Cluster Spacecraft Survey of the Electric Field and Potential Well Structure of Multiple Current Sheet Crossings Near a Reconnection Region in the Tail on October 1, 2001

In this talk, we present a survey of ~40 complete and partial thin current sheet crossings in the tail near ~19 Re geocentric distance using electric and magnetic field data from the Electric Field and Wave and Fluxgate Magnetometer instruments on the Cluster spacecraft array. These data were obtained on October 1, 2001 between 9:40 UT and 9:50 UT when the spacecraft spacing was about ~2000 km. The scale sizes, magnitude, and symmetry of the electric potential well structure associated with the normal component of the electric fields are determined. This time interval is characterized by large scale ~(20,000 km), long period (~100 second) current sheet undulations which propagate at 200-300 km dusk ward perpendicular to B. These undulations are large enough amplitude to rotate the current sheet normal direction into the y-gse direction. The electric field measurement plane is in the x-y gse plane. This affords the opportunity to estimate the normal component of the electric field (Wygant et. al., 2005). Approximately nine complete crossings have been observed by individual Cluster spacecraft with Bx-gse varying from -10 nT to +10 nT with the normal close to the y-gse direction. About half of these were associated with strong symmetric bipolar electric fields coinciding with the current sheet and centered on the magnetic field reversal. The bipolar fields had magnitudes which varied between +/- 10 mV/m to +/-80 mV/m. Scale sizes from periphery to center of the potential well are on the order of 80 km for a very small scale current sheet to 2000 km. The potential wells associated with these structures had a depth of 5 kV to 20 kV. We shall also present examples of passes in which the quasi-static potential structure observed is dominated by the high amplitude turbulent electric fields.