SM21A-0300
On-Line Explorer-45 Plasmapause-Crossing Database and Related Ionospheric Satellite Measurements
Near equatorial-plane plasmapause crossings (below 5.2 RE) were determined from Explorer-45 electric-field measurements [Maynard and Cauffman, JGR, 78, 4745, 1973]. The crossings were determined when the electric field detector went out of saturation outbound or into saturation inbound. A hard copy listing of these crossings was compiled by N. Maynard and was available to us. This information has now been converted to digital form and is available on-line from the National Space Science Data Center. We plan to use these data, in conjunction with ISIS-2 ion mass spectrometer and ISIS-1 and -2 topside-sounder measurements, to infer H+ dominance through the low-latitude trough boundaries in order to address the ambiguity in the literature as to the relationship between midlatitude trough structures and the plasmapause. Some studies have shown a close relationship between the electron-density trough and the plasmapause, e.g., the comparison of ionospheric tomographic imaging and EUV/IMAGE plasmapause determinations by Yizengaw and Moldwin [GRL, 32, L09105, 2005], while others show only a rough correlation, e.g., the comparison of Explorer-45 plasmapause crossings and Ariel-4 and ISIS-2 ionospheric data by Grebowsky et al. [Planet. Space Sci., 24, 1177, 1976]. The magnetic-field models in these databases were very simple, however, and didn't account for inflation of the equatorial fields. Explorer-45, ISIS-1 and ISIS-2 orbit data have been added to the GSFC Space Physics Data Facility SSCWeb orbits/conjunctions system so that we are now able to search for magnetic conjunction between these satellites, using up-to-date magnetic-field models, and then select cases where a plasmapause crossing is accompanied by ion density measurements and/or electron-density profiles on the same field line in the ionosphere.
SM21A-0301
Estimations of the convection electric field from plasmaspheric images and geostationary energetic particle measurements; direct comparison
Global scale electric fields control the dynamics of low energy plasma in the inner magnetosphere. Through the study of plasmaspheric images from the IMAGE EUV instrument it is possible to estimate the zero energy Alfven layer by tracking convection and corotation motion of bulk plasmaspheric plasma. From the zero energy Alfven layer the convection electric field is derived based on a Volland-Stern field pattern. This work presents these observations, as well as a comparison with an estimation method based on LANL geostationary observations of the plasma sheet electron cutoff energy. Co-temporal observations agree in terms of electric field strength using both techniques. However, the EUV images add another dimension to the derivation, providing additional information that can be used to enhance the determination of electric field structure. This combination of techniques determines the electric field structure more completely. Based on this structure the dynamics of much of the inner magentosphere can be approached, such as the overlap of the plasmasphere/plasmapause and the drift paths of radiation belt particles, as well as the interactions made possible by this overlap.
SM21A-0302
Plasmaspheric Ion Refilling Rates
Recently there has been intense interest in estimation of the equatorial mass density based on measurements of field line resonance frequencies with ground magnetometers. Using cross-phase analysis of magnetometer array data, we determined the equatorial mass density during a moderate geomagnetic storm that followed several days of magnetically quiet conditions. Early in the storm recovery phase (Kp = 6+), the field line eigenfrequency over L = 2.3 – 3.8 was unusually high, corresponding to very low mass densities and flux tube depletion. Over the next few days the eigenfrequency at these L values progressively decreased, indicating refilling of the flux tube to pre-storm levels, superimposed upon diurnal variations. By comparing density measurements we determined the daytime ion refilling rates and fluxes at the 1000 km level for the L = 2.3, 2.6, 3.3, and 3.8 flux tubes. The upward ion fluxes decreased with increasing L-value, being around 4 x 108 amu/cc/sec at L=2.3 and 1.5 x 108 amu/cc/sec at L=3.8, respectively. We compare these observations with daytime upward electron fluxes measured by VLF whistler techniques, and investigate the L-value dependence in refilling rate. The latter may be attributed to solar zenith angle control of ion production rates.
SM21A-0303
Simulation of H+ and He+ Dynamics During Plasmasphere Refilling
The refilling of the H+ and He+ plasmaspheres is simulated over long times (days) using the SAMI2 (Sami2 is Another Model of the Ionosphere) code[1]. It is shown that the plasmaspheric He+ population reaches saturation more rapidly than the H+ population and that, if left undisturbed, the H+ density at L=3 can continue to increase for as long as 10 weeks. [1] Huba, J.D., G. Joyce, and J.A. Fedder, JGR, 105, 23,035, 2000 Work supported by ONR
SM21A-0304
The Effects of Plasma Density Irregularities on the Pitch Angle Scattering of Energetic Radiation Belt Electrons due to VLF Signals from Ground Based Transmitters.
