The Impact of a Warm Ocean Eddy on Typhoon Morakot (2009): A Preliminary Study from Satellite Observations and Numerical Modelling
The Impact of a Warm Ocean Eddy on Typhoon Morakot (2009): A Preliminary Study from Satellite Observations and Numerical Modelling
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DOI：
10.3319/tao.2011.08.19.01(tm
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发表时间：
2011-12
影响因子：
0.8
通讯作者：
I. Lin;M. Chou;Chun‐Chieh Wu
中科院分区：
文献类型：
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作者：
I. Lin;M. Chou;Chun‐Chieh Wu
2009年8月6日，台风莫拉克在北太平洋西部的南部涡流丰富区遇到了一个大约700公里乘500公里的巨大暖洋涡流。在经过温暖的海洋涡流后不久，莫拉克达到了2级的最高强度。基于多个卫星观测和数值模拟的结果表明，在莫拉克早期发展阶段，温暖的海洋涡流提供了非常有利的海洋条件。据发现，在所观察到的暖海洋涡的存在下，上层海洋热含量显着增加了~ 100%，从~60至120千焦cm-2。这种非常深和温暖的次表层温度有效地减少了台风引起的海洋冷却的负反馈。因此，风暴期间的海面温度保持在29 - 30°C左右。台风期间非常温暖的海面温度（SST）使海气焓通量供应增加了~200%（即，在暖涡情况下约为500 W m（上标-2），在无涡情况下约为170 W m（上标-2）。另外，由于台风期间海温持续偏高，水汽供应增加，增强了对流活动。使用天气研究和预报（WRF）模式的数值试验表明，暖海洋涡旋的存在并没有改变莫拉克的整体结构或特征。相反，它有助于莫拉克降水量增加约10%。研究表明，除了季节内振荡或西南季风气流等有利的大气条件外，莫拉克早期发展阶段还存在着由暖海洋涡旋提供的有利海洋条件。基于全物理台风-海洋耦合模式的进一步研究需要量化上层海洋特征在影响莫拉克演变中的作用，包括其在台湾的降雨。
On 6 August 2009, typhoon Morakot encountered a giant warm ocean eddy approximately 700 km by 500 km in the southern eddy rich zone of the western North Pacific Ocean. Soon after passing over the warm ocean eddy, Morakot reached its peak intensity at category 2. Results based on multiple satellite observations and numerical modelling suggest very favourable ocean conditions provided by the warm ocean eddy during this earlier developmental stage of Morakot. It is found that in the presence of the observed warm ocean eddy, the upper ocean heat content increased significantly by ~100%, from ~60 to 120 KJ cm-2. This very deep and warm subsurface temperature effectively reduced the negative feedback of typhoon-induced ocean cooling. As a result, the during-storm sea surface temperature remained high at ~29 - 30°C. This very warm duringtyphoon sea surface temperature (SST) provided an increase in air-sea enthalpy flux supply by ~200% (i.e., ~500 W m(superscript -2) under the warm eddy situation .vs. the ~170 W m(superscript -2) under the without eddy situation). Also, since the during-typhoon SST remained high, the moisture supply was increased to enhance convective activities. Numerical experiments using the Weather Research and Forecasting (WRF) model suggest that the presence of the warm ocean eddy does not change the overall structure orcharacteristics of Morakot. Rather, it contributes to a ~10% increase in Morakot’s precipitation. This research shows that in addition to the favourable atmospheric conditions such as the Intra-Seasonal Oscillation or the southwestern monsoon flow, there also exist favourable ocean conditions provided by the presence of a warm ocean eddy during the early developmental stage of Morakot. Further studies based on a full-physics typhoon-ocean coupled model are needed to quantify the role of the upper ocean features in affecting the evolution of Morakot, including its rainfall over Taiwan.