SM33A-1099
Evidence of Residual Plasmaspheric Plumes
Plasmaspheric erosion produces plumes of plasma that extend sunward from the main torus. When geomagnetic activity decreases, a given plume loses its sunward orientation, rotating eastward and wrapping itself around the plasmasphere torus. The residual plume is a major feature of the recovery phase plasmasphere, and is suspected to be an important influence upon the loss rates of energetic particles. In this study, comparison between in situ observations of the Los Alamos National Laboratory (LANL) Magnetospheric Plasma Analyzers (MPA) and output of a plasmapause test particle (PTP) simulation for the moderately disturbed interval 18--20 January 2000 reveals evidence of plasmaspheric plumes that wrapped completely around the main torus and lasted for at least 40 hours and possibly as long as 60 hours. The presence of long-lived multiple wrapped residual plumes suggests that the global plasmaspheric density distribution preserves some memory of prior epochs of erosion and recovery.
SM33A-1100
Plasma Measurements at Geosynchronous Orbit From the Los Alamos Magnetospheric Plasma Analyzers
Since 1989 Los Alamos has fielded a series of geosynchronous satellites that carry instruments to monitor the charged-particle environment from 1 eV to several MeV. The Magnetospheric Plasma Analyzers (MPA) cover the range from ~1 eV to ~45 keV for both ions and electrons. With as many as six instruments working simultaneously at a given time, we now have over 70 satellite-years of measurements, covering more than one and a half solar cycles. MPA observations have produced a rich harvest of scientific knowledge, in areas ranging from plasmasphere structure and refilling to storm-time ring current physics. The database will be described briefly, and some significant applications will be presented.
SM33A-1101
Mass Density at Geosynchronous Orbit Inferred From Toroidal Alfven Frequencies
Frequencies of the toroidal Alfven field line resonance mode can be used to infer magnetospheric mass density, a technique sometimes referred to as magnetoseismology. Geosynchronous orbit is an ideal location for this technique since a geosynchronous spacecraft approximately corotates with the plasma leading to a relatively stationary wave signal for Fourier analysis. Here we present results from magnetoseismology, with special emphasis on results at geosynchronous orbit. These include a solar cycle dependence with mass density higher at solar maximum, increased mass density with geomagnetic activity, a local time dependence with density higher in the afternoon local time sector, and a field line dependence which is relatively flat along the field line at morning local time, but peaked at the magnetic equator at afternoon local time, especially during geomagnetically active times.
SM33A-1102
Simulation of the 18 April 2002 Sawtooth Event Using the Rice Convection Model
We present simulation results of the 18 April 2002 sawtooth event using the Rice Convection Model (RCM) where we treat this event as a series of recurrent substorms with a period of 2-4 hours. The simulation uses the storm time magnetic field model as well as the time dependent plasma sheet model as inputs to RCM. During the substorm expansion phase, we use an empirical substorm current wedge model in order to dipolarize the magnetic field on the nightside and we deplete flux tube content on the outer boundary over a wide range of local time. The simulated energetic proton fluxes at the geosynchronous orbit show a well-defined global sawtooth pattern and the calculated ENA fluxes show that oxygen is enhanced more significantly after the substorm onset than hydrogen, which is consistent with the IMAGE/HENA observations.
SM33A-1103
Geosynchronous Orbit: Life near the boundary of stable trapping
New numerical methods[1-3] enable us to model and classify electron spectra near the geostationary orbit in terms of both energy and pitch angle. Our analysis of pitch-angle-resolved SOPA data focuses special attention on small pitch angles that mirror at or above the latitude of GPS space vehicles traversing this region of Earth's magnetosphere. In addition to the stably-trapped relativistic electron population, characterized by a dearth of small-pitch-angle particles and remarkably exponential high-energy tails, we also observe regions of quasi- trapping, characterized by a dearth of high-energy particles and little, if any, pitch-angle variation at small pitch angles, i.e., a filled-up loss cone. At least two types of precipitation events occur regularly in the geostationary region, both characterized by extreme pancake distributions and a loss cone filled up with low-energy electrons, but empty of high-energy electrons; the two types are distinguished by the presence or absence of an energy- dependent critical pitch angle below which the population vanishes. When the feature just mentioned is absent, we observe a different energy-dependent feature in the near-perpendicular population. Perhaps these two features indicate scattering losses by field-line curvature on the one hand, and by wave-particle interactions on the other. Several illustrative examples will be shown from high-speed-stream driven events of 2007. 1. T. E. Cayton, "Application of a Maximum-Likelihood-Estimation-using-Expectation-Maximization Algorithm to the Deconvolution of CXD Electron Spectra II: Continuity and Smoothness," technical report LA-UR-07-3683. 2. R. R. White, "Space Weather Multi-tool," technical report LA-UR-07-2037. 3. T. E. Cayton and R. D. Belian, "Numerical Modeling of the Synchronous Orbit Particle Analyzer (SOPA, Version 2) that Flew on S/C 1990-095: Final Report," Los Alamos Report LA-14335.
