Recent improvements of general circulation model (AFES-Venus) and data assimilation system (ALEDAS-V) for the Venus Atmosphere

We have developed the Venusian general circulation model (GCM) named AFES-Venus (Atmospheric GCM for the Earth Simulator for Venus) [1, 2] and the data assimilation system based on the Local Ensemble Transform Kalman Filter (LETKF) named ALEDAS-V (AFES-LETKF data assimilation system for Venus) [3]. Here, we will introduce recent improvements of AFES-Venus and ALEDAS-V and newly obtained results.

So far, AFES-Venus reproduced the cold collar in the polar region [4], the planetary-scale streak structure observed by Akatsuki infrared (IR2) camera [5], a fully developed super-rotation [6], and spontaneous gravity waves radiated from the thermal tides [7]. The thermal tides [8] and the planetary-scale short periods (Kelvin and Rossby) waves [9, 10] consistent with observations were also reproduced by improving the profiles of static stability and solar heating. Dependency of the super-rotation on the magnitude of horizontal hyper diffusion was investigated with medium- and high-resolution simulations [11]. Recently we have implemented radiative and cloud microphysical processes into AFES-Venus (Fig.1). We have also investigated disturbances [12] and energy cycles [13] in the Venus atmosphere using Bred vectors.

ALEDAS-V improved the horizontal structures of thermal tides with the data assimilation of horizontal winds derived by cloud tracking of ultra-violet images (UVI) from Venus Express [14] and Akatsuki [15]. Although the observed horizontal winds are limited to low latitudes on the day side, the zonal-mean zonal winds and temperature were also modified globally [15]. The first analysis data in which horizontal winds obtained by Akatsuki UVI are assimilated will be released soon. The cold collar was also realistically reproduced in the analysis data [16]. We have also conducted several observing system simulation experiments (OSSEs) assuming Akatsuki Longwave Infrared Camera (LIR) observations [17]. Now we are trying to assimilate temperature obtained by Akatsuki LIR.

Fig.1: Zonal mean zonal wind [m s−1] (contours) and static stability [K km−1] (shading) for the original AFES-Venus (left: EXP-DYN) and that with a new radiative transfer process (EXP-RAD).

References: [1] Sugimoto+2014 JGR-Planets, 119, 1950–1968. [2] Sugimoto+2014 GRL, 41, 7461–7467. [3] Sugimoto+2017 Sci. Rep.. 7, 9321. [4] Ando+2016 Nature Comm., 7, 10398. [5] Kashimura+2019 Nature Comm., 10, 23. [6] Sugimoto+2019 GRL, 46, 1776–1784. [7] Sugimoto N+2021 Nature Comm., 12, 3682. [8] Suzuki+2022 JGR-Planets, 127, 7243. [9] Takagi+2022 JGR-Planets, 127, 7164. [10] Takagi+2023, JGR-Planets, 128, 7922. [11] Sugimoto+2023 Earth, Planets and Space, 75, 44. [12] Liang+2024 JGR-Planets, 129, 8067. [13] Liang+2025 GRL, 52, 112663. [14] Sugimoto+2019 GRL, 46, 4573–4580. [15] Fujisawa+2022 Sci. Rep., 12, 14577. [16] Ando+2023 JGR-Planets, 128, 7689. [17] Sugimoto+2022 Geoscience Lett., 9, 44.