Multiple‐spacecraft and correlated riometer study of magnetospheric substorm phenomena

Abstract

Substantial progress has been made in recent years toward the separation of spatial and temporal effects within the magnetosphere through the use of simultaneous multipoint measurements. From 1977 to the present we have had identical energetic particle instruments in geostationary orbit on the two spacecraft, and during 1977–1978 these satellites were separated by ∼4.5 hours in local time. During this same epoch, 13 variously located riometer stations provided broad latitudinal and longitudinal ground‐based coverage of substorm activity. Throughout this period of coordinated investigation we have found numerous examples of substorm growth phase features at widely separated local times. Simultaneous measurements of the magnetosheath and interplanetary magnetic field (north‐south) orientation during substorm growth phases suggest quite close correlations between energy input to the magnetosphere and the development of growth‐phase‐related stresses near geostationary orbit. Thus the results of this study demonstrate the broad local time region in which growth phase features are observable in spacecraft data, and they also support the concept of storage of energy prior to substorms, with the sudden release of this energy at substorm expansion onset.