On the basis of analytical models, it is commonly believed that VLF signals from powerful ground based transmitters determine the lifetimes of energetic radiation belt electrons (100 keV - 1.5 MeV) on L shells in the range 1.3 - 2.8 [e.g., Abel and Thorne, 1998]. The primary mechanism of interaction is believed to be gyro- resonance. To test this hypothesis, one needs to know the characteristics of the VLF signals in the radiation belts, as well as the characteristics of the energetic electron precipitation produced by these VLF signals. To these ends, Stanford University has recently carried out a series of experiments in which the 21.4 kHz signals from the US Navy transmitter in Hawaii (NPM) are keyed in a regular OFF/ON pattern designed to reveal any energetic electron precipitation that may be attributed to the transmitter signals. The subject of the present paper concerns the characteristics of the 21.4 kHz signals in the radiation belts. VLF plasma wave observations from the DEMETER spacecraft suggest that the plasma on the L shells illuminated by the NPM transmitter often contain small-scale magnetic-field-aligned plasma density irregularities. VLF waves propagating within these irregularities will generally excite lower-hybrid waves through linear mode coupling. At any given point along an L shell, the excited lower-hybrid waves will resonate with electrons of higher energy than those which resonate with the input wave. Thus the energetic electron precipitation signature due to an input VLF pulse will be different when magnetic-field-aligned plasma density irregularities are present. We compare the precipitation signatures obtained both with, and without, the irregularities and discuss how our results compare with steady state models such as that of [Abel and Thorne, 1998].
SM21A-0305
Properties of a Shielding Effect in the Inner Earth Magnetosphere
An electric field in the inner magnetosphere could be considered as a sum of two components. The first one ('outer'): an imposed electric field originating from the solar wind and the second ('inner'): an electric field created by ionosphere-ring current interactions. The presence of the latter component results in decrease of magnitude of imposed field at low geomagnetic latitudes. This effect is known as a shielding effect. Using self-consistent model of electric field in the inner magnetosphere (based on 'Vasyliunas loop') we performed a number of numerical experiments to study the shielding properties. The shielding is described by two different approaches: a) by a variation of a potential along a half-circle of r=L at the nightside equatorial magnetosphere; b) the extent to which plasma sheet ions are prohibited from penetration into the inner magnetosphere due to the shielding. We study the dependence of the shielding effect on proton temperature (1.8--15 keV) and concentration (0.25--2 cm-3) at a polar boundary of modeled region. The relation between two definitions of the shielding is considered.
SM21A-0306
Rice Convection Model simulations of the injection of plasma bubbles into the inner magnetosphere
Magnetic reconnection in the magnetotail or other forms of current sheet disruption are believed to produce bubbles, which consist of flux tubes that have entropy content PV5/3 lower than their surroundings. In this study, Geotail observations during a bubble-injection event are used to specify the tailward boundary conditions for the Rice Convection Model (RCM). Model results are compared to ground-based and in situ measurements such as Dst and geosynchronous particle fluxes. We present results from the injection of RCM-computed bubbles and their effects on the plasma bulk properties, electric field, ring current, and Birkeland currents in the inner magnetosphere. Some first results are also presented from a series of computer runs designed to examine sensitivity of model predictions to overall magnetospheric conditions, including standoff distance, convection rate, pre-existing ring current, and northward turning of interplanetary magnetic field (IMF). http://www.owlnet.rice.edu/~jichunz/
SM21A-0307
Cavity resonance triggered by inward movement of a plasmaspheric plume
We investigate an event in the duskside inner magnetosphere where a sudden inward movement of a pre- existing plasmaspheric plume triggers a cavity resonance between the plume and the plasmapause. The event is recorded by five spacecraft (four Cluster and GOES 8) located in different positions in the cavity: one spacecraft within the plasmapause region and four in the cavity within L =4-6.6. All four spacecraft observe ULF wave mode at ~5 mHz at the same frequency and in the same phase even though the spacecraft are widely separated, indicating that the wave is a fundamental mode cavity resonance. The resonance is first left-hand polarized but changes into the right-hand polarized in the middle of the event at all locations. The event ends on each spacecraft when the spacecraft enters the plume. The plume movement is caused by a sudden change in geomagnetic activity, causing fast convection outside the plume that pushes the plume from L=8-10 to L=6-8.
SM21A-0308
Telescope of Extreme ultraviolet (TEX) onboard Japan's lunar orbiter (SELENE): Imaging of the inner magnetosphere from the moon
The Upper Atmosphere and Plasma Imager (UPI) is launched in 2007, and goes to the moon. From the lunar orbit, two telescopes direct toward the Earth. The moon has no atmosphere, which leads no active emission near the spacecraft, thus we will have a high quality image of the near-Earth environment. Moreover the moon orbits the Earth once a month and the Earth will be observed from many different directions. This is called a "science from the Moon". The two telescopes are mounted on 2-axis gimbal system, Telescope of Extreme ultraviolet (TEX) and Telescope of Visible light (TVIS). TEX detects the O II (83.4nm) and He II (30.4nm) emissions scattered by ionized oxygen and helium, respectively. The targets of EUV imaging are the polar ionosphere, the polar wind, and the plasmasphere and the inner magnetosphere. The maximum spatial and time resolutions are 0.09 Re and 1 minute, respectively.
SM21A-0309
Polarization properties of the fundamental mode and higher harmonics of standing shear Alfven waves in non-axisymmetric background magnetic fields.
We present results concerning periods and polarizations of cold plasma ultra-low frequency (ULF) guided Alfven waves in a non-axisymmetric geomagnetic field model. The two fundamental modes which are differed by their polarizations, as well as their harmonics are included in the analysis. The background geomagnetic field is approximated by a compressed dipole model for which we propose a simple description in terms of Euler potentials. This study is motivated by the problem of outer-radiation belt electron energization by ULF waves, for which the polarization of the wave is of paramount importance. We consider an approximation in which Alfvenic waves are decoupled from compressional modes and find that the polarization of both the fundamental modelsas well as that of their harmonics can change significantly with local time. As a consequence, we find that the ULF wave's contribution to the MeV electron energization process can be localized in space. Furthermore, different harmonics of the fundamental mode also contribute to the electron energization in different regions of space.
