FG7. MIC Electrodynamics

Conveners: Joshua Semeter (jls@bu.edu) and Bill Lotko (william.lotko@dartmouth.edu)

“M-I coupling” constitutes a broad range of topics that are important to both the GEM and CEDAR initiatives. The MICET focus group was born in 2006 from the M-I coupling campaign in order to maintain continuity in this topical area. The MICET focus group hosted two breakout sessions at the 2008 workshop. As demonstrated in the highlights below, progress in M-I coupling continues to be strong in both the theoretical and observational domains. In particular, the emergence of new diagnostic capabilities associated with the THEMIS and AMISR projects, and new models capable of making predictions that may be directly compared with these measurements, underscores the need to continue M-I coupling activities in some form after the completion of the MICET focus group in 2009.

Session 1 - "M-I coupling: New measurements, new models, new methods"

The modeling and observational characterization of M-I coupling is complicated by the fact that M-I coupling processes are locally enabled while being globally regulated and impressed. This breakout session explored various manifestations of this dichotomy from both the theoretical and observational perspectives. With the MICET focus group coming to a close, much of the discussion focused on strategies for moving forward on these topics. Also, due to the overlap with the CEDAR meeting, the session also served as a forum to highlight new developments in observational capabilities, in addition to highlighting new developments and challenges emerging from theoretical work. A brief summary of the individual presentations follows.

Paul Song presented results of a one-dimensional, time-dependent model of M-I coupling driven by a change in magnetospheric flow at the top boundary. Steady state required ~20 Alfven transit times, but during the transition, the flows and currents were significantly enhanced and varied in both magnitude and direction with altitude. He concluded that using Ohm’s law in the neutral wind frame for M-I coupling will miss important electrodynamics at the beginning, and important neutral wind dynamics later.

Eric Lund discussed the physical origin of the parallel electric field in the auroral acceleration region. He compared the E-parallel contribution of various individual components of the momentum equation. The dominant terms are the pressure gradient and mirror force (although their signs are opposite), with anomalous resistivity accounting for only 10% of the total E-parallel.

Bob Lysak described the limitations of treating the ionosphere boundary in terms of current continuity imposed on height-integrated conductivities—namely, Hall conductivity introduces magnetic compressibility, tilt of field lines can couple curl-free electric fields to compression even in absence of Hall conductivity, and finite frequency and small perpendicular wavelength limit penetration of Alfvén wave into ionosphere. He proposed a more general model for the ionosphere, which requires a determination of the magnetic potential in the lithosphere-ionosphere region.

On the observational end, Phil Erickson described constraints on M-I coupling derivable from the Millstone Hill incoherent scatter radar (ISR). He focused on mid-latitude physics associated with the plasmasphere boundary layer (PBL), at the interface between the auroral magnetosphere and the ionosphere/thermosphere dominated inner region. He discussed specific outstanding questions regarding SED, SAPS, wave/particle interactions, and optically driven hallmarks of magnetosphere/ionosphere coupling such as stable auroral red (SAR) arcs. He also presented a wide list of unanswered questions concerning PBL dynamics that require consideration of the full range of magnetosphere-ionosphere-thermosphere coupling effects. These topics highlight the need for close collaboration between the GEM and CEDAR communities.

Joshua Semeter discussed new opportunities for studying auroral M-I coupling enabled by the recently completed Poker Flat ISR (or PFISR). A component of the AMISR project, PFISR has an electronically steerable antenna, enabling the construction of volumetric images of ionospheric densities, temperatures, and motions. A movie was presented, showing the evolution of ionospheric densities in the 90-to130-km altitude range at 14-s cadence during an auroral activation, highlighting features that would be ambiguous using traditional line-of-sight ISR measurements. (The movie is available for download at http://heaviside.bu.edu/~josh/PFISR/11Nov2007/PFISR_11Nov2007.mpg)

Lastly, Frederick Wilder discussed observations of potential saturation associated with reverse convection cells. The study was based on combined analysis of ACE solar wind data and SuperDARN measurements between 1998 and 2005.

Session 2 - "MI coupling and magnetotail transport" (joint with the PET)

Heavy ions of ionospheric origin can at times be the dominant contributor to the mass density in the plasma sheet. Plasma sheet transport processes also exhibit signatures in the ionosphere that can be used to constrain plasma sheet transport models. This breakout focused on addressing the following core topics: (i) the ionosphere as a source of plasma sheet populations and determining the heavy ion distribution in the plasma sheet for various IMF conditions; (ii) signatures of plasma sheet transport processes in the ionosphere (e.g. are there signatures of plasma sheet turbulence in the ionosphere?); and (iii) the effect of ionospheric/heavy ions on plasma sheet transport and solar wind entry.

Discussion leaders included Jay Johnson, Bill Lotko, Matthew Zettergren, Bill Peterson, and Paul Kintner.