Observations of quasi-perpendicular propagating electromagnetic waves near the ionopause current sheet of Venus

Abstract

Due to the lack of an intrinsic magnetic field at Venus, the Venus ionosphere acts as the obstacle to the incoming solar wind flow. Induced currents flowing on the ionopause resist the penetration of the solar wind magnetic fields into the ionosphere. The Venus Express magnetometer occasionally observes plasma waves near the ionopause. These waves propagate quasi-perpendicularly to the background magnetic field, which are distinctively different from the lightning-generated whistler waves. Both case and statistical studies are performed on the Venus Express magnetometer data in 32Hz and 128Hz resolutions for these quasi-perpendicular propagating waves. These waves are found to be strongly associated with current sheets near the ionopause, either occurring at the center of a sharp current, or occurring at the edge of a current. The earlier Pioneer Venus Orbiter electric field observations also detected plasma waves associated with field-aligned currents near the ionopause region, and the wave studies in this paper are possibly the magnetic counterparts of those earlier observations. These waves could be generated from the free energy of currents at the ionopause and could lead to dissipation of those currents. Copyright 2012 by the American Geophysical Union.