17:15 〜 19:15
[PPS05-P10] Synoptic-scale vortices in the cloud layer on Venus studied by AFES-Venus GCM
★Invited Papers
キーワード：金星、大気力学、GCM
A synoptic-scale vortex was observed as a spiral cloud feature in mid-latitudes of the nightside northern hemisphere of the Venusian atmosphere by the 2-µm camera (IR2) onboard the Venus Climate Orbiter, Akatsuki. Using a general circulation model (GCM) named AFES-Venus, we reproduced vortices consistent with the observation. The result shows that the cyclonic vortex with a longitudinal scale of ~5000 km develops in mid-latitudes at ~60 km altitude within the middle cloud layer, accompanied by upward (downward) winds on the downstream (upstream) side of the zonal-mean zonal wind. The spiral cloud feature could be formed by the meridional and vertical winds associated with the vortex. The linear stability analysis suggests that the synoptic-scale vortices, with an e-folding time of 4.3 days, could be generated by barotropic instability due to the meridional shear of the mid-latitude jet, which is consistent with the present GCM result. The vortices and mid-latitude jets develop and decay alternately in both hemispheres because the growing and decaying vortices in the southern and northern (northern and southern) hemispheres induce the northward (southward) angular momentum transport across the equator and enhance the mid-latitude jet in the northern (southern) hemisphere, which generates a new vortex by barotropic instability in the northern (southern) hemisphere.
The GCM result indicates that the negative temperature deviation with a zonal wavenumber-1 structure, in which the synoptic-scale vortex develops, could be associated with the mid-latitude Rossby wave of the 5.8-day wave (Takagi et al., 2022, 2023). However, it remains unclear how the planetary-scale wave is related to the synoptic-scale cyclonic vortex. To better understand the synoptic-scale vortex, along with theoretical and numerical investigations, further observations in the cloud layer are necessary. Those should include approximately one-month long observations to capture the vortex’s growth and decay phases, providing insights into its lifetime, the variability of mid-latitude jets, and the aerosol properties around the vortex.
The GCM result indicates that the negative temperature deviation with a zonal wavenumber-1 structure, in which the synoptic-scale vortex develops, could be associated with the mid-latitude Rossby wave of the 5.8-day wave (Takagi et al., 2022, 2023). However, it remains unclear how the planetary-scale wave is related to the synoptic-scale cyclonic vortex. To better understand the synoptic-scale vortex, along with theoretical and numerical investigations, further observations in the cloud layer are necessary. Those should include approximately one-month long observations to capture the vortex’s growth and decay phases, providing insights into its lifetime, the variability of mid-latitude jets, and the aerosol properties around the vortex.