ satellite observations, we calculate that the anomalous diffusion seen by large‐scale plasma waves can be 5 orders of magnitude larger than the ambipolar diffusion coefficient.
Temporal relationship between midtail traveling compression regions and substorm onset: Evidence for near‐Earth neutral line formation in the late growth phase
Authors: Taguchi S. , Slavin J. A. , Kiyohara M. , Nose M. , Reeves G. D. , Lepping R. P.
Published: February 2004

The timing of the near‐Earth neutral line (NENL) formation relative to substorm onset signatures has been a central debate in substorm research for some time. Several recent studies have suggested that the direct identification of the reconnection site, at least in its initial stage, is difficult because it may be a very limited region spatially. Our approach to this timing problem is the examination of the midtail lobe traveling compression regions (TCRs) relative to onset during substorm events. Fifty‐nine midtail TCRs in the IMP 8 magnetotail observations are analyzed. These midtail TCRs differ from the distant tail TCRs in that they lack the first half of the north and south tilting of the field during the compression. The flat Bz phase preceding the south tilting interval in these midtail compression regions has been interpreted as being due to the close proximity to the growing plasmoid bulge just prior to plasmoid ejection down the tail. The results of our analysis show that these TCRs start a few minutes before or simultaneously (accuracy of 1 min) with Pi2 onset at low‐latitude or midlatitude ground stations and the particle injection at the geosynchronous orbit. Before the plasmoid bulge formation starts, the NENL must start to form in the plasma sheet; that is, the formation of NENL must initially occur on closed field lines to form the plasmoids which compress the lobes to cause the TCRs. Our results support this view and allow us to conclude that NENL forms before ground and geosynchronous substorm onset signatures, i.e., in the late growth phase. The implications of these results for magnetospheric substorm models are discussed.
JULIA radar studies of equatorial spread F
Authors: Hysell D. L. , Burcham J. D.
Published: February 2004

This paper presents coherent scatter radar observations of plasma irregularities in the equatorial F region ionosphere made with the JULIA (Jicamarca unattended long‐term studies of the ionosphere and atmosphere) radar and discusses model equations and simulations pertinent to their interpretation. The data set shows that bottom‐type and bottomside scattering layers are prevalent throughout solar minimum equinox. Bottom‐type layers are undifferentiated and relatively weak layers confined to a narrow range of altitudes falling within regions of the ionosphere driven by the E region dynamo. These layers are often precursors to large‐scale radar plumes as well as to bottomside layers, which are broader, more structured, and more intense layers than the bottom‐type variety. Bottomside layers are the source of intermediate‐scale plasma depletions that can ascend and penetrate through to the topside. Fluid simulations of the collisional interchange instability suggest that dynamo theory explains why one kind of layer emerges at a given time and altitude.
Small‐scale, dispersive field line resonances in the hot magnetospheric plasma
Authors: Streltsov A. V. , Lotko W. , Johnson J. R. , Cheng C. Z.
Published: February 2004

The formation, temporal behavior, and spatial structure of field line resonance (FLR) layers formed by shear Alfvén waves standing along auroral magnetic field lines between the ionospheres are investigated when the layer develops transverse structure on the scale of the ion Larmour radius. Using a new numerical model including full ion Larmour radius correction in dipole magnetic geometry with realistic distributions of background plasma temperature and density, the following is shown: (1) Hot magnetospheric ions significantly retard the development of a parallel electric field in ion gyroscale dispersive Alfvén waves. (2) A fundamental FLR forming near L = 7.5 can contract to a transverse scale size of several hundred of meters in the direction perpendicular to the geomagnetic field at ionospheric altitudes, with a parallel electric field sufficient to produce a k V potential drop along the resonance field line from the ionosphere up to ∼ 4 RE altitude, in the region where the wave dispersion is due to the finite electron inertia. (3) A plasma density depletion in the lower auroral magnetosphere (≈ 2–5 RE geocentric distance) enables the formation of a nonradiative fundamental FLR. (4) Dispersive FLRs for the higher harmonics are more radiative at the equatorial magnetosphere than the fundamental mode.
Electron‐impact excitation and emission cross sections of the H2 Lyman and Werner Systems
Authors: Liu Xianming , Shemansky D. E. , Ahmed Syed M. , James G. K. , Ajello J. M.
Published: February 2004

