Tidal variations in the Martian lower atmosphere inferred from Mars Express Planetary Fourier Spectrometer temperature data

Abstract

We report on the characteristics of tidal variations in the Martian lower atmosphere (<45 km) using the Mars Express (MEX) Planetary Fourier Spectrometer (PFS) temperature data for about three Martian years (between the ends of MY26 and MY29). The PFS data, which widely cover local time, enable us to investigate diurnal variations in the atmospheric temperature at various altitudes. We focus on diurnal variations in the atmospheric temperature and on longitudinal temperature variability in a fixed local time frame. We find that the latitudinal and diurnal variations at 0.52 mbar (∼25 km) during the dust‐clear period (Ls = 30°–60°) are consistent with general characteristics presented by previous numerical simulations. The characteristics of the diurnal variations as a function of altitude in the tropics are also explained as results from the propagation of the migrating diurnal tide. The longitudinal temperature variability in the dayside (14.36–14.94 LT) equatorial regions (10°S–5°S) near the northern summer solstice (Ls= 76°–83°) in MY28 are investigated. The longitudinal temperature structure has two local maxima at 2.85 mbar (∼10 km) but is relatively uniform at 0.52 mbar. We find that the wave‐3 structure is apparent at 0.11 mbar (∼40 km) in the present case. This structure would be strongly dependent on activities of the atmospheric waves, e.g., the diurnal Kelvin wave 2 (DK2).