bluuebunny/crossref_metadata_2025 huggingface dataset:
Multisatellite comparisons of the radiation belt response to the Geospace Environment Modeling (GEM) magnetic storms
Authors: McAdams K. L. , Reeves G. D. , Friedel R. H. W. , Cayton T. E.
Published: February 2004

We present a compilation of observations of relativistic radiation belt electrons during the four Geospace Environment Modeling (GEM) storms from instruments on 10 separate spacecraft. While these four magnetic storms have very different solar wind and magnetospheric conditions, there are several characteristics of the relativistic electron response which are applicable to all four storms. We find that although the evolution of the spectral shape of the electrons at a specific L shell does not vary from storm to storm, the evolution is very different at L = 4.2 and L = 6.6. Calculations of the phase space density (PSD) show that the evolution of the PSD depends on both radial position and the value of the first adiabatic invariant. The evolution of the greater than 1‐MeV electron flux at L = 4.2 and L = 6.6 for the four storms is consistent with the findings of Reeves et al. [1998c]. The flux at L = 4.2 peaks quickly after the storm (12 hours), while the fluxes at geosynchronous altitudes take several days to rise. We suggest that the common characteristics identified in the four storms that are the subject of this paper can provide a useful basis for comparisons with other storms and for development of a more complete theoretical description of relativistic electron events in general.
Reconstruction of electron precipitation characteristics from a set of multiwavelength digital all‐sky auroral images
Authors: Janhunen P.
Published: February 2004

We present a method for reconstructing the precipitating electron flux from a set of multiwavelength digital all‐sky auroral images. The method involves solving a large linear inversion problem, and it works for any number of all‐sky imager stations and wavelengths. The idea in our method is to invert the energy‐dependent precipitating electron flux directly and not the three‐dimensional volume emission rate as an intermediate step. In this way, the inversion is automatically restricted to physical emission rate profiles. We show the effectiveness of the method in the all‐sky camera case by simulated examples. The method is also applied to real data. The method is capable of correctly reconstructing not only auroral arc positions but also the precipitating electron energy and number fluxes, although not necessarily the full differential flux. A natural limitation is that arcs that are significantly off‐zenith and are viewed sideways by only one all‐sky camera station are smeared out. However, even for these arcs the average arc position and energy characteristics come out with reasonable accuracy.
Nonlinear emission mechanism for continuum radiation in Jupiter's magnetosphere
Authors: Macek Wieslaw M.
Published: February 2004

The question of how continuum radiation trapped in Jupiter's magnetosphere might be generated is considered. It is shown that the efficiency of the linear conversion is not sufficient to account for the observed intensity of the emission. We discuss nonlinear processes that can more easily provide the required conversion efficiency. The field strengths of upper hybrid waves required to generate the fundamental harmonic emissions are ∼0.5 ÷ 4 mV m−1. Comparison of the results of the discussed model with electric fields reported in the Jovian magnetosphere shows that the model adequately explains the generation of continuum radiation trapped in the planetary cavity.
Interstellar hydrogen atom distribution function in the outer heliosphere
Authors: Izmodenov Vladislav V. , Gruntman Mike , Malama Yury G.
Published: February 2004

We study the evolution of the velocity distribution function of interstellar hydrogen atoms in the heliospheric interface, the region of solar and interstellar wind interaction. The velocity distribution is a key tool to evaluate uncertainties introduced by various simplified models of the interface. We numerically solve the kinetic equation for neutral gas self‐consistently with the hydrodynamical equations for plasma. Neutral and plasma components efficiently coupled by charge exchange. This interaction disturbs the atom velocity distribution, which is assumed to be Maxwellian in the circumsolar local interstellar medium. It is shown that besides “original” interstellar atoms, there are three other important atom populations originating in the heliospheric interface. We present velocity distribution functions of these populations in various locations of the interface region and discuss their kinetic properties.
Complete wave‐vector directions of electromagnetic emissions: Application to INTERBALL‐2 measurements in the nightside auroral zone
Authors: Santolík O. , Lefeuvre F. , Parrot M. , Rauch J. L.
Published: February 2004

We present several newly developed methods for wave propagation analysis. They are based on simultaneous measurement of three magnetic field components and one or two electric field components. The purpose of these techniques is to estimate complete wave vector direction and the refractive index. All the analysis results are validated by well defined simulated data. Propagation analysis of natural emissions in the night‐side auroral zone at high altitudes is done using the data of the MEMO (Mesures Multicomposantes des Ondes) experiment onboard INTERBALL‐2. The results show that a bursty whistler mode emission propagates toward the Earth near the resonance cone. Upward propagating auroral kilometric radiation in the R‐X mode represents another example demonstrating the potential of such analysis for future applications.
Convection electric field observations near the Arecibo HF heater beam
Authors: Peria W. J. , Kelley M. C.
Published: February 2004

