Measurements of thermal structure and thermal contrasts in the atmosphere of Venus and related dynamical observations: Results From the four Pioneer Venus Probes

Abstract

Thermal structure of the atmosphere of Venus, and differences in structure with latitude (up to 60°) and clock hour (from midnight to 8 A.M.) have been measured in situ from an altitude of 126 km to the surface by instruments on the four Pioneer Venus entry probes. Several indications from the preliminary analyses are confirmed by the current analysis: Thermal contrasts below 45 km are a few K, with the mid‐latitudes warmer than both equatorial and the high latitudes. Sizeable temperature and pressure differences with latitude develop in the clouds (25 K and 20 mbar at the 200 mbar level). At 30° latitude, diurnal differences were small throughout the lower atmosphere from midnight to 7 A.M. A major stable layer 25 km deep exists just below the clouds. Waves of global extent were observed within this layer. A locally stable layer is indicated in the deep atmosphere, between 10 and 20 km, at latitudes up to 30°. In the middle cloud and immediately below the deep stable layer, the atmosphere is approximately neutrally stable, and there is evidence for convective overturning below the stable layer. Just above the clouds, the lapse rate becomes stable, and a ‘stratosphere’ begins which extends upwards to 110 km, becoming isothermal above 85 km. The stratospheric temperature profiles were essentially the same in three widely separated soundings. Upward of 110 km, there is evidence of large amplitude temperature oscillations with altitude, believed to signify the presence of large amplitude waves, perhaps thermal tides. By comparing data of several experiments, it is found that the large diurnal variations in the upper atmosphere begin at an altitude ∼115 km. Agreement of structure data from other Pioneer Venus experiments with the present results is generally excellent. Our measurements of the winds derived from Doppler data agree well with DLBI results and indicate a retrograde zonal velocity of 113 m/s at 63 km altitude and 30° latitude. The zonal winds predicted at cloud levels from pressure differences between 60° latitude and the mid‐latitude probes by assumption of cyclostrophic balance are in first order agreement with the observed winds. At latitudes below ∼30°, however, cyclostrophic balance of the zonal winds is not the dominant process. At altitudes from 60 to 105 km, the measured pressure differences and the assumption of cyclostrophic balance indicate zonal wind velocities peaking at 155 m/s at 68 km, remaining above 120 m/s up to 95 km, then decreasing rapidly.

Multiple Equilibrium States Appearing in a Venus-Like Atmospheric General Circulation Model

“…The real heating rate is estimated as about 3.0 × 10 −3 K day −1 at 0−10 km altitude, and the heating rate provided in this study is, nonetheless, too high for the real Venus near the ground (Tomasko et al 1980). Figure 2 shows the reference temperature T 0 (z), which is based on an observed value (Seiff et al 1980). The model temperature is adjusted to this reference temperature.…”

Venus Atmospheric Thermal Structure and Radiative Balance

“…Our current knowledge about this region is therefore based on a very small number of profiles from the Venera (Marov et al 1973;Avduevsky et al 1976Avduevsky et al , 1979 and Pioneer Venus probes (Seiff et al 1980) to 12 km altitude and only one profile below 12 km (VeGa 2 lander). A detailed description of the deep Venus atmosphere can be found in Seiff (1983).…”

“…Subsequently the VeGa 2 lander returned lower atmospheric temperature data (Linkin et al 1986a) which reveal a slightly different lapse rate. Additionally, temperature data from the SNFR instrument were compared with the Atmospheric Structure experiment on Pioneer Venus (Seiff et al 1980) which provide additional information about the errors and confirmation of the general structure above 12 km altitude.…”

“…Due to lack of actual measurements below about 12 km from the Pioneer Venus probes, temperature values were extrapolated downwards to the mean surface using the adiabatic lapse rate (Seiff et al 1980). Subsequently the VeGa 2 lander returned lower atmospheric temperature data (Linkin et al 1986a) which reveal a slightly different lapse rate.…”

“…Longitudinal differences from surface to the cloud tops (∼ 70 km) are < 5 K in low latitudes (Seiff et al 1980;Kliore 1985) and can be ∼ 20 K in higher latitudes (> 60°). In the deep atmosphere, at 10 km altitude, winds are as fast as 5 m s −1 (Counselman et al 1980), suggesting at least some meridional temperature gradient must exist if the flow is cyclostrophic.…”