Pi1B pulsations observed on the ground and in space by GOES and THEMIS satellites

Ground-based observations of Pi1B pulsations at substorm onset have been reported by several researchers, using data from various ground-based platforms. Some recent evidence indicates that these pulsations may drive Alfvenic aurora at onset, providing, at least in part, a source for the initial brightening during substorms. Arnoldy et al. [1998] showed that these pulsations can also be observed at geosynchronous orbit at substorm onset, with such observations having a reasonable correlation to ground observations. The occurrence of Pi1B pulsations at geosynchronous orbit implies that they originate near or beyond this region, perhaps providing a means to couple energy from deeper in the tail to the ionosphere at onset. In order to better understand the apparent relationship between ground-based and geosynchronous observations of Pi1B pulsations, we have investigated a number of events, using GOES and THEMIS data. We find that 1) nearly all ground-based observations of Pi1B have a corresponding signature in GOES data, and 2) THEMIS observations show similar signatures and these events coincide with observations of Earthward-moving fast flows. Arnoldy, R. L., J. L. Posch, M. J. Engebretson, H. Fukunishi and H. J. Singer, Pi1 magnetic pulsations in space and at high latitudes on the ground, JGR, 103, A10, 23581-23592, doi:10.1029/98JA01917