Discovery of a New Auroral Signature of Solar Wind Pressure Pulses.

M.PINNOCK
British Antarctic Survey, UK.

A review of all noon sector keogram data (630 and 427 nm auroral emissions) for the austral winter 1999 from S. Pole station has revealed a phenomena associated with solar wind pressure increases impacting the magnetosphere. A short duration (10 minute) pulse of auroral emission is triggered in both wavelengths across the whole field of view (80 to 70 degrees AACGM) at the time a pressure pulse impacts the magnetosphere. Examination of two event sequences (using all-sky images) suggests a two stage response. The first response is a longitudinally narrow emission which leaps equatorward at velocities too fast to be resolved with the resolution of the experiment. The second response is a longitudinally extended equatorward bulge of the auroral oval which commences several minutes after the first response. These observations are significantly different from earlier reports of the response to solar wind pressure pulses [1] but bear a close resemblance to events tentatively associated with FTEs [2]. Our initial interpretation is framed in the context of an equatorially propagating fast mode wave (similar to nightside super-fast auroral waves) and a later shear-mode Alfven wave.

1. Frey et al., The aurora during the passage of the May 27, 1996 magnetic cloud, GRL, 25, 2605, 1998.

2. Mende et al., Magnetic impulses and associated optical signatures in the dayside aurora, GRL, 17, 131, 1990.

Acknowledgments: We are very grateful to Drs. Mende and Frey of the Space Sciences Laboratory, University of California for making available on the World Wide Web their database of S. Pole keograms ( http://sprg.ssl.berkeley.edu/atmos/data/).

Session Index

Proceedings Index