SM21A-0310
Study of Electromagnetic Ion Cyclotron Instability in Dipole Geometry
The Electromagnetic Ion Cyclotron (EMIC) wave is commonly observed in the Earth's magnetosphere. It is believed to be excited when a large number of particles are injected into the dusk side of the magnetosphere during substorms. Theoretical works have suggested that EMIC waves may contribute significantly to Relativistic Electron Precipitation (REP) by pitch-angle scattering. REP events are one of the important aspect of the radiation belt dynamics. We will be using a hybrid code simulation to study EMIC waves in dipole geometry, including instability, wave propagation, and wave-particle interaction. Up to date results will be shown in this poster.
SM21A-0311
Modeling the Loss of Energetic Ions and Electrons by EMIC Waves
We study the effect of electromagnetic ion cyclotron (EMIC) wave scattering on ring current ions and radiation belt electrons during several geomagnetic storms. We use our global physics-based model, which calculates the evolution of H+, O+, and He+ ions and electrons due to time-dependent earthward transport and acceleration. All major loss processes are included in our kinetic model, which is coupled with a time-dependent plasmasphere model. The anisotropic ring current populations generate plasma waves that accelerate and/or scatter radiation belt particles. The generation and propagation characteristics of the EMIC waves depend strongly on the presence of both cold and energetic heavy ions (mainly He+ and O+) in the plasmas. We calculate the excitation of EMIC waves self-consistently with the evolving ring current ion populations as the storms progress. We find that the regions of maximum EMIC wave growth are usually located inside plasmaspheric plumes and/or near the plasmapause. In our kinetic model wave-particle interactions are evaluated according to quasi-linear theory using diffusion coefficients for multi-component plasma and including not only field-aligned but also oblique EMIC waves. Pitch angle scattering by these waves cause significant ion precipitation into the atmosphere and generation of detached subauroral proton arcs. Furthermore, EMIC waves cause pitch angle scattering and loss of radiation belt electrons at energies larger than few hundreds keV. Global images of electron precipitating fluxes and first studies of the electron precipitation development with local time are presented.
SM21A-0312
Self-Consistent Model of Magnetospheric Electric Field, RC and EMIC Waves
Electromagnetic ion cyclotron (EMIC) waves are an important magnetospheric emission, which is excited near the magnetic equator with frequencies below the proton gyro-frequency. The source of free energy for wave growth is provided by temperature anisotropy of ring current (RC) ions, which naturally develops during inward convection from the plasmasheet. These waves strongly affect the dynamics of resonant RC ions, thermal electrons and ions, and the outer radiation belt relativistic electrons, leading to non-adiabatic particle heating and/or pitch-angle scattering and loss to the atmosphere. The rate of ion and electron scattering/heating is strongly controlled by the wave power spectral density and the wave spatial/temporal distributions. Unfortunately, the currently available observational information regarding EMIC wave power spectral density is poor. So combinations of reliable data and theoretical models should be utilized in order to obtain the power spectral density of EMIC waves over the entire magnetosphere throughout the different storm phases. In this study, we present the simulation results, which are based on two coupled RC models that our group has developed. The first model deals with the large-scale magnetosphere-ionosphere electrodynamic coupling, and provides a self- consistent description of RC ions/electrons and the magnetospheric electric field. The second model is based on a coupled system of two kinetic equations and self-consistently treats a micro-scale electrodynamic coupling of RC and EMIC waves; one equation describes the RC ion dynamics and another equation describes the power spectral density evolution of EMIC waves. So far, these two models have been applied independently. However, the large-scale magnetosphere-ionosphere electrodynamics controls the convective patterns of both the RC ions and plasmasphere altering conditions for EMIC wave-particle interaction. In turn, the wave induced RC precipitations change the local field-aligned current distribution and the ionospheric conductances, which are crucial for a large-scale electrodynamics. The initial results from this new self-consistent model of the magnetospheric electric field, RC and EMIC waves will be shown in this presentation.
SM21A-0313
Investigating EMIC Wave Generation and Relativistic Electron Resonance
Wave-particle interaction of relativistic electrons with electromagnetic ion cyclotron (EMIC) waves is thought to play an important role in radiation belt dynamics, and may be a dominant electron precipitation mechanism. We use data from the LANL MPA instruments to investigate the temperature anisotropy of ring current protons that may drive EMIC waves during relativistic electron precipitation events. These data are used as input to the WHAMP plasma dispersion code to solve for EMIC wave frequencies in a multi-species magnetized plasma. The minimum electron resonance energy is calculated and compared to balloon observations of precipitating electron energy spectra. We also use LEPA data from CRRES to investigate ion distributions during EMIC wave events identified in the Meredith et al. (2003) study.