Electric fields have been observed at the westward edge of the Arecibo HF heater beam, at the F region reflection altitude, by a sounding rocket. We first show that the floating double probe used for these measurements is functioning reliably. The data are shown to be free of sheath rectification effects within the heated volume. Away from the heater beam the double probe data show primarily motional emf, consistent with Earth frame fields of less than 2 m V m−1 (typical, on average, of summer post‐midnight conditions over Arecibo), while near the heater beam, significant Earth frame fields are observed. The convective drift due to these fields is consistent with the apparent drift of simultaneously measured heater‐induced field‐aligned irregularities. The measured convection electric field magnitude is used to estimate the strength of the current maintaining it against the background conductivity, yielding 5 mA m−1. Estimates of the current due to ponderomotive force are lower than this value, unless one invokes electrostatic waves with electric fields roughly 8 times that of the pump field. Temperature gradient currents are estimated as well and are a possible source. The observed shear in the convection electric field is used to estimate a field‐aligned current density of 0.5 μA m−2. We conclude that the heater is indeed driving convection on the scale size of the heated volume but are unable to definitively determine how the corresponding electric fields are being produced.
A new model of solar EUV irradiance variability: 1. Model formulation
Authors: Warren H. P. , Mariska J. T. , Lean J.
Published: February 2004

We present a new model of solar irradiance variability at extreme ultraviolet wavelengths (EUV, 50–1200 Å). In this model, quiet Sun, coronal hole, and active region intensities for optically thin emission lines are computed from emission measure distributions determined from spectrally and spatially resolved observations. For optically thick emission lines and continua, empirical values are used. The contribution of various solar features to the spectral irradiance variability is determined from a simple model of limb‐brightening and full‐disk solar images taken at the Big Bear Solar Observatory and by the Soft X‐Ray Telescope on Yohkoh. To extend our irradiance model beyond the time period covered by the available images, we use correlations with proxies for solar activity. Comparisons with the available irradiance data from the Atmospheric Explorer E (AE‐E) spacecraft show that our model is capable of reproducing the rotational modulation of the EUV irradiance near solar maximum. The AE‐E data, however, show systematically more solar cycle variability than our model estimates.
Using transient decreases of cosmic rays observed at Voyagers 1 and 2 to estimate the location of the heliospheric termination shock
Authors: Webber W. R. , Lockwood J. A. , McDonald F. B. , Heikkila B.
Published: February 2004

We have examined the intensity‐time profiles of outward moving transient decreases of anomalous and galactic cosmic rays observed by Voyager 1 (Vl) and Voyager 2 (V2) in 1998 and 1999 in the outer heliosphere. The goal of this study is to compare these intensity‐time profiles with those obtained by le Roux and Fichtner [1999] using numerical simulations of the time‐dependent cosmic ray modulation produced by the passage of large global merged interaction regions. Their calculations show that when these interaction regions reach the heliospheric termination shock, they weaken rapidly causing the intensity of both galactic and anomalous cosmic rays to increase rapidly. They suggest using this time of rapid increase and the propagation times of these events to determine the location of the termination shock. Three outward propagating transient decreases were observed during the 1998–1999 time period. Because of local temporal variations the first two events did not exhibit a le Roux‐Fichtner type of rapid recovery. However, the third event starting on day 50 of 1999 at V1 exhibited a very sharply defined intensity‐time profile with a very rapid recovery starting on day 88 ± 3 of 1999 that was observed in three energy channels on V1. From this time delay we are able to determine that the termination shock was 9.5–10.7 AU beyond V1 or at a distance of 82.6–83.8 AU at this time. The intensity‐time profile at V2 was less sharp, but the rapid recovery that was observed occurred at the same time (±5 days) as that at V1, thus confirming the conclusions from the V1 data. At its present outward speed of 3.6 AU yr−1, V1 would be expected to encounter the termination shock at this location as early as the last quarter of 2001.
Dynamics of the substorm expansive phase
Authors: Friedrich E. , Samson J. C. , Voronkov I. , Rostoker G.
Published: February 2004

Meridian‐scanning photometer (MSP) and magnetometer data from the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) ground‐based array have been used to study the dynamics of the substorm expansive phase. The relative latitudinal motions of the MSP 630.0, 557.7, and 486.1 nm emissions for eight isolated events have been studied. The data show the expansive phase to comprise three stages: an explosive (tens of seconds) onset; rapid poleward motion of 557.7 nm emissions of the order of a few minutes; and a period of slower (tens of minutes) poleward moving 630.0 nm emissions. We interpret the rapid poleward motion of the 557.7 nm data in terms of a region of instability, expanding rapidly down the magnetotail, possibly accelerating plasma sheet electrons as it proceeds. All events show that lobe flux reconnection occurs after near‐Earth onset, with typical time delays between 1 and 5 min. The extremely short time interval between near‐Earth onset and the beginning of lobe flux reconnection presents a severe observational constraint on any substorm model which attempts to explain the substorm expansive phase. Magnetometer data from the CANOPUS Churchill line have been used to study the dynamics of the substorm electrojets during the growth and early expansive phases of the substorm. The borders of these electrojets closely follow the motion of the MSP data during the growth and expansive phases. At the instant of expansive phase onset the growth phase electrojets (as observed along the Churchill meridian line) disappear, being replaced by the substorm westward electrojet associated with the current wedge. The equatorward border of the substorm westward electrojet is embedded within the proton aurora emissions and appears at expansive phase onset ∼2° equatorward of the growth phase electrojets, further showing the near‐Earth proximity of expansive phase onset. No indication of reconnection on closed field lines prior to expansive phase onset was observed in either the magnetometer or the photometer data.
Earthward flow bursts, auroral streamers, and small expansions
Authors: Nakamura R. , Baumjohann W. , Schödel R. , Brittnacher M. , Sergeev V. A. , Kubyshkina M. , Mukai T. , Liou K.
Published: February 2004

