SM53A-01
Eigenmode Analysis of Pitch-Angle Diffusion of Energetic Electrons in the Outer Zone
We determine the eigenfunctions and eigenvalues of the pitch-angle diffusion operator predicted by quasilinear diffusion theory and approximate plasma wave parameters for energetic electrons in the outer zone. We consider scattering alone and in concert from three wave populations: hiss, chorus, and EMIC. By projecting ptich-angle distributions observed by CRRES into the eigenfunctions, we can determine whether the pitch-angle distributions are consistent with the assumed diffusion process. Eigenmodes with shorter decay times (i.e., larger negative eigenvalues) ought to represent a comparatively smaller portion of the total flux in the pitch angle distribution. We use this technique to compare quiet-time and storm-time pitch-angle distributions, and to infer the relative contribution of different waves to the angular diffusion during those times.
SM53A-02
Enhancements of Relativistic Electrons in the Inner Magnetosphere Associated with an Interplanetary Shock on November 7, 2004
An interplanetary shock was clearly registered by both ACE and Geotail on Nov. 7, 2004, impacting on the Earth's magnetopause around 18:25 UT. Soon afterwords, great enhancements of relativistic electrons in the inner magnetosphere were measured by CLUSTER, Polar, SAMPEX, HEO, and GPS. The interplanetary shock was certainly associated with these electron enhancements. A fast inward radial transport due to the shock-induced electric field is a viable mechanism. However, there was no continuous measurement of the electrons near the equatorial region in the inner magnetosphere. The exact cause and detailed physical processes leading to the observed enhancements is still to be determined. Nonetheless, this is a very interesting event.
SM53A-03
Observational constraints on relativistic electron dynamics: temporal evolution of electron spectra and flux isotropization
Models of energization of electrons in the Earth's outer radiation belts invoke two classes of processes, radial transport and in-situ wave-particle interactions. Temporal evolution of electron spectra and flux isotropization during energization events provide useful observational constraints on models of electron energization. Events dominated by radial diffusion result in pancake type pitch angle distributions whereas some in-situ wave-particle energization mechanisms include pitch angle scattering leading to rapid flux isotropization. We present a survey of flux isotrpization time scales and electron spectra during relativstic electron enhancement events. We will use data collected by detectors onboard SAMPEX in low earth orbit and Polar which measures electron fluxes at higher altitude to measure flux isotropization. Electron spectra are obtained by pulse height analyzed data from the PET detector onboard SAMPEX.SAMPEX measurements cover the entire outer zone for more than a decade from mid 1992 to mid 2004 and Polar covers the time period from mid 1996 to the present.
SM53A-04
Energy Transport, Storage, and Dissipation in the Magnetosphere During Substorms.
Magnetospheric substorms represent a global interaction between the solar wind, magnetosphere, and ionosphere. Energy transported from the solar wind into the magnetosphere is largely stored in the tail until it is released (primarily into the ionosphere and the ring current). The Akasofu epsilon parameter (ε=4π L / μ v B2 sin 4 θ / 2), and multiple empirically determined formulas for energy dissipation into the ionosphere (joule heating and particle precipitation) and the ring current have been considered for such global interactions. An energy budget and estimation of total energy in the tail has been created for 12 isolated substorms that occurred during 2001. Considerable complexity and individuality of substorms is observed with substantial differences in the input and dissipation pattern for individual events. Our analysis is compared with previous published results.
SM53A-05
Global Distribution, Spectral Distribution, and Physical Characteristics of ULF Waves in the Earth's Magnetosphere
Fluctuations in the Earth's magnetic and electric fields on mHz timescales, so-called ultra low frequency (ULF) fluctuations, have been shown to be a major contributing factor in the dynamics of energetic radiation belt electrons. There have been several research efforts undertaken to determine the characteristics of those ULF waves that are the most effective in energizing and transporting radiation belt electrons. These efforts have identified the following properties as the most relevant to the energization and transport of outer zone electrons: (i) spectral distribution at frequencies including mω_d where ω_d is the particle drift frequency and m is (ii) the azimuthal mode structure of the interacting waves; (iii) the global distribution (radial and azimuthal extent) of the waves, which largely determines the rate at which an azimuthally drifting electron will be energized; and (iv) the direction of propagation, which determines whether the particles will effectively interact with the waves. The global nature of these properties makes analysis from single-point, in-situ spacecraft measurements somewhat difficult. This is particularly true for properties (ii), (iii) and (iv). To circumvent this issue, we present results from global, 3-d magnetohydrodynamic simulations of the solar wind/magnetosphere interaction, driven by idealized solar wind conditions. The controlled nature of this experiment allows us to isolate a known solar wind driver of magnetospheric ULF waves, for example shear waves on the flanks driven by high speed solar wind streams, and study the aforementioned characteristics of the ULF waves generated. The results presented here will provide a global context for interpreting results from the upcoming NASA Radiation Belt Storm Probes (RBSP) mission.
