POYNTING VECTOR MEASUREMENTS OF ELECTROMAGNETIC ION-CYCLOTRON WAVES IN THE PLASMASPHERE

Although Pc 1-2 emissions have been measured from the ground and from satellites for a long time, relatively few studies exist in which E, B, and sigma-N are all analyzed. In this paper, we revisit one such example: the June 6, 1985, Pc 1 event investigated by LaBelle et al. (1988), which occurred in the duskside overlap region between the plasmaspheric bulge and the ion ring current. Although this observation was made within a few degrees of the equator, equal amplitudes of R and L modes are observed, i.e., linear polarization. Poynting vector analysis of the R and L mode components show them to both be characterized by northward Poynting vector, indicating energy flux away from the equator. The value of the Poynting vector is about 3-mu-Wm-2, consistent with comparable previous measurements when convergence of the magnetic field is taken into account. Minimum variance analysis of the magnetic field fluctuations implies that the wavevector is nearly parallel to the background B. For parallel propagation, the crossover frequencies and bi-ion hybrid frequencies may be calculated; the waves turn out to be nearly at the crossover frequency if oxygen ions are included in the calculation. This is the simplest explanation for the linear polarization. The absence of density fluctuations associated with the waves seems to eliminate the possibility that a linear electrostatic mode is being observed in this case.