SM41C-01 INVITED
The role of wave-particle interactions in controlling relativistic electron variability
In the inner magnetosphere where the plasmasphere, ring current and radiation belts co-exist, energy and momentum are transferred between different plasma populations by plasma waves. Resonant interaction with these waves can lead to both energization and loss of radiation belt electrons, resulting in the highly variable flux of these particles. This talk will review our current understanding of wave-particle interactions in the radiation belts. Though significant theoretical progress has been made, the relative importance of different processes has not been experimentally established in many cases. Examples of observable quantities that can be directly compared with theoretical predictions will be discussed.
SM41C-02
Electromagnetic Ion Cyclotron Waves, Plasma Drainage Plumes and Geomagnetic Storms
It is known that electromagnetic ion cyclotron (EMIC) waves make an important contribution to localized ring current loss during geomagnetic storms, and also radiation belt electron losses . More recently it has been shown that EMIC waves observed by the GOES and POLAR satellites are associated with extended plasma drainage plumes seen in the plasmasphere and magnetosphere by the IMAGE-EUV instrument, and supported by LANL geostationary satellite thermal energy plasma data. In this study we will investigate the properties of EMIC waves seen by the fluxgate magnetometers onboard the CRRES elliptically orbiting satellite and the GOES geostationary satellites during pre-storm quiet times, and the main and recovery phases of geomagnetic storms. Also considered is the relationship between EMIC waves and associated plasma drainage plumes observed in IMAGE-EUV imaging data, CRRES plasma wave experiment electron density data and LANL satellite thermal energy plasma data. Two individual case studies and statistics over 24 selected storms will be presented. The results will provide new results on conditions in the magnetosphere under which EMIC wave generation occurs.
SM41C-03
Eigenmode Analysis of Energy and Pitch-Angle Diffusion of Energetic Electrons in the Outer Zone: 0.1-5 MeV
We extend our earlier eigenmode analysis of pitch-angle diffusion for 1-5 MeV electrons in the outer zone to a broader energy range: 0.1-5 MeV, and we include energy diffusion as well. The study is motivated by the fact that the projection of the observed particle distribution into the longest-lived eigenmode ought to be larger than the projection into shorter-lived eigenmodes. The analysis consists of determining the eigenvalues and eigenmodes of the drift-bounce averaged pitch-angle and energy diffusion operator under various assumptions about the ambient wave and plasma environment. In this study, we examine the relative contributions from chorus, hiss, and electromagnetic ion-cyclotron (EMIC) waves. By examining electron pitch-angle and energy distributions, we can refine our constraints on the contribution of EMIC waves (which primarily affect higher energy electrons) relative to hiss and chorus. We tune the free parameters of a simple model of the wave environment to achieve the greatest similarity between the observed energy and pitch-angle distribution and the first eigenmode of the diffusion operator. Thus, we are able to constrain the wave distribution on the entire drift shell from local energy- and pitch-angle distributions observed at a single location.
SM41C-04
Resonnant Drift Interaction Between Radiation Belt Electrons and ULF Waves of high Azimuthal Order
The low-altitude radiation belt at L<3.3, inside the plasmasphere, often shows multiple peaked electron energy spectra with up to 12 maxima between 0.4 and 2.5 MeV. These structures, dispersed with latitude, appear mainly during magnetic storms main phases inside the plasmasphere and down to L value as low as 1.1. As these structures are repeatedly measured onboard the Demeter satellite during a four year period, we conclude they are a characteristic of the low altitude radiation belts and are linked to storm associated changes in the magnetic fields. After eliminating a cyclotron resonnance cause, we examine the possibility that these structures are due to the interaction of drifting electron with ULF waves (T> 45 secondes) with high azimuthal orders. Numerical simulations of these interactions are performed and are shown to be in general agreement with the meassured structure and evolution of the peaked structures.
SM41C-05 INVITED
Radiation belt energy and pitch angle distributions resulting from shock-drift injections
In comparison with the Earth's outer zone radiation belts, sudden large variations in inner zone energetic particle fluxes are rare, occurring only during very large geomagnetic storms, usually initiated by coronal mass ejection (CME) driven interplanetary shocks. The violent geomagnetic storms of Oct-Nov 2003 mark the beginning of strong activity characterizing the declining phase of solar cycle No. 23. During the 29 Oct 2003 storm, ultra-relativistic (>10 MeV) electrons were injected below L = 3 producing a stably trapped radiation belt population that persisted for months following this event. We present results from a numerical study of shock-induced transport and heating of electrons in the 1-7 MeV range resulting in a newly formed 10-20 MeV belt; where test-particle trajectories are followed in time-dependent fields from an MHD magnetospheric model simulation of the 29 Oct 2003 Storm Sudden Commencement (SSC), driven by solar wind parameters measured at ACE. Both outer zone and solar energetic electron (SEE) sources for the new belt are considered. Energy and pitch angle distributions resulting from these two different possible sources are compared.
SM41C-06
Effect of Externally-Driven Magnetospheric ULF Variations on Energetic Electron Dynamics in the Radiation Belts
Variations in the Earth's electric and magnetic fields at ULF (mHz) frequencies can have a significant effect on the transport, energization, and loss of energetic electrons in the radiation belts. Direct driving by the solar wind can lead to a variety of ULF waves in the inner magnetosphere. In particular, velocity shear along the flanks of the magnetopause may set up Kelvin-Helmholtz waves at ULF frequencies in the dawn and dusk sector, and variations in the solar wind pressure can lead to ULF variations broadly distributed in local time across the dayside. Simulations using a global magnetohydrodynamic (MHD) model of the solar wind/magnetospheric interaction have been undertaken to characterize the global ULF wave activity that results from direct driving by the solar wind [Claudepierre et al., JGR 2008]. Here the simulations are run using controlled input parameters designed to excite and isolate waves driven by specific features in the solar wind. These studies have suggested that different sources of ULF activity will interact most effectively with different specific particle populations in various regions in the radiation belts. In this work, we conduct test particle simulations representing radiation belt electrons interacting with the directly-driven waves suggested by the global MHD simulations, and examine the efficiency with which different wave sources drive electron transport. We comment on those aspects of solar wind driving which contribute most significantly to the dynamics of different particle populations, and discuss the implications for radiation belt acceleration and loss.
SM41C-07
Spatial Structure of Simultaneous Magnetic and Riometer Πρ5 Pulsations
Several events with intense Pc5 pulsations at the recovery phase of a magnetic storm are considered in detail. A global structure of disturbance is studied with the data from world-wide array of magnetometers and riometers augmented with the data from particle detectors and magnetometers at the geosynchronous orbit. A local spatial structure is examined using the Finnish riometer array and IMAGE magnetometers. Though a general similarity between the quasi-periodic magnetic and riometer variations is observed, their local propagation patterns turned out to be different. To interpret the observations, the hypothesis of the coupling between two oscillatory systems – magnetospheric Alfven resonator and the system turbulence + electrons, has been suggested. The comparison of energetic electron enhancements at LANL satellites and ULF activity demonstrates that the solar wind flow is not the only driver of magnetospheric Pc5 pulsations, but the wave generation is stimulated by electron injection.