Excitation functions of the H2 Lyman (Ly) (
B1∑∑u ‐ X1∑∑g) and Werner (W) (C1∏u ‐ X1∑∑g ) band systems have been reanalyzed using a combination of measurements and theoretical considerations. These systems are prominent emitters in outer planet atmospheric dayglow and auroral activity and can be used to infer energy deposition and heating rates. Earlier measurements of the cross sections reported by Shemansky et al. [1985a] have been found to be inaccurate in the threshold energy region. A combination of high‐resolution spectral and shape function measurements obtained at the Jet Propulsion Laboratory (JPL) in low‐ and medium‐energy regions have been used to obtain relative excitation shape functions of the two systems. At energies above 250 eV, we have used the measurements obtained earlier by De Heer and Carrière [1971] in order to define the first two terms of the Born electric dipole collision strength. The complete set of collision strength terms is obtained by combining the JPL and De Heer and Carrière [1971] data. We have found that, contrary to results of Shemansky et al. [1985a], the shape functions of the H2 Ly and W systems, expressed in units of threshold energy, are the same within experimental error. Absolute cross sections of the H2 Ly and W systems are established using the theoretical oscillator strengths of Abgrall et al. [1987, 1993a, b, c] and Abgrall and Roueff [1989]. The atomic hydrogen H Ly α emission cross section resulting from dissociative excitation of H2 at 100 eV obtained from relative intensities of H2 W emission lines is also derived and compared with other experimental measurements. At a gas temperature of 300 K and electron energy of 100 eV, the cross sections for the H Ly α, H2 Ly, and W emissions are (0.716 ± 0.095) × 10−17, (2.62 ± 0.34) × 10−17, and (2.41 ± 0.31) × 10−17 cm2, respectively. The accuracy of the absolute values and shape functions is limited primarily by electron gun performance, as was the case for Shemansky et al. The rotational dependence of the transition dipole matrix elements and perturbations between the B 1∑+u and C1∏+u states have a significant effect on the cross sections.
Solar cycle variability of hot oxygen atoms at Mars
Authors: Kim Jhoon , Nagy Andrew F. , Fox Jane L. , Cravens Thomas E.
Published: February 2004

The population of hot oxygen atoms in the Martian exosphere is reexamined using newly calculated hot O production rates for both low and high solar cycle conditions. The hot oxygen production rates are assumed to result from the dissociative recombination of O2+ ions. These calculations take into account the calculated vibrational distribution of O2+ and the new measured branching ratios. Furthermore, these calculations also consider the variation of the dissociative recombination cross section with the relative speed of the participating ions and electrons, the rotational energy of the O2+ ions, and the spread of the ion and electron velocities. These production rates were next used in a two‐stream model to obtain the energy dependent flux of the hot oxygen atoms as a function of altitude. Finally, the calculated flux at the exobase was input into an exosphere model, based on Liouville's theorem, to calculate the hot oxygen densities as a function of altitude in the exosphere and the resulting escape flux. It was found that hot oxygen densities vary significantly over the solar cycle; the calculated densities vary from about 2×103 to 6×103 cm−3 at an altitude of 1000 km. The escape flux also varies from about 3×106 to 9×106 cm−2s−1.
Occurrence of equatorial F region irregularities: Evidence for tropospheric seeding
Authors: McClure J. P. , Singh S. , Bamgboye D. K. , Johnson F. S. , Kil Hyosub
Published: February 2004

We present a new gap‐free version of the seasonal and longitudinal (s/l) variations of PEFI, the equatorial F region irregularity (EFI) occurrence probability, based on data from the AE‐E spacecraft. The agreement of this and three earlier partial PEFI patterns verifies all four. We reinterpret another earlier gap‐ridden pattern, that of
a topside ionogram index of average darkening by range spread F. We comparent with PEFI and, using ionosonde radio science considerations, we conclude that = PEFI times a factor depending on the average number of topside plasma bubbles visible to the ionosonde. The s/l variations of thus imply s/l variations in the average spacing of bubbles, whose seeds have an occurrence probability pattern Pseed. For discussion we assume PEFI = PinstPseed, where Pinst is the pattern of F region instability. The PEFI pattern, which is by definition independent of seed and/or bubble spacing, is far too complex to be explained by the dominant paradigm, that of changes in Pinst by simple changes in the F region altitude and/or north–south asymmetry. We examine evidence behind this dominance, and find it unconvincing. Both the asymmetry and sunset‐node/altitude hypotheses of 1984 and 1985, respectively, seem to be partly based on misunderstood data, and their features appear displaced in time and space from those of our repeat able PEFI pattern. In contrast, if Pseed variations influence the PEFI pattern and depend on thermospheric gravity waves from tropospheric convection near the dip equator, then the seasonal maxima (minima) of PEFI could be explained, since they all occur above relatively warm (cold) surface features, where convection is maximal (minimal). Also, the hypothesis of the dominance of the Pseed term could explain an unusual December/January PEFI maximum in the deep, wide, normal Pacific minimum in the one data set obtained in El Niño years. Based on the experiments we consider, we predict that the s/l variations of Pseed will be found to be similar to those of PEFI, and largely to explain them. Finally, we find reasons, based on the similarity of the

variations to s/l patterns of the average scintillation index, for not using, as is commonly done, such scintillation patterns as substitutes for PEFI or Pinst patterns.
Two spacecraft observations of transient shocks and ejecta in the interplanetary medium
Authors: González‐Esparza J. Américo , Bravo Silvia
Published: February 2004

