*************************** ** THE GEM MESSENGER ** *************************** Volume 11, Number 25 August 6, 2001 --------------------------------------------------- Reports of 2001 GEM Snowmass Workshops: GEM Tail/Substorm Observations Working Group Report --------------------------------------------------- From: Mark Moldwin and Shin Ohtani (ohtani at fluxgate.jhuapl.edu) The Tail/Substorm Observations working group held 3 sessions at the 2001 NSF/GEM Snowmass workshop in June. The substorm community currently is studying the causal relationship between processes in the mid-tail and the near-geosynchronous orbit (NGO) region during substorm onset. The debate can be summarized as attempting to understand the relationship of mid-tail reconnection (the near-Earth-neutral-line (NENL) model) with processes in the NGO (current disruption model). The Tail/Substorm Observations Working Group attempted to clarify the observations used to understand those processes. Two invited speakers (Erickson, Voronkov) described the observational evidence for substorm onset initiation occurring in the near-Earth geosynchronous region while Shiokawa and Kepko summarized the observational evidence for substorm initiation beginning in the mid-tail. The observational evidence presented in favor of the near geosynchronous region being the substorm onset initiation region included (1) the auroral brightening usually starts far equatorward of the open/close boundary and then expands poleward. (2) The Poynting flux observed in the NGO at substorm onset almost always is consistent with a local source opposed to propagation of wave energy in from the tail and (3) there is no precursory auroral signature moving equatorward which corresponds to BBFs prior to substorm onsets. The observational evidence presented in favor of the NENL being the initiator of substorm onset included (1) mid-tail earthward high speed flows are often seen prior to substorm onset signatures in the near geosynchronous region (2) the waveform of ground Pi2 agrees well with the modulation of the BBF flow velocity suggesting that Pi2 is a consequence of the braking of BBFs and (3) plasmoid and TCR observations in the mid and distant tail are consistent with release at substorm onset. The conclusion of the working group sessions were that multipoint in situ observations combined with global auroral images and ground based optical and magnetometer arrays is the most promising way to resolve the current controversy to statistically study the role of the near-geosynchronous and near-Earth magnetotail in the substorm onset process. Future plans of the working group include the publication of a special companion set of papers in JGR later this year and the examination of how ENA global images can contribute to our understanding of the substorm onset process at next summers GEM meeting. Mark Moldwin (mmoldwin at igpp.ucla.edu), Shin Ohtani (ohtani at fluxgate.jhuapl.edu) +-------------------------------------------------------------------------+ |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. | +-------------------------------------------------------------------------+