Table of Contents ============================================================================ 1. Posters for 2007 GEM Summer Workshop (Zermatt, Utah, June 17-22, 2007) 2. GEM GGCM Modules and Methods Breakout Session "Modeling Magnetic Reconnection in Large Systems" ============================================================================ *************************** ** THE GEM MESSENGER ** *************************** Volume 17, Number 17 June 3, 2007 ---------------------------------------------------------------------------- 1. Posters for 2007 GEM Summer Workshop (Zermatt, Utah, June 17-22, 2007) ---------------------------------------------------------------------------- From: Frank Toffoletto As of June 1, we have only about a dozen posters submitted. In order to get a reasonable estimate of how many poster boards we will need, please send in your poster title ASAP. http://gem.rice.edu/~gem/gem2007/index.html Thanks! Frank Toffoletto Umbe Cantu ---------------------------------------------------------------------------- 2. GEM GGCM Modules and Methods Breakout Session "Modeling Magnetic Reconnection in Large Systems" ---------------------------------------------------------------------------- From: John C. Dorelli The GGCM Modules and Methods Focus Group will hold a breakout session at the GEM workshop this year (June 17-22, Zermatt Resort, Utah). The discussion will revolve around issues which arise in the attempt to model magnetic reconnection on the global magnetospheric scale. Currently, resistive MHD is the most popular approach for addressing the global properties of magnetospheric reconnection (e.g., the global topology and geometry of reconnection). However, resistive MHD suffers from the well known Sweet- Parker time scale problem: the reconnection rate depends sensitively on the Lundquist number. Global modelers usually sidestep this problem by invoking a version of the "Axford Conjecture" (Axford, W. I., Space Sci. Rev., 7, 149-157, 1967), which states that the rate of magnetic reconnection is determined by the imposed boundary conditions, with the diffusion region adjusting to accommodate the externally imposed electric field. However, recent studies using global MHD codes tell a different story. Specifically, several different global MHD codes (the OpenGGCM, the LFM code and the ISM) have now observed (under a variety of resistivity models, including current dependent resistivity) that magnetic reconnection occurs via a flux pileup mechanism, implying that the reconnection rate decreases rapidly with decreasing plasma resistivity. This effect makes it difficult to model reconnection in the high Lundquist number limit (in which the resistivity is uniformly small) and motivates the use of an ad hoc anomalous resistivity. Local kinetic simulations suggest that the Sweet-Parker time scale problem can be solved by including various nonideal terms in Ohm's law. For example, the GEM Reconnection Challenge suggested that Hall electric fields can prevent Sweet-Parker current sheets from forming; the current density instead becomes more localized and Petschek-like, allowing fast reconnection to occur at a rate which is insensitive to the dissipation physics. Recent PIC results with open boundary conditions, however, suggest that the GEM Reconnection Challenge results may not scale up to large system sizes. This issue is still not resolved, and the answer to this question has important implications for global kinetic modeling of magnetospheric reconnection. In our breakout session, we will address the following two questions: 1) Can global resistive MHD models accurately model fast reconnection at the magnetopause and in the magnetotail in the high Lundquist number limit? 2) How do local kinetic simulations of fast reconnection (which is insensitive to the dissipation physics) "scale up" to large system sizes? 3) How does one efficiently include kinetic scale physics into a global code? Our session will consist of several short talks to motivate discussion. If you would like to participate by giving a short presentation, please contact either John Dorelli (john.dorelli@unh.edu) or Mike Shay (shay@udel.edu) at your earliest convenience. +-------------------------------------------------------------------------+ |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 | | | |Please use plain text as the format of your submission. | | | |URL of GEM Home Page: http://www-ssc.igpp.ucla.edu/gem/Welcome.html | |Workshop Information: http://gem.rice.edu/~gem | +-------------------------------------------------------------------------+