11:15 AM - 11:30 AM
[PPS04-13] Long-term temperature and thermal-tides variations in upper cloud layer of Venus observed by Akatsuki/LIR
★Invited Papers
Keywords:Venus, Akatsuki, LIR, Thermal tides
While the basic state of Venusian atmosphere (i.e. super-rotation) is stable, it has been recognized that there are lots of variations with various time scales from 4-5 day period to decadal scale in Venusian atmosphere from Venus Express and Akatsuki’s long-term observation. As for the long-term variations, Lee et al (2019) indicated significant variations in UV albedo (more than twice, 20 % to 40 %) and zonal wind speed (more than 30 m s-1) with decadal scale, and Lee et al. (2020) also suggested a 630-day variation in UV albedo. Since these variations have huge amplitudes and are global scale, they should be worth to be considered for understanding global-scale dynamic momentum/material transportation in Venusian atmosphere.
In this study, we focused on long-term temperature data for more than 8 years obtained by Longwave Infrared camera (LIR) onboard Akatsuki to investigate the possible long-term variations. Because long-term temperature data may contain both mean temperature variation and thermal tide variation, which has the largest amplitude in LIR data, we conducted a sliding window analysis by averaging LIR data for more than one Venusian year in terms of local time and latitude that can exclude the thermal-tide component by FFT analysis. From the result, there was a clear quasi-periodical variation in diurnal tide-amplitude in mid-high latitudes whose time scale was 600 – 800 days, while a similar time-scale variation was also confirmed in mean temperature in low-mid latitudes although the amplitude was faint (less than 1 K). Because of the time-scale similarity, the UV albedo variation with a time scale for 630 days might relate these variations.
In this study, we focused on long-term temperature data for more than 8 years obtained by Longwave Infrared camera (LIR) onboard Akatsuki to investigate the possible long-term variations. Because long-term temperature data may contain both mean temperature variation and thermal tide variation, which has the largest amplitude in LIR data, we conducted a sliding window analysis by averaging LIR data for more than one Venusian year in terms of local time and latitude that can exclude the thermal-tide component by FFT analysis. From the result, there was a clear quasi-periodical variation in diurnal tide-amplitude in mid-high latitudes whose time scale was 600 – 800 days, while a similar time-scale variation was also confirmed in mean temperature in low-mid latitudes although the amplitude was faint (less than 1 K). Because of the time-scale similarity, the UV albedo variation with a time scale for 630 days might relate these variations.