JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A12206, doi:10.1029/2007JA012395, 2007

Energetic particle precipitation into the middle atmosphere triggered by a coronal mass ejection

M. A. Clilverd1, C. J. Rodger2, R. M. Millan3, J. G. Sample4, M. Kokorowski5, M. P. McCarthy5, Th.Ulich6, T. Raita6, A. J. Kavanagh7, E. Spanswick8

1Physical Sciences Division, British Antarctic Survey, Cambridge, U.K.,
2Dept of Physics, University of Otago, Dunedin, New Zealand,
3Dept of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire, USA,
4Space Sciences Lab, Dept of Physics, University of California, Berkeley, California, USA,
5Dept of Earth and Space Science, University of Washington, Seattle, Washington, USA,
6Sodankylä Geophysical Observatory, Sodankylä, Finland,
7Space Plasma Environment and Radio Science Group, Dept of Communication Systems, University of Lancaster, Lancaster, U.K.,
8Dept of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada


Precipitation of relativistic electrons into the atmosphere has been suggested as the primary loss mechanism for radiation belt electrons during large geomagnetic storms. Here we investigate the geographical spread of precipitation as a result of the arrival of a coronal mass ejection (CME) on 21 January 2005. In contrast to previous statistical studies we provide one of the first attempts to describe the geographic and temporal variability of energetic particle precipitation on a global scale using an array of instruments. We combine data from subionospheric VLF radio wave receivers, the high-altitude Miniature Spectrometer (MINIS) balloons, riometers, and pulsation magnetometers during the first hour of the event. There were three distinct types of energetic electron precipitation observed, one globally, one on the dayside, and one on the nightside. The most extensively observed form of precipitation was a large burst starting when the CME arrived at the Earth, where electrons from the outer radiation belt were lost to the atmosphere over a large region of the Earth. On the dayside of the Earth (10–15 MLT) the CME produced a further series of precipitation bursts, while on the nightside dusk sector (∼20 MLT) a continuous precipitation event lasting ∼50 min was observed at 2.5 < L < 3.7 along with Pc 1–2 pulsations observed with a ground-based magnetometer. These observations suggest that the generation of energetic electron precipitation at the inner edge of the outer radiation belt from electromagnetic ion cyclotron (EMIC) wave scattering into the loss cone is the most direct evidence to date connecting EMIC activity and energetic precipitation.

© 2007 by the American Geophysical Union. Further electronic publication not allowed.

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