SM21A-0314
Proton auroral observation using a meridian-scanning filter-tilting photometer at a subauroral latitude
We have been observing Hbeta emissions in proton aurora with a meridian-scanning filter-tilting photometer at the Athabasca station, Canada (54.7N, 246.7E, MLAT=62.6N) since September 2005. The photometer was installed with a highly sensitive monochromatic all-sky imager and an induction magnetometer. The Athabasca station is located equatorward of the auroral oval, where proton aurora measurement has not been made frequently from ground. The energy of auroral protons can be measured through Doppler-shift of the hydrogen Balmer line (486.1nm), by tilting a narrow-band interference filter. However, it has been difficult to measure wavelength of the Doppler shift accurately, because the peak wavelength of the filter drifts due to changes of the filter temperature. We have developed a meridian-scanning filter-tilting photometer with a new interference filter, for which the temperature drift coefficient (0.002 nm/K) is about 1/10 of that of previous filters. In the presentation, we will show two-years results of the proton aurora measurement in Athabasca.
SM21A-0315
ICME and CIR Geomagnetic Storms as Seen by ENA Images and Ring Current Distributions
Geomagnetic storms in the Earth's magnetosphere have been classified as due to solar wind dominated by interplanetary coronal mass ejections (ICMEs) or by corotating interaction regions (CIRs). The different characteristics of these storms have been determined primarily from measurements at geosynchronous orbit and ground magnetometers. Borovsky and Denton [2006] have identified 21 differences between ICME and CIR driven storms. We present ENA images and deconvolved proton distributions from MENA and HENA onboard the IMAGE satellite for storms during 2004. The density, temperature, and pressure of the trapped ring current protons with energies from a few keV to more than 30 keV for the inner magnetosphere are presented during various phases of the two kinds of storms. Differences between ICME and CIR driven storms are affirmed and/or modified based upon these observations.
SM21A-0316
Flux enhancement mechanism of the outer radiation belt electrons associated with coronal hole streams
The Earthfs outer radiation belt electrons increase when the magnetosphere is surrounded by the high speed solar wind stream, while the southward interplanetary magnetic field (IMF) is also known as an important factor for the flux enhancement. In order to distinguish the two different kinds of solar wind parameter dependence statistically, we investigate the response of the outer belt to stream interaction regions (SIRs). We classify the SIR events from 1994 to 2005 into two groups according to so-called gspring-toward fall-awayh (STFA) rule: (A) IMF sector polarity after the stream interface is toward in spring or away in fall, and (B) vice versa. According to the Russell-McPherron effect, the groups A and B have a significant negative and positive offset of the IMF Bz after the stream interface. Comparing the groups A and B, by superposing about the stream interface, only IMF Bz dependence can be obtained because the other solar wind parameters change in the same manner. As a result, the greatest flux enhancement is found in the high-speed streams with a southward offset of the IMF Bz, indicating that only the solar wind speed by itself is not a sufficient condition for the large flux enhancement. Based on the obtained dependence on the STFA rule and the solar wind speed, it is possible to operate a probabilistic space weather forecast of relativistic electrons at geosynchronous orbit for secure satellite operations. The probability is defined by the number of events with daily maximum flux above the NOAA alert levels, and the stream interface is used as a precursor of coming coronal hole stream in the forecast algorithm. We report how it works and evaluate the skill score of our test operation of the probabilistic forecast.
SM21A-0317
Storm-Dependent Radiation Belt Dynamics
Outer radiation belt electrons have their largest variations during magnetic storms. Taking advantage of recently published phase space density (PSD) data as a function of L* and time, we have developed a comprehensive radial diffusion model, in which both the electron lifetime and source rate are included and parameterized as a function of geomagnetic indices. The PSD data at L*=6 is used as the outer boundary source and the modeled results are directly compared with the PSD data at L*=4. We conclude that the main acceleration mechanism, inward radial diffusion vs in situ acceleration, responsible for the enhancement of outer belt electrons at L*=4 is storm-dependent: in one storm, the enhancement of outer radiation belt electrons can be well explained by inward radial diffusion while in situ acceleration (violating the first adiabatic invariant) has to be invoked to explain the enhancement of the outer belt electrons during another storm.
SM21A-0318
The seasonal dependence of relativistic electron fluxes in the Earth's outer van Allen Belt
It is well known that geomagnetic activity shows a marked seasonal dependence. This effect has been attributed to the seasonal variation of the Earth's dipole tilt angle exposing the magnetosphere to an increased southward component of the interplanetary field (the Russell-McPherron effect) or an increased solar wind velocity (the axial/equinoctial effect). We examine the seasonal dependence of relativistic electron fluxes in the Earth's outer Van Allen belt. An earlier investigation by Baker et. al., (1999) found that the relativistic electron fluxes do show a strong seasonal dependence with the equinoctial electron fluxes being almost three times higher than the solstitial fluxes. We extend this previous investigation using data obtained by sensors onboard SAMPEX. This study of the seasonal dependence is based on data with a higher time resolution as compared to the earlier study. The results of our analysis show that the peak electron fluxes are shifted in time from the nominal equinoctial times. We discuss some possible implications of our observations in the context of electron energization in the Earth's magnetosphere. Baker, D.N., S.G. Kanekal, T.I. Pulkkinen, and J.B. Blake, Equinoctial and solstitial averages of magnetospheric relativistic electrons: A strong semiannual modulation, Geophys. Res. Lett., 26, No. 20, 3193-3196, 1999.
