Internal gravity waves in atmospheres with realistic dissipation and temperature part II. Thermal tides excited below the mesopause

Abstract

The formalism developed in Part I for studying atmospheric tides and other internal gravity waves in atmospheres with realistic structure and dissipation is discussed further, and used to study the atmosphere's response to thermotidal excitation due to insolation absorption by ozone, water vapor and the ground. It is shown that the main diurnal propagating mode becomes unstable near 85 km. The instability is shown to cease at 108 km—suggesting an explanation of the turbopause. It is also shown that the semidiurnal tide is attenuated by molecular dissipation before nonlinear terms become dominant. Another result found is that the inclusion of eddy and molecular viscosity and conductivity, Newtonian cooling and surface heating do not significantly alter the predicted phase of the semidiurnal surface pressure oscillation from the value obtained from inviscid theory with excitation due only to insolation absorption by water vapor and ozone. A discrepancy of about 40 minutes exists between theory and observation. This discrepancy is discussed and it is concluded that the discrepancy is probably due to an error in the calculation of ozone semidiurnal excitation.