Observations of Electron Holes and Their Relationship to Magnetic Reconnection

Recent observations from the Polar satellite and new 3d particle simulation results have provided evidence suggesting that electron holes may play an important role in the dynamics of reconnection. Solitary waves (the electric field signature of electron holes) are commonly observed in and near the magnetopause current layer during subsolar, equatorial crossings of the magnetopause. The solitary waves had amplitudes up to 40 mV/m, velocities from ~150 km/s to >2000 km/s, and scale sizes the order of a kilometer (comparable to the Debye length). Almost all the observed solitary waves were positive potential structures with potentials of ~0.1 to 5 Volts. Positive potential solitary waves moving with velocities of 1000's of km/s are consistent with electron phase-space holes. Drake et al. [2002] have shown that electron holes develop in 3d particle simulations of reconnection, which include a guide magnetic field. The electron holes strongly scatter the electrons, and produce anomalous resistivity. The experimental and theoretical results provide strong support for the idea that electron holes play a critical role in the reconnection process at the Earth's magnetopause and may, therefore, be important in other regions where reconnection occurs. We will discuss Polar and Cluster observations of electron holes at the magnetopause to address this idea.