SM21A-0319
Modulation of the Fluxes of Energetic Particles in the Inner Magnetosphere Associated With Storm Conditions
During storms, induced electric and magnetic fields within the magnetosphere lead to the build up of energetic particles within the ring current and radiation belts. Two important processes that can lead to particle energization and increased inward transport are compression of the magnetosphere by enhanced solar wind dynamic pressure, which accompanies many magnetic storms, and pumping from storm-time substorms. These two processes are examined with single particle-tracking coupled to global multi-fluid simulations. This combined approach allows a consistency to be kept for the influence of heavy ions on the dynamics of the system. Two cases are examined: with and without insufficient O+ outflow to produce cross-polar cap saturation. It is shown during the early stages, where the compressional effects dominate, the energization of the particles and their inward motion are approximately the same. During the later stages, where storm-time substorms are important, the energization and inward motion is very different between the two cases.
SM21A-0320
Using Particle Observations from Geosynchronous Orbit as a Proxy for Whistler and EMIC Mode Wave Growth
There is still much to learn about the factors that affect the production of relativistic electrons in the magnetosphere. Multipoint LANL geosynchronous plasma data may be used to examine the characteristics of the electron source population related to the growth of whistler mode waves. Superposed epoch analysis is ideal to infer the local time evolution of whistler mode waves during geomagnetic storms. Using this technique, above average growth of whistler mode waves in the late recovery phase correlates with above average fluxes of relativistic electrons in the same time period. Quasi-linear wave theory can also be used to develop a proxy for electromagnetic ion cyclotron (EMIC) wave growth depending on the ion anisotropy and density. We will apply the same technique of superposed epoch analysis to look at EMIC wave growth during plasmaspheric plumes and geomagnetic storms. Together, the extensive particle observations from geosynchronous orbit serving as a proxy for two different wave modes may shed light on the relationship between competing source and loss mechanisms for relativistic electrons during storms.
SM21A-0321
Whistlers observed outside the plasmasphere: Correlation to plasmaspheric/plasmapause features and implications for the scattering of radiation-belt electrons
Magnetospherically reflected, lightning-generated whistler waves are an important potential contributor to pitch- angle scattering loss processes of the electron radiation belts. While lightning-generated whistlers are a common feature at, and just inside, the plasmapause, they are infrequently observed outside the plasmasphere. As such, their potential contribution to outer radiation belt loss processes is more tenuous. Recently, Platino et al. [2005] has reported on whistlers observed outside the plasmasphere by Cluster. Here, we present correlative global observations of the plasmasphere, for the reported periods of Cluster-observed whistlers outside the plasmasphere, using IMAGE-EUV data. The intent of this study is to seek the underlying mechanisms that result in whistlers outside the plasmasphere and consequently the anticipated morphology and significance these waves may have on radiation belt dynamics.
SM21A-0322
Radiation belt electron precipitation into the atmosphere: recovery from a geomagnetic storm
Large geomagnetic storms are associated with electron population changes in the outer radiation belt and the slot region, often leading to significant increases in the relativistic electron population. The increased population decays in part through the loss, i.e., precipitation from the bounce loss cone, of highly energized electrons into the middle and upper atmosphere (30-90 km). However, direct satellite observations of energetic electrons in the bounce loss cone are very rare due to its small angular width. In this study we have analyzed ground-based subionospheric radio wave observations of electrons from the bounce loss cone at L=3.2 during and after a geomagnetic disturbance which occurred in September 2005. Relativistic electron precipitation into the atmosphere leads to large changes in observed subionospheric amplitudes. Satellite-observed energy spectra from the CRRES and DEMETER spacecraft were used as an input to an ionospheric chemistry and subionospheric propagation model, describing the ionospheric ionization modifications caused by precipitating electrons. We find that the peak precipitated fluxes of >150 keV electrons into the atmosphere were 3500±300 el. cm-2s-1 at midday and 185±15 el. cm-2s-1 at midnight. For six days following the storm onset the midday precipitated fluxes are approximately 20 times larger than observed at midnight, consistent with observed day/night patterns of plasmaspheric hiss intensities. The variation in DEMETER observed wave power at L=3.2 in the plasmaspheric hiss frequency band shows similar time variation to that seen in the precipitating particles. Consequently, plasmaspheric hiss with frequencies below ~500 Hz appears to be the principal loss mechanism for energetic electrons in the inner zone of the outer radiation belts during the non-storm time periods of this study, although off-equatorial chorus waves could contribute when the plasmapause is L<3.0.
SM21A-0323
Dynamics of the Plasmasphere and the Outer Radiation Belt
During geomagnetic disturbances, significant dynamics are observed in the location of the plasmapause as well as in outer radiation belt radial location and energetic particle populations. The plasmapause separates cold dense plasma in the inner magnetosphere from hot, low-density outer magnetosphere plasma, a distinction also exhibited in the characteristic plasma waves for these regions. Various wave-particle interactions inside and outside the plasmasphere are understood to be responsible for outer radiation belt particle energization and loss. We identify the plasmaspheric signature in the ionosphere--specifically the light ion trough--using DMSP spacecraft measurements. Over ten years of such observations are available from multiple DMSP satellites, coinciding with energetic particle observations by the SAMPEX spacecraft. The light ion trough is semi- automatically identified from DMSP Retarding Potential Analyzer observations of H+ densities, then mapped along magnetic field lines to the equatorial plane. Comparisons with IMAGE EUV measurements show good agreement on plasmapause locations, with indications of plasmaspheric notches and plumes identifiable in the DMSP observations. The radial movement of the plasmapause location identified by DMSP during geomagnetic disturbances correlates well with the movement of the outer radiation belt zone and SAMPEX microburst observations. We are developing an extensive database of plasmapause locations, with the goal of improving understanding of the relationship between the plasmapause location and the outer radiation belt.
