Ring Current and Radiation Belts II Posters
Presiding: X Li, Laboratory for Atmospheric and Space Physics, University of Colorado; G V Khazanov, NASA Goddard Space Flight Center
SM43B-01 1330h
Remote Imaging of Storm-Phase Ion Heating
The MENA (Medium Energy Neutral Atom) instrument onboard the IMAGE spacecraft allows for global imaging of the magnetosphere in neutral atoms with energies ranging from 1 to 60 keV. Using known charge exchange cross sections and the properties of the instrument, the measured neutral atom energy spectra along each line-of-sight of the instrument can be converted into ion energy spectra. By fitting the ion energy spectra with a Maxwellian velocity distribution, global maps of the ion temperature during periods of elevated activity can be generated [Scime et al., 2002]. In this work, we combine remote ion temperature imaging using neutral atoms with an image processing algorithm that accounts for variations in the viewing geometry due to orbital precession and seasonal variations to sum images from eight large geomagnetic storms. Storm time images were separated into four intervals, pre-storm, main phase, early recovery, and late recovery. To distinguish between storms with differing convection electric field strengths, the storms were sorted by cross polar cap potential drops obtained from DMSP satellite measurements of ion flows. We find that storms with strong polar cap potential drops (i.e. < - 80 kV) exhibit more ion heating during the main phase and throughout the recovery than storms with more mild potential drops (i.e. ~ -50 kV). Ion heating clearly localized to the ring current region is also more apparent in those storms with stronger polar cap potential drops.
SM43B-02 1330h
Ring Current Dynamic in the Presence of Electromagnetic Ion Cyclotron Waves
The effect of Electromagnetic Ion Cyclotron (EMIC) waves, generated by ion temperature anisotropy in Earth's ring current (RC), is the best known example of wave-particle interaction in the magnetosphere. Also, there is much controversy over the importance of EMIC waves on RC depletion. Under certain conditions, relativistic electrons, with energies 1-3 MeV, can be removed from the outer radiation belt (RB) by EMIC wave scattering during a magnetic storm. That is why the calculation of EMIC waves must be a very critical part of the space weather studies. The new RC model that we have developed and present for the first time has several new features that we have combine together in a one single model: (a) several lower frequency cold plasma wave modes are taken into account; (b) wave tracing of these wave has been incorporated in the energy EMIC wave equation; (c) no assumptions regarding wave shape spectra have been made; (d) no assumptions regarding the shape of particle distribution have been made to calculate the growth rate; (e) pitch-angle, energy, and mix diffusions are taken into account together for the first time; (f) the exact loss-cone RC analytical solution has been found and coupled with bounce-averaged numerical solution of kinetic equation; (g) the EMIC waves saturation due to their modulation instability and LHW generation are included as an additional factor that contributes to this process; and (h) the hot ions were included in the real part of dielectric permittivity tensor. We compare our theoretical results with the different EMIC waves models as well as RC experimental data.
SM43B-03 1330h
Global Ring Current Ion Distributions Obtained by IMAGE/HENA DURING STORMS AND SUBSTORMS
Global Energetic Neutral Atom (ENA) images of the Hydrogen and Oxygen ring current in the 10-200 keV range have been obtained by IMAGE/HENA for five years. Approximately 40 storms have been succesfully imaged. Over the years a constrained linear inversion technique has been developed that can retrieve the equatorial ring current ion distributions from the ENA images. It uses the Tsyganenko [2003] magnetic field model and assumes pitch-angle distributions based on in-situ data. We investigate the general morphology of the ring current during storm times with special attention to the question of how much the storm-time substorm injections contribute to the ring current pressure. We discuss and compare observations with ring current models.
SM43B-04 1330h
Inner-Magnetospheric Data Assimilation With an Ensemble Kalman Filter
The Ensemble Kalman Filter is a data assimilation technique that incorporates observational data into a physical model to estimate the state of a system, using Monte Carlo methods to estimate the model error statistics. The application of this technique to the inner-magnetospheric kilovolt plasma environment is explored in a series of identical twin experiments, using the Magnetospheric Specification Model (MSM) to represent the inner-magnetospheric state. Simulated IMAGE/HENA data is incorporated into the MSM, using a forward modeling algorithm to relate the observed ENA intensity to MSM variables. Results from experiments with different ensemble sizes, sampling strategies, and analysis schemes are presented, and the sensitivity of the assimilation to various sources of error is investigated.
SM43B-05 1330h
Scattering Efficiency of a High-Voltage Tether in Space
A high altitude nuclear detonation could produce an intense artificial radiation belt (RB) of relativistic electrons. Earth satellites operating in this region could be adversely affected. Several concepts have been proposed to remediate the effects of this artificial RB. Among them is the high-voltage electrostatic tether. Preliminary analyses that have been carried out by several groups suggest, that this technique shows promise of controlling the relativistic electron content in artificial RB. The relativistic electron population is one of the most important topics of space weather studies because of its potential damage to civilian and military space assets. There are several fundamental issues that should be examined in order to validate high-voltage tether remediation of artificial RB. Among them are: power consumption, size and stability of the plasma sheath around the tether, and scattering efficiency of the high-voltage system that is related to the plasma sheath size. This study would be focused on the scattering process itself and artificial RB remediation assuming that power consumption and the size of the plasma sheath are known.
