Semiperiodic variations in CO2 abundance on Venus

Tests of the uniqueness of periodicity in the strength of the P branch (P2-P38) of the 8689 A CO2 band on Venus are described. It was found that the observed 4-day periodicity was not unique. The periodicity indicated an increasing asymmetry between the northern and southern hemispheres with approach to inferior conjunction or with increasing phase angle. When the slit positions of the various scans were referred to the planet or atmospheric equator rather than to the intensity equator, at inferior conjunction, the slit positions having a factor of two greater CO2 abundance or line strength were over the polar latitudes of the atmosphere. Similarly, the lower-abundance slit positions were over the equatorial latitudes of the atmosphere. It is thus concluded that the level of line formation must be lower over polar latitudes than over equatorial regions.