SM21A-0324
Sawtooth Events at GPS Orbit
Sawtooth events have been identified as large-amplitude quasi-periodic oscillations of the energetic particle fluxes at geosynchronous orbit. The sharp flux increase and gradual decrease of each tooth are associated with strong dipolarization and stretching, respectively, of the magnetic field at geosynchronous orbit. Sawtooth events occur during storm intervals and have a characteristic periodicity of 2-4 hours. They are particularly prominent in the energetic proton fluxes but can also be seen in the energetic electron fluxes. Here we examine the effect of these events inside geosynchronous orbit (L<6.6) using relativistic electron flux data from the GPS satellite constellation (since the proton energy channels do not correspond to the correct energy for sawtooth observations). We find that, in some cases, relativistic electron fluxes near L=4 show substantial increases associated with a depolarization during a sawtooth event. Our goal is to determine whether these events are consistent with true particle injections deep into the radiation belts or whether the flux variations seen at GPS can be accounted for by adiabatic variations alone (due to the extreme field stretching and dipolarization effects that accompany sawtooth events). To exclude adiabatic effects, the L* value of the satellites is estimated using the Tsyganenko 2001 storm magnetic field model and also an event oriented magnetic field model that fits observed satellite magnetic field data.
SM21A-0325
Comparison of Model VLF Power Distributions with IMAGE and OGO Satellite Data
Anthropogenic radiation in the kHz range (VLF) is present throughout much of the inner magnetosphere and has been shown to play a significant role in enhancing the pitch-angle diffusion of energetic particles (> ~ 0.5 MeV) in the inner radiation belts and increasing the net particle loss rate. Over the last 30 years, much work has been performed to model the distribution of VLF waves throughout the inner magnetosphere. The present study compares results from the recently developed AFRL 3D raytracing code AMPTRACE with a ducted propagation model [Inan, et al, JGR, 1984], as well as wave data from the IMAGE and OGO satellites.
SM21A-0326
Properties and Possible Causes of Low Latitude Broadband Accelerated Electron Events During Large Storms From FAST and Altitude Dependence of PSBL Alfven Waves From Polar
A variety of phenomena which occur during large geomagnetic storms (DST<-75 nT) are not yet fully understood. One such phenomenon, which affects ionospheric conditions and may be useful as a diagnostic for processes occurring at ~3-6 Re, is the occurrence of low latitude (ILat<65) broadband accelerated electron events observable at altitudes of ~2000-4000 km by the FAST satellite. Results of an initial study of 3+ years of FAST data indicate that such electrons are observed in ~6% of the low latitude, nightside (21- 03 MLT) FAST data during large storms versus <~1% during non-storm times. Individual storms have observed occurrence probabilities as high as 24%. Although properties of the events, and thus likely causes, vary, many events are accompanied by particle distributions and wave signatures that are similar to those observed during Alfvén-wave accelerated electron events on the plasma sheet boundary layer (PSBL). Alfvén- wave acceleration of electrons on the PSBL has been and continues to be well studied. Results of a recent study of PSBL Alfvén-wave events observed with Polar that may provide additional insight will also be discussed. That study compares altitude dependencies of wave properties at ~3-9 Re and differences in these dependencies between major storm and non-storm events.
SM21A-0327
Properties of Chorus Emissions Observed by the Polar Plasma Wave Investigation
The orbit of the Polar spacecraft often skims along the boundary of the plasmapause as it travels from high latitudes down to the equatorial plane, and from the equator back to high latitudes again. This orbit provides a different perspective on the role of whistler mode chorus in accelerating radiation belt electrons from earlier studies using spacecraft such as CRRES, which was not polar-orbiting. From March 1996 to September 1997, the Polar Plasma Wave Investigation (PWI) made observations of plasma waves between frequencies of 0.1 Hz and 800 kHz. Although the time period when Polar PWI data were available was close to solar minimum, it included several well-studied geomagnetic storms, such as the January 10-14, 1997 International Solar- Terrestrial Physics (ISTP) event. We will examine the locations of chorus observations in the Polar PWI data set and explore how the intensity of chorus emissions depends upon magnetic local time, magnetic latitude, and L- shell. Possible correlations between chorus emissions and energetic electrons observed by the Polar Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment will be presented. We will also discuss how chorus generation and the related electron acceleration processes depend upon the Kp and Dst geomagnetic indices.
SM21A-0328
Relativistic electron acceleration in the generation process of whistler-mode chorus by a self- consistent particle simulation
We study acceleration of relativistic electrons in a self-consistent particle simulation with a dipole magnetic field model reproducing chorus emissions with rising tones. The simulation result shows that the majority of electrons lose energy contributing to the generation of chorus emissions and that a fraction of resonant electrons having large pitch angles are accelerated through nonlinear wave trapping by the generated chorus emissions. A small fraction of resonant electrons are effectively accelerated while they show a characteristic behavior, turning their motion from equatorward to poleward during the acceleration process, which is explained by the relativistic turning acceleration (RTA) process. Simulation result reveals that trapped electrons are effectively accelerated by the RTA process over 100 keV during 2500 gyro-periods. The present study demonstrates that the role of nonlinear wave trapping is significant in the energization process of relativistic electrons by narrowband whistler- mode chorus emissions.
