10:00 AM - 10:15 AM
[PPS04-10] Derivation of vertical profiles of sulfur dioxide (SO2) in the Venus cloud layer by the Akatsuki radio occultation measurements
Keywords:Venus, sulfur dioxide, SO2, radio occultation measurement, cloud
On Venus, clouds exist at the altitudes from 45 to 70 km, covering the entire planet. This thick cloud layer plays a key role in controlling the heat budget in Venus atmosphere. One of the missing information is the vertical distribution of the sulfur dioxide (SO2), which is the major chemical compound in forming the sulfuric acid clouds. The previous observations of SO2 vertical distribution in the cloud layer have been limited to in-situ measurements conducted by the VEGA probes and the radio occultation (RO) measurements of the Venus Express. The former showed only two vertical profiles of the SO2 mixing ratio from the surface to 60 km. The latter derived the mean SO2 mixing ratio at 51-54 km.
In the present study, we proposed the method to derive the SO2 vertical profiles in the cloud layer (50-55 km) using the data obtained by the RO measurements in the Japanese Venus climate orbiter mission, “Akatsuki”. Provided that sulfuric acid vapor cannot be supersaturated in the cloud layer, we attributed any attenuations of radio waves that exceed the saturation curve of sulfuric acid vapor to the attenuations by SO2. We examined the SO2 errors caused by the uncertainties in the absorption coefficients, the determination of the saturation pressure of sulfuric acid vapor, and other noise components included in the received intensity of radio waves. The estimation showed that the magnitude of the errors in the SO2 mixing ratio for a snapshot observation was about 80-100%. When all observations (28 profiles) were averaged, the magnitude of the errors was expected to decrease to about 20%.
The averaged profile showed the SO2 mixing ratio of about 300 ppm at 50 km and 80 ppm at 55 km, decreasing with altitude. Our results were consistent with the previous results of the VEGA probes and Venus Express RO measurements. Additionally, we found a local time dependence of SO2 mixing ratio with a decrease during the daytime in the cloud layer, similar with previous observations conducted above the cloud layer. Long-term variations were not found in the present analysis.
In the present study, we proposed the method to derive the SO2 vertical profiles in the cloud layer (50-55 km) using the data obtained by the RO measurements in the Japanese Venus climate orbiter mission, “Akatsuki”. Provided that sulfuric acid vapor cannot be supersaturated in the cloud layer, we attributed any attenuations of radio waves that exceed the saturation curve of sulfuric acid vapor to the attenuations by SO2. We examined the SO2 errors caused by the uncertainties in the absorption coefficients, the determination of the saturation pressure of sulfuric acid vapor, and other noise components included in the received intensity of radio waves. The estimation showed that the magnitude of the errors in the SO2 mixing ratio for a snapshot observation was about 80-100%. When all observations (28 profiles) were averaged, the magnitude of the errors was expected to decrease to about 20%.
The averaged profile showed the SO2 mixing ratio of about 300 ppm at 50 km and 80 ppm at 55 km, decreasing with altitude. Our results were consistent with the previous results of the VEGA probes and Venus Express RO measurements. Additionally, we found a local time dependence of SO2 mixing ratio with a decrease during the daytime in the cloud layer, similar with previous observations conducted above the cloud layer. Long-term variations were not found in the present analysis.