SM14B-01 INVITED 

New insights on radiation belt physics from global data assimilation models

* Reeves, G D (reeves@lanl.gov), Los Alamos National Lab., Mail Stop D-466 Space Sciences, ISR-1, Los Alamos, NM 87544,

As we have progressed toward an integrated, predictive space weather system, space physics has undergone dramatic changes in both our understanding of the underlying physics and in the methods used to develop that understanding. Radiation belt dynamics and their connection to the broader heliophysical system are a powerful example. In recent decades a shift from single spacecraft observations to multi-spacecraft systems analysis precipitated fundamental changes in our understanding of radiation belt physics. Variations in intensity by many orders of magnitude were observed throughout the system on time scales as short as minutes. The connection between radiation belt events and geomagnetic storms was revealed to be both more complex and less predictable than previously imagined. Simple drivers such as high speed streams evolved into comparative studies of heliospheric structures such as CMEs and CIRs. As a result, new theories of diffusion and wave- particle interactions were developed to explain radiation belt acceleration, transport, and losses. Now, a different analysis methods based on application of the techniques of data assimilation are able to test and develop highly sophisticated, physics-based models of the radiation belts and the coupled inner magnetosphere system. Data assimilation-based modeling not only provides a specification of the global state of the magnetosphere but also provides tools for understanding the dynamics, testing specific theoretical predictions, and developing more complete (but still physically constrained) radiation belt models. In this paper we discuss how data assimilation- based radiation belt models are being used by different research groups to develop new physical insights and improved models. We will also highlight recent results from the DREAM model that test the effects of magnetopause shadowing, electron precipitation, the Dst effect, and VLF wave-particle acceleration.

SM14B-02 

Acceleration and Losses of Relativistic Radiation Belt Electrons Due to Wave-Particle Interactions: SCATHA Observations

* Roeder, J L (james.roeder@aero.org), The Aerospace Corporation, Mail Stop M2-260, P. O. Box 92957, Los Angeles, CA 90009, United States Fennell, J F), The Aerospace Corporation, Mail Stop M2-260, P. O. Box 92957, Los Angeles, CA 90009, United States Thorne, R M), University of California, 7127 MS, P. O. Box 951565, Los Angeles, CA 90095, United States

Various mechanisms have been proposed as the cause of acceleration and losses of radiation belt electrons in the inner magnetosphere. These include radial diffusion influenced by ULF pulsations, and interactions with several types of low frequency plasma waves such as whistler-mode chorus emissions. Present models idealize these effects as quasilinear diffusion of the particles in energy and/or pitch angle. The P78-2 SCATHA satellite is one of the few missions to simultaneously measure both the energetic electrons and plasma waves. The SCATHA energetic electron observations are analyzed to provide insights into these phenomena. Profiles of the electron phase space density at constant values of the first two adiabatic invariants are constructed for several storm-time intervals. These profiles are examined for the signatures of local processes such as pitch angle diffusion. The evolution of the phase space density is analyzed with the concurrent observations of whistler-mode chorus wave intensity by SCATHA. These amplitudes are used to compute model quasilinear diffusion coefficients which are then compared with the observed gradients in electron phase space.

SM14B-03 

Refilling of the Slot Region Between the Inner and Outer Electron Radiation Belts During Storms

* Thorne, R M (rmt@atmos.ucla.edu), UCLA, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, United States Shprits, Y Y (yshprits@atmos.ucla.edu), UCLA, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, United States Meredith, N P (nmer@bas.ac.ek), British Antarctic Survey, Madingly Road, Cambridge, CB30ET, United Kingdom Horne, R B (r.horne@bas.ac.uk), British Antarctic Survey, Madingly Road, Cambridge, CB30ET, United Kingdom Li, W (moonli@atmos.ucla.edu), UCLA, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, United States

Energetic electrons (>50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm-time injection at lower energies, but does not explain the rapid appearance of higher energy electrons (> 150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler-mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the October 10, 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enhancement in 200-700 keV electrons in the outer slot region near L = 3.3. Radial diffusion is much less effective, but may partially contribute to the flux enhancement at lower L. Subsequent outward expansion of the plasmapause during the storm recovery phase effectively terminates local wave acceleration in the slot, and prevents acceleration to energies higher than 700 keV. A statistical analysis of energetic electron flux enhancements and wave and plasma properties over the entire CRRES mission supports the concept of local wave acceleration as a dominant process for refilling the slot during the main and early recovery phase of storms. For moderate storms, the injection process naturally becomes less effective at energies greater than 1 MeV, due to the longer wave acceleration times and additional precipitation loss from scattering by EMIC waves. However, during extreme events when the plasmapause remains compressed for several days, conditions may occur to allow wave acceleration to multi-MeV energies at locations normally associated with the slot.

