*************************** ** THE GEM MESSENGER ** *************************** Volume 11, Number 28 August 20, 2001 -------------------------------------------------------- Reports of 2001 GEM Snowmass Workshops: Inner Magnetosphere/Storms Campaign WG2: Radiation Belts -------------------------------------------------------- From: Geoff Reeves Report on the IM/S WG2 (Radiation Belts) sessions at the 2001 GEM workshop by working group chairs Richard Thorne and Geoff Reeves. Five 2-hr sessions on the radiation belts were held at the 2001 GEM meeting. They were: ``New Insights from the GEM storms'' ``Observations of Stormtime Radiation Belt Variability'' ``Observations of ULF and VLF Waves during Storms'' ``Theoretical Studies of Radiation Belt Particle Acceleration and Loss'' ``The Role of Substorms in Relativistic Electron Acceleration'' Our WG2 sessions were very stimulating, attracting more than 50 participants including a large number of students and younger scientists. The major emphasis was devoted at understanding the acceleration and loss of relativistic electrons during storms. Rather than itemize the separate contributions we will simply summarize the major advances made over the last year and outline our plans for further study in the coming year. Observational Advances * The different response to storms has been characterized as a function of energy and L. * Data have been analyzed to yield the particle phase space density as a function of L for constant first and second adiabatic invariant. * Evolution of the electron spectral properties has been measured during acceleration events. * Variation of the peak flux location seems to be controlled by the storm strength. * The solar wind parameters have a major controlling influence on subsequent relativistic electron enhancements. * The relativistic electron pitch-angle distributions have been measured during acceleration events. Precipitation Loss * Microbursts of precipitating relativistic electrons have been seen in associated with VLF chorus emissions. * Balloon X-ray observation, have been linked to relativistic electron scattering by EMIC waves. * There is evidence for strong relativistic electron loss during the main phase of a storm. * Losses during the recovery phase appear to be much weaker, as indicated by the pitch-angle distributions. Acceleration Processes * Radial inward diffusion. There is convincing statistical evidence that electron enhancements at geosynchronous orbit are associated with sustain levels of enhanced ULF waves. * Local stochastic acceleration. Electron enhancements during the recovery phase of storms are also associated with enhanced levels of VLF whistler-mode chorus emissions. This supports theoretical studies on the viability of local stochastic energy diffusion by such waves but further work is needed to quantify this process. * Substorm dipolarization. MeV electrons can be directly injected into the outer radiation zone during dipolarization events. Whether this contributes to stormtime enhancement remains to be determined. Maturing Models * Empirical models have been developed to predict the behavior of relativistic electrons at geosynchronous orbit, based only on solar wind input parameters. * A three-dimensional diffusion model (Salammbo) has been developed to study radiation belt particle dynamics during conditions when the adiabatic invariants are violated. Future Plans * There is a general realization that all three adiabatic invariants can be violated during storm conditions. Future work should concentrate on a quantification of the competing acceleration and loss process. * ULF driven radial diffusion seems to be an important process at geosynchronous orbit but further work is needed to assess whether it is rapid enough to account for electron flux enhancements near L=4. * The role of VLF waves in causing precipitation loss and energy diffusion needs to be quantified. * We need to study the loss process of electrons during the storm main phase. * There is a need for better observational information from multi-point satellite observations. Status of Campaign Storm Studies The focus on four storms for analysis in campaign mode has proven to be very helpful for this campaign and those analyses have become fairly mature. These storms are being studied jointly by working groups 1 and 2 and address the needs of both ring current/plasmasphere and radiation belt groups. There was consensus to extend this effort by 1) Using the May 1997 storm as a focus for combining models into a more complete and comprehensive picture of the storm-time response. May 1997 was a relatively "simple" storm and is well-suited to combining, for example, ring current models and radiation belt models to determine the magnitude and asymmetries of the "Dst effect" on relativistic electrons. 2) October 2000 was added to the campaign studies. This is an exceptionally good storm for comparing various measures of the ring current through modeling, satellite observations, ENA observations, and ground perturbation maps. 3) March-April 2001 was added to better understand the effects of "superstorms" and extreme events. All interested parties are encouraged to participate in these studies. +-------------------------------------------------------------------------+ |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. | +-------------------------------------------------------------------------+