SM33A-1104
Sources and sinks of equatorially mirroring energetic charged particles in the earth's inner magnetosphere
The Imaging Proton Spectrometer (IPS) and the Imaging Electron Spectrometer (IES) on the Polar satellite have measured temporary deviations in the isotropy of the pitch angle distributions (PADs) of charged particles in the inner magnetosphere. As Polar passes through the nightside equatorial region, the IPS and IES observe dropouts of charged particles with pitch angles near 90°, known as butterfly distributions caused by the shadowing of the magnetopause. Additionally, Polar observes a lower energy (< 60 keV) injection of locally mirroring ions while simultaneously detecting butterfly PADs in both higher energy ions and electrons. With these observations and the modeling of single particle motion, it can be shown that the magnetopause may act as both a source and a sink for energetic ions within the earth's magnetosphere.
SM33A-1105
Response of the magnetic field in the geosynchronous orbit to solar wind dynamic pressure pulses
We do a statistical survey of solar wind dynamic pressure (Pd) pulses and geosynchronous magnetic fields observed between 1998 and 2005. In geomagnetic quiet times with Dst>-50nT, we find 111 solar wind dynamic pressure pulses which produce geosynchronous magnetic field responses. These responses are often observed by two or three GOES spacecraft at different local times in geosynchronous orbit. The magnitudes of the geosynchronous magnetic field changes (dBz) have a peak near the noon meridian, similar to the results obtained in the study of the response of the geosynchronous field to the large and sharp solar wind dynamic pressure variations. However, the relative change of the geosynchronous magnetic field dBz/AV-Bz (where AV-Bz is the average of the geosynchronous magnetic field Bz observed during the response to the pressure pulse) depends weakly on the local time, thus the change of Bz(dBz) is proportional to the average field (AV-Bz). As the magnitude of the relative change of solar wind dynamic pressure (dPd/Pd) increases, the rate of geosynchronous magnetic field variation increases correspondingly. These results imply that the magnitude of the geosynchronous magnetic field response could be determined by AV-Bz. In addition, the interplanetary field orientation does not affect the response significantly. Using an MHD code which models the global behavior of the solar wind-magnetosphere-ionosphere system, we reproduce the main characteristics of the observations.
SM33A-1106
Variations of Magnetic Fields at Geosynchronous Orbit: Relative to the Location of Substorm Expansion
The magnetospheric configuration is tail-like when the interplanetary magnetic field is southward. The magnetosphere turns into a dipole-like configuration during a substorm expansion. The dipolarization region can be identified from an increase in the Z component of the magnetic fields at geosynchronous orbit. Variations of the magnetic fields at geosynchronous orbit during substorms were studied in terms of magnetic local time. However, their magnetic variations in terms of the relative distance of the foot point of a satellite to the location of a substorm expansion have not been studied. In this study, we calculate inclination angles that indicate the stretching or dipolarization level of the magnetic field lines using GOES 8 and 9 magnetic fields data for a list of substorm events identified from Polar Ultraviolet Imager auroral images. Magnetic variations for all the events are organized in averages with epoch zero to the substorm expansion onset under the various relative distances. These results show that the region where the inclination angle reaches its smallest value (or the largest stretching of the field lines) is found at one hour of local time west of the onset location before the onset. Also, the region where has the largest dipolarization (or the largest increase in the inclination angle during the substorm expansion) is found at one hour of local time east of the onset location after the onset. We will discuss the implication of these results in the presentation.
