Electrostatic electron cyclotron waves generated by low-energy electron beams

Abstract

We report the results of an investigation of waves observed by the Polar spacecraft at high altitudes and latitudes and at frequencies just above the cyclotron frequency. These observations are made frequently when the spacecraft is over the polar cap as well as near the dayside cusp and the nightside auroral region and for ratios of gyrofrequency to plasma frequency, f p/fg ∼ 1. We investigate the role of electron beams with E ≲ 1 keV in the generation of these waves. Observed plasma parameters are used as input to a modification of the Waves in Homogeneous, Anisotropic Multi-component Plasmas (WHAMP) computer code to place constraints on the free energy source and growth of these waves. We conclude these waves are an indicator of the presence of low-energy electron beams and a cold electron component (E ≲ 0.2 eV) in regions with fp/fg ≲ 1. Copyright 2002 by the American Geophysical Union.