Whistler mode turbulence generated by electron beams in Earth's bow shock

Abstract

In this study, the Landau and cyclotron growth rates of whistler mode waves in earth's bow shock are calculated by using electron distribution functions obtained with the fast plasma experiment on ISEE 2. Three electron distribution functions measured within the transition region of the shock are analyzed. An important feature of these electron distribution functions is the presence of a field‐aligned beam with a T⊥ > T∥ anisotropy. The beam velocity vector is directed toward the magnetosheath. The calculations show that the electron distribution functions spontaneously generate whistler mode waves with plasma rest frame frequencies between about 0.1 and 100 Hz. The wave normal angles of the generated whistlers range from 0° to the resonance cone angle. Electromagnetic Landau resonance and/or cyclotron resonance contribute to wave growth over the range of velocity distributions observed. The waves that are generated by the normal cyclotron resonance have wave vectors directed toward the solar wind, while those that are generated by the Landau and the anomalous cyclotron resonances have wave vectors directed toward the magnetosheath. The predictions of the study are in qualitative agreement with observations of whistler mode waves near earth's bow shock.