SM14B-04 

Long-term Average Spectral and Spatial Distributions of Plasmaspheric Hiss Observed by the Akebono and IMAGE Satellites

* Goto, Y (ygotou@is.t.kanazawa-u.ac.jp), Graduate School of Natural Science and Technology, Kanazawa Univ., Kakuma-machi, Kanazawa, 920-1192, Japan Fung, S F (shing.f.fung@nasa.gov), Laboratory for Heliospheric Physics, Code 672, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States Kasahara, Y (kasahara@is.t.kanazawa-u.ac.jp), Graduate School of Natural Science and Technology, Kanazawa Univ., Kakuma-machi, Kanazawa, 920-1192, Japan

The radiation belt slot region is known to result from losses of energetic electrons by enhanced pitch-angle scattering by whislter mode waves associated with plasmaspheric hiss emission. The distributions of whistler mode waves in the slot L range are therefore important for understanding the electron radiation belt. The sources and distributions of the waves are, however, still controversial. In the present study, using the Akebono/MCA data [1989-2005] and the IMAGE/RPI data [2000-2005], we have constructed the average plasmaspheric hiss spectral distributions over a broad frequency range. In addition, we have investigated the spatial distributions of plasmaspheric hiss with the wave map technique [Green et al.(2005)]. Our study shows that the broadband plasmaspheric hiss are distributed in the frequency range of 100Hz to several kHz, and exhibit a broad intensive peak. The frequency of the intensity peak tends to increase with magnetic latitude. The frequencies of the most intense waves in the nominal slot L range (2-50nT) are found to be between 300Hz and 600Hz on average. During high storm activity (Dst <-150nT), however, the peak frequencies become slightly lower. The intensity of plasmaspheric hiss clearly depends on substorm activity as measured by the AE index, consistent with Meredith et al.(2004). The hiss wave intensity maps also show a strong local time asymmetry. The large amplitude waves are observed at 6:00-19:00 MLT. From our extensive analysis, we have also found an L dependence of hiss activity, with the larger amplitude waves being observed at lower L during substorm active conditions. The same tendency can be found for solar activity. The average intensities of the waves during 1989-1991 and 2000-2001 are a few dB larger than those during 1992-1997 and 2005. The most intense waves are observed at lower L during high solar activity. The statistical study on spectrum features of the plasmaspheric hiss together with the spatial distribution show clear dependences of storm, substorm and solar activities. Acknowledgments: The authors wish to thank Akebono/VLF members for their contribution to the VLF instrument and its data analyses. The authors also wish to thank B. W. Reinisch and CDAWeb for providing the IMAGE/RPI dynamic spectrogram data. References: Green, J. L., S. Boardsen, L. Garcia, W. W. L. Taylor, S. F. Fung, and B. W. Reinisch (2005), On the origin of whistler mode radiation in the plasmasphere, J. Geophys. Res., 110, A03201, doi:10.1029/2004JA010495. Meredith, N. P., R. B. Horne, R. M. Thorne, D. Summers, and R. R. Anderson (2004), Substorm dependence of plasmaspheric hiss, J. Geophys. Res., 109, A06209, doi:10.1029/2004JA010387.

SM14B-05 

The origin of plasmaspheric hiss

* Bortnik, J (jbortnik@gmail.com), University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095, United States Thorne, R M (rmt@atmos.ucla.edu), University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095, United States Meredith, N P (nmer@bas.ac.uk), British Antarctic Survey, National Environment Research Council, Madingly Road, Cambridge, CB3 OET, United Kingdom

Plasmaspheric hiss is an electromagnetic emission found ubiquitously within the plasmasphere, and other high density regions such as plasmaspheric drainage plumes. It has been known for some time that hiss is an important scattering (loss) mechanism for the high energy electrons that populate the Van Allen (radiation) belts, and lead to the radiation-belts" well-known two-zone structure. However, the origin of plasmaspheric hiss has been a hotly debated topic since its discovery, over four decades ago. The two leading theories are: (1) the evolution of lightning-generated, magnetospherically reflected whistler waves into the incoherent hiss band, and (2) the in-situ growth of wave energy due to cyclotron interactions with energetic particles. Both theories suffer from significant deficits and cannot explain all of the observed features of hiss. In the present work, we present a new theory: the evolution of ELF/VLF chorus waves into the hiss spectrum, and show on the basis of extensive ray tracing that chorus is able to leak into the plasmasphere, and reproduce the observed hiss bandwidth, day/night asymmetry, and wave normal angle distribution. The modeling work is compared against current and previous satellite observations.

