[A-AS06] Advances in Tropical Cyclone Research: Past, Present, and Future

[AAS06-P04] The analysis of the asymmetric inner-core structure in a typhoon using the experiments of a differentially-heated and β-effect rotating fluid annulus

*Misaki Hishinuma¹, Fudeyasu Hironori¹, Satoki Tsujino², Kosuke Ito³, Naohito Otobe⁴, Matsuoka Daisuke⁵ (1.Yokohama National University, 2.Meteorological Research Institute, 3.Ryukyu National University, 4.Fukuoka National University, 5.Japan Agency For Marine-Earth And Technology)

Keywords:Typhoon, Rotating fluid annulus, β-effect

The purpose of this study is to reveal a typhoon asymmetric inner-core structures, especially the polygonal eye-wall clouds. The polygonal eye-wall clouds of a typhoon, which were frequently observed by the satellite observations, were studied by several researchers. They indicated that the asymmetric inner-core structure of a typhoon formed due to the vortex Rossby wave, using the numerical simulations such as Himawari-8. To analysis the real fluid phenomena, this study conducted the experiments of a differential-heated orographic-β-effect rotating-fluid annulus. Rotating experiments were originally conducted to study the general circulation of the Earth's atmosphere. By reversing the temperature conditions of the original rotating experiment, the horizontal temperature gradient in the inner core region of a typhoon can be reproduced. Since the maximum vorticities occur at the eye wall region and the vorticity decreases inside and outside the wall cloud, an orographic-β-effect was added in our rotating-fluid annulus. Three types of experiments were conducted: a no-wall-cloud experiment with no vorticity gradient, an inner-wall-cloud experiment with vorticity inside and outside the wall cloud reproduced by water depth, and an outer-wall-cloud experiment. In each experiment, 145 experiments were conducted with a water depth of 4 cm or 6 cm and a rotation speed of 1 to 12 rpm (at 1 rpm intervals) under condition (1) a temperature difference of 20 °C and condition (2) no temperature difference.
As results of rotating experiments, we observed the waves generated under the conditions of experimental time, vorticity gradient, and rotation speed, and summarized the characteristics of each. In the experiment without wall cloud, the flow in the basic field without vorticity gradient could be observed. Clockwise flow was observed in condition (1), and counterclockwise flow was observed in condition (2). Experiments inside the wall cloud allowed us to observe the behavior of vortex Rossby waves and tilted pressure instability waves inside the wall cloud. there was a difference in the waves generated between the 10-minute and 20-minute experiments. even if no waves were generated in 10 minutes, waves were generated after 20 minutes. In addition, the propagation direction of the waves was counterclockwise. By conducting the experiment outside the wall cloud, we observed the behavior of vortex Rossby waves and tilted pressure instability waves outside the wall cloud. there was a difference in the waves generated between the 10-minute and 20-minute experiments. Even the waves were generated in the 10-minute experiment, waves were generated after 20 minutes. In addition, the direction of wave propagation was clockwise.