10:45 AM - 11:00 AM
[PPS04-11] Role of a Kelvin wave in the formation of Venusian clouds
★Invited Papers
Keywords:Venus, cloud, atmospheric dynamics
Venus is surrounded by sulfuric acid clouds that are essential to the planet's climate system. The upper part of the cloud is thought to be of photochemical origin, while the lower part of the cloud is highly variable and will be more affected by atmospheric dynamics causing condensation and evaporation of sulfuric acid. The specific dynamical processes responsible for the variability are poorly understood.
Observations using near-infrared window wavelengths have revealed large opacity variations, which mostly occur in the lower part of the cloud layer. A significant feature is the planetary-scale dark cloud propagating with a period of 4.9-5.5 days, discovered through ground-based observations (Crisp et al. 1991). The IR2 camera aboard the Venus orbiter Akatsuki observed this phenomenon in more detail and found that the planetary-scale cloud discontinuity that spans in the north-south direction characterizes the propagating structure (Satoh et al. 2017; Peralta et al. 2020). The relatively large amplitude near the equator and the zonal propagation faster than the background atmosphere indicate that the cloud opacity variation is mainly induced by a Kelvin wave.
A Venus GCM reproduced a 5.5-day periodicity in the thickness of the lower cloud driven by a Kelvin wave with a zonal wavenumber of unity (Ando et al. 2021). However, the observed sharp discontinuity was not reproduced in previous models. The present study proposes mechanisms for the cloud discontinuity from the viewpoint of atmospheric dynamics and cloud microphysics. A simplified dynamical model and a microphysical model are used to reproduce the phenomenon. This study aims to understand the role of the Kelvin wave in the formation of the lower cloud and the conditions necessary for the appearance of the observed sharp discontinuity.
Observations using near-infrared window wavelengths have revealed large opacity variations, which mostly occur in the lower part of the cloud layer. A significant feature is the planetary-scale dark cloud propagating with a period of 4.9-5.5 days, discovered through ground-based observations (Crisp et al. 1991). The IR2 camera aboard the Venus orbiter Akatsuki observed this phenomenon in more detail and found that the planetary-scale cloud discontinuity that spans in the north-south direction characterizes the propagating structure (Satoh et al. 2017; Peralta et al. 2020). The relatively large amplitude near the equator and the zonal propagation faster than the background atmosphere indicate that the cloud opacity variation is mainly induced by a Kelvin wave.
A Venus GCM reproduced a 5.5-day periodicity in the thickness of the lower cloud driven by a Kelvin wave with a zonal wavenumber of unity (Ando et al. 2021). However, the observed sharp discontinuity was not reproduced in previous models. The present study proposes mechanisms for the cloud discontinuity from the viewpoint of atmospheric dynamics and cloud microphysics. A simplified dynamical model and a microphysical model are used to reproduce the phenomenon. This study aims to understand the role of the Kelvin wave in the formation of the lower cloud and the conditions necessary for the appearance of the observed sharp discontinuity.