SM43B-06 1330h
RHESSI Observations of Relativistic Electron Precipitation at L=1.0-2.6 Following Large Solar Energetic Particle Events
The past eighteen months have produced the largest solar energetic particle events in the current solar cycle. We present a preliminary investigation of the effects of large solar storms on trapped electron populations in the magnetosphere using observations from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) following the 28 October 2003, 27 July 2004, and 10 November 2004 storms. Although RHESSI's germanium detectors were designed to measure solar hard x-rays and gamma rays, they are large enough (7.1 cm diameter x 8.5 cm) to stop penetrating electrons and measure their energy up to 17 MeV, as well as detect bremsstrahlung radiation from the precipitating electrons. We first obtain raw counts spectra, which are a superposition of bremsstrahlung and direct electron detection signatures. We then apply a GEANT simulation model of the spacecraft and instrument in order to infer the original spectra of incoming electrons from the measured spectra. After the October 2003 storm, RHESSI detected electrons up to ~5 MeV that were transported into the slot region (below L=2.6), and subsequently began to diffuse away. In the month following the storm, the spectrum became softer as high-energy electrons receded from the L=1.0-2.6 region. By the end of November 2003, the highest-energy electrons detected dropped to ~2 MeV. At the beginning of June 2004, six months after the original storm, the relativistic electrons disappeared completely. A similar spectral analysis is done for the July 2004 and November 2004 storms.
SM43B-07 1330h
Specification of >2 MeV Geosynchronous Electrons Based on Solar Wind Measurements
Relativistic electron flux measurements from geosynchronous satellites show a local-time dependence. This local-time dependence is due to the radial profile of the electron fluxes, the dayside/nightside asymmetry of the Earth's magnetosphere and is also affected by geomagnetic activity, which is in turn affected by the solar wind. Statistical Asynchronous Regression (SAR) was recently used to determine the relationship between electron fluxes measured at different local times, as a function of the Kp index [O'Brien et al. 2001]. In this study, we use measurements directly from the solar wind, instead of the Kp index, as the basis for determining the local-time dependence of geosynchronous energetic electron fluxes. We use solar wind parameters as input in our model to map GOES-10 > 2 MeV electron measurements to other local times and compare with the electron measurements from five LANL geosynchronous satellites, widely spaced in longitude, when they pass through these local times. We explore the effects of solar wind velocity, dynamic pressure, and density on the local-time dependence of geosynchronous electron fluxes. We found that, for the given 3 year data set, only using solar wind velocity gives rise to the best results.
SM43B-08 1330h
Relativistic electron flux enhancement on October 28, 2003
Abrupt enhancement of relativistic electron (E > 2MeV) flux was observed by geosynchronous and polar orbit satellites at 11:50 UT on Oct. 28, 2003 after an intense X17 solar x-ray burst at 11:10 UT. The relativistic electron enhancement occurred before the magnetic storm starting at 6:00 UT on the next day and was directly correlated with the Solar Energetic Particle (SEP) event in the upstream solar wind. Observations by SAMPEX (E > 1MeV), NOAA/POES (E > 0.3MeV), Polar and Cluster spacecraft show that the abrupt electron enhancements. The increase of electron flux lasted for several days, with its peak being clearly in conjunction with the arrival of an interplanetary shock at the Earth. This study will focus on the relativistic electron behavior in the inner magnetosphere and radiation belt region. The implications for this event will be discussed.
SM43B-09 1330h
A Numerical Study of the Injection of Relativistic Electrons into the Radiation Belts During the 29-31 Oct 2003 (Haloween) Geomagnetic Storm.
We numerically investigate the injection of relativistic electrons into the radiation belts during the 29-31 OCT 2003 (Haloween) geomagnetic storm. Test particle Lorentz trajectories are computed in fields from a Lyon-Feder-Mobarry (LFM) global MHD simulation of the Haloween storm using measured solar wind parameters to study the role of non-adiabatic effects on magnetospheric entry and trapping of 10-20 MeV electrons. A relativistic gamma factor ~20-40 for these ultrarelativistic electrons means that their gyro-radii approach the scale lengths of magnetic field gradients in the outer radiation belts, suggesting that a generalization of Störmer theory to time dependent fields may provide a mechanism for the injection and trapping of relativistic electrons, as has previously been shown for solar energetic ions (Kress et al. Fall AGU 2004).
SM43B-10 1330h
Analysis of Pc5 Wave Modes Observed by CRRES and GOES Satellites During a Relativistic Electron Enhancement Event
A possible mechanism for relativistic electron acceleration in the magnetosphere is drift-resonance interaction with ULF waves. Effective acceleration is expected if there exists a resonant condition between the electron drift periods and wave periods, so that azimuthally drifting electrons will periodically experience the same electric perturbation fields and be accelerated. In order to confirm the acceleration mechanism, it is important to identify the wave mode responsible for the acceleration. We have made a detailed analysis of the perturbation electric and magnetic field data taken during a relativistic electron acceleration event [Tan et al., 2004]. We found that both toroidal and poloidal wave components are present in the ULF wave data and that both components have discrete frequency spectra that are consistent with the discrete Alfven wave spectra typically measured on the ground. By interpreting the relative phases of the observed perturbation field quantities in the context of global MHD wave structure in the magnetosphere, we have determined the CRRES and GOES spacecraft positions relative to the nodes of the magnetospheric MHD waves, and therefore determined the wave modes of the observed Pc5 waves. In this paper, we will describe our wave analysis and discuss the implications of our results on relativistic-electron acceleration in the magnetosphere. Tan, L. C., S. F. Fung, and X. Shao (2004), Observation of magnetospheric relativistic electrons accelerated by Pc-5 ULF waves, Geophys. Res. Lett., 31, L14802, doi:10.1029/2004GL019459.