Two substorm studies of relations between westward electric fields in the outer plasmasphere, auroral activity, and geomagnetic perturbations

In two case studies of magnetospheric substorms, temporal variations of the westward component of the magnetospheric convection electric field in the outer plasmasphere were compared with auroral activity near L = 7 and with variations in the geomagnetic field at middle and high latitudes. The substorms occurred on July 29, 1965, near 0530 UT and on August 20, 1965, near 0730 UT. The results on the westward electric field E w were obtained by the whistler method with data from Eights, Antarctica ( L ∼ 4). All‐sky camera records were obtained from Byrd, Antarctica ( L ∼ 7), located within about 1 hour of Eights in magnetic local time. It was found that E w within the outer plasmasphere increased rapidly to substorm levels of ∼0.5 mv/m about the time of auroral expansion at nearby longitudes. This behavior differs from results obtained from electrostatic probes on balloons, which show E w reaching enhanced levels before the expansion. A close temporal relation was found between the rapid substorm‐associated increases in E w and a well‐known type of nightside geomagnetic perturbation. Particularly well defined was the correlation of E w rise with a large deviation of the D component at middle latitudes.