A long-lasting phytoplankton bloom, characterized by high chlorophyll-a (Chl-a) concentrations in an eddy-like feature, was detected in MODIS satellite imagery of the northwestern Pacific following the passage of Typhoon Krosa in August 2019. Satellite datasets, Argo measurements, and regional ocean models were analyzed to determine the occurrence and abundance of high-Chl-a concentrations and the upper-ocean conditions associated with them before and after the passage of the typhoon. Remote sensing data revealed that the typhoon triggered sharp increases in surface Chl-a concentrations more than five times the pre-typhoon average, which lasted for two weeks. The elevated post-typhoon concentrations coincided with a pre-existing oceanic cyclone that was detected as an altimetry-based sea surface height anomaly. The typhoon looped around the oceanic cyclone and lingered for two days at slow speeds (less than 2 m/s), producing an unusual sea-surface cooling of up to approximately 9 °C in the cyclonic eddy region. Our model successfully captured the typhoon-induced cold-core cyclonic circulation, which corresponded to the region of high Chl-a concentration. Model–data comparisons revealed that the looping motion of the slow-moving typhoon enhanced the pre-existing cyclonic circulation, resulting in strong vertical mixing and upwelling, consequently initiating a phytoplankton bloom due to increased nutrient supply to the euphotic zone.

中文翻译：

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西北太平洋台风引发的浮游植物绽放和相关的上层海洋条件：来自卫星遥感，Argo资料和海洋环流模型的证据

在2019年8月台风克罗萨通过后，在西北太平洋的MODIS卫星图像中检测到了一种持久的浮游植物水华，特征是叶绿素a（Chl-a）浓度高，呈涡流状。进行测量，并分析区域海洋模型，以确定台风通过前后高Chl-a浓度的发生和丰度以及与之相关的上层海洋条件。遥感数据显示，台风引发的表面Chl-a浓度急剧上升，超过持续两周的台风前平均值的五倍以上。台风后浓度升高与先前存在的海洋气旋相吻合，后者被检测为基于测高仪的海面高度异常。台风绕着海洋气旋绕圈，并以低速（小于2 m / s）徘徊了两天，在旋风涡流区域产生了异常高的海面冷却，最高温度约为9°C。我们的模型成功地捕获了台风诱发的冷芯气旋循环，这对应于高Chl-a浓度区域。模型与数据的比较表明，缓慢移动的台风的环状运动增强了先前存在的气旋环流，导致强烈的垂直混合和上升流，因此由于向富营养区的营养物供应增加而引发了浮游植物的爆发。我们的模型成功地捕获了台风诱发的冷芯气旋循环，这对应于高Chl-a浓度区域。模型与数据的比较表明，缓慢移动的台风的环状运动增强了先前存在的气旋环流，导致强烈的垂直混合和上升流，因此由于向富营养区的营养物供应增加而引发了浮游植物的爆发。我们的模型成功地捕获了台风诱发的冷芯气旋循环，这对应于高Chl-a浓度区域。模型与数据的比较表明，缓慢移动的台风的环状运动增强了先前存在的气旋环流，导致强烈的垂直混合和上升流，因此由于向富营养区的营养物供应增加而引发了浮游植物的爆发。