A Modeling Study of Rainbands Upstream from Western Japan during the Approach of Typhoon Tokage (2004)

Atmosphere

Yu-Ming Tsai¹  Tzu-Chun Lin²  Chung-Chieh Wang²  Dong-In Lee³  Kazuhisa Tsuboki⁴ 

[1] Central Weather Bureau, Taipei 100006, Taiwan;Department of Earth Sciences, National Taiwan Normal University, Taipei 11677, Taiwan;Department of Environmental Atmospheric Sciences, Pukyong National University, Busan 48513, Korea;Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan;

关键词: rainband;    terrain blocking;    Froude number;    Typhoon Tokage;    CReSS model;   

DOI  :  10.3390/atmos12101242

来源: DOAJ

【 摘 要 】

During 19–20 October 2004, a series of spectacular arc-shaped rainbands developed south or southeast of southwestern Japan when Typhoon Tokage (TY0423) approached the region from the southwest. As the typhoon moved closer and the upstream Froude number (Fr) continued to increase, these rainbands first remained quasi-stationary but eventually retreated backward. Using the Nagoya University Cloud-Resolving Storm Simulator (CReSS) at 1-km grid size, these rainbands were successfully simulated, and their behavior during the transition period from a relatively low-Fr to a high-Fr regime was investigated and compared with idealized two-dimensional (2D) model results from theoretical studies. In the present case, the rainbands were found to develop along a low-level frontal convergence zone between the southerly flow associated with the typhoon and the northerly flow from the Sea of Japan. The northeasterly winds accelerated through gaps between topography and fed the offshore flow at the backside of the rainbands, producing a strong resistance that allowed the rainbands to remain stationary under significantly higher Fr values (at least 1.2) than predicted by 2D simulations (of about 0.3–0.5) for the retreat to occur in conditionally unstable flow with a convective available potential energy of about 1300 J kg⁻¹. Typically ≤ 500 m in depth with a potential temperature (θ) deficit of 2–4 K across the rainband, the cooler offshore flow was also found to be enhanced by evaporative cooling as in some other events. The cooling effect helped the rainbands to hold their position until Fr of the upstream flow became too large, and the rainband with stronger cooling behind was able to withstand a higher Fr before retreat. Once the retreat started, the offshore layer became thinner and the θ deficit also reduced, and the rainbands were washed back by the strengthening upcoming flow.

【 授权许可】

Unknown