SM43B-01
Another unexpected origin of plasmaspheric hiss?
Plasmaspheric hiss is an electromagnetic emission confined to the plasmasphere and responsible for electron loss from the radiation belts, particularly in the slot region (2 < L < 3) but also inside plasmaspheric plumes, the outer radiation belt and the upper part of the inner belt during magnetically disturbed periods. Therefore, understanding the origin(s) of this whistler-mode propagating emission is of fundamental importance to forecast the distribution of relativistic electrons and the dynamics of the radiation belts. Recent studies have shown that chorus, another whistler-mode emission but generated just outside the plasmasphere, can propagate inside the plasmasphere and evolve into hiss [Santolík et al., 2005; Bortnik et al., 2008]. Other studies have shown that lightning-generated whistlers can account for the hiss wave power above 2 kHz [Green et al., 2005; Meredith et al., 2006]. As a reminder plasmaspheric hiss is a structureless emission, banded in frequency between ~100 Hz to several kHz and its power is on average one order of magnitude more intense below than above 1 kHz. Mid-latitude hiss is another type of whistler- mode emission found, like chorus, in the outskirts of the plasmasphere, with propagation characteristics similar to chorus as detected by the European Space Agency Cluster mission [Masson et al., 2004]. For the first time, ray-tracing calculations will be presented showing if this electromagnetic emission can also be regarded as an embryonic source of plasmaspheric hiss.
SM43B-02
Post Storm Energetic Electron Flux Enhancement and Decay
Energetic electron observations from HEO and SAMPEX satellites were used to study the electron response to several magnetic storms in the inner magnetosphere during 1998 through 2004 with emphasis on the post storm flux decays. The observations cover L values in the range 1.75 < L < 6. In addition, the HEO3 observations of the post-storm electron flux decays were examined for all storms in the 1998-2001 period to obtain the e-folding decay times at L = 3, near the peak of the outer zone. The >1.5 MeV electron fluxes were found to have three distinct 1/e decay times of about 5, 10.5, and 17.5 days. The 5 and 10.5 day e- folding times occurred in the first several days after the post-storm fluxes peaked during 2000-2001 and 1998 periods, respectively. The longer e-folding times occurred late in the decay history. The flux decay times obtained from SAMPEX and HEO3 for a subset of the storms compared relatively well but the HEO3 energy that compared best (>630 keV) was lower than expected. The energy dependence of the decay times was examined for the HEO3 data. The >630 keV electron decay times compared well with those of the >450 keV and >1.5 MeV electrons for 2.75 < L < 4. The >3 MeV decay times were longer than those at lower energies. The times for the post main phase flux enhancements as a function of L will also be presented. At times, the >3 MeV enhancements at lower L values, could be delayed several days relative to those at lower energies. The enhancement and decay time frames will be discussed in terms of the transport and loss processes.
SM43B-03
Using Particle Observations from Geosynchronous Orbit as a Proxy for Whistler and EMIC Mode Wave Growth During High Speed Stream Driven Storms
Multipoint LANL plasma data from geosynchronous orbit can be used to infer characteristics of whistler mode and electromagnetic ion cyclotron mode (EMIC) wave growth using linear theory. Recent work has shown that these inferences demonstrate significant differences in the statistical distributions of these waves during geomagnetic storms. Specifically, storms with higher post-storm relativistic electron fluxes exhibit above- average whistler wave activity and below-average EMIC wave activity in the recovery phase. This is consistent with whistler mode waves primarily being a growth mechanism for relativistic electrons and EMIC waves causing losses. The controlling factors for the net flux levels of relativistic electrons are still not clear. This study will examine plasma characteristics and wave properties specifically for high speed stream driven storms to discern how effective these processes are as compared to more typical storms. Though weak in traditional ring current signatures, high speed stream driven storms are particularly effective for the enhancement of relativistic electrons in the outer magnetosphere. By shedding light on this question, it may be possible to isolate particular controlling characteristic factors for radiation belt growth.
SM43B-04
Differentiating Loss Mechanisms of Outer Radiation Belt Relativistic Electrons from Multi- point Satellite Observations
The harsh environment of relativistic electrons (E>.511MeV) has an obvious impact on space weather. Therefore understanding the physical processes controlling relativistic electron dynamics—acceleration, loss and transport—in the Earth's outer radiation belt is the prerequisite for development of space weather forecast models. Compared to recent progress on understanding acceleration and transport processes, loss processes are much less understood and characterized. Although several loss mechanisms have been proposed (e.g., the precipitation caused by wave-particle interactions and the outward diffusion associated with magnetopause shadowing), it is still unclear which of those has the dominant role and where and when. Analyzing in-situ observations, especially long-term and/or simultaneous observations from satellite observations, is a powerful approach to differentiate the above competitive loss mechanisms. Here we will perform case and statistical studies of electron observations from two groups of satellites: One includes GPS, LANL GEO, Polar, and SCATHA that measure the trapped electron population at different L-shells from high altitude; the other is SAMPEX and NOAA POES that measure near-loss-cone electrons from low altitude at several local times. First we will develop an empirical model that describes the precipitation as functions of electron energy, longitude, latitude, L-shell, local time, season, geomagnetic activity level, and solar-cycle phase. Then by comparing the decay rate of trapped electrons observed near the equatorial plane to the precipitation rates observed at low altitude, we can quantitatively determine the role of precipitation on the loss of relativistic electrons, especially for the portion of radiation belt with L>4, during the main phase of storms.
