MGS radio occultation measurements of temperature versus pressure and longitude. Pressure is given in pascals, with 100 Pa = 1 mb. The contour interval is 5 K. The figure was constructed from 2 days of measurements that include 24 profiles spread evenly in longitude near 2 deg N latitude. The season was summer in the northern hemisphere (Ls = 147 deg) and the local time of all measurements was 0408 (predawn). The dashed line shows the pressure at the surface. A strong nighttime radiative temperature inversion appears in the lowest few kilometers above the ground, most notably at 150-270 deg E.
The most striking aspect of the temperature field is the strong inversion that appears at higher altitudes above Tharsis (210-270 deg E). At 250 deg E, temperature increases from less than 165 K at 100 Pa to more than 190 K at 50 Pa. A similar though weaker inversion also appears near 80 deg E. Simulations with the GFDL Mars general circulation model (GCM) suggest that thermal tides are responsible for producing this inversion (John Wilson, personal communication, 2000). Topographic modulation of the sun-synchronous diurnal tide excites non-sun-synchronous tidal modes, resulting in an enhanced response above Tharsis. (Data courtesy of David Hinson and the MGS Radio Science Team.)