SM21A-0329
Parameterization of radiation belt electron loss timescales due to interactions with chorus waves
In this study parameterizations for the loss of the radiation belt electrons to the atmosphere due to the resonant pitch-angle scattering by chorus waves are developed. By analyzing the dependence of the loss rates on L-value and energy we find dependencies for the lifetime of the radiation belt electrons. Parameters of the functional dependences are obtained using a linear regression technique. To create parameterizations of loss rate as a function of geomagnetic indices, we also analyzed the statistical data from day-side lower band chorus observations in the range of geomagnetic latitudes from 20œ to 30œ. The combined parameterizations of the wave amplitudes and scattering rates indicate that electron loss due to chorus waves strongly depends on energy and geomagnetic activity. During storm-time conditions the lifetimes of relativistic electrons, in the heart of the outer zone are on the order of a day and are on the scale of hours at lower energies. The developed parameterizations may be used in particle tracing codes and radial diffusion codes.
SM21A-0330
Calculation of Path-integrated Growth of Whistler-mode Chorus Waves With the HOTRAY Code Based on CRRES Observation
Whistler-mode chorus waves are excited in the low-density region outside the plasmapause by the injection of plasmasheet electrons into the inner magnetosphere. During substorm injection, electron anisotropy increases as electrons move from the plasmasheet to lower L shells conserving the first adiabatic invariant. On the other hand, electron scattering by chorus waves reduces the electron anisotropy. We fit 5 minute-averaged CRRES data of the electron phase space density (PSD) at different equatorial pitch-angles for various energy channels (between 0.1 keV and 20 keV) with an analytical distribution function to calculate the hot electron density and anisotropy. The path-integrated growth of chorus waves is simulated with the HOTRAY code by tracing chorus waves in a hot magnetized plasma. The results show that substorm-injected electrons are responsible for the intensification of the whistler-mode chorus and higher electron anisotropy than that obtained from the 5 minute- averaged electron PSD data is needed to reproduce the observed wave intensity by CRRES during a substorm injection event. We also suggest that the electron anisotropy is reduced due to pitch-angle scattering by the enhanced chorus waves within the 5 minutes interval over which the CRRES data are analyzed.
SM21A-0331
3D Simulations of Quasilinear Diffusion in the Radiation Belts
Bounce-averaged diffusion is a promising means of simulating the dynamics of radiation belt electrons. It is now becoming feasible, and necessary, to assess the results of different wave models and to compare the resulting dynamical particle distributions. This involves complications not fully addressed by previous, qualitative simulations. Here, we report progress on two technical aspects: the rapid and accurate approximation of quasilinear diffusion rates, for hiss, chorus and EMIC waves; and the extension to 3D while preserving the effects of energy/pitch angle cross diffusion under evolving conditions.
SM21A-0332
Effects of off-diagonal terms and oblique wave propagation on calculations of radiation belt electron fluxes
Cyclotron-resonance interactions with whistler-mode chorus waves are thought to be an important mechanism for energizing electrons in the radiation belts. With a recently developed code, which uses Monte Carlo SDE (stochastic differential equation) methods to solve the bounce-averaged energy-pitch-angle quasilinear diffusion equation, we have investigated the effects of (i) ignoring off-diagonal diffusion terms, and (ii) assuming purely parallel-propagating waves. For diffusion coefficients corresponding to a model of storm-time chorus waves at L = 4.5, we find that at small pitch angles ignoring off-diagonal terms overestimates particle flux by as much as a factor of 2~5 for 0.5 MeV electrons, and by more than an order of magnitude for 2 MeV electrons. The parallel propagation assumption leads to errors of more than an order of magnitude in flux for both 0.5 MeV and 2 MeV electrons at some equatorial pitch-angles. For pitch angles near 90 degrees the effects of ignoring off- diagonal terms and oblique waves are relatively small, but overall these effects should be included to obtain more accurate particle fluxes.
SM21A-0333
Numerical Calculations of Relativistic Electron Drift Loss Effect
It has been suggested that drift loss to the magnetopause can be one of the major loss mechanisms contributing to the relativistic electron flux dropout. In this study, we examine details of relativistic electrons' drift physics to determine the extent to which the drift loss through the magnetopause is important to the total loss of the outer radiation belt. We have numerically computed drift paths of relativistic electrons' guiding center for various pitch angles, various positions and different solar wind conditions using Tsyganenko T02 model. We specifically demonstrate how the drift loss effect depends on these various parameters. It is shown that the drift loss effect is more likely expected for a higher pitch angle and near midnight and then spreads to lower pitch angles and dusk and dawn MLT regions as the dynamic pressure increases or IMF BZ becomes more southward. Most importantly, we present various estimates of relative changes of omni-directional flux of 1MeV electrons between two different solar wind conditions based on a simple form of the directional flux function. For a change of the dynamic pressure from 4 nPa to 10 nPa with a fixed IMF BZ=0 nT, our estimate indicates that the omni- directional flux for the 10 nPa pressure at the equator at midnight near geosynchronous altitude decreases by ~56 to 97%, depending on a specific pitch angle dependence of the directional flux function, compared to that for the 4 nPa pressure. The effect is somewhat lower at pre- and post-midnight MLTs, and rapidly declines at inner regions than geosynchronous orbit. It however becomes more substantial at measurement positions away from the equator. A qualitatively similar, but quantitatively different, result has been obtained for two different conditions of IMF BZ.