Earthward flow bursts associated with small auroral expansions, including pseudobreakups, and auroral streamers are studied by using Geotail plasma and magnetic field data and Polar ultraviolet imager data. These flow bursts are accompanied by dipolarization and decrease in the plasma pressure, which are consistent with the characteristics of so‐called bubbles, and have a timescale of 2.5 min on average. Based on a statistical study of the flow bursts, it is shown that the location of the flows are centered about 0.4 hour magnetic local time east of the center of auroral expansion and are localized with a width of 3 – 5 RE. This relationship supports the idea that a dawn‐to‐dusk polarization electric field is created in the bubble to enhance the flows. The flow bursts associated with the small expansions, which are mainly observed in the region earthward of 15 RE, show more distinct signatures of compression at the front side of the flow, which possibly leads to the stopping of these flows. Flow bursts related to auroral streamers, which are observed mainly tailward of 15 RE, take place during relatively thick plasma sheet configurations, and are accompanied by stronger flow shear.
Energetic neutral atom imaging of the heliospheric boundary region
Authors: Gruntman Mike , Roelof Edmond C. , Mitchell Donald G. , Fahr Hans J. , Funsten Herbert O. , McComas David J.
Published: February 2004

Energetic neutral atom (ENA) imaging is a powerful technique, which can remotely probe the properties of distant hot plasmas. Hot plasmas are abundant at the heliospheric boundary, the region where the expanding solar wind meets the surrounding local interstellar cloud. Here we present a new concept for imaging this boundary in ENA fluxes. Heliospheric ENAs are born from charge exchange between energetic protons and the background interstellar atomic hydrogen gas. The technique is ideal for studying the asymmetric three‐dimensional heliospheric interface region remotely, from 1 AU. We show that ENA imaging in the 0.2–6 keV energy range will establish the nature of the termination shock and properties of hot proton populations in the heliosheath. We also examine how the evolution of pickup proton populations at and beyond the shock can be explored. Global heliosphere ENA images will distinguish among the competing models of the interaction between the Sun and the local interstellar medium, and they will reveal the physics of important processes in the interface region. Heliospheric ENA fluxes are exceptionally weak, which makes imaging implementation difficult. Nonetheless, we show how single‐pixel ENA sensors can image the heliosphere from a spinning spacecraft on a typical mission near 1 AU. The required instrumentation is briefly discussed.
On the power‐velocity relationship for 12‐ and 50‐MHz auroral coherent echoes
Authors: Makarevitch R. A. , Ogawa T. , Igarashi K. , Koustov A. V. , Sato N. , Ohtaka K. , Yamagishi H. , Yukimatu A.
Published: February 2004

Nearly simultaneous observations of 12‐ and 50‐MHz coherent echoes at the Antarctic Syowa station are considered for studying the power‐Doppler velocity relationship at these significantly different radar frequencies. We concentrate on postmidnight measurements when both 12‐ and 50‐MHz echoes were seen as narrow bands (∼150–200 km) of strong backscatter at short distances of <500 km. First, we examine the slant range profiles for the power and Doppler velocity by averaging data for nine separate events in March 1997. At 50 MHz the power was found to increase with velocity. At 12 MHz a power increase was found only in the velocity range of 100–350 m s−1. For larger velocities a saturation of 12‐MHz echo power and even some power decrease were seen. To further explore the effect, we restricted the database to only almost simultaneous records at 12 and 50 MHz. We show that overall measured 12‐ and 50‐MHz velocity values are similar, with significant deviations at some moments. We again found a power increase with velocity for 50‐MHz echoes. We also confirm a 12‐MHz power increase for relatively low velocities, in between 50 and 450 m s−1. For larger 12‐MHz velocities, data indicate clear saturation of the power and power decrease, though the latter effect is very subtle. We argue that the 12‐MHz power saturation and decrease at large velocities are not due to smaller electrojet irregularity intensity at these velocities but, rather, to irregularity intensity decrease with height and 12‐MHz radio wave focusing on the top of the electrojet layer.
Near‐simultaneous Polar and DMSP measurements of topside ionospheric field‐aligned flows at high latitudes
Authors: Zeng W. , Horwitz J. L. , Stevenson B. A. , Wu X.‐Y. , Su Y.‐J. , Craven P. D. , Rich F. J. , Moore T. E. , Tu J.‐N.
Published: February 2004

