16:00 〜 16:15
[PPS04-03] Retrieval of the Venusian cloud-top sulfur dioxide distribution from Akatsuki UV images
キーワード：金星、大気、二酸化硫黄、リトリーバル、放射輸送計算
The distribution of sulfuric acid clouds in the Venusian atmosphere is an essential factor that influences the solar energy absorbed by the planet. Understanding how sulfur dioxide, the precursor of sulfuric acid, is transported from the lower atmosphere to the cloud top, where the cloud particles are photochemically formed from sulfur dioxide, is essential for understanding the Venusian climate system controlled by the cloud layer.
UVI/Akatsuki has been taking images of the Venusian disk at multiple wavelengths from the elliptical equatorial orbit. Retrieving the sulfur dioxide distribution from these data sets and monitoring its temporal variation would help in understanding various dynamical processes at meso- to planetary-scales that induce the transport of sulfur dioxide. We primarily use images taken at the wavelengths of 283 nm, which is in a strong absorption band of sulfur dioxide. However, the 283 nm images reflect not only the amount of sulfur dioxide but also the effects of sulfuric acid aerosols, the unidentified UV absorber, making interpretation difficult. Therefore, in this study, we have developed a method to separate the effects of absorption by sulfur dioxide and the unidentified UV absorber by also using images taken simultaneously at 365 nm, which are sensitive mainly to the unidentified UV absorber and cloud particles, assuming the cloud structure fixed. We estimated the volume mixing ratios of sulfur dioxide at the cloud top from about 15,000 pairs of 283 nm and 365 nm images taken in 2016 to 2022.
We retrieved distributions of sulfur dioxide from all pairs of UV images. We focused only on the varieties on the local time and obtained the mean distribution of sulfur dioxide on the local time-latitude coordinates from the retrieved sulfur dioxide maps. The mean value of the volume mixing ratio of sulfur dioxide is from 80 to 200 ppb at the cloud top on the dayside, consistent with previous studies. We found that the local time variation of sulfur dioxide has a single peak in the afternoon, which is seemingly different from that of the SPICAV-UV/Venus Express nadir observation (Marcq et al., 2020) from 2006 to 2014, with two peaks in the morning and afternoon. The difference could be due to the conditions of the observation. On the other hand, our results are qualitatively consistent with the result of a Venus GCM, which includes photochemistry (Stolzenbach et al., 2023). The enhancement of sulfur dioxide in the afternoon is attributed to the vertical transport of sulfur dioxide induced by thermal tides based on the wave structures reproduced by the Venus GCM by Takagi et al. (2018).
UVI/Akatsuki has been taking images of the Venusian disk at multiple wavelengths from the elliptical equatorial orbit. Retrieving the sulfur dioxide distribution from these data sets and monitoring its temporal variation would help in understanding various dynamical processes at meso- to planetary-scales that induce the transport of sulfur dioxide. We primarily use images taken at the wavelengths of 283 nm, which is in a strong absorption band of sulfur dioxide. However, the 283 nm images reflect not only the amount of sulfur dioxide but also the effects of sulfuric acid aerosols, the unidentified UV absorber, making interpretation difficult. Therefore, in this study, we have developed a method to separate the effects of absorption by sulfur dioxide and the unidentified UV absorber by also using images taken simultaneously at 365 nm, which are sensitive mainly to the unidentified UV absorber and cloud particles, assuming the cloud structure fixed. We estimated the volume mixing ratios of sulfur dioxide at the cloud top from about 15,000 pairs of 283 nm and 365 nm images taken in 2016 to 2022.
We retrieved distributions of sulfur dioxide from all pairs of UV images. We focused only on the varieties on the local time and obtained the mean distribution of sulfur dioxide on the local time-latitude coordinates from the retrieved sulfur dioxide maps. The mean value of the volume mixing ratio of sulfur dioxide is from 80 to 200 ppb at the cloud top on the dayside, consistent with previous studies. We found that the local time variation of sulfur dioxide has a single peak in the afternoon, which is seemingly different from that of the SPICAV-UV/Venus Express nadir observation (Marcq et al., 2020) from 2006 to 2014, with two peaks in the morning and afternoon. The difference could be due to the conditions of the observation. On the other hand, our results are qualitatively consistent with the result of a Venus GCM, which includes photochemistry (Stolzenbach et al., 2023). The enhancement of sulfur dioxide in the afternoon is attributed to the vertical transport of sulfur dioxide induced by thermal tides based on the wave structures reproduced by the Venus GCM by Takagi et al. (2018).