We compare Ulysses observations of 22 forward transient shocks (FTSs) and 11 ejecta during the first 19 months of its mission, with observations near Earth by IMP, in order to infer some properties of the propagation of these transient events in the interplanetary medium. We found that 13 of the 22 FTSs detected by Ulysses were also detected by IMP. The average of the mean radial transit speed of these 13 FTSs from 1 AU to Ulysses was about 504 km/s, which is slower than previous reports of transit speeds within 1 AU, suggesting shock deceleration beyond 1 AU. We found that whenever (in all cases) the two spacecraft detected the same FTS, the spacecraft were located within the same magnetic sector. During the period of the study we found 9 FTSs detected only by Ulysses and 10 FTSs detected only by IMP. For 16 of these shocks the two spacecraft were located within different magnetic sectors. The results suggest that magnetic sectors play a role in the propagation of transient shocks. Of the 11 ejecta detected by Ulysses, 7 of them also passed by IMP. The average of the mean radial transit speed of the 7 ejecta was about 407 km/s. In every case the radial width of the ejecta was larger at Ulysses than at IMP, showing a radial expansion with heliocentric distance. In the four events that we could estimate the shock‐ejecta radial separation at 1 AU and Ulysses, we found that this radial distance was larger at Ulysses.
Dynamic features of the polar wind in the presence of hot magnetospheric electrons
Authors: Barakat A. R. , Demars H. G. , Schunk R. W.
Published: February 2004

A time‐dependent macroscopic particle‐in‐cell (mac‐PIC) model was used to study the temporal evolution of the polar wind under the influence of a hot electron population. First, the steady state results of the mac‐PIC model were found for a wide range of hot/cold electron temperature ratios and compared with the results of the well‐established time‐independent semikinetic model, and excellent agreement was found. Second, simulations were conducted to study the temporal evolution of a plasma that was originally in a steady state condition, and then a hot electron population was suddenly introduced. The profiles of the plasma moments again displayed discontinuities, which oscillated with a decreasing amplitude until they reached their steady state values. As the hot electron temperature increased, the oscillation amplitude increased, and the altitude of the discontinuity decreased, while the period of oscillation and decay rate remained essentially unchanged. Third, simulations were conducted for plasma flux tubes as they drifted across the subauroral, cusp, polar cap, and auroral regions. It was found that as soon as the plasma entered the polar cap, the signatures of the hot electrons were observed. The strength of these signatures varied with time owing to the variation in the instantaneous values of the density and temperature of the thermal electrons. After the plasma exited the polar cap the signatures of the hot electrons persisted for a while, and a density bump formed. For more energetic hot electrons the signatures of the hot electrons became more pronounced in the polar cap and persisted longer after the flux tube left the polar cap. The results of this study were shown to explain some interesting features of the polar wind that were observed by the POLAR satellite.
Electron temperature in the solar wind: Generic radial variation from kinetic collisionless models
Authors: Meyer‐Vernet Nicole , Issautier Karine
Published: February 2004

We calculate analytically the radial profile of the average electron temperature in the solar wind with a kinetic collisionless model. The electron temperature profile at large distances r is the sum of a term oc r−4/3 plus a constant, with both terms of the same order of magnitude near r ∼ 1AU. This result is generic as it is weakly dependent on the particle velocity distributions in the corona. It provides a natural explanation for the observed electron temperature profile near 1 AU, which is in the low or middle part of the range between isothermal and adiabatic behaviors. The r−4/3 term comes from the isotropically distributed electrons confined by the heliospheric electric potential, which is found to have a similar radial variation. The constant term comes from the parallel temperature of the electrons energetic enough to escape. The calculated profile flattens as r increases and tends to be flatter in the high‐speed wind. We also give simple explicit expressions for the electron temperature and density at large distances and for the terminal wind velocity as a function of coronal parameters when the electron velocity distribution is a Kappa function, which is close to a Maxwellian with a suprathermal tail.