Engebretson, M. J.2; Yeoman, T. K.2; Oksavik, K.2; Søraas, F.2; Sigernes, F.2; Moen, J. I.2; Johnsen, M. G.2; Pilipenko, V. A.2; Posch, J. L.2; Lessard, M. R.2; Lavraud, B.2; Hartinger, M. D.2; Clausen, L. B. N.2; Raita, T.2; Stolle, Claudia1
1 National Space Institute, Technical University of Denmark2 unknown
An isolated burst of 0.35 Hz electromagnetic ion cyclotron (EMIC) waves was observed at four sites on Svalbard from 0947 to 0954 UT 2 January 2011, roughly 1 h after local noon. This burst was associated with one of a series of ~50 nT magnetic impulses observed at the northernmost stations of the IMAGE magnetometer array. Hankasalmi SuperDARN radar data showed a west-to-east (antisunward) propagating vortical ionospheric flow in a region of high spectral width ~ 1–2° north of Svalbard, confirming that this magnetic impulse was the signature of a traveling convection vortex. Ground-based observations of the Hα line at Longyearbyen indicated proton precipitation at the same time as the EMIC wave burst, and NOAA-19, which passed over the west coast of Svalbard between 0951 and 0952, observed a clear enhancement of ring current protons at the same latitude. Electron precipitation from this same satellite indicated that the EMIC burst was located on closed field lines, but near to the polar cap boundary. We believe these are the first simultaneous observations of EMIC waves and precipitating energetic protons so near to the boundary of the dayside magnetosphere. Although several spacecraft upstream of Earth observed a steady solar wind and predominantly radial interplanetary magnetic field orientation before and during this event, data from Geotail (near the morning bow shock) showed large reorientations of the interplanetary magnetic field and substantial decreases in ion density several minutes before it, and data from Cluster (near the afternoon bow shock) showed an outward excursion of the bow shock simultaneous with it. These upstream perturbations suggest that a spontaneous hot flow anomaly, a bow shock related instability, may have been responsible for triggering this event, but do not provide enough information to fully characterize that instability.
Journal of Geophysical Research, 2013, Vol 118, Issue 6, p. 2975-2997