Near‐simultaneous observations of topside O+ parallel flows are presented for four periods of measurement by the Polar and DMSP satellites during April 1996. The Polar measurements were from southern perigee measurements near 5000 km altitude, while the DMSP measurements were from 840 km altitude. In general, the velocities were upward at expected cleft and auroral latitudes, typically about 2–10 km s−1 at 5000 km altitude, and 0–2 km s−1 at 840 km altitude. At the highest, polar cap latitudes, downward velocities were more frequent at both altitudes, but especially at the lower 840 km altitude. The downward velocities were typically a few hundred meters per second at 840 km altitude, and 0–1 km s−1 at 5000 km altitude. In some instances, downward velocities were observed at 840 km altitude while upward O+ flows were observed at 5000 km altitude, possibly on the same flux tube. The O+ densities were characteristically 1–10 O+ cm−3 at 5000 km altitude and 103 – 104 O+ cm−3 at 840 km altitude, while the O+ fluxes were characteristically 105 – 107 O+ cm−2 s−1 at 5000 km altitude and characteristically 107 – 109 O+ cm−2 s−1 at 840 km altitude. We have also examined the dual‐altitude parameter measurements for a polar cap field line, the Polar and DMSP measurements approximately 30 min apart, and compared them with results from a transport simulation. The simulated high‐altitude velocity altitude profiles for the period during and after the initiation of the auroral processes generally bracketed the observations, but the observed downward velocities (500 – 600 m s−1) at 840 km altitude were much larger in magnitude than those in the transport simulation, and the simulated densities were several times higher than those observed at both altitudes.
Investigation of magnetopause reconnection models using two colocated, low‐altitude satellites: A unifying reconnection geometry
Authors: Boudouridis A. , Spence H. E. , Onsager T. G.
Published: February 2004

Ion precipitation data from two co‐orbiting Defense Meteorological Satellite Program satellites (F6 and F8) are used to investigate magnetopause reconnection models. We examine differential fluxes between 30 eV and 30 keV, from a Southern Hemisphere, prenoon pass during the morning of January 10, 1990. Data from the first satellite to pass through the region (F6) show two distinct ion energy dispersions ∼1° of latitude apart, between 76° and 79° magnetic latitude. The electron data exhibit similar features at around the same region but with no or little energy dispersion, consistent with their high velocities. We suggest that the two energy dispersions can be explained by two separate injections resulting from two bursts of magnetopause reconnection. Data from the second satellite (F8), which moved through the same region l min later, reveal the same energy‐dispersed structures, only further poleward and with less overall flux. This temporal evolution is consistent with two recently reconnected flux tubes releasing their plasma as they move antisunward away from dayside merging sites. However, an observed overlap between the two ion energy dispersions suggests a more complex reconnection geometry than usual models can accommodate. We propose a generalized reconnection scenario that unifies the Bursty Single X‐Line and the Multiple X‐Line Reconnection models. A simple time‐of‐flight particle precipitation model is constructed to reproduce the ion dispersions and their overlap. The modeling results suggest that for time‐dependent reconnection the dispersion overlap is observed clearly at low altitudes only for a short period compared with the evolution timescale of the ion precipitation.
Impact of model differences on quantitative analysis of FUV auroral emissions: Total ionization cross sections
Authors: Germany G. A. , Lummerzheim D. , Richards P. G.
Published: February 2004

A sensitivity study was performed in which the peak height of modeled FUV auroral emissions was displaced in altitude, an effect that can result from several causes in the modeling process. The purpose of the study was to examine the impact of such displacements on energy parameters extracted from FUV auroral observations. For this study, the N2 total ionization cross section was modified above 1 keV. Cross‐sectional modifications are investigated for a variety of reasons including the fact that they can directly impact modeled emission height profiles and because different cross‐section sets are adopted by different modelers. Though physically unrealistic, the magnitude of the change in cross section considered here is large enough that this study covers the expected range of uncertainties within a single model or between two or more different models. The values reported here can thus be viewed as upper limits for these uncertainties. The high‐energy modifications result in changes of up to 3 km in the altitude of peak emission for FUV emissions excited by 10‐keV electrons. For calculations using data from the Polar Ultraviolet Imager, derived energy flux and mean energy are changed by up to 16% and 23%, respectively, for 10‐keV incident electrons.
Seasonal and solar cycle variations of the ionospheric peak electron density: Comparison of measurement and models
Authors: Richards P. G.
Published: February 2004

This paper examines the ability of empirical and physical models to reproduce the peak electron density of the midlatitude ionospheric F2 region (NmF2) from 1976 to 1980. The data from all midlatitude stations show a tendency toward a semiannual variation in noon NmF2 with peaks at the equinoxes for all levels of solar activity. The Southern Hemisphere semiannual variation is more pronounced than in the Northern Hemisphere primarily because the winter density is relatively low in the Southern Hemisphere. At most locations the equinox density peaks are approximately equal. However, the September peak is much weaker than the March peak at most Australian stations. This leads to a distinct longitudinal variation between the Australian and South American sectors. On the other hand, there is remarkably little longitudinal variation in the Northern Hemisphere. We present calculations from the field line interhemispheric plasma (FLIP) model from 1976 to 1980 at six representative midlatitude stations around the globe. The FLIP model reproduces the average seasonal and solar cyclical behavior of the measured NmF2 remarkably well most of the time. The greatest differences of 50% occur at the March equinox in the South American region and at the September equinox in the Australian region during September solstice solar maximum. The international reference ionosphere (IRI) model reproduces the average NmF2 even better than the FLIP model but, unlike the FLIP model, it has little day‐to‐day variation. A factor of 2 increase in the solar EUV ion production rate and in the atomic to molecular density ratio at the F2 region peak height (hmF2) produces a factor of 4 increase in NmF2 over a solar cycle. Most of this increase takes place before the average solar activity index (F10.7) reaches 175. At solar maximum in 1979 and 1980, there is little relationship between daily F10.7 and NmF2. Changes in the atomic to molecular density ratio at hmF2 are primarily responsible for the semiannual variation in the FLIP model NmF2. The inclusion of vibrationally excited N2 in the FLIP model improves the relative seasonal and solar cycle NmF2 variations in the FLIP model, but it causes the overall NmF2 to be too low at most stations.
Period and phase comparisons of near‐decadal oscillations in solar, geomagnetic, and cosmic ray time series
Authors: Juckett David A.
Published: February 2004

