HF-RADAR OBSERVATIONS OF THE DAYSIDE MAGNETIC MERGING RATE - A GEOSPACE ENVIRONMENT MODELING BOUNDARY-LAYER CAMPAIGN STUDY

Goose Bay HF-radar data have been used to determine the dayside reconn ection electric field which transports energy from the solar wind into the Earth's magnetosphere and ionosphere. The speed of the ionospheri c plasma flow perpendicular to the open/closed boundary is determined in the rest frame of the boundary along each of the 16 beam directions of the HF radar. The observations were made during one of the Geospac e Environment Modeling program's boundary layer campaigns. The period from 1200 to 1600 UT on March 29, 1992, was one of generally southward interplanetary magnetic field (IMF). The y component of the IMF was n egative for most of the time. Despite the generally steady IMF conditi ons, the merging rare observed by the radar shows a great deal of temp oral structure. The radar observations have been compared with the res ults from the assimilative mapping of ionospheric electrodynamics (AMI E) procedure. Initially, the merging inferred from the radar observati ons accounts for a significant portion of the total polar cap potentia l drop, suggesting that a majority of the potential drop was generated within the radar field of view and must therefore be due to magnetic merging at the magnetopause. At the end of the period, however, the po tential drop derived from the radar measurements is distinctly less th an that derived from the AMIE procedure. At that time, however, satell ite and ground magnetometer data show that a substorm was in progress, and there is substantial evidence for a strong nightside contribution to the polar cap potential drop. An additional feature that appears i n this data set is that the orientation of the open/closed magnetic fi eld separatrix with respect to magnetic latitude is well correlated to the y component of the IMF.