A119-0011
Inner-core Tangential Winds in an Inner Eyewall Dissipation of Typhoon Trami (2018): A Quantitative Estimation based on the Himawari-8 Satellite

Friday, 11 December 2020
Poster
Satoki Tsujino1, Takeshi Horinouchi1, Taiga Tsukada1, Hung-Chi Kuo2, Hiroyuki Yamada3 and Kazuhisa Tsuboki4, (1)Hokkaido University, Sapporo, Japan, (2)National Taiwan University, Taipei, Taiwan, (3)University of the Ryukyus, Nishihara, Japan, (4)Nagoya University, Institute for Space–Earth Environmental Research, Nagoya, Japan
Abstract:
Strong tropical cyclones (TCs) often have concentric eyewalls (CEs), and experience eyewall replacement cycles (ERCs). The formation of the CE structure leads to an increase in the storm size. The storm with the CE structure can drastically change the maximum wind and the radius of maximum wind speed during an ERC. Dynamics of changes in intensity and structure during ERCs remain an open question. Recently, a geostationary satellite of Himawari-8 was launched by the Japan Meteorological Agency. The satellite has an observation with a temporal interval of 2.5 min over a target area of 1000 km × 1000 km, following typhoon tracks. Time series of imageries in the high-frequency observation allow us to trace each cloud and estimate wind speed represented by the cloud motion. To clarify the dynamics of the inner eyewall dissipation, a quantitative estimation of inner-core tangential wind fields based on highly frequent observation images with the 2.5-min temporal resolution in the Himawari-8 satellite is applied to Typhoon Trami (2018) with a CE structure. A high tangential wind speed of 50 m s-1 is estimated at a radius of 30 km, which is located in the inner edge of the inner eyewall, during an active stage of the inner eyewall. The estimated tangential wind rapidly decreases to about 20 m s-1 at a radius of 24 km in the inner eyewall dissipation. Coincided with the rapid decrease in the tangential winds, the vorticity field retrieved by the satellite-based tangential winds during the inner eyewall dissipation has a rapid decrease in the outer part of the eye. A numerical experiment of an idealized barotropic vortex with concentric eyewalls and examination on an absolute angular momentum coordinate indicate that the vorticity decrease in the inner eyewall is mainly due to vorticity rearrangement associated with asymmetric eddies through the barotropic instability across the moat.
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