A more complete understanding of the periodic dynamics of the Sun requires continued exploration of non‐11‐year oscillations in addition to the benchmark 11‐year sunspot cycle. In this regard, several solar, geomagnetic, and cosmic ray time series were examined to identify common spectral components and their relative phase relationships. Several non‐11‐year oscillations were identified within the near‐decadal range with periods of ∼ 8, 10, 12, 15, 18, 22, and 29 years. To test whether these frequency components were simply low‐level noise or were related to a common source, the phases were extracted for each component in each series. The phases were nearly identical across the solar and geomagnetic series, while the corresponding components in four cosmic ray surrogate series exhibited inverted phases, similar to the known phase relationship with the 11‐year sunspot cycle. Cluster analysis revealed that this pattern was unlikely to occur by chance. It was concluded that many non‐11‐year oscillations truly exist in the solar dynamical environment and that these contribute to the complex variations observed in geomagnetic and cosmic ray time series. Using the different energy sensitivities of the four cosmic ray surrogate series, a preliminary indication of the relative intensities of the various solar‐induced oscillations was observed. It provides evidence that many of the non‐11‐year oscillations result from weak interplanetary magnetic field/solar wind oscillations that originate from corresponding variations in the open‐field regions of the Sun.
Ion composition of the near‐Earth plasma sheet in storm and quiet intervals: Geotail/EPIC measurements
Authors: Nosé M. , Ohtani S. , Takahashi K. , Lui A. T. Y. , McEntire R. W. , Williams D. J. , Christon S. P. , Yumoto K.
Published: February 2004

We investigate the ion composition of the near‐Earth plasma sheet in storm and quiet intervals, using energetic (9–210 keV) particle flux data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particle and ion composition (EPIC) instrument on the Geotail spacecraft. In 1998 four magnetic storms (minimum Dst<−50 nT) occurred when Geotail was located in the near‐Earth plasma sheet (X≥−10 RE). For each of the storms, we have selected a corresponding quiet interval from time periods when Geotail revisited the near‐Earth plasma sheet under the condition Dst>−20 nT. The energy density of the H+, He+, and O+ ions was computed from the EPIC/STICS data for these storm and quiet‐time events. We obtained the following results: (1) The energy density is higher during storms than during quiet times for all ion species (H+, He+, and O+); (2) the He+/H+ energy density ratio during storms is 0.01–0.02, while that during quiet times is ∼0.01; and (3) the O+/H+ energy density ratio is significantly larger during storms (0.2–0.6) than during quiet times (0.05–0.1). To explain these results we suggested a current sheet acceleration mechanism in which ions are energized by the dawn‐to‐dusk convection electric field in a mass‐dependent way in the course of interaction with the current sheet.
Modeling the quiet time inner plasma sheet protons
Authors: Wang Chih‐Ping , Lyons Larry R. , Chen Margaret W. , Wolf Richard A.
Published: February 2004

In order to understand the characteristics of the quiet time inner plasma sheet protons, we use a modified version of the Magnetospheric Specification Model to simulate the bounce averaged electric and magnetic drift of isotropic plasma sheet protons in an approximately self‐consistent magnetic field. Proton differential fluxes are assigned to the model boundary to mimic a mixed tail source consisting of hot plasma from the distant tail and cooler plasma from the low latitude boundary layer (LLBL). The source is local time dependent and is based on Geotail observations and the results of the finite tail width convection model. For the purpose of self‐consistently simulating plasma motion and a magnetic field, the Tsyganenko 96 magnetic field model is incorporated with additional adjustable ring‐current shaped current loops. We obtain equatorial proton flow and midnight and equatorial profiles of proton pressure, number density, and temperature. We find that our results agree well with observations. This indicates that the drift motion dominates the plasma transport in the quiet time inner plasma sheet. Our simulations show that cold plasma from the LLBL enhances the number density and the proton pressure in the inner plasma sheet and decreases the dawn‐dusk asymmetry of the equatorial proton pressure. From our approximately force‐balanced simulations the magnetic field responds to the increase of pressure gradient force in the inner plasma sheet by changing its configuration to give a stronger magnetic force. At the same time, the plasma dynamics is affected by the changing field configuration and its associated pressure gradient force becomes smaller. Our model predicts a quiet time magnetic field configuration with a local depression in the equatorial magnetic field strength at the inner edge of the plasma sheet and a cross‐tail current separated from the ring current, results that are supported by observations. A scale analysis of our results shows that in the inner plasma sheet the magnitude of the Hall term in the generalized Ohm's law is not small compared with the quiet time electric field. This suggests that the frozen‐in condition E = −v×B is not valid in the inner plasma sheet and that the Hall term needs to be included to obtain an appropriate approximation of the generalized Ohm's law in that region.
Solar variability and climate
Authors: Sofia Sabatino , Li Linghuai H.
Published: February 2004

