DOUBLE VISION - REMOTE-SENSING OF A FLUX-TRANSFER EVENT WITH ISEE-1 AND ISEE-2

A flux transfer event recorded by the ISEE 1 and 2 spacecraft in the n orthern hemisphere near local noon is examined using analysis techniqu es developed recently for determination from single satellite magnetom eter data of the orientation and cross-sectional shape of a two-dimens ional disturbance moving along the magnetopause. The analysis is perfo rmed independently on the magnetic field data recorded by each satelli te, enabling us to check the consistency of the results and thus to be nchmark the method. The analysis is also extended to utilize the dual magnetometer measurements for determination of the event speed and siz e (which for a single spacecraft requires use of three-dimensional pla sma velocity data to obtain a deHoffmann-Teller frame velocity) and fo r accommodating acceleration of the magnetopause normal to itself, whi ch results in a curved spacecraft trajectory in the frame of reference moving with the disturbance. The analysis of the disturbance reveals that while its overall size is about 34,000 km in a direction parallel to the magnetopause but perpendicular to the event axis, the actual s ize of the bulge causing the field disturbance may have been as small as 9000 km with a dimension perpendicular to the magnetopause of the o rder of 1200 km. The bulge is found to be traveling at a speed of abou t 140 km/s toward the northern dawn quadrant of the dayside magnetopau se. While plasma data from ISEE 2 provides evidence of plasma jetting, which suggests the event may be associated with reconnection, the ori entation of the flux tube axis obtained from the analysis is significa ntly different from the expected reconnection line direction, A discus sion of possible interpretations of this bulge orientation and motion is provided.