SM33A-1107
Self-consistent Inner Magnetosphere Magnetic Field and Comparison With Geosynchronous Measurements
For accurate physical understanding and modeling of inner magnetosphere dynamics one needs to take into account the coupling between particles and fields. Indeed, observations consistently show the magnetic field in the inner magnetosphere to be significantly depressed during active times such as geomagnetic storms. The field changes are caused by large amounts of injected plasma into the region, and they in turn strongly influence the dynamic evolution of both the plasma and the outer radiation belts. We have developed a self-consistent inner magnetosphere code that includes the field/plasma interaction, by coupling a kinetic ring current model with an Euler potential-based 3D plasma equilibrium code; in our approach, the magnetic field is computed in force balance with the kinetic model anisotropic pressures and then fed back into the kinetic code to drive its evolution. Here we report results from recent improvements to our approach that allow us to compute the self-consistent magnetic field at geostationary orbit and thus validate model output vs. geosynchronous (e.g. GOES) field measurements. This is now possible through the expansion of the model boundary into the plasma sheet (at 10 Earth radii), achieved through a new Euler potential technique in the 3D equilibrium code, coupled with the use of a statistical pressure model to expand geosynchronous pressure observations to larger distances. The new Euler potential choice also allows much more freedom in imposing the model magnetic boundary; for example, realistic storm-time empirical models such as T04S, which were difficult to use previously due to their strong asymmetry, can now be easily employed. We present output from our improved self-consistent model during both quiet times and geomagnetic storms, focusing on the computed 3D magnetic field and how it compares with both empirical model fields and in situ measurements (including from geosynchronous GOES satellites, but also from POLAR and CLUSTER when available). Finally, we compare model-computed with observed Dst during selected storms, and analyze how much of the Dst depression is due to the tail current, i.e. current systems outside geosynchronous orbit.
SM33A-1108
Extreme Magnetic Field Variations Observed at Geosynchronous Orbit
Magnetic field signatures observed at geosynchronous orbit provide important information for diagnosis of solar- terrestrial conditions. For this reason many studies have utilized data from the Geosynchronous Operational Environmental satellites (GOES) magnetometers during both quiet and disturbed conditions. In spite of this significant body of work, there still remains considerable interest in quantifying the most extreme variations at geosynchronous orbit and identifying the responsible solar wind conditions. For example, there are times when extreme distortions of the field are observed in the transverse components, sometimes as large as 40 nT in the east-west component and 70 nT in the radial component with a 100 nT background field. These and other extreme perturbations will be reported on, as well as results examining background field variations in response to the solar wind and geomagnetic conditions.
SM33A-1109
Temporal and spatial variation of outer radiation belt electron pitch angles: Cluster RAPID observations.
The Earths radiation belts are the longest studied regions of the magnetosphere, in terms of in situ measurements, and are still the subject of intense study. Of particular interest are the source and dynamics of the relativistic particles in these regions. Previous studies have focused on two primary mechanisms of transport and acceleration: radial diffusion from the magnetosphere and wave-particle energization. Recent studies have firmly established that in-situ energization is more dominant [Chen et al., 2007], yet the source of the electrons that are locally accelerated must ultimately be the near-earth plasma sheet. Access of untrapped plasmasheet electrons into the quasi-stable trapping region just outside geosynchronous orbit may provide not only the seed population for relativistic electrons but also the source of free energy for gyroresonant wave fields such as whistler chorus. Additionally, once electrons are accelerated to relativistic electrons, outward radial diffusion/transport may be an important loss mechanism for the outer edge of the radiation belts. In this study we investigate energetic electron measurements at the edge of the radiation belt (L=8-9) made by the Cluster RAPID IES instrument. In particular we examine local spatial and temporal variance measurements of the electron pitch angle distribution, as the 4 spacecraft pass through a narrow range of local time during each orbit (every ~56 hours), in order to better constrain the source, transport, and losses in this region.
SM33A-1110
3D Simulations of the Dynamics of the Relativistic Electrons in the Outer Radiation Belt
The evolution of the relativistic electron fluxes in the radiation belts may be described by the 3D modified Fokker- Planck equation in terms of radial distance, pitch-angle, and energy. We present the results of numerical simulations using a 3D radiation belt diffusion code newly developed at UCLA. Quasi-liner diffusion coefficients are computed for resonance scattering by hiss waves inside plasmasphere, chorus waves outside plasmasphere and EMIC waves in the regions of plumes. We show that radial diffusion, pitch-angle scattering, energy diffusion, and various feedback mechanisms play an important role in the evolution of the relativistic electron fluxes in the radiation belts. Our results indicate that peaks in phase space density are produced by local acceleration in a distributed source region located near L~5.5. We also present comparison of the simulations with in-situ observations of the relativistic electron fluxes.
