Heating of the Martian Upper Atmosphere by the Dissipation of Acoustic‐Gravity Waves

Abstract Highly variable thermal structures in the Martian upper atmosphere were revealed by recent spacecraft observations. Acoustic–gravity waves, which are ubiquitous in planetary atmospheres, are a potential mechanism for these variations. These waves can propagate into the upper atmosphere and dissipate through molecular viscosity and thermal conduction, releasing wave energy into the background atmosphere and causing thermal variations. In this study, wave heating mechanisms are investigated using a linear wave model. The results indicate that heating is primarily determined by the sensible heat flux, which depends on the amplitude and phase difference between the perturbed vertical velocity and temperature. For high‐frequency acoustic waves, velocity and temperature perturbations are nearly in phase during compression and expansion, leading to upward transport of sensible heat and heating of the entire atmosphere. The total heating rate associated with acoustic waves can reach several hundred Kelvin per Martian day. For gravity waves, the vertical velocity and temperature are not strictly in quadrature in the lower atmosphere, resulting in upward transport of sensible heat. As gravity waves propagate to higher altitudes, molecular viscosity and thermal conduction shift the temperature phase beyond relative to the vertical velocity, causing energy deposition from the upper to lower regions. Consequently, gravity waves cool the upper atmosphere while heating lower regions.