Latitudinal Variations of Sulfur Compounds in the Venus Atmosphere Based on the Correlation Between VLA Observations and Radio Occultation Results

M.A. Kolodner, S.H. Suleiman (Georgia Inst. of Tech.), B.J. Butler (NRAO), P.G. Steffes (Georgia Inst. of Tech.)

To identify the presence of potential spatial variations in the distributions of sulfur compounds (H tex2html_wrap_inline11 SO tex2html_wrap_inline13 (g) and SO tex2html_wrap_inline11 ) across the disk of Venus, a dual-frequency radio observation was performed with the NRAO/VLA at 14.94 GHz (2 cm) and 22.46 GHz (1.3 cm) on April 5, 1996. The resulting brightness maps have been compared with a radiative transfer model, which shows both equatorial and polar limb darkening beyond that due to a simple CO tex2html_wrap_inline11 /N tex2html_wrap_inline11 atmosphere. Our radiative tranfer model shows that the measured darkening results directly from the microwave opacity of SO tex2html_wrap_inline11 and H tex2html_wrap_inline11 SO tex2html_wrap_inline13 (g).

Specifically, in the equatorial regions, it has been found that the limb darkening corresponds to that expected from an H tex2html_wrap_inline11 SO tex2html_wrap_inline13 (g) abundance profile such as that derived from the equatorial Mariner 10 radio occultation experiment, and from a nominal subcloud SO tex2html_wrap_inline11 abundance of 75 ppm. In the polar regions, the increased limb darkening is consistent with the more broad vertical distribution of gaseous H tex2html_wrap_inline11 SO tex2html_wrap_inline13 such as that derived from Magellan radio occultation experiments in high latitude regions. The magnitude of the polar limb darkening also requires a corresponding elevation in the sub-cloud SO tex2html_wrap_inline11 abundance to 150 ppm or more.

This work was supported by the NASA Planetary Atmospheres Program under grants NAG5-4190 and NAGW-533.