*************************** ** THE GEM MESSENGER ** *************************** Volume 14, Number 41 September 29, 2004 ------------------------------------------------------------------------- Report on MI Coupling Working Group 1 on Plasma Outflow Sessions Held at the GEM Summer Workshop in Snowmass June 23-25, 2004 ------------------------------------------------------------------------- From: Bill Peterson and Robert Winglee , Co-Chairs The Magnetosphere-Ionosphere Campaign WG 1 on plasma outflow sponsored a tutorial by Prof. Robert Schunk, Utah State University, entitled: "The Extended Ionosphere" and four breakout workshop style sessions, one of which was jointly sponsored by the GGCM Campaign. The Schunk Tutorial set the tone for the discussions that followed. An electronic copy of the tutorial is available on the GEM tutorial web site: http://www-ssc.igpp.ucla.edu/gem/tutorial/index.html The tutorial was followed by extended presentations by Takume Abe and Matt Huddleston focused on recent polar wind observations from the Japanese Akebono and NASA Polar satellites. Abe summarized the extensive (14 year data set over the altitude range 500-11,000 km) polar wind mass-resolved density, temperature, and velocity observations from Akebono. He made the point that all the evidence shows that thermal O+ escapes due to hydrodynamic expansion in response to plasma pressure gradients along magnetic field lines during quiet ionospheric conditions, which makes it an integral part of the polar wind. He also presented evidence in the extensive Akebono data set that solar illumination is responsible for generating the plasma pressure gradients driving the O+ component of the polar wind. Huddleston summarized an extensive study of the polar wind intensity observed over many years at ~1RE during Polar perigee passes by the TIDE instrument. He used these data as an input to a transport model and showed that the observed polar wind intensity is strong enough to account for all of the plasma in the Earthˇ¦s magnetosphere. In the discussion following these talks it was suggested by Huddleston and Peterson that reasonable estimates based on several data sets show that both the solar and polar wind are independently capable of supplying all of the plasma in the magnetosphere. The problem, then, seems to be that the sinks and escape routes for magnetospheric plasma are not well understood. Other extended introductory talks were given by Mike Liemohn, Vahe Peroomian, Aaron Ridley, and Tony Lui addressing the subjects of where does ionospheric plasma go and what processes does it modify and/or control. Robin Coley, Karen Remic, Jay Johnson, Steve Mende, Robert Winglee, Bob Strangeway, Laila Andersson, Chris Mouikis, Shin Ohtani and many others made contributions. The discussions in the break out sessions were lively. Topics included: What is the dominant source of magnetospheric plasma? What are the physical manifestations of ionospheric outflow? and what are the viable modeling approaches to addressing these questions? On the topic of the dominant plasma source: Joe Borovsky, using LANL and ISEE data, made a very convincing argument that solar wind plasma dominates the magnetosphere at all times. Joeˇ¦s presentation was made earlier in the week in the Global Interaction Campaign sessions. As noted above the presentations in the MI Coupling Campaign came to the conclusion that the outflow of ionospheric ions is intense enough at all times to account for all of the magnetospheric plasma. The conclusion seemed obvious at the end of the Working Group 1 discussions: More emphasis needs to be placed on loss, not source, processes. On the topic of the physical manifestations of ionospheric outflows: The presentations and discussions identified modification of the reconnection rate (Ridley), reconnection structure (Winglee), and saturation of the cross polar cap potential as the most important physical consequences of the varying concentration of heavy ions in the magnetosphere. On the topic of modeling approaches: The question is how to incorporate the ionospheric source into the model. Single particle tracing approaches presented showed remarkably different results when they focused on the solar wind source (Peroomian) and the ionospheric source (Liemohn/Moore). We had an extended discussion on the strengths and weaknesses of including ion outflow in single and multiple fluid MHD codes. Working Group 1 held a joint session with the GGCM Campaign on Wednesday afternoon addressing the topic: Can ion outflows be reliably specified simulated or specified? Aaron Ridley was the GGCM Co-Convener and chaired the session. An interval (14:30 on 3/18/97 to 02:00 on 3/19/97) with well defined solar wind conditions and mass resolved ion outflow data available from Akebono, Polar and FAST was selected as an example. Data for this interval is available at the URL: ftp://willow.colorado.edu/pub/exchange/GEM/ Presentations were made by Bob Strangeway, Peter Chi, John Lyon, Robert Winglee, Aaron Ridley, J. Schoendorf (by Aaron Ridley), Jimmy Raeder, and Laila Andersson. There was a spirited discussion of what is possible and what is wistful thinking in this well attended session. One conclusion was apparent after the discussion however. The "gap" region from the topside ionosphere to the region where global models start at, 2 or 3 RE, is where ion acceleration occurs and where potential drops decouple magnetospheric and ionospheric electric fields. Processes occurring in the "gap" region therefore are important to global models in that they modify ion outflow trajectories and convection patterns. None of the current models attempt to address processes occurring in the gap region. Tony Lui, in his extended talk on the last day, summarized the unresolved critical issues relating to the ionospheric plasma source in magnetospheric models. 1) What is the relative contribution of the polar and solar winds to the current sheet in the magnetic tail? 2) What are the effects of varying mass composition on the location and rate of reconnection? 3) What are the effects of varying mass composition on the distribution of pressures within the magnetosphere, and 4) How can we effectively use ionospheric components as tracers of transport in the magnetosphere. +-------------------------------------------------------------------------+ |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 | +-------------------------------------------------------------------------+