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.

中文翻译：

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台风 Tokage 逼近期间日本西部上游雨带的建模研究 (2004)

2004 年 10 月 19 日至 20 日，当台风 Tokage（TY0423）从西南方向接近该地区时，日本西南部以南或东南部形成了一系列壮观的弧形雨带。随着台风逼近，上游弗劳德数（Fr）不断增加，这些雨带先是保持准静止，但最终后退。使用 1 公里网格大小的名古屋大学云解析风暴模拟器 (CReSS)，成功模拟了这些雨带，以及它们在从相对低的Fr到高Fr的过渡期间的行为研究并与理论研究的理想化二维 (2D) 模型结果进行了比较。在目前的情况下，发现雨带沿着与台风相关的南风和来自日本海的北风之间的低层锋辐合带发展。东北风加速穿过地形之间的间隙，并在雨带背面馈送离岸气流，产生强大的阻力，使雨带在比二维模拟预测的Fr值（至少 1.2）高得多（约 0.3 –0.5) 后退发生在条件不稳定的流动中，对流可用势能约为 1300 J kg ^-1. 通常 ≤ 500 m 深度，跨雨带的潜在温度 ( θ ) 赤字为 2–4 K，与其他一些事件一样，还发现蒸发冷却增强了较冷的海上流动。冷却效应帮助雨带保持其位置，直到上游气流的Fr变得太大，而后面冷却更强的雨带在撤退之前能够承受更高的Fr。撤退开始后，离岸层变薄，θ赤字也减少，雨带被即将到来的加强气流冲回。