15:45 〜 16:05
[PPS05-02] Development of mesoscale structures at the Venusian cloud top
★Invited Papers
キーワード：金星、雲、メソスケール、あかつき
Venusian clouds are composed of sulfuric acid and globally cover the planet. UV images of Venus obtained from the previous Venusian spacecraft visualized mesoscale structures at the cloud top. Patchy structures are predominantly observed in the low latitude, while streaky features dominate in the mid- and high latitudes. The dynamics responsible for these structures might play crucial roles in transporting momentum, energy, and chemical species; however, their formation mechanisms remain unresolved due to insufficient information on temporal development.
Akatsuki's Ultraviolet Imager (UVI) and 2-micron Camera (IR2) continuously obtained Venusian cloud images at 2-hour intervals, allowing tracking of the temporal evolution of mesoscale structures. The UVI images at a wavelength of 365 nm reflect the spatial distribution of unknown UV absorbers, while the IR2 images at a wavelength of 2.02 micrometers map the cloud top altitude. We investigated the temporal relationship of the mesoscale morphology between these wavelengths to reveal the processes forming the patchy structures in the low latitude. A correlation coefficient analysis showed that the formation of mesoscale structures observed at 365 nm precede that at 2.02 micrometers. This finding is consistent with the hypothesis proposed by Toigo et al. (1994), who suggested that the inhomogeneous distribution of the UV absorbers causes an inhomogeneous solar heating distribution and then drives horizontal convection to change the cloud top altitude.
To understand the formation of streaky structures in the mid-latitude, ellipses were fitted to the dark spots and the temporal developments of the shapes and orientations of the ellipses were tracked. It was revealed that patchy structures created near the equator transform into streaky features as they are transported by winds. The winds responsible for the extension of the ellipse are interpreted as the combination of the superrotation, whose angular velocity is larger at higher latitudes, and the poleward flow associated with the Hadley circulation and planetary-scale waves.
Akatsuki's Ultraviolet Imager (UVI) and 2-micron Camera (IR2) continuously obtained Venusian cloud images at 2-hour intervals, allowing tracking of the temporal evolution of mesoscale structures. The UVI images at a wavelength of 365 nm reflect the spatial distribution of unknown UV absorbers, while the IR2 images at a wavelength of 2.02 micrometers map the cloud top altitude. We investigated the temporal relationship of the mesoscale morphology between these wavelengths to reveal the processes forming the patchy structures in the low latitude. A correlation coefficient analysis showed that the formation of mesoscale structures observed at 365 nm precede that at 2.02 micrometers. This finding is consistent with the hypothesis proposed by Toigo et al. (1994), who suggested that the inhomogeneous distribution of the UV absorbers causes an inhomogeneous solar heating distribution and then drives horizontal convection to change the cloud top altitude.
To understand the formation of streaky structures in the mid-latitude, ellipses were fitted to the dark spots and the temporal developments of the shapes and orientations of the ellipses were tracked. It was revealed that patchy structures created near the equator transform into streaky features as they are transported by winds. The winds responsible for the extension of the ellipse are interpreted as the combination of the superrotation, whose angular velocity is larger at higher latitudes, and the poleward flow associated with the Hadley circulation and planetary-scale waves.