Solar magneto-atmospheric waves and penumbral waves. Final report Sep 74--30 Sep 76

Technical Report · Wed Dec 22 04:00:00 EST 1976

OSTI ID:7276671

Thomas, J H; Nye, A H; Clark, A Jr

The linearized theory of magneto-atmospheric waves (involving the combined restoring forces due to buoyancy, compressibility, and magnetic field) is developed for the case of a horizontal magnetic field which may vary with height. The convective stability of the basic atmosphere is considered, and it is shown that a nonuniform horizontal magnetic field may be destabilizing as well as stabilizing. It is found that penumbral waves may be identified with magneto-atmospheric waves of the plus type that are vertically trapped at photospheric levels. Although most of the wave energy is contained in the penumbral photosphere and subphotosphere, the maximum vertical velocity occurs in the chromosphere where the waves are evanescent (and where they are observed in H alpha). An exact analytical solution for magneto-atmospheric wave modes is found in the case of an isothermal atmosphere permeated by a uniform horizontal magnetic field, without making the usual short-wavelength approximation. The exact solution mentioned above is also used in conjunction with a simple two-layer model of a sunspot penumbra to study further the mode of running penumbral waves. The lowest plus eigenmode of the model is in good agreement with observations of penumbral waves.

• Research Organization: Rochester Univ., N.Y. (USA). Dept. of Mechanical and Aerospace Sciences
• OSTI ID: 7276671
• Report Number(s): AD-A-046276
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
COMPRESSIBILITY
CONVECTIVE INSTABILITIES
HYDROMAGNETIC WAVES
INSTABILITY
MAGNETIC FIELDS
MECHANICAL PROPERTIES
OSCILLATION MODES
PLASMA INSTABILITY
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SUNSPOTS
WAVE PROPAGATION