Acoustic wave heating of the thermosphere

A numerical model is used to study the dissipation in the thermosphere of u pward propagating acoustic waves. Whereas dissipating gravity waves can coo l the upper atmosphere through the effects of sensible heat flux divergence , it is found that acoustic waves mainly heat the thermosphere by viscous d issipation. Though the amplitudes of acoustic waves in the atmosphere are p oorly constrained, the calculations suggest that dissipating acoustic waves can locally heat the thermosphere at rates of tens of kelvins per day and thereby contribute to the thermospheric energy balance. It is shown that vi scous heating cannot be calculated from the divergence of the wave mechanic al energy flux. Acoustic waves that are barely detectable at mesopause heig hts can become significant heaters of the atmosphere high in the thermosphe re. We suggest that acoustic waves might be responsible for heating the equ atorial F region to produce the hot spot observed in the O I 630 nm airglow over the Andes Mountains.