AN ANALYSIS OF WHISTLER WAVES AT INTERPLANETARY SHOCKS

We present an analysis of whistler wave magnetic and electric field am plitude ratios from which we compute wave propagation angles and energ ies of electrons in resonance with the waves. To do this analysis, we compute the theoretical dependence of ratios of wave components on the whistler wave propagation angle theta for various combinations of ort hogonal wave components. Ratios of wave components that would be obser ved by a spinning spacecraft are determined, and the effects of arbitr ary inclinations of the spacecraft to the ambient magnetic field and t o the whistler wave vector are studied. This analysis clearly demonstr ates that B/E, the ratio of magnetic to electric field amplitudes, can not be assumed to be the wave index of refraction, contrary to assumpt ions of some earlier studies. Therefore previous interpretations of wh istler wave observations based on this assumption must be reinvestigat ed. B/E ratios derived using three orthogonal wave components can be u sed to unambiguously determine theta. Using spin plane observations al one, a significant uncertainty occurs in the determination of theta. N evertheless, for whistler waves observed downstream of several interpl anetary shocks by the Ulysses plasma wave experiment we find that thet a is highly oblique. We suggest that the analysis of wave amplitude ra tios used in conjunction with traditional stability analyses provide a promising tool for determining which particle distributions and reson ances are likely to be dominant contributors to wave growth.