Ground-Based Observations of Mars and Venus Water Vapor during 1972 and 1973

Abstract

The Venus water vapor line at 8197.71 Å has been monitored at several positions on the disk of Venus and at phase angles between 22° and 91°. Variations in the abundance have been found with both position and time. The total two-way transmission has varied from less than 5 to 77 μ of water vapor. Comparisons will be made between the water vapor abundances, presence of UV features, and the CO2 abundances determined from near simultaneous observations of CO2 bands at the same positions on the disk of Venus.The amount of Martian atmospheric water vapor has been monitored during the past two years at McDonald Observatory using the échelle coudé scanner of the 272 cm reflector. Two periods of the Martian year have been monitored. The first period was during and after the great 1971 dust storm (L8 = 280° to 20° or summer in the southern hemisphere). The results obtained will be compared to the Mariner 9 IRIS and Mars 3 observations made during the same period.During the second period (L8 = 124° to 266°) observations were made to follow the seasonal latitudinal and diurnal changes in the water vapor abundance in the Martian atmosphere. The water vapor abundance declines from a maximum of 20–35 μm at L8 = 125° to the 5–15 μm level at L8 = 180°. Then it remained relatively constant until L8 = 250° when the increase to 20–25 μm occurred in the southern latitudes. Studies of the latitudinal and diurnal water vapor distributions indicate the location of maximum and minimum abundances for this season are positively correlated with surface temperature variations.