SM53A-06
Kappa Velocity Distribution Results from Modeling Thermal Fluctuations in a Turbulent Plasma-sheet
Kappa velocity distributions are common to laboratory and space plasmas, and exhibit long power law (suprathermal) tails in comparison to Maxwell-Boltzmann distributions. Various processes, including spontaneous scattering by Langmuir and ion-sound waves, charge fluctuations, polydispersity in diffusing particle or random media sizes, induced scattering by photons, and other processes may generate kappa velocity distributions. Since electron and ion velocity measurements in the plasma sheet suggest a highly turbulent state, we consider whether thermal fluctuations in MHD turbulence are sufficient to generate kappa velocity distributions. We model the thermal fluctuations by Langevins equation with a white noise driver. The noise variance is set proportional to the expectation of the square of the local Kolmogorov speed in the turbulent plasma. The modeled variance fluctuates at times sampled from an exponential distribution representing independent increments in mean waiting interval between times of particle interaction with the turbulent plasma. The histogram for the resulting velocity distribution is plotted at pre-selected times, demonstrating the evolution from a chosen initial distribution to the kappa distribution.
SM53A-07
Space Technology 5 Observations of Short-Period ULF Waves: Temporal and Spatial Patterns
The three microsatellites that comprise the Space Technology 5 (ST5) mission were launched into a dawn-dusk, 300 x 4500 km sun-synchronous orbit in a "pearls-on-a-string" configuration, with spacings ranging from >5000 km down to under 50 km. Fluxgate magnetometers on board each spacecraft collected vector magnetic field data from March 26 through June 30, 2006. In this study we present the first results of a survey of ULF waves in the Pc 1-2 frequency range, with a total of 105 events, recorded by these spacecraft. Waves in the middle magnetosphere (L from 4 to 7) were observed to have a nearly uniform diurnal occurrence rate. At higher latitudes (L > 7) occurrence was maximum in the dawn-noon sector, consistent with stimulation by magnetospheric compressions. Only five wave events were observed at L < 4. The temporal occurrence distribution roughly followed the occurrence of Pc 1-2 activity recorded at Halley, Antarctica (L = 4.5), in that the number and intensity of events was increased during magnetospheric compressions, during the recovery phase of magnetic storms, and during one extended interval of disturbed but only modestly negative Dst. Somewhat surprisingly, only eight events were observed by all three spacecraft as they passed over similar L shells, and only 14 events, including two each on three days, were observed by two spacecraft. Nearly all of these events occurred during storm recovery. We interpret the lack of more multi-spacecraft observations as indicating the highly localized nature of regions in the magnetosphere that become unstable to electromagnetic ion cyclotron instabilities.
SM53A-08
Spatio-temporal dynamics of the magnetosphere during geospace storms
The magnetospheric response to strong driving by the solar wind is highly structured, and spatially resolved data are essential for the understanding of the spatio-temporal dynamics. The global features of the magnetosphere have been studied extensively using nonlinear dynamical techniques. A database of the solar wind data from ISEE3 and IMP8 spacecraft, and ground-based magnetometer data from high latitude stations [Kamide et al., JGR, 17,705, 1998] is used to study the magnetospheric response to solar wind variables by mutual information functions. A key feature of the mutual information function is its ability to bring out the linear as well as nonlinear correlations and such functions are needed to study the magnetospheric dynamics, which is inherently nonlinear. The minimum window length required for computing robust functions is found to be about 6 hrs. Another window length of 24 hrs is used in these studies to analyze the dynamics on longer time scales. The spreads in the average mutual information show strong correlations with the solar wind convective electric field and the sudden changes in the dynamic pressure. The time evolution of mutual information shows a westward expansion of the disturbed region in the night side magnetosphere, starting from near the midnight sectors. In order to study the spatial structure in more detail the magnetic field perturbation at 39 ground stations during year 2002 and the corresponding solar wind data are compiled. The ground magnetometer data are from the two chains of stations: CANOPUS (13) and IMAGE (26). This new data set, with 1-minute resolution, is used to study the spatio-temporal structure. A technique that utilizes the daily rotation of the Earth as a longitudinal sampling process is used to construct a two dimensional representation of the high latitude magnetic perturbations both in magnetic latitude and magnetic local time. This model is used to predict the spatial structure of geomagnetic disturbances during intense geospace substorms, which are important natural hazards.
SM53A-09
Sources and sinks of equatorially mirroring protons and electrons within the nightside magnetosphere
The Imaging Electron Spectrometer (IES) and Imaging Proton Spectrometer (IPS) on the Polar satellite have frequently measured temporary deviations in the isotropy of the pitch angle distributions (PADs) in the nightside region of the magnetosphere inside of 10 RE. Depressions in the observed fluxes of electrons occur with pitch angles around 90° in the equatorial zone, while the more field aligned electrons remain largely unchanged. These butterfly distributions are a regular feature of the equatorial magnetosphere. The orbital precessions of Polar have allowed much of the inner magnetosphere to be observed, approximately 2 ~ 10 E. Electron and proton paths of motion are simulated varied pitch angles for a specific event on 26 October 1999. In addition to a normal butterfly PAD on this day, Polar also observes a short, but intense localized injection of 90° pitch angle ions. The modeling effort can suggest that the magnetopause can play a significant role in both the loss and injection of equatorially drifting particles within the outer regions of the inner magnetosphere.