Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977ap%26ss..48..365e&link_type=abstract
Astrophysics and Space Science, vol. 48, no. 2, May 1977, p. 365-377. Research supported by the U.S.-Israel Binational Science
Astronomy and Astrophysics
Astrophysics
11
Astronomical Models, Comet Tails, Kelvin-Helmholtz Instability, Plasma Cylinders, Plasma Waves, Solar Wind, Incompressible Flow, Interplanetary Magnetic Fields, Kohoutek Comet, Magnetohydrodynamic Flow, Morehouse Comet
Scientific paper
Oscillations of type-1 comet tails with plasma compressibility taken into account are studied. A comet tail is treated as a plasma cylinder separated by a tangential discontinuity surface from the solar wind. The dispersion equation obtained in the linear approximation is solved numerically with typical plasma parameters. A sufficient condition for instability of the cylindrical tangential discontinuity in the compressible fluid is obtained. The phase velocity of helical waves is shown to be approximately coincident with Alfven speed in the tail in the reference system moving with the bulk velocity of the plasma outflow in the tail. The instability growth rate is calculated. This theory is shown to be in good agreement with observations of the tails of Comets Kohoutek, Morehouse, and Arend-Roland. It is concluded that helical waves observed in type-1 comet tails are produced due to the Kelvin-Helmholtz instability and that the model under consideration is justified. If so, one may estimate the comet-tail magnetic field from the pressure balance at the tangential discontinuity; it turns out to be of the order of the interplanetary magnetic field.
Ershkovich A. I.
Heller Ana B.
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