*************************** ** THE GEM MESSENGER ** *************************** Volume 10, Number 32 July 12, 2000 -------------------------------------------------------- Report of 2000 Snowmass Workshop: Inner Magnetosphere: WG2 Sessions on Theory and Modeling -------------------------------------------------------- From: Richard Thorne (rmt at atmos.ucla.edu) There seems to be a healthy surplus of theoretical ideas for the acceleration of electrons to relativistic energies during storm conditions. The loss of such electrons is also very important for understanding the ultimate flux of relativistic electrons in the outer zone. The following presentations were made at the theory and modeling sessions: Lui Chen has developed transport equations including both diffusive and convective effects due to resonant interactions with ULF waves (omega << omega(+)). He reported on published work which gave transport coefficients based on a quasi-linear approach. Mary Hudson discussed further refinements of the thesis work of Scott Elkington on drift resonant acceleration of equatorial electrons by ULF waves. The work has been extended to induce a broad spectrum of waves with both poloidal and toroidal polarity. The results have been used to construct radial diffusion coefficients which scale as D_LL ~ D_0 * L^11. Danny Summers reported on two separate studies related to relativistic electron acceleration. In the first, which has been published in JGR, a one dimensional diffusion equation was constructed to consider the effects of stochastic acceleration by a spectrum of whistler-mode chorus, together with loss by pitch-angle scattering which was treated as an adjustable parameter. This competition of acceleration and loss leads to a Kappa-like equilibrium distribution, characteristic of the observed high energy population. In the second study, Fermi acceleration of electrons by resonant ULF waves and determined acceleration times comparable to a few hours. Xui Lui Li reported on the development of an empirical model to simulate the temporal variability of geosynchronous electrons based only on solar wind parameters (V; dV/dt; BZ). The model parameters were optimized for one year of data and then applied to give a remarkable fit to subsequent years. Mike Schulz has developed a model to treat the pitch-angle scattering of energetic electrons over a period of several weeks following a storm. The model was used to account for the presence of such electrons observed on a low altitude satellite. Richard Thorne described ongoing studies on the effect of VLF waves on relativistic electrons. He gave examples of the pitch-angle scattering rate of electrons due to resonance with electromagnetic whistler-mode hiss and chorus during storm periods and pointed out that the resultant relativistic electron loss was due to weak pitch angle scattering for typical observed wave amplitudes (Bw~10-30pT). More intense EMIC waves can also resonate with electrons (>1 MeV) and yield strong diffusion scattering in very localized regions. Resonant interaction with high frequency waves (omega ~ omega_e) can also lead to stochastic energy diffusion and examples of the resonant diffusion surfaces for chorus were shown. Finally, he briefly described a computational study (by Boscher et al.) of multi-dimensional diffusion using the Salammbo code, which have been interpreted as evidence of recirculation near the plasmapause. This is an ongoing study that will be refined by the inclusion of scattering by chorus emissions of enhanced hiss during storms. Anthony Chan described the development of a quasi-linear gyrokinetic equation to consider the effect of low frequency (omega