IMPROVED ANALYSIS OF PLASMASPHERE MOTION USING THE VLA RADIO INTERFEROMETER

Observations using the very large array (VLA) radio interferometer dur ing the past five years have enabled the discovery of a new type of pl asmasphere disturbance, the magnetic eastward-directed wave. Previous work indicated these disturbances were likely frozen to the geomagneti c field as determined from their azimuth distributions. This work prov ides a method to explain more accurately the azimuth distribution, the reby allowing the calculation of the disturbances' location in the pla smasphere independently of the measured velocity. The measurable veloc ity due to corotation is calculated and subtracted from the measured t race velocity. This difference, or deviation from corotation, is attri buted to electrodynamic convection; the measurement of plasmaspheric c onvection may lead to the eventual monitoring of mid-latitude electric fields. Disturbances are seen convecting predominantly westward, with the fastest having angular velocities greater than the anticorotating VLA line of sight. The direction of convection and conditions of obse rvations indicate that the disturbances are likely the same phenomenon seen by the Los Alamos satellite beacon array.