SM33A-1111
Seasonal Variation of MeV Electron Flux at Geosynchronous Orbit
Recent detailed observations of the outer belt MeV electrons by many satellites revealed the dependence of rebuilding location of the outer radiation belt on the magnitude of the storms; i.e. the location of the newly appeared outer belt is inversely proportional to the storm bigness. An interesting observation is the simultaneous appearance of intense whistler mode chorus emissions around the peak position of MeV electron flux. Puzzling aspect of the increase of MeV electrons is the increase around the geosynchronous orbit during non-storm-time period. The increase of MeV electrons has close relationship with the plasma wave activity. Supply of intermediate-energy electrons is evident, corresponding to the substorm injections. These seed electrons are likely accelerated by the waves to MeV energy range. Well known phenomena of the increase of the relativistic electron flux around the geosynchronous orbit is the dependence on the solar wind velocity. We have newly found that increase of the MeV electron flux strongly depends on the IMF polarity. In the autumn season the electron flux increases very much during away polarity, while in the spring season the electron flux increases very much during toward polarity. Observations by the Japanese DRTS satellite are largely consistent with so-called Russell- McPheron effect, in which the substorm activity depends on the IMF polarity especially in spring and autumn seasons. We will compare the MeV electron data at geosynchronous orbit with the data from MDS-1 satellite, which has a geosynchronous transfer orbit, to consider outer radiation belt dynamics from the magnetic activity point of view.
SM33A-1112
Magnetospheric ULF Oscillations Driven by Interior Kelvin-Helmholtz Modes
Observations of field line resonances in the magnetosphere are characterized by a discrete set of ULF band frequencies. Determining the magnetospheric process that is responsible for this discrete set of frequencies has received much attention in the literature. The Kelvin-Helmholtz instability at the magnetopause boundary has been suggested as a possible candidate but it can only account for at most two discrete frequencies. Cavity mode oscillations have also been proposed but the geometric assumptions that must be made cannot account for the lowest frequency observations. In addition, cavity mode oscillations are seldom seen in magnetospheric observations. We present results from global magnetohydrodynamic (MHD) simulations of the solar wind/magnetosphere interaction that suggest the generation of interior Kelvin-Helmholtz (KH) modes inside the magnetosphere. These KH modes are generated locally, in the post dusk and pre dawn sectors of the magnetosphere. They arise as a result of counterstreaming sunward and tailward flows during periods of strong magnetospheric convection. We demonstrate how these interior KH modes can drive strong ULF oscillations inside the magnetosphere. A feature of these driven ULF oscillations is a discrete set of ULF band frequencies, a common feature of field line resonance observations.
SM33A-1113
Broadband electrons during storm-time substorm: Simultaneous FAST and Double Star observations
We report on broadband electrons (BBEs) observed simultaneously by the FAST and Double Star TC1 satellite during a storm-time substorm on 25 July 2004. The BBEs were observed at 13:55 UT by FAST at ~6.1 MLT, 66° ILAT, and an altitude of ~4000 km. The BBEs observed by FAST were electron flux enhancements over a broad energy range (50 eV-30 keV) at lower latitude side of the auroral oval (at 61-66° ILAT for this event). The pitch angle distribution of BBEs was isotropic at a higher energy range above ~0.5 keV. At a lower energy range below ~0.5 keV, field-aligned electron fluxes tend to be larger than the perpendicular fluxes. At this time, the Double Star TC1 satellite was located near the magnetic equator at L= 5.7 (65° ILAT) in nearly the same local time as that of FAST. At ~13:51 UT (4 min before the BBE observation by FAST), TC1 observed a clear dipolarization (decrease in Bx and increase in Bz). Geomagnetic field data obtained at ground-based stations showed that positive H-bay took place at this time. These facts indicate that a storm- time substorm started at 13:51 UT. At the same time, TC1 observed field-aligned upward electrons and downward ions, and intense low frequency (<10 Hz) waves. From 13:52 UT, TC1 observed drastic enhancements of electron and ion fluxes at ~0.5-30 keV, suggesting that particle acceleration was occurring in the inner magnetosphere at L= 5.7 associated with the substorm. Field aligned electron fluxes within pitch angles of ~10° at TC1 altitude can precipitate to the FAST altitude. Flux intensity of the field aligned components in the enhanced electrons at 0.5-30 keV observed by TC1 comparable to those observed by FAST. We suggest that the enhanced and field aligned higher-energy electrons at TC1 altitude became isotropic as they approach to the FAST altitudes by mirror force so that they were observed as the isotropic higher energy components of the BBEs by FAST. Note that the energy spectra of electrons observed by FAST show flux enhancements over a broad energy range not only at ~0.5-30 keV but also at ~0.05-0.5 keV. The field aligned lower energy components of BBEs could be locally accelerated in field-aligned directions near the FAST altitude.
