Magnetoacoustic wave propagation in current sheets.

Details Magnetoacoustic wave propagation in current sheets. Magnetoacoustic wave propagation in current sheets.

Nov 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...327..377s&link_type=abstract

Astronomy and Astrophysics, v.327, p.377-387

Astronomy and Astrophysics

Astrophysics

20

Mhd, Sun: Corona, Sun: Magnetic Field, Sun: Oscillations, Solar System: Earth

Scientific paper

Magnetoacoustic waves in a Harris neutral current sheet are investigated. The magnetic field strength, Alfven speed, sound speed and plasma density vary continuously across the structure. The sheet supports body, surface and hybrid modes. Two surface modes exist (a kink and a sausage). 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 limit the phase speed of the fundamental kink body mode and sausage surface 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 value of the sound speed, c_s_^max^. For all modes, in the inner part of the current sheet, the gas pressure is out of phase with the magnetic pressure, with the gas pressure dominating (a property of a slow mode). In the outer part of the sheet the magnetic pressure is in phase with 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 profile, 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 emission of the solar corona and neutral sheet oscillations in the Earth's magnetotail. Calculated periods of oscillation are in good agreement with observations.

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