*************************** ** THE GEM MESSENGER ** *************************** Volume 13, Number 26 July 8, 2003 ------------------------------------------------------------- Snowmass Report from Proposed New GEM Campaign on Solar Wind Interaction with the Magnetosphere (SWIM) ------------------------------------------------------------- From: C. T. Russell The GEM Steering Committee asked two groups to study possible new GEM Campaigns. One of these two groups (SWIM) held three working group sessions that examined the status of two outstanding problems and solicited ideas for the possible foci of the new campaign and how it would be organized. The first working group session, chaired by Pat Reiff, examined properties of the cross polar cap potential drop. Jerry Goldstein opened the session by reporting a delay of about 30 minutes in the erosion of the plasmasphere after a southward turning of the IMF. This same time delay has been found in the initiation of the main phase of geomagnetic storms and possibly indicates the time needed to establish a new convection pattern. Tom Hill reviewed the development of the Hill potential that predicts a saturation in the polar cap potential. George Siscoe presented his understanding of the Hill potential in terms of current limitation imposed by the dynamic pressure dependent Chapman-Ferraro current on the magnetopause. Mark Hairston, Dan Ober and Simon Shepherd reviewed a variety of datasets on the CPCP saturation. Many data now exists for study and a campaign addressing this problem seems quite feasible at this time. One interesting feature of the data is that the response of the polar cap to the interplanetary electric field seems more linear the longer is the averaging interval over which the IEF and polar cap response are intercompared. This dependence suggests that at least part of the apparent saturation may be due to induction effects. Other speakers stressed the importance of the apparent differences in the potential drop in the northern and southern polar caps, and the evolving magnetospheric geometry as reconnection proceeds. At the second session, chaired by Bob Strangeway, Phil Pritchett reviewed our understanding of reconnection based on fully kinetic simulations. It takes only a weak, ~0.1 Bo perpendicular field to magnetize electrons. This guidefield then will suppress reconnection. Thus what is referred to in the magnetospheric community as antiparallel reconnection has some theoretical basis. Finite plasma beta also helps restrict reconnection to near antiparallel directions. Michael Hesse examined a Harris sheet configuration and also found that reconnection favors antiparallel merging. Bill Mattheus reported on Hall effects on reconnection and turbulence. Nelson Maynard reported on observations of reconnection at high latitudes and reminded us that the timing of solar wind discontinuities was vital. Finally, he reported on the use of the green 557.7 nm line to track the reconnection point. Several global observations point to the need for antiparallel field in reconnection. Paul O'Brien showed how dipole tilt affected reconnection. Jimmy Raeder showed how dipole tilt affected the production of FTEs in his global MHD simulation. Chris Russell showed how the neutral line on the magnetosphere would change with IMF clock angle and dipole tilt. This study suggests that increasing dipole tilt reduces the merging line length (and rate) for all clock angles and that the maximum neutral line length occurs for clock angles away from due south for tilted dipole directions. John Wygant closed the session with a discussion of his model of bouncing ions near the reconnection x point. The third SWIM session began with a discussion of the state of the global hybrid simulation codes by N. Omidi. A tutorial talk early in the meeting by X. Blanco-Cano had established that the magnetosphere underwent phase transitions as the scale size of the interaction normalized by the ion inertial length increased in two-dimensional hybrid simulations. Omidi who has been leading the effort to develop these codes gave more details on the nature of these transitions and presented three dimensional simulations that verified the results of the two dimensional simulations at small ratios (of order 1) of the global scale normalized by the ion inertial length. Omidi's talk was followed by presentations by Fedder and Wang on the need for magnetosheath studies and the importance of studies of the solar wind control of the magnetosphere by M. Lessard and by X-L. Li. Then followed a discussion of the structure of the campaign and it was decided that there would be two working groups, one concentrating on the solar wind control of the magnetosphere and one concentrating on the nature of the physical processes that underlie this control. This program was presented for public comment on Thursday evening and for a decision by the GEM Steering committee. Since this program was a departure from the latest direction of GEM and would bring in a new community, it met some opposition from those who would like to keep working on old problems until they were solved. C. T. Russell June 28, 2003 +-------------------------------------------------------------------------+ |To subscribe GEM Messengers, send an e-mail to | | with the following command in the body of your e-mail message: | | subscribe gem | |To remove yourself from the mailing list, the command is: | | unsubscribe gem | | | |To broadcast a message to the GEM community, please contact Peter Chi at | | | | | |URL of GEM Home Page: http://www-ssc.igpp.ucla.edu/gem/Welcome.html | |Workshop Information: http://gem.rice.edu/~gem | +-------------------------------------------------------------------------+