SM33A-1114
EMIC scattering of relativistic electrons at geosynchronous orbit: an event study
We present here detailed observations of a relativistic electron dropout event observed on August 4, 2002 by spacecraft LANL-97a. The observations where in the post-noon sector and coincided with observations of a plasma plume, which is one of the necessary conditions that enables EMIC resonance interactions with relativistic (> 500keV) electrons. Comparisons of the evolution if the pitch angle distributions of these energetic electrons with theoretical modeling of the evolution of an energetic particle distribution in the presence of pitch angle diffusion due to EMIC waves showed rough consistency: the loss of particles near the loss cone affects a wider range of near-parallel electrons for higher energy particles, and the loss is relatively quick, occurring over 10's of minutes, – both these effects are observed in the data.// We attempt here to fill in the last piece of evidence for an EMIC loss mechanism: determination of the presence of the waves. Since there are no direct wave measurements on the LANL geosynchronous spacecraft, we intend to use an indirect method by estimating the potential instability and growth rates of EMIC waves based on the detailed observation of the particle distribution function of the ring current ions that need to support EMIC wave growth.
SM33A-1115
The influence of Epoch Time selection when doing Superposed Epoch Analysis on ACE and MPA LANL data
The influence of the reference time selection in superposed epoch analysis was examined for intense storms at solar maximum. The events were selected according to the pressure-corrected Dst, Dst*, being less than -100 nT. Solar wind data from ACE was used, along with near-Earth data from the magnetospheric plasma analyzer (MPA) instruments on the LANL-operated geosynchronous spacecraft. Numerous choices for the zero epoch time were used, ranging from the storm sudden commencement (SSC), the peak of the ring current enhancement (maximum Dst* slope), to the time of the storm peak (minimum Dst* value). Our results suggest that when doing superposed epoch analysis, the choice of the time stamp can be very important; for different choices, different storm characteristics are revealed in the averaged data. In the ACE data we find that when using SSC as a time reference, the SSC-related jump in solar wind parameters is very well revealed, but near the storm peak, Bz does not follow the well-known criteria for intense storms (Bz<-10nT for more than 3 hours). When the zero epoch time is chosen near the storm peak, the jump in solar wind parameters is not as sharp (and eventually lost) but the criterion for Bz is met. Regarding the MPA data, there are certain parameters that require the choice of a certain epoch time in order to reproduce an accurate behavior and others that are less sensitive to the choice of the epoch time when doing the superposed epoch analysis, since they appear to be less distinct in their temporal and spatial location. For instance, the night-side and morning-side hot ion density along with the hot ion anisotropy are main phase traits and a zero epoch time near the peak of the ring current enhancement is required to make these features distinct. Conversely, the hot electron density exhibits less structure requiring a particular epoch time choice.
SM33A-1116
Pi2 modulation of aurora as observed by all-sky TV image and magnetometers on board two geosynchronous satellites
We analyzed the auroral event of January 24 1986 using all-sky TV images and magnetometer data from two geosynchronous satellites (Goes5 and Goes6) separated by 2 hours of local time. From those analyses we found that poleward expansion of aurora following the auroral onset by 1 min was accompanied by surface waves excited in the midnight sector. The surface waves demonstrated out-of-phase relation in the D component (dipole east) and in-phase relation in the V component (radial outward) at GOES5 and GOES6 meridians, respectively. The oscillations in V-D plane led to CCW polarizations in the dawn side of aurora and CW polarizations in the dusk side. Simultaneous observations of those polarization patterns by ground magnetometers in auroral zone suggested an FLR structure in the midnight magnetosphere. We found that auroras ignited between GOES5 and GOES6 meridians were intensified when the largest eastward and westward bending of field lines occurred in the dawn and dusk side of aurora. The latitudinal extent of auroral modulations by surface waves expanded in geomagnetic latitudes up to 70N. Surface waves excited in the midnight magnetosphere might act as possible wave energy sources for auroral acceleration regions in lower altitudes. Those surface waves may also be a driving source of slow shock that supplies kinetic energies (bulk plasma flow) directly to the acceleration regions. A slow shock model based on double adiabatic equations of state was constructed. This theoretical model showed that although slow shock cannot carry particles having pitch angle distributions that are peaked perpendicular to the field lines, slow shock carry particles having isotropic pitch angle distributions. It is supposed that magnetic mirror force is responsible for this effect.