2020年10月西北太平洋热带气旋群发的原因分析

Cause Analysis of the Group Occurrence of Tropical Cyclