17:15 〜 19:15
[PPS05-P04] Distributions and Variations of Sulfur Dioxide at the Venusian Cloud Top
The clouds on Venus, composed of sulfuric acid droplets, are a crucial factor affecting the solar energy absorbed by Venus through its albedo. The series of processes by which sulfur dioxide, a precursor of the clouds, is transported from the cloud formation region to the cloud top altitude and then converted into sulfuric acid through photochemical reactions needs to be better understood. Additionally, the unidentified UV absorber, which absorbs the near-UV to visible rays where solar energy is most intense, affects the solar energy incident on Venus. Therefore, their distribution and variation are essential for understanding the climate system.
In our previous work, we developed the method to retrieve the sulfur dioxide and the imaginary part of the refractive index of the cloud particles, the proxy of the unidentified absorber, using approximately 15,000 two-wavelength (283 nm and 365 nm) UV images taken by the UltraViolet Imager onboard Akatsuki from 2016 to 2022. The daytime sulfur dioxide mixing ratio was found to range from 80 to 200 ppb—consistent with solar occultation measurements by Venus Express/SOIR (Belyaev et al., 2012)—and showed a latitudinal distribution that we interpret as driven by Hadley circulation, along with a local time distribution showing an afternoon maximum suggestive of the distribution by thermal tides.
Our current focus shifts to short-term variations of sulfur dioxide at the cloud top to examine temporal changes at approximately two-hour intervals. Drivers of these short-term variations likely include upwelling from lower atmospheric layers, photochemical consumption influenced by solar radiation, and large-scale dynamical waves such as Kelvin waves. By investigating these phenomena through our high time-resolution dataset, we aim to understand photochemical and dynamical processes occurring on timescales previously inaccessible, thereby advancing our understanding of sulfur dioxide variability and the broader climate system of Venus. In this presentation, we will focus on some of the variations that appeared in this new analysis.
In our previous work, we developed the method to retrieve the sulfur dioxide and the imaginary part of the refractive index of the cloud particles, the proxy of the unidentified absorber, using approximately 15,000 two-wavelength (283 nm and 365 nm) UV images taken by the UltraViolet Imager onboard Akatsuki from 2016 to 2022. The daytime sulfur dioxide mixing ratio was found to range from 80 to 200 ppb—consistent with solar occultation measurements by Venus Express/SOIR (Belyaev et al., 2012)—and showed a latitudinal distribution that we interpret as driven by Hadley circulation, along with a local time distribution showing an afternoon maximum suggestive of the distribution by thermal tides.
Our current focus shifts to short-term variations of sulfur dioxide at the cloud top to examine temporal changes at approximately two-hour intervals. Drivers of these short-term variations likely include upwelling from lower atmospheric layers, photochemical consumption influenced by solar radiation, and large-scale dynamical waves such as Kelvin waves. By investigating these phenomena through our high time-resolution dataset, we aim to understand photochemical and dynamical processes occurring on timescales previously inaccessible, thereby advancing our understanding of sulfur dioxide variability and the broader climate system of Venus. In this presentation, we will focus on some of the variations that appeared in this new analysis.