Friday, June 22, 2007

GEM workshop, Thursday breakout sessions

In the afternoon I attended two breakout sessions on diffuse aurora, continuing the breakout session from the previous afternoon.

Speakers in the first session were Mike Schultz (Lockheed) on theoretical particle tracing in a Dungey magnetosphere, Margaret Chen (Aerospace) on simulations in the Dungey magnetosphere, Richard Thorne (UCLA, on behalf of Richard Horne and Nigel Meredith of BAS) on diffuse aurora scattering rates by chorus emissions and ECH waves, Jacob Bortnik (UCLA) on modeling the global characteristics of chorus propagation, Wen Li (UCLA) on ray tracing with the HOTRAY code, Jay Albert (AFRL) on approximations of quasilinear diffusion coefficients, and R. P. Sharma (IIT) on nonlinear kinetic Alfvén waves and their role in particle precipitation. The reason Schultz and Chen use the Dungey magnetosphere is because it is analytically tractable, and an explicit Hamiltonian can be derived from a suitable electric field model (Brice-Nishida, Volland-Stern, or AMIE). Thorne pointed out the difficulty of scattering particles with 90 degree pitch angles at the equator. Bortnik showed that the lowest frequency chorus waves can propagate to the highest latitudes. Albert showed a method for calculating approximate diffusion coefficients which is significantly more accurate than the Summers method yet still represents a substantial speedup (factor of ~200) from the full calculation, which requires an infinite sum of triple integrals.

After the break, the topic was future plans for this focus group. It was decided that at this stage it is important to gather a list of relevant available data sets, and modeling efforts will proceed later. The most relevant data set for waves is THEMIS (it is necessary for the satellite to be in an equatorial orbit). For particles there are various geosynchronous satellites as well as low altitude satellites (DMSP and FAST) to look at precipitating particles. Ground-based measurements, especially all-sky cameras and meridian scanning photometers, are also of great importance for the study.

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