On the azimuthal size of flux ropes near lunar orbit

摘要

We present Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) dual-probe observations of flux ropes in the Earth's magnetotail near lunar orbit. On 15 July 2011 between 0400 and 0500 UT, the ARTEMIS probes (P1 and P2) are separated by ～ (9/10/3) R_E(X_(GSW)/Y_(GSW)/Z_(GSW)). GSW denotes the Geocentric Solar Wind coordinate system and differs from the GSM coordinate system in that its X axis is antiparallel to the solar wind. P1 is near midnight and P2 in the postmidnight sector at ～ -13 R_E Y_(GSW). During a ～ 50 min interval on 15 July 2011, P1 crossed the current sheet and encountered a flux rope thereafter. During the same interval, P2 observed only one flux rope near the time P1 crossed the current sheet but no flux rope or traveling compression region (TCR) for P1's subsequent flux rope observation. A Tsyganenko-Fairfield model and minimum variance analysis during the current sheet crossing are used to infer the current sheet location with respect to the probes. We find the distance between P2 and the plasma sheet boundary to be less than 3 R_E. Under these circumstances, P2 would be expected to observe a TCR if the flux rope observed by P1 extended to the postmidnight location of P2. The lack of such observations indicates that, contrary to previous models and simulation results, flux ropes may be spatially confined in the dusk-dawn direction and do not extend across the entire cross section of the tail near lunar orbit.