Recent precise observations of solar global parameters are used to calibrate an upgraded solar model which takes into account magnetic fields in the solar interior. Historical data about sunspot numbers (from 1500 to the present) and solar radius changes (between 1715 and 1979) are used to compute solar variability on timescales of years to centuries. The results show that although the 11 year variability of the total irradiance is of the order of 0.1%, additional, longer‐lived changes of the order of 0.1% may have occurred in the past centuries. These could, for example, account for the occurrence of climate excursions such as little ice ages.
Periodicity of 151 days in outer heliospheric anomalous cosmic ray fluxes
Authors: Hill M. E. , Hamilton D. C. , Krimigis S. M.
Published: February 2004

Statistically significant variations have been observed in the differential flux of ∼27‐MeV anomalous cosmic ray (ACR) oxygen, helium, and protons at the Voyager 1 spacecraft during 1998 and 1999 (at a helioradius of ∼73 AU). The quasiperiodic variations are in phase, with oxygen and helium having periods near 151 days, while protons exhibit a period of ∼146 days. The Voyager 1 ACRs vary by ∼30% with respect to the trend, and similar galactic cosmic ray variations, if they exist, must be less than ∼5%, probably much less. No similar, significant periodicities have been detected for these same ACR species at Voyager 2 (at 57 AU) during this period. We report on these and other periodicities in the Voyager Low Energy Charged Particle experiment measurements and address the possible connection between this ∼151‐day ACR periodicity and the previously discovered ∼154‐day periodicities in solar flares, the interplanetary magnetic field, and other phenomena.
Seasonal and solar cycle variations of the polar wind
Authors: Demars H. G. , Schunk R. W.
Published: February 2004

Until recently, theoretical models of the polar wind were one‐dimensional. In these models, reasonable but ad hoc boundary conditions were fed to a mathematical model, which was then solved to provide either a steady state or time‐dependent description of the plasma along a particular field line. These models were inherently unable to address the three‐dimensional structure of the polar wind. Now, a truly global model of the polar wind has been developed. This model is a three‐dimensional, time‐dependent, fluid model that self‐consistently couples the ionosphere and the polar wind. It describes the plasma dynamics in a large number of high‐latitude flux tubes as they move under the combined influence of corotational and convection electric fields. The model incorporates realistic models of the high‐latitude convection and auroral electron precipitation. In this study, the global model of the ionosphere and polar wind was used to illuminate the seasonal and solar cycle variability of the polar wind's three‐dimensional structure. In particular, the three‐dimensional distribution of both H+ and O+ ions in the polar wind was examined for both solar maximum and minimum conditions and for both summer and winter solstices, as well as for various levels of geomagnetic activity. Over 1000 flux tubes of plasma are modeled for each set of geophysical conditions considered in this study, providing a horizontal resolution that is much finer than in previous applications of the global model. The modeling results are compared with relevant observational databases.
Predicted Voyager observations of the Bastille Day 2000 coronal mass ejection
Authors: Wang C. , Richardson J. D. , Paularena K. I.
Published: February 2004

The most powerful solar flare detected so far this solar cycle occurred on July 14, 2000. At approximately the same time, the Large‐Angle Spectrometric Coronograph instruments on Solar and Heliospheric Observatory observed a bright, fast, halo coronal mass ejection (CME) headed earthward at ∼1300 to 1800 km s−1. The ejecta reached Earth on July 15 and produced a very significant magnetic storm and aurora. At 1 AU the IMP 8 spacecraft recorded a strong forward shock with a speed increase from ∼600 to over 1000 km s−1. In this study, we use numerical models which include the mutual influence of the interstellar and solar wind plasma and the interstellar neutral hydrogen to study the propagation of the strong CME shock to the locations of Voyagers 1 and 2, the termination shock, and the heliopause. We predict that Voyager 2 will see a relatively strong forward shock with a speed jump of ∼65 km s−1 and a compression ratio of ∼1.9 in January 2001. Voyager 1 will see a similar shock in March 2001 with a speed jump of ∼60 km s−1 and a compression ratio of ∼1.8. This strong shock will continue its journey through the heliosphere and is expected to arrive at the termination shock and heliopause in March and December 2001, respectively. The impingement of this strong interplanetary disturbance on the denser plasma past the heliopause could trigger the next 2–3 kHz heliospheric radio emission event, which would then occur at the end of 2001.
Relationships of models of the inner magnetosphere to the Rice Convection Model
Authors: Heinemann M. , Wolf R. A.
Published: February 2004

