The upper atmosphere of Venus during morning conditions

The structure and composition of the Venus upper atmosphere between 130- and 650-km altitude were measured for a solar zenith angle of approximately 60 degrees by the neutral gas mass spectrometer on board the Pioneer Venus multiprobe bus. Below 180 km a wavelike structure is quite evident in the CO2 and He number density profiles. For altitudes above 100 km a one-dimensional model of the Venus upper atmosphere during morningside conditions (MS model) is presented. Number densities at 150-km altitude are as follows: CO2 = 4.9 x 10(9), N-2 = 1.1 x 10(9), CO = 2.8 x 10(9), and He = 4.8 x 10(6) cm(-3). The exospheric temperature is 275 K. The vertical compositional structure is best described by an eddy coefficient K = 1.4 x 10(13)n(a)(-1/2) cm(2)/s, where n(a) is the total number density in units per cubic centimeter. The homopause altitudes for N-2 and He are at 136 and 130 kin, respectively.