SO2 in the Middle Atmosphere of Venus: IR Measurements from Venera-15 and Comparison to UV Data
✍ Scribed by L.V. Zasova; V.I. Moroz; L.W. Esposito; C.Y. Na
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 788 KB
- Volume
- 105
- Category
- Article
- ISSN
- 0019-1035
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✦ Synopsis
We present and compare two sets of Venus (\mathrm{SO}{2}) measurements: IR spectra from the USSR Venera 15 orbiter and UV spectra from the US Pioneer Venus orbiter and sounding rockets. We choose the (40-\mathrm{mb}) pressure level for this comparison. At low and mid latitudes, both data sets give a mixing ratio (\left(f{\mathrm{sO}{2}}\right)) of tens of parts per billion and (\mathrm{SO}{2}) scale height ( (\mathrm{H}{\mathrm{SO}{2}}) ) of (1.5-2.5 \mathrm{~km}), which are in good agreement with photochemically predicted values. This confirms that photochemical processes dominate in this latitude range. Both data sets show the (\mathrm{SO}{2}) abundance increasing to several hundred parts per billion at high latitudes. The derived scale heights, however, are discrepant for high latitudes: IR data show great variability associated with dynamic features such as the cold collar, high diffuse clouds, the hot dipole and the polar cap; UV data show a decrease to (\boldsymbol{H}{\mathrm{SO}{2}}=1 \mathrm{~km}). From the IR data, we derive (H{\mathrm{SO}{2}}=3-5 \mathrm{~km}) outside the cold collar, and (f{\mathrm{SO}{2}}=100-200) ppb in the hot dipole (increasing of (f{\mathrm{SO}{2}}=1000 \mathrm{ppb}) in regions with high diffuse clouds). For the cold collar, Ithe IR data yield (f{\mathrm{SO}{2}}=1-10 \mathrm{ppb}) and (H{\mathrm{SO}{2}} \approx 1 \mathrm{~km}). To explain the differences between the IR and UV results, we conclude that the (\mathrm{SO}{2}) scale height may decrease above (69 \mathrm{~km}) altitude ( (P=40 \mathrm{mb}) ): the scale height differences are explained by the different viewing angles and the different opacity at UV and IR wavelengths. It is possible that temporal variations also contribute. 1993 Academic Press, Inc.