Ideal magnetohydrodynamics is known to be inaccurate for the Earth's inner magnetosphere, where transport by gradient‐curvature drift is nonnegligible compared to E × B drift. Most theoretical treatments of the inner plasma sheet and ring current, including the Rice Convection Model (RCM), treat the inner magnetospheric plasma in terms of guiding center drifts. The RCM assumes that the distribution function is isotropic, but particles with different energy invariants are treated as separate guiding center fluids. However, Peymirat and Fontaine [1994] developed a two‐fluid picture of the inner magnetosphere, which utilizes modified forms of the conventional fluid equations, not guiding center drift equations. Heinemann [1999] argued theoretically that for inner magnetospheric conditions the fluid energy equation should include a heat flux term, which, in the case of Maxwellian plasma, was derived by Braginskii [1965]. We have now reconciled the Heinemann [1999] fluid approach with the RCM. The fluid equations, including the Braginskii heat flux, can be derived by taking appropriate moments of the RCM equations for the case of the Maxwellian distribution.

The physical difference between the RCM formalism and the Heinemann [1999] fluid approach is that the RCM pretends that particles suffer elastic collisions that maintain the isotropy of the distribution function but do not change particle energies. The Heinemann [1999] fluid treatment makes a different physical approximation, namely that the collisions maintain local thermal equilibrium among the ions and separately among the electrons. For some simple cases, numerical results are presented that illustrate the differences in the predictions of the two formalisms, along with those of MHD, guiding center theory, and Peymirat and Fontaine [1994].
Ulysses observations of magnetohydrodynamic turbulence in corotating interaction regions
Authors: Gulamali M. Y. , Cargill P. J.
Published: February 2004

During its mission around the poles of the Sun, the Ulysses spacecraft encountered a number of well‐developed corotating interaction regions (CIRs) at midlatitudes. In this paper we discuss the character of magnetohydrodynamic (MHD) turbulence within defined regions of these CIRs. We examine magnetic field power spectra at a fixed wave number, and the normalized cross helicity, in order to describe solar wind fluctuations. We find that each CIR has a complicated turbulent signature. Magnetic field power spectra show evidence for the turbulent mixing of plasma at large distances from the Sun, and there are possible signs of instabilities arising at stream interfaces. Statistical analyses of our data set show that there does not appear to be any clear dependence of turbulence in the CIRs upon heliographic latitude but that there is a clear trend in magnetic field power and Alfvénicity with CIR structure. We also find that the variation of the solar cycle during Ulysses observations of these CIRs has a clear effect upon the turbulent character of the solar wind and thus provides further evidence that the source of the majority of turbulent fluctuations in the solar wind is the Sun.
Modeling the properties of high‐m Alfvén waves driven by the drift‐bounce resonance mechanism
Authors: Ozeke L. G. , Mann I. R.
Published: February 2004

High‐m Alfvén waves can be driven by drift‐bounce resonance with energetic protons in the magnetosphere. We calculate the trajectories of protons in a dipole magnetosphere, including the effects of corotation and convection electric fields. We propose that the boundary between open and closed orbits, following a partiale injection, can represent a region where unstable particle distributions with df/dW > 0 can develop. Hence we can model the energetically favorable locations in particle energy, W, and L shell space for high‐m wave growth by finding the positions where the open‐closed orbit boundary intersects a drift‐bounce resonance curve. Our model can provide a physical explanation for the observed asymmetry between the properties of high‐m Alfvén waves in the morning and afternoon sectors, and it predicts wave properties which are in excellent agreement with observations. In particular, the observed properties of storm‐time Pc5 waves in the afternoon sector and giant pulsations (Pgs) in the morning sector are in excellent agreement with our model, these waves predicted to be fundamental (N = 0) and second harmonic (N = 1) resonances, respectively. Moreover, our model can explain why Pgs are so monochromatic, so highly localized in latitude, and only produced in the auroral zone.
Electromagnetic heavy ion cyclotron instability: Anisotropy constraint in the solar corona
Authors: Gary S. Peter , Yin Lin , Winske Dan , Ofman Leon
Published: February 2004

The electromagnetic proton cyclotron anisotropy instability is driven by T⊥p/T‖p > 1 where p represents protons and the directional subscripts denote directions relative to the background magnetic field. Fluctuating field growth leads to wave‐particle scattering, which in turn imposes an upper bound on the anisotropy of the form T⊥p/T‖p − 1 = Sp/β‖pαp, where β‖p ≡ 8πnpkBT‖p/B02, and the fitting parameters Sp ≲ 1 and αp ≃ 0.4. Recent SOHO observations indicate that minority heavy ions are substantially hotter and more anisotropic than protons in the solar corona. Here linear theory and hybrid simulations have been carried out in a model of a homogeneous, magnetized, collisionless plasma with anisotropic minority oxygen ions (denoted by subscript O). These calculations show that the electromagnetic oxygen ion cyclotron anisotropy instability also leads to wave‐particle scattering, which constrains that anisotropy by the form

, where
SO ∼ 10 and αO ∼ 0.4. This constraint should be observable in the solar corona.
Evidence for pitch angle diffusion of solar wind protons in resonance with cyclotron waves
Authors: Marsch E. , Tu C.‐Y.
Published: February 2004

