MAGNETOACOUSTIC WAVE-PROPAGATION IN CURRENT SHEETS

Magnetoacoustic waves in a Harris neutral current sheet are investigat ed. The magnetic field strength, Alfven speed, sound speed and plasma density vary continuously across the structure. The sheet supports bod y, surface and hybrid modes. Two surface modes exist (a kink and a sau sage). In addition, fundamental and harmonic body waves are found when their phase speeds approach the maximum Alfven speed in the sheet. As the phase speeds of the modes decrease, the waves have properties of both body and surface modes - a hybrid wave. In the long wavelength li mit the phase speed of the fundamental kink body mode and sausage surf ace mode approach the maximum Alfven and tube speeds respectively. At short wavelengths, the phase speeds tend to constant values, each pair of kink and sausage modes merging after passing through the maximum v alue of the sound speed, c(s)(max). For all modes, in the inner part o f the current sheet, the gas pressure is out of phase with the magneti c pressure, with the gas pressure dominating (a property of a slow mod e). In the outer part of the sheet the magnetic pressure is in phase w ith the total pressure (a fast mode characteristic). No purely fast or slow mode exists. For uniform density a minimum in the group velocity occurs only for the fundamental kink mode. For the Epstein density pr ofile, minima in the group velocity are found for the other modes also . Impulsively generated waves are expected to show temporal variations that are similar to observations of oscillations of radio and X-ray e mission of the solar corona and neutral sheet oscillations in the Eart h's magnetotail. Calculated periods of oscillation are in good agreeme nt with observations.