*************************** ** THE GEM MESSENGER ** *************************** Volume 11, Number 21 July 23, 2001 -------------------------------------------------------------------------- Reports of 2001 GEM Snowmass Workshops Workshop on Inner Magnetosphere/Storms, WG1: Plasmasphere and Ring Current -------------------------------------------------------------------------- From: Mike Liemohn and Dennis Gallagher (working group #1 co-chairs) The IM/S WG1 sessions revealed new connections between the drivers of inner magnetosphere dynamics and the ring current and plasmasphere. New opportunities for advancing our fundamental knowledge of these plasmas are now available through observations and analysis techniques. For both the ring current and plasmasphere, the roles and inter-dependencies between plasma sources and losses and the role of electric fields on all scales must now be determined. Below are brief highlights of the individual sessions. Solar Wind Drivers of Inner Magnetospheric Dynamics: A resolution was reached that the polar cap potential grows nonlinearly with the driving solar wind parameters and that it actually saturates for extreme solar wind values. Such instances are the July 2000 and March 2001 superstorms, where linear prediction models estimated the potential drop to peak at over 600 kV, while in reality it most likely remained below 300 kV throughout both events. A major limiting effect, it appears, is the magnetic disturbance created by the region 1 Birkeland currents, as first proposed by Hill 25 years ago. Perturbations from high-latitude currents were also shown to have a significant signature in mid-latitude magnetometer records at certain times during storms. Electric Fields and the Stormtime Plasmapause: Stormtime subauroral electric fields in the ionosphere and magnetosphere seem to have two (related) sources: undershielding (or overshielding) of the high-latitude electric fields, which typically last less than an hour (until the region 2 current system can reconfigure), and a noon-midnight two-cell pattern driven by the ionospheric closure of the stormtime partial ring current, which lasts at least throughout the main phase. Several speakers demonstrated the effects of these fields on the plasmaspheric and hot ion populations, particularly for creating plasmapause features and rapidly injecting the plasma sheet into the inner magnetosphere. Sources of the Stormtime Ring Current: There is a resurgent interest in the relationship between storms and substorms, especially with the advent of global imaging techniques from energetic neutral atom (ENA) observations. A few highlights are as follows: (1) stormtime substorm influences can be seen all the way in to L=3, although this effect is a small perturbation on the preexisting hot ion population; (2) spectral hardening of the inner magnetospheric ion distributions occurs during substorms; and (3) periodic "sawtooth" oscillations can start up after substorms. The Stormtime Plasmasphere: There is new promise of thermal plasma observations all along echo paths for the IMAGE Radio Plasma Imager signals and other wave sources. Many of these paths appear to be field aligned, which may be due to confinement by plasma ducts. Various techniques were presented and their applications discussed. The IMAGE EUV instrument observations also show great promise for both supporting in situ measurements by providing a global context and for enabling entirely new analysis of plasmasphere dynamics, such as the first global observation of an azimuthal standing wave pattern on the nightside. Ring Current Decay Mechanisms: A variety of presentations showed that the community is conducting a thorough examination of the ring current loss processes. New approaches included inner magnetospheric tomography of the geocorona using hot ion drift trajectories, analysis of observations of ring currents many R_E upstream of the bow shock, and pressure-driven interchange instabilities creating vortices in the outer ring current region near dusk. Wrap-Up Sessions: The possibility of review articles on the major topics being addressed by the IM/S campaign was discussed. If you are eventually invited to write one of these reviews, please accept the offer. The GEM-Storms Campaign: There has been great success in focusing the community's efforts on a few selected events (May 15, 1997; September 25, 1998; and October 19, 1998), and the comparative analysis has resulted in significant advancements of our understanding of stormtime inner magnetospheric dynamics. However, none of these events are from the IMAGE era and none are for solar maximum conditions. Therefore, a new set of initiatives (in addition to the existing set) was discussed and agreed upon: (1) October 4-6, 2000: This storm is interesting in that it has a very long main phase, and data coverage is excellent throughout the storm interval. It is being added to the list for detailed comparative analysis. (2) March 31 - April 2, 2001: This superstorm (Dst reached -360 nT) had extreme solar wind values driving it, with unshocked solar wind seen at geosynchronous orbit. It is being selected as a pathological case for comparison against the other "normal" storms. (3) May 15, 1997 -- An IM/S Challenge: This GEM-Storm event has been chosen for an intensive, coordinated investigation, with the goal being to predict, simulate, and explain the observed features of inner magnetospheric dynamics throughout the storm interval. Members the two IM/S working groups are asked to provide data and simulation products for community-wide dissemination, and to help others to interpret and use this information in their examinations of this storm. Please seriously consider including these campaign initiatives in your activities over the next year, as they will be the focus of much of the IM/S discussion at the next GEM workshop. +-------------------------------------------------------------------------+ |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. | +-------------------------------------------------------------------------+