The structure of the venusian atmosphere at high latitudes

Abstract

The vertical and horizontal structure of the middle atmosphere of Venus (from 55 to 95 km altitude) at high latitudes (> 55° N) derived from Venera-15 data is discussed. Dynamical processes generate very complicated structures here, which have been observed in the thermal infrared spectral region. A cold collar was observed as a thermal feature at the altitudes 60–70 km, with the temperature difference dT as large as 40K at the 100 mb level (near 65 km). There were found several temperature minima at the latitudes of cold collar (60–80° N). The minimal temperature and the lowest position of the clouds was observed at the day morning side. Cold collar is pretty stable solar related feature: the temperature minima were found at the same local solar times by Pioneer-Venus and Venera-15, at times about 5 years apart. A hot “dipole” was observed as a “hole” in the upper cloud level at the altitudes 56–64 km.