Theoretical studies of Electron Cyclotron Harmonic (ECH) waves based on experimental data from Geos-1

Three wave events demonstrating the 4 classes of electron cyclotron harmonic (ECH) waves observed by GEOS-1 are presented. Models of the electron distribution function were constructed from the simultaneously observed particle data and used to solve the electrostatic dispersion relation and calculate the wave spatial growth rates. In the first event it is shown that changes in the cold electron distribution were responsible for large wave amplitude variations of strong ECH waves near the local upper hybrid frequency fu. In the second event it is shown that strong cyclotron damping and wave propagation effects in a plasma density gradient were responsible for the apparent frequency jumping of very weak ECH waves near fu. In the third event it is demonstrated that complex variations in the electron distribution 1keV led to the change in wave emission class.