WHISTLER WAVE INTERACTION WITH A DENSITY STRIATION - A LABORATORY INVESTIGATION OF AN AURORAL PROCESS

Whistler waves are launched toward a field-aligned density striation in a laboratory plasma. Characteristic scale length and frequency ratios are scaled to closely reproduce situations found in the auroral ionosphere. Detailed measurements show that at the striation edge nearest the wave-launching antenna, besides a reflected and a transmitted whistler wave, lower hybrid waves are also stimulated on both sides of the striation boundary in a manner consistent with the linear mode-conversion model. We find that the energy density of the mode-converted lower hybrid waves is typically 10% of the incident whistler wave energy density, reaching a maximum of 30% in one region. Lower hybrid waves are confined to within 2-3 perpendicular wavelengths in the interaction zone. Our results show that the interaction of electromagnetic whistler mode waves with density striations can cause significant amounts of energy to be deposited in the largely electrostatic lower hybrid mode and that it may therefore be a significant generation mechanism for these waves in certain regions of the ionosphere.