What causes seasonal variation of migrating diurnal tide observed by the Mars Climate Sounder?

We use two Martian years' temperature data from Mars Climate Sounder (MCS) cross‐track observations to extract the migrating diurnal tide (MDT) and investigate its spatial and seasonal variation from the perspective of classical tidal theory by Hough mode decomposition. The results suggest that during the equinox the vertically propagating (1, 1) mode is dominant at all altitudes from the near surface to ~0.1 Pa with the magnitude growing with height. The trapped modes (1, −2), (1, −4), and (1, −6) are restricted to the lower altitudes with a similar vertical structure. Both the (1, 1) and (1, −2) modes have clearly semiannual variations. The comparison between Hough modes components of MDT and dust and water ice heating rate indicates that both the dust and water ice contribute to tidal excitation. However, both the annual and semiannual variations of dust heating rate are out of phase with those in MDT, while semiannual variation of the water ice heating rate is in phase, indicating that the water ice may contribute to the semiannual variation of MDT. Using model wind results, we also find that the zonal mean zonal wind and its latitudinal shear at the low latitudes modify the vertical propagation condition of the MDT (1, 1) mode and further affect its seasonal variation. The semiannual variations of equatorial MDT and its corresponding mechanism on Mars are comparable to those on Earth, suggesting that the two planets may have more common characteristics.