Middle atmosphere of Venus and its clouds: Latitude and solar time variations

The structure of the middle atmosphere of Venus and its upper clouds, derived from infrared spectrometry (from 250 to 1650 cm(exp -1)) on Venera 15 are discussed. Poleward increasing of temperature, monotonous on the average, at altitudes h greater than 70 km changes to poleward decreasing at h less than 60 km. Temperature inversion at 85-95 km at low latitudes was observed as a half-day wave with two minima near 9:00 a.m. and 9:00 p.m, with a more pronounced morning feature. At high latitudes the inversion with temperature minimum near 64 km exists. There are several minima depending on solar time, but the most pronounced is one on the dayside, where the depth of inversion may reach more than 40 K (near 10:00 a.m.; we have no observations closer to noon). Another minimum is situated symmetrically on the nightside. Usually in the polar region the temperature inversion is situated deeper in the atmosphere (near 62 km). A jet at latitudes 50-55 deg N divides Venus into two drastically different latitude zones: pretty homogeneous at 56-95 km zone less than 50 deg N with diffuse clouds and daily temperature variations near cloud tops about several degrees, and zones greater than 55 deg N (where such dynamic structures as cold collar and hot dipole were observed) with dense low clouds (with the exceptions of the regions at 55-80 deg N outside the cold collar). We separate Venus into four latitudinal zones with approximate latitude boundaries, where the different IR-features were observed.