Quasi‐linear theory predicts that ions in resonance with transverse ion cyclotron waves suffer merely pitch angle diffusion while conserving their total kinetic energy in the frame moving with the wave phase speed. For the first time, direct observational evidence from Helios plasma data is shown for the occurrence of this pitch angle diffusion of solar wind protons, induced by resonance with parallel ion cyclotron waves propagating away from the Sun. Parts of the isodensity contours in velocity space are well outlined by a sequence of segments of circles centered at the adapted wave phase speed, which is assumed to vary slightly and to be due to dispersion smaller than the local Alfvén speed. This observation confirms the validity of basic concepts of resonant wave‐particle interactions as described by quasi‐linear theory. The solar wind proton velocity distributions show a “plateau” defined by a vanishing pitch angle gradient in the resonant regime, implying marginal stability of the distribution function. The implications of these results for solar wind ion heating and kinetic transport are discussed.
Damping of fast and ion cyclotron oblique waves in the multi‐ion fast solar wind
Authors: Li Xing , Habbal Shadia Rifai
Published: February 2004

A detailed linear analysis of the behavior of oblique fast waves in a multi‐ion low‐beta Vlasov plasma such as the solar wind is presented. It is shown that at very oblique propagation angles, proton fundamental and second harmonic cyclotron damping become dominant. The property of oblique fast waves can also be significantly changed in the presence of minor ions. Depending on their abundance and relative speed with respect to protons, minor ions can change the wave polarization from right‐handed at small wave numbers to left‐handed at larger wave numbers for some propagation angles. Consequently, a power law spectrum of oblique fast waves originating at the Sun may preferentially heat and accelerate alpha particles rather than protons and electrons in the fast solar wind. Furthermore, it is shown that oblique fast waves can heat minor ions more than oblique Alfvénic ion cyclotron waves thus making them a potentially more important candidate for the preferential heating of minor ions in the solar wind than ion cyclotron waves.
Stochastic growth of waves over Earth's polar cap
Authors: Cairns Iver H. , Menietti J. D.
Published: February 2004

Bursty waves with widely varying electric fields persist over a wide range of altitudes ∼ 2‐7 RE at polar cap latitudes in Earth's inner magnetosphere. These “PF” waves have frequencies near expected values of the electron plasma frequency (PF), well below the electron gyrofrequency, and are believed to be generated by electron beams. Here it is demonstrated that stochastic growth theory (SGT) can account well for the detailed field statistics of the archetypal PF wave event, by showing that the observed distributions P(log E) of envelope electric fields E are well fitted by the lognormal function predicted by SGT. Weak evidence exists that a nonlinear wave process coexists with stochastic growth physics at large fields ≳ 1 mV m−1 on the basis of fits of the observed PM(log E) distribution to the SGT prediction that includes a nonlinear process at high fields and on the discovery of a class of low‐frequency waves that may be produced by nonlinear decay of PF waves. An analytic model is developed for why the waves evolve to an SGT state, on the basis of waves driven by an electron beam in MHD density turbulence and the development of fluctuations in the electron beam due to wave growth occurring in localized regions. The model is viable for the polar cap plasma parameters considered, predicting that the wave burstiness should be of order that observed and that the beam fluctuations should have timescales ∼ 10 ms that are below current detection capabilities. SGT thus accounts well for the burstiness and wave statistics, as well as the persistence of the waves and driving distribution. The consistency of the PF wave statistics with SGT also implies the presence of local electron beams over much of the polar cap, whose source is currently unknown. This application brings to five the number of contexts in which SGT applies, suggesting that SGT is widely applicable in space plasmas.
The relationship between suprathermal heavy ion outflow and auroral electron energy deposition: Polar/Ultraviolet Imager and Fast Auroral Snapshot/Time‐of‐Flight Energy Angle Mass Spectrometer observations
Authors: Wilson G. R. , Ober D. M. , Germany G. A. , Lund E. J.
Published: February 2004

Ionospheric ions are energized to suprathermal energies (10–1000 eV) in the auroral zone. This produces a much larger quantity of escaping O+ ions than would otherwise occur, given typical ionospheric energies. Until recently, only limited work had been done relating ion upflow characteristics to nearby, contemporaneous auroral forms. We present our results comparing the characteristics of the suprathermal outflowing O+ ions, as measured by the Time‐of‐Flight Energy Angle Mass Spectrometer instrument on the Fast Auroral Snapshot (FAST) spacecraft, to the auroral forms seen at the foot point of the associated field line, as observed by the Ultraviolet Imager (UVI) on Polar. We present data from FAST nightside auroral zone passes between January 25 and February 11, 1997. During this interval, FAST made ∼100 auroral zone passes in the Northern Hemisphere where the aurora was simultaneously imaged by the UVI. Close examination of 50 such passes shows that the regions where suprathermal O+ outflow occurs closely follow the local aurora regardless of how convoluted the auroral forms may be. Taken together, these data show that the flux of escaping O+ ions increases by over a factor of 100 as the auroral intensity in the 1600–1800 Å band increases from 0 to 4 kR. Also, the delay between auroral intensification and saturation O+ flux reaching 3000‐ to 4000‐km altitude is ∼5–10 min.