11:15 〜 11:30
[PPS04-13] LIRの観測から得られた金星雲上層高度での平均温度と熱潮汐波の長期変動
★招待講演
キーワード：金星、あかつき、LIR、熱潮汐波
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.