NEW RESONANCE IN THE SOLAR ATMOSPHERE .1. THEORY

We consider a horizontally stratified isothermal model of the solar atmosphere, with vertical and uniform B0, and vA2≫vs2. The equations of motion are linearized about a background which is in hydrostatic equilibrium. A homogeneous wave equation results for the motions perpendicular to B0; this wave equation is similar to the equation for the MHD fast mode. On the other hand, the equation for the parallel motions is inhomogeneous, containing 'driving terms' which arise from the presence of the fast mode; the homogeneous form of this equation is identical to the equation describing vertically-propagating gravity-modified acoustic waves. We demonstrate that a resonance can exist between the (driving) fast wave and the (driven) gravity-modified acoustic wave, in such a way that very large parallel velocities can be driven by small perpendicular velocities. Applications of this resonance to solar spicules, 'jets', and other phenomena are discussed. © 1979 D. Reidel Publishing Co.