*************************** ** THE GEM MESSENGER ** *************************** Volume 9, Number 23 July 5, 1999 --------------------------------------------------- Report of 1999 Snowmass Workshop - Objectives of the GEM Radiation Belts Working Group --------------------------------------------------- From: Geoff Reeves (reeves at nis-pop.lanl.gov) At the 1999 Snowmass workshop the Radiation Belts Working Group formulated two principal objectives for the campaign: 1) To evaluate the relative contribution of various proposed acceleration processes through theory, modeling, and comparison with data 2) To create time-dependent phase space density profiles of the radiation belts that will more accurately represent their structure and dynamics than fixed-energy profiles Theory and Models of Relativistic Electron Acceleration Radial Diffusion/Recirculation Salammbo is the best developed model It reproduces the gross features of radiation belts quite well No explicit solar wind input It needs geosynchronous boundary conditions over a broad range of energies It needs plasmapause location and wave intensities Does not currently include adiabatic "Dst" effect Could be improved with improved knowledge of time-dependent diffusion coefficients and plasmapause wave intensities Shock Acceleration Clearly effective in some storms such as March 1991 General contribution to other events is unknown If it contributes then how much and how often? If it does not act alone then what other processes contribute? Substorm Contributions What is the contribution of particles injected in substorms? Do substorms provide a "seed population" or are they sufficient themselves? Simulations show a 20 keV particle at 20 Re can become 900 keV at 6.6 Re Need to know Ey across the magnetotail, plasma sheet density, and electron temperature Drift Resonance Good success by Dartmouth group using wave fields from global MHD simulations Toroidal oscillations with radial electric field resonate with particle drifts Azimuthal electric fields are even more effective because of enhanced radial transport Pc5 waves with enhanced amplitudes are observed in Geo particles and fields as well as ground magnetometers Ground magnetometers show strong correlation between Pc5 and Vsw Multi-storm comparison not yet complete VLF Whistler Resonance Several possible contributions a) resonance with substorm-associated chorus that randomly changes magnetic moment and energy b) resonance with plasmaspheric hiss and EMIC waves responsible for "local recirculation" and acceleration Some results already incorporated in Salammbo New results suggest LO mode particularly effective Development of Phase Space Density Maps 1) "Removes" adiabatic responses such as the "Dst effect" 2) This is required to know when and where acceleration is taking place (e.g. non-adiabatic in at least one of the invariants 3) Phase space density as a function of the three drift invariants and time a) requires time-dependent storm-time magnetic field models to calculate invariants b) need to do spectral fitting and/or extrapolation for detectors with finite energy bands c) need to know time evolution of the pitch angle distributions 4) Both single-spacecraft and multi-spacecraft studies can contribute to better understanding of both particle dynamics and global magnetic field models 5) What solar wind parameters control the structure and dynamics of the radiation belts and what are the relative contribution of external (solar wind) vs internal (waves, ring current etc) processes? 6) Does the pre-existing condition of the inner magnetosphere and/or plasmasheet affect radiation belt enhancements? 7) What are the relative roles of "losses" compared to "redistribution" 8) To what extent does loss into the atmosphere affect the global electrodynamics and/or chemistry? 9) How important are azimuthal asymmetries in the ring current and radiation belt particle drifts? Relationship to GGCM 1) The radiation belt module will probably not feed back information to the spine of the GGCM because mass, current, and energy densities are too low 2) Depending on the amount of information needed from the spine the radiation belt module could run separate from the spine or may need to run embedded 3) Although no direct two-way exchange of information is envisioned the radiation belt module could provide important test and verification of the GGCM by means of information such as the intensity of wave fields or consistency of particle drifts with magnetic field configurations Send suggestions and corrections to Geoff Reeves (reeves at lanl.gov) +-------------------------------------------------------------------------+ |To add name to the mailing list or for a message to the GEM community | | please contact: editor at igpp.ucla.edu | | | |URL of GEM Home Page: http://www-ssc.igpp.ucla.edu/gem/Welcome.html | |Please update your e-mail address. | +-------------------------------------------------------------------------+