THE EFFECTS OF A HOT OUTER ATMOSPHERE ON ACOUSTIC-GRAVITY WAVES

We examine the effects of a hot chromosphere and corona on acoustic-gr avity waves in the Sun. We use a simple solar model consisting of a ne utrally stable polytrope smoothly matched to an isothermal chromospher e or corona. The temperature of the isothermal region is higher than t he minimum temperature of the model. We ignore sphericity, magnetic fi elds, changes in the gravitational potential, and nonadiabatic effects . We find a family of atmospheric g-modes whose cavity is formed by th e extremum in the buoyancy frequency at the transition region. The f-m ode is the zero-order member of this family. For large values of the h armonic degree l, f-mode frequencies are below the classic f-mode freq uency, mu = (gk)(1/2), whereas at small values of l, the f-mode is ide ntical to the classical f-mode solution. We also find a family of g-mo des residing in the low chromosphere. Frequency shifts of p-modes can be positive or negative. When the frequency is less than the acoustic cutoff frequency of the upper isothermal atmosphere, the frequency shi ft is negative, but when the frequency is above this cutoff, the shift s can be positive. High-frequency acoustic waves which are not reflect ed by the photospheric cutoff are reflected at the corona by the high sound speed for moderate values of l and v. This result is independent of the solar model as long as the corona is very hot. The data are in consistent with this result, and reasons for this discrepancy are disc ussed.