SM21A-0334
Quantifying ULF Waves in the Inner Magnetosphere and Their Effects on Radiation Belt Electrons
Identifying and determining the acceleration, transport, and loss mechanisms that populate, maintain, and modify radiation belt electrons remains one of the major open scientific questions in the magnetospheric community. We demonstrate new ways to characterize and study the ultra-low-frequency (ULF) waves in the inner magnetosphere that are critical for controlling radiation belt electron dynamics. A statistical study of Geosynchronous Operational Environmental Satellite (GOES) magnetic field data reveals the characteristics of ULF wave spectra at geosynchronous orbit during different solar wind conditions and levels of geomagnetic activity. In order to understand the dynamic behavior of radiation belt electrons in ULF wave fields, a global, realistic, self-consistent, and time-dependent magnetospheric model is needed. Therefore, we compare Lyon- Fedder-Mobarry (LFM) code predictions with geosynchronous measurements to assess model performance and to quantify the field fluctuations in the inner magnetosphere. Next, the dynamics of radiation belt electrons are simulated using global magnetic and electric fields from the LFM code, driven by idealized solar wind over a range of velocities. We follow the trajectories of electrons, starting at different local times and radii for the same first adiabatic invariant, to understand their transport and energization through collective wave-particle interactions. Finally, we quantify the ULF wave effects on radiation belt electrons by calculating the radial diffusion coefficients from the LFM simulation results. Our results demonstrate that the derived coefficients as a function of solar wind velocity are comparable to observational results after normalizing for wave power.
SM21A-0335
Energetic Electron and Pc5 ULF wave interactions during magnetic storms
There has been increased interest in relativistic electrons in the inner magnetosphere mainly due to the correlation between the occurrence of enhancing relativistic electron flux and spacecraft operation anomalies or even failures [e.g., Baker et al, 1994]. However, the dominant processes which accelerate magnetospheric electrons to MeV energies are not well understood. Many recent observations suggested that enhancement of energetic electrons are closely associated with ULF waves in Pc4 (7-22 mHz) or Pc5 (1-7 mHz) frequency ranges. Our goal is to examine the electron drift-resonance interaction with Pc5 ULF waves during magnetic storm time. Here, we will show the results of observations from ground based magnetometers, Polar spacecraft, LANL Geosynchronous satellites and the CRRES Medium Energy A (MEA) spectrometer. We observed very strong Pc5 oscillations during the great magnetic storm of March 24, 1991 [ Lee et al., 2007] and electron flux simultaneously oscillating with the same frequencies in the time domain. We also characterized a number of other events and present an examination of the relationship between the electron flux modulation and Pc5 ULF pulsations.
SM21A-0336
Radial diffusion with outer boundary determined by geosynchronous measurements: Storm and post-storm intervals
Work is underway by several groups to quantify diffusive radial transport of radiation belt electrons, including a model for pitch angle scattering losses to the atmosphere. The radial diffusion model conserves the first and second adiabatic invariants and breaks the third invariant. We have developed a radial diffusion code which uses the Crank Nicholson method with a variable outer boundary condition. For the radial diffusion coefficient, DLL, we have several choices, including the Brautigam and Albert (JGR, 2000) diffusion coefficient parameterized by Kp, which provides an ad hoc measure of the power level at ULF wave frequencies in the range of electron drift (mHz), breaking the third invariant. Other diffusion coefficient models are Kp-independent, fixed in time but explicitly dependent on the first invariant, or energy at a fixed L, such as calculated by Elkington et al. (JGR, 2003) and Perry et al. (JGR, 2006) based on ULF wave model fields. We analyzed three periods of electron flux and phase space density (PSD) enhancements inside of geosynchronous orbit: March 31 – May 31, 1991, and July 2004 and Nov 2004 storm intervals. The radial diffusion calculation is initialized with a computed phase space density profile for the 1991 interval using differential flux values from the CRRES High Energy Electron Fluxmeter instrument, covering 0.65 - 7.5 MeV. To calculate the initial phase space density, we convert Roederer L* to McIlwain's L- parameter using the ONERA-DESP program. A time averaged model developed by Vampola1 from the entire 14 month CRRES data set is applied to the July 2004 and Nov 2004 storms. The online CRESS data for specific orbits and the Vampola-model flux are both expressed in McIlwain L-shell, while conversion to L* conserves phase space density in a distorted non-dipolar magnetic field model. A Tsyganenko (T04) magnetic field model is used for conversion between L* and L. The outer boundary PSD is updated using LANL GEO satellite fluxes. After calculating the phase space density time evolution for the two storms and post-injection interval (March 31 – May 31, 1991), we compare results with SAMPEX measurements. A better match with SAMPEX measurements is obtained with a variable outer boundary, also with a Kp-dependent diffusion coefficient, and finally with an energy and L-dependent loss term (Summers et al., JGR, 2004), than with a time-independent diffusion coefficient and a simple Kp-parametrized loss rate and location of the plasmapause. Addition of a varying outer boundary which incorporates measured fluxes at geosynchronous orbit using L* has the biggest effect of the three parametrized variations studied. 1Vampola, A.L., 1996, The ESA Outer Zone Electron Model Update, Environment Modelling for Spaced-based Applications, ESA SP-392, ESTEC, Nordwijk, NL, pp. 151-158, W. Burke and T.-D. Guyenne, eds.