SM14B-06 INVITED 

Discovery of Very large Amplitude Whistler-mode Waves in the Outer Radiation Belt and Their Effects on Relativistic Particles

* Cattell, C A (cattell@fields.space.umn.edu), School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55416, United States Wygant, J R (jwygant@fields.space.umn.edu), School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55416, United States Goetz, K), School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55416, United States Kersten, K), School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55416, United States Kellogg, P), School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55416, United States von Rosenvinge, T), NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States Blake, J B), The Aerospace Corporation, Space Sciences Department, Los Angeles, CA 90009, United States Bale, S D), Space Science Laboratory, University of California, Berkeley, CA 94720, United States Roth, I), Space Science Laboratory, University of California, Berkeley, CA 94720, United States Temerin, M

Hudson, M K), Dept. of Physics, Dartmouth College, Honover, NH 03755, United States Mewaldt, R A), Downs Laboratory, California Institute of Technology, Pasadena, CA 91125, United States Wiedenbeck, M), Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, United States Maksimovic, M), LESIA, UMR CNRS 8109, Observatoire de Paris, Meudon, MD 92195, France Ergun, R), Laboratory for Atmospheric and Space Physics, Unversity of COlorado, Boulder, CO 20771, United States Acuna, M), NASA, Goddard Space Flight Center, Greenbelt, MD 20771, United States Russell, C T), Institute of Geophysics and Planetary Physics, Uuniversity of California, Los Angeles, CA 20771, United States Lavraud, B), ISR-1, Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM 87545, United States

A longstanding problem in the physics of the Earth's radiation belts is determining the mechanism or mechanisms that accelerate electrons to relativistic energies and those that cause their loss. We report the discovery of obliquely-propagating whistler-mode waves in the radiation belt with electric field amplitudes (>250 mV/m) more than an order of magnitude larger than other whistlers. The waves were observed as STEREO-B traversed the dawn-side outer radiation belt, shortly after a substorm injection was observed by geosynchronous satellites. Simulations show that these large amplitude waves can energize electrons by the order of an MeV in less than 0.1s, explaining the rapid enhancement in relativistic electron intensities observed between the STEREO-A and STEREO-B encounters with the dawn-side outer radiation belt. The simulations also show that some electrons are scattered by large angles (10s of degrees) in a single wave encounter, suggesting that the relativistic electron microbursts observed simultaneously by SAMPEX are also due to the large amplitude whistlers. Our results show that the usual quasi-linear theoretical models of electron energization and scattering via small-amplitude waves, with timescales of hours to days, are inadequate for understanding radiation belt dynamics.

SM14B-07 

Observations of Very High Amplitudes of Whistler-Mode Chorus: Consequences for Nonlinear Trapping of Energetic Electrons in the Outer Radiation Belt

* Santolik, O (os@ufa.cas.cz), IAP ASCR, Bocni II 1401, Prague, 14131, Czech Republic * Santolik, O (os@ufa.cas.cz), Charles University, V Holesovickach 2, Prague, 18000, Czech Republic Gurnett, D A (donald-gurnett@uiowa.edu), University of Iowa, Department of Physics & Astronomy, Iowa City, IA 52242, United States Pickett, J S (pickett@uiowa.edu), University of Iowa, Department of Physics & Astronomy, Iowa City, IA 52242, United States

Whistler mode chorus has recently regained attention as a possible agent in acceleration of electrons to relativistic energies in the outer Van Allen belt. As theoretical and simulation studies show, sufficiently high amplitudes of chorus wave packets are needed. We present analysis of observations of high resolution magnetic field waveforms by the four Cluster spacecraft. The results show that chorus can reach amplitudes of several nT but only for a very small fraction of wave packets. We systematically analyze a large data set of measured waveforms to verify signatures of nonlinear wave trapping of energetic electrons. Fine structure embedded in the chorus elements mainly reflects simultaneous presence of waves at different frequencies (sidebands) although separate wave packets are also observed. The observed frequency differences (time scales of subpackets) as a function of wave amplitude are compared to theoretical estimates of the nonlinear trapping frequency. http://os.matfyz.cz/papers/agu2007/

SM14B-08 

Theory and Simulation of the Generation of Whistler-mode Chorus

* Omura, Y (omura@rish.kyoto-u.ac.jp), RISH, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan Katoh, Y (yuto@pparc.geophys.tohoku.ac.jp), RISH, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan Katoh, Y (yuto@pparc.geophys.tohoku.ac.jp), Tohoku University, Sendai, Miyagi, 980-8578, Japan Summers, D (dsummers@math.mun.ca), Memorial University of Newfoundland, Elizabeth Ave, St. Jones, NF A1C 5S7, Canada

The generation process of whistler-mode chorus emissions is analyzed by both theory and simulation. Driven by an assumed strong temperature anisotropy of energetic electrons, the initial wave growth of chorus is linear. After the linear growth phase, the wave amplitude grows nonlinearly. It is found that the seeds of chorus emissions with rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. We derive the relativistic second-order resonance condition for a whistler-mode wave with a varying frequency. Wave trapping of resonant electrons near the equator results in the formation of an electromagnetic electron hole in the wave phase space. For a specific wave phase variation, corresponding to a rising frequency, the electron hole can form a resonant current that causes growth of a wave with a rising frequency. Seeds of chorus elements grow from the saturation level of the whistler-mode instability at the equator, and then propagate away from the equator. In the frame of reference moving with the group velocity, the wave frequency is constant. The wave amplitude is amplified by the nonlinear resonant current, which is sustained by the increasing inhomogeneity of the dipole magnetic field over some distance from the equator. Chorus elements are generated successively at the equator so long as a sufficient flux of energetic electrons with a strong temperature anisotropy is present.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.