5:15 PM - 6:30 PM
[PPS02-P06] Data assimilation of horizontal wind obtained from Akatsuki UVI observations focusing on thermal tides and attempts to produce Venus first analysis
Keywords:Akatsuki, Venus atmosphere, Data assimilation
Observations of the Venus Orbiter “Akatsuki” provide us with horizontal distributions of the horizontal wind derived from cloud tracking of the UVI camera and of temperature observed by the LIR camera. However, these observations are very limited with respect to the altitude, local time (day or night side), and frequency. It is difficult to elucidate the general circulation including various temporal and spatial scales only from observations. In this study, we aim to produce a Venus objective analysis that has high temporal and spatial resolutions by assimilating the Akatsuki observations into a general circulation model.
At the top of the cloud layer of Venus, there are planetary-scale atmospheric waves that are excited by solar heating and move with the sun, called the thermal tides. In the previous studies, it is pointed out that phases of thermal tides in our atmospheric general circulation model “AFES-Venus” 1 are different from those of Akatsuki observations. Sugimoto et al. (2019) 2 assimilated horizontal wind data of the Venus Express into AFES-Venus by the Venus atmospheric data assimilation system “ALEDAS-V” 3 based on the Local Ensemble Transform Kalman Filter (LETKF) and confirmed that phases of thermal tides are improved. In this presentation, we assimilate the horizontal wind obtained from the UVI (365 nm) of Akatsuki using cloud tracking (Ikegawa and Horinouchi, 20164) to the altitude of 70 km of ALEDAS-V for the period from September to December 2018, and show the results of an attempt to improve phases of the thermal tides as in Sugimoto et al. (2019).
The figure shows the latitude-longitude cross sections calculated by the composite means over November 2018 at the sub-solar point (fixed at the center of each panel). Each figure is a weighted mean between altitudes of 53 km and 81 km using the LIR weighting function based on Taguchi et al. (2007) 5. Figure (a,c,e) are the results without data assimilation (free run forecast; “frf”), and figure (b,d,f) are the results of horizontal wind assimilation.
For zonal wind, the assimilated result (b) shows a shift of the structure of the zonal wave number 2 near the equator by about 30 degrees in the direction opposite to the rotation compared to frf (a), and the phase of the thermal tide successfully improved. For temperature, the assimilated result (f) shows a shift in the structure of the zonal wavenumber 2 near the equator compared to frf (e), and the assimilation of the horizontal wind improved the phase of temperature as well as wind speed.
For the future work, we plan to release these assimilation results as the objective analysis data of Venus for the first time in the world.
[1] Sugimoto, N., M. Takagi, and Y. Matsuda (2014a), J. Geophys. Res. Planets, 119, 1950–1968.
[2] Sugimoto, N., T. Kouyama, and M. Takagi (2019a), Geophys. Res. Lett., 46, 4573–4580.
[3] Sugimoto, N., A. Yamazaki, T. Kouyama, H. Kashimura, T. Enomoto, and M. Takagi (2017), Scientific Reports, 7(1), 9321.
[4] Ikegawa, S. and T. Horinouchi (2016), Icarus, 271:98–119.
[5] Taguchi, M., T. Fukuhara, T. Imamura, M. Nakamura, N. Iwagami, M. Ueno, M. Suzuki, G. L. Hashimoto, and K. Mitsuyama, (2007), Adv. Space Res., 40, 861–868.
At the top of the cloud layer of Venus, there are planetary-scale atmospheric waves that are excited by solar heating and move with the sun, called the thermal tides. In the previous studies, it is pointed out that phases of thermal tides in our atmospheric general circulation model “AFES-Venus” 1 are different from those of Akatsuki observations. Sugimoto et al. (2019) 2 assimilated horizontal wind data of the Venus Express into AFES-Venus by the Venus atmospheric data assimilation system “ALEDAS-V” 3 based on the Local Ensemble Transform Kalman Filter (LETKF) and confirmed that phases of thermal tides are improved. In this presentation, we assimilate the horizontal wind obtained from the UVI (365 nm) of Akatsuki using cloud tracking (Ikegawa and Horinouchi, 20164) to the altitude of 70 km of ALEDAS-V for the period from September to December 2018, and show the results of an attempt to improve phases of the thermal tides as in Sugimoto et al. (2019).
The figure shows the latitude-longitude cross sections calculated by the composite means over November 2018 at the sub-solar point (fixed at the center of each panel). Each figure is a weighted mean between altitudes of 53 km and 81 km using the LIR weighting function based on Taguchi et al. (2007) 5. Figure (a,c,e) are the results without data assimilation (free run forecast; “frf”), and figure (b,d,f) are the results of horizontal wind assimilation.
For zonal wind, the assimilated result (b) shows a shift of the structure of the zonal wave number 2 near the equator by about 30 degrees in the direction opposite to the rotation compared to frf (a), and the phase of the thermal tide successfully improved. For temperature, the assimilated result (f) shows a shift in the structure of the zonal wavenumber 2 near the equator compared to frf (e), and the assimilation of the horizontal wind improved the phase of temperature as well as wind speed.
For the future work, we plan to release these assimilation results as the objective analysis data of Venus for the first time in the world.
[1] Sugimoto, N., M. Takagi, and Y. Matsuda (2014a), J. Geophys. Res. Planets, 119, 1950–1968.
[2] Sugimoto, N., T. Kouyama, and M. Takagi (2019a), Geophys. Res. Lett., 46, 4573–4580.
[3] Sugimoto, N., A. Yamazaki, T. Kouyama, H. Kashimura, T. Enomoto, and M. Takagi (2017), Scientific Reports, 7(1), 9321.
[4] Ikegawa, S. and T. Horinouchi (2016), Icarus, 271:98–119.
[5] Taguchi, M., T. Fukuhara, T. Imamura, M. Nakamura, N. Iwagami, M. Ueno, M. Suzuki, G. L. Hashimoto, and K. Mitsuyama, (2007), Adv. Space Res., 40, 861–868.