SM43B-05
Effect of Low Frequency Waves on the Lifetime of Protons in the Earth's Inner Radiation Belt
Commercial electronics on LEO satellites are affected by protons in the 30-100 MeV range trapped in the inner radiation belt mainly when transiting the South Atlantic Anomaly (SAA). As the feature size of commercial electronic components shrinks to 65 nm, the probability of single event upsets increases by two to three orders of magnitude, reducing the utility of LEO orbiting satellites and making micro-satellites obsolete. Reduction of the flux of energetic protons in the inner belts,in the range of 1.5-1.8 becomes national priority. The paper examines the physics requirements for reducing the lifetime of the energetic protons in the inner belts from 10-20 years to 1-2 years. In reviewing the current understanding of the proton lifetimes we note that the lifetime of the outer belt protons is by more than four orders of magnitude shorter than in the inner belts. The reason for this sharp lifetime gradient is that the lifetime in the outer belts is controlled by fast pitch angle scattering of the protons into the loss cone by resonant interaction with naturally generated Alfven waves. Since these waves are constrained to regions with L>2, the inner belt lifetimes are controlled by slowing down of the protons exciting and ionizing oxygen atoms in the thermosphere. Results, obtained using a global plasma code indicate that injection of Alfven waves, from the ground or satellites, in the frequency range of 1-5 Hz with average amplitude 20-30 pT can reduce the energetic proton lifetime in the inner belts to 1- 2 years. The paper concludes by presenting the energy and power requirements for achieving such lifetime reduction as well as brief discussion.
SM43B-06
The nonlinear interaction of radiation-belt electrons with large amplitude chorus
The recent discovery of large amplitude (1 nT) chorus has prompted questions regarding the boundaries of applicability of quasilineat theory, traditionally employed in the study of radiation-belt dynamics. In this talk, we use a general, relativistic, oblique, test-particle code to evaluate the effect of large amplitude chorus on energetic, radiation-belt electrons. Three cases are examined: (A) low-amplitude waves interacting at low- latitudes, exhibit the expected, linear scattering which leads to large-scale diffusive behavior. (B) large- amplitude waves interacting at low-latitudes result in monotonic decreases in pitch-angle and energy due to a resonance dislocation effect, leading to large-scale de-energization and particle loss. (C) large-amplitude waves interacting obliquely at high latitudes, result in a combination of the above behaviors, as well as nonlinear phase-trapping which leads to rapid, dramatic increases in both energy and pitch-angle of a small portion of the test-particles. These results suggest that the intensity of individual, discrete wave elements is critical for quantifying the large-scale dynamics of the radiation-belts.
SM43B-07
Global modeling of Pc5 ULF Wave Activity and Relativistic Electron Dynamics following a Large Geomagnetic Storm
Ground-based observations during an interval of narrow-band ULF activity following a geomagnetic storm on November 25, 2001 are used to constrain the temporal and spatial characteristics of waves produced by a global model for ULF waves in the magnetosphere. This event is characterized by a long interval of high solar wind speed, and a strong field line resonance (FLR) localized to the local dusk sector. Both Polar and Cluster satellite observations during the interval of interest indicate that MHD fast waves produced by the Kelvin-Helmholtz instability along the dusk magnetopause flank are the likely source of wave power for the FLR. Based on this interpretation, an anti-sunward propagating ULF wave source is prescribed along the magnetopause boundary of the ULF wave model. The model is constrained by adjusting parameters that specify the source power distribution and bandwidth to improve local comparisons between the model output and observed time-series for field lines mapping to ground-based magnetometer stations. In order to assess the effects of these ULF waves on the relativistic electron population within the magnetosphere, the output from the ULF wave model is used to provide a time dependent magnetic field input for the bounce-averaged electron dynamics model developed by M-C Fok. This model computes the non-diffusive transport of electron phase space density (PSD) due to electrostatic and electromagnetic perturbations, assuming initial and outer boundary conditions for PSD that are dependent on solar wind parameters. The first results of this study will be presented.
SM43B-08
Comparison of low frequency equatorial waves at Earth and Saturn: Polar and Cassini observations
Low-frequency electromagnetic emissions are often detected near the Earth's geomagnetic equator. Recent studies show that these fast magnetosonic equatorial waves may accelerate electrons and can thus potentially play an important role in radiation belt dynamics. The Polar Plasma Wave Instrument (PWI) often detected these waves near the geomagnetic equator. These emissions were usually detected below a few hundred Hz and showed a wide range of frequency structure, from macroscopic (funnel-shaped spectrum) to finer (narrow frequency bands with a spacing of only a few Hertz). The Cassini spacecraft, just finishing its four year prime mission, often detects low frequency emissions (<100 Hz) near the Saturnian magnetic equator. Unlike the fast magnetosonic waves at Earth, equatorial waves at Saturn are primarily electrostatic and show little fine structure. These emissions are detected from about 6 to 10 Saturn radii and are often accompanied by enhanced electron cyclotron harmonic (ECH) emissions. A survey of properties of each of these emissions will be presented and the similarities and differences will be discussed.