Observations of electromagnetic ion cyclotron waves during geomagnetic storms: Wave occurrence and pitch angle scattering

This paper addresses the occurrence of low-L (3.5 < L < 5) electromagnetic ion cyclotron (EMIC) waves during magnetic storms. Using similar to 10 year s of data, a statistical analysis indicates that EMIC waves in the equatori al magnetosphere occur 5 times more often during magnetic storms than durin g quiet times. EMIC wave occurrence during magnetic storms is important bec ause EMIC waves pitch angle scatter energetic protons and thus represent a ring current loss mechanism. Observations in the equatorial magnetosphere, acquired by the Dynamic Explorer 1 (DE: 1) satellite, are used to show the simultaneous occurrence of EMIC waves and enhanced proton fluxes in the los s cone. The study involves three cases selected only on the basis of observ ed EMIC wave activity and the availability of energetic ion data. The obser vations show that EMIC waves indeed scatter protons into the loss cone. Mod el calculations of the loss cone heat-flux density compare favorably to the observed proton flux in the loss cone. These calculations are then used to estimate the effect of EMIC waves on ring current energy loss, assuming an effective area of wave activity and the duration of the wave activity. It is found that large-amplitude, long-duration EMIC waves can produce the obs erved recovery in the Dst index.