Dartmouth Events

Abstract: We use two-dimensional simulations in a meridian of the Earth's dipole magnetosphere to investigate the properties of electromagnetic ion cyclotron (EMIC) waves and their effect on relativistic electrons. When heavy ions are present, EMIC waves occur in multiple wave bands such as the H band with frequency above the He+ gyrofrequency and the He band with frequency below the He+ gyrofrequency. He band waves tend to be dominant in high density plasma such as the plasmasphere. Precipitation caused by pitch angle scattering due to resonant interaction with EMIC waves has been considered to be a significant loss mechanism for relativistic electrons. But recent observations have suggested that the dominant energy of electrons precipitated to the atmosphere may often be relatively low, less than 1 MeV, whereas the minimum resonant energy of the highest amplitude waves is often greater than 2 MeV. Here we show that significant pitch angle scattering can occur due to interaction with low amplitude short wavelength EMIC waves. In the case we examined, these waves are in the H band, even though the highest amplitude waves were in the He band frequency range. We also present wave power distributions for 29 EMIC simulations in straight magnetic field line geometry that show that the high wave number portion of the spectrum is in every case mostly due to the H band waves. Relativistic electron precipitation may occur when He band waves are dominant because the higher density conditions that favor He band waves lower the resonant energy. Nevertheless, there are significant differences in the distribution of EMIC waves and that of relativistic electron precipitation, which we will discuss.