Full wave calculations of gravity wave propagation through the thermosphere

Full wave calculations have been performed within the frequency range of gravity waves (10−3 ≤ ω ≤ 10−2 sec−1) for a thermospheric model between 150 and 500 km altitude. In this altitude range gravity waves are coupled with heat conduction waves. Reflection, transmission, conversion, and coupling from one wave type into the other one is described by the elements of the scattering matrix. The dependence of these elements on height and angle of incidence is discussed. The transmission coefficients of gravity waves calculated by full wave theory are compared with simple ray calculations and show that ray treatment is a sufficient approximation for obliquely upward propagating gravity waves and that gravity waves predominate throughout the thermosphere. The thermosphere reacts like a selective filter with respect to upward propagating gravity waves with optimal transmission at kx ∼ ω/C (ω = angular frequency; C = velocity of sound; kx = horizontal wave number).