"Magnetic reconnection" is often invoked to explain the relationship between the solar wind and geomagnetic activity. Over the last fifty years, ample evidence has accumulated implicating magnetic reconnection in such phenomena as aurorae, magnetic storms and magnetospheric substorms. However, recent large scale fluid modeling of the magnetosphere has revealed two difficult challenges standing in the way of a complete understanding of the role of reconnection in solar wind-magnetosphere coupling. First, while it is clear that microscopic processes (on the scale of single particle orbits) play an essential role in explaining observed rapid reconnection rates, we do not yet know how to model these processes on a large scale (brute force compuational approaches are not yet feasible). Second, comparing the simulated large scale structure to spacecraft data has turned out to be quite difficult. In this talk, I briefly review progress on these two fronts.
Flux transfer events (FTEs) are characteristic bipolar signatures of the magnetic field component normal to the magnetopause. The FTEs were originally interpreted as evidence for the passage of elbow-shaped flux tubes that originate via patchy reconnection. They have also been pictured as quasi-two-dimensional cylindrical flux ropes formed via reconnection along extended obliquely oriented subsolar lines. We use the global magnetohydrodynamic (MHD) code BATS-R-US developed at the University of Michigan to model the three-dimensional structure of FTEs during quasi-steady solar wind conditions on May 20. 2007 (THEMIS dayside event). The global structure of FTEs will be illustrated using advanced visualization tools developed at the Community Coordinated Modeling Center.
The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) provides images, spectra, and light curves of solar flares in >3keV X-rays and gamma-rays with an unprecedented combination of spatial, spectral, and temporal resolution. Equally important, for all observed flares the data can be analyzed in arbitrarily selected photon energy bands and time intervals, and spectra can be obtained for selected sources or source regions in flare images. This resolution and flexibility, as well as RHESSI's broad spectral coverage (3 keV to 17 MeV), have allowed substantial insights to be obtained into both the magnetic and thermal evolution of flares and particle acceleration and propagation. I will summarize some of the most important advances in our knowledge and understanding of solar flares obtained from the analysis of RHESSI observations.