Martian Gravity Waves Observed by the Thermal Emission Imaging System (THEMIS) During Northern Summer

Abstract

Martian gravity waves (GW) greatly impact the atmospheric circulation and formation of clouds, but many GW observations of the lower atmosphere are confined to specific orientations and wavelengths, leaving many gaps in the continuum of waves. To overcome the issue, we analyze eight Mars years of data during the season of Ls = 120°–150° from Band 10 (14.9 µm) of the Thermal Emission Imaging System (THEMIS), sensitive to GWs at ∼25 km altitude. All horizontal orientations at wavelengths below ∼40 km are detectable, with the potential to detect north-south oriented GWs up to ∼1,000 km in length. Most THEMIS observations have brightness temperature variances compatible with GW disturbances. Intense GW activity concentrates poleward of 60°S, with normalized magnitudes up to 10−4 K2 K−2; activity decreases toward the equator and remains low throughout the northern hemisphere. The interannual intensity of GWs varies by latitude within three regimes of GW length: short (<20 km), medium (20–100 km), and long (>100 km). Gravity wave orientations that are detectable in all directions do not favor a single direction; that is, Martian GWs at 25 km altitude are isotropic. Finally, interannual variability seems to emerge from interactions with dust storms, orography, and planetary waves.