FG8. Near Earth Magnetosphere: plasma, fields, and coupling

Co-chairs:

• Sorin Zaharia (szaharia [at] lanl.gov)
• Stan Sazykin (sazykin [at] rice.edu) and
• Benoit Lavraud (Benoit.Lavraud [at] cesr.fr)

June 2008 GEM meeting report

The Near Earth Magnetosphere focus group held 3 breakout sessions in its 2nd year of activity at the 2008 GEM Summer Workshop in Zermatt, UT. The main goal of the focus group is to improve physical knowledge and modeling of near-Earth magnetosphere and its coupling with outer magnetosphere. The focus group is coordinated by Sorin Zaharia, Stan Sazykin and Benoit Lavraud.

The three focus group sessions, held on Tuesday and Wednesday (06/24-25) were well attended and featured short presentations and discussions of progress on the two main research fronts the focus group has concentrated to achieve its goals:

1. Data-based/empirical models - short presentations described both continuing progress on empirical modeling (such as the UNH IMEF E-field model), as well as a significant number of new research efforts on this front, from new magnetic field to plasma pressure models; below is a synopsis of the main topics discussed:

• Empirical plasma sheet specification – either for use in models (C. Lemon, a plasma sheet property database for geosynchronous orbit) or validating model results, e.g. observational verification of ring current injection from the plasma sheet (C.-P. Wang, Themis observations)
• Empirical E-field specification: overview of improvements in the UNH IMEF model based on Cluster data - the model is now publicly available (H. Matsui, P. Puhl-Quinn); its first use in a physics-based ring current model (V. Jordanova, RAM); dichotomy between convective electric field dependence on IMF southward turning in the plasma sheet vs. earthward of it (Y. Nishimura)
• Empirical B-field: M. Sitnov, new dynamical model (with a dramatic increase in spatial resolution); J. Zhang, T89GS - model constrained by spacecraft observations that satisfies force balance near spacecraft; R. Denton – adjusting TS05 model to better fit GOES observations; N. Ganushkina - event-oriented B-field model – modification of Tsyganenko model (good for studying detailed magnetic field variations for a specific event, time period, or magnetospheric region)
• Empirical plasma pressure model of the inner magnetosphere (P. Brandt – obtained by combining in-situ with global ENA observations)
• Radar observations of ionospheric convection (L. Lyons, Poker Flats AMISR; J. Baker, mid-latitude SuperDARN); qualitatively similar features observed in model results (Lyons, RCM)

2. The second research area, physics-based modeling, tackled mostly the coupling between different elements in the models (plasma, electric and magnetic fields); highlights from the presentations include:

• Modeling many events with simple setup (model works better for one storm type, i.e. sheath-driven storms, suggesting different storm drivers lead to more or less complex inner magnetosphere physics) (M. Liemohn, HEIDI - Michigan RAM)
• Ballooning instability in RCM-E; continued driving, simulating a growth phase, pushes the magnetosphere toward both MHD and fast MHD unstable states (F. Toffoletto)
• Substorm simulations: with RCM-E (J. Yang, using Geotail data to set up boundary; results consistent with observations); with a “bubble” imposed (RCM with new T89GS force-balanced model - J. Zhang; injection of bubble leads to higher pressure in the near-Earth magnetosphere)
• Wave studies: analytical pitch-angle diffusion - three lowest eigenvalues for the pitch-angle diffusion coefficient (M. Schulz; results could be used in ring current models); connection theory/observations - whistler modes (derived from LANL plasma observations + linear theory; enhanced growth rates found in the recovery phase; E. MacDonald)
• Effect of plasma boundary on RC injection (cold dense plasma more geoeffective; local time boundary distribution also very important - B. Lavraud, RAM; in simulations with self-consistent E-field, higher plasma sheet pressure causes quicker shielding of the penetration E-field - M. Gkioulidou, RCM)
• 1-way coupling of RAM with self-consistent B-field with SWMF (using SWMF pressure on RAM boundary) reconfirms previous results that cold, dense plasma sheet –a common feature in MHD models – is more “geoeffective,” i.e. leads to higher inner magnetosphere plasma pressure) (S. Zaharia)

The second half of the 3rd breakout session was devoted to a community discussion in which a future modeling challenge relevant to Focus Group goals emerged. The challenge will entail several near-Earth/inner magnetosphere models simulating, with same (or equivalent) input, both an idealized and a real event (geomagnetic storm). The challenge will bring together researchers from all major near-Earth magnetosphere modeling groups : RAM-SC B (LANL); HEIDI (Michigan RAM), RCM, RCM-E, CRCM, M. Chen’s model. The challenge will involve 3 stages: 1). Idealized event, with simple inputs/physics (with the goal of setting a baseline for all models). The second and third stage will involve full-physics modeling of an idealized and real event, respectively (thus the 3rd stage will involve both modelers and data analysts). More details about the challenge/model setup will be communicated to the community via e-mail and the new Focus Group Wiki. It is expected that the first stage be completed by and results presented at the 2008 GEM Mini-workshop (Sunday before AGU Meeting) in December, where the focus group plans to have a session. The 2009 Summer Workshop will then see initial results from the simulation of an idealized event with full model capabilities, with the goal of finding out the relative role of different physics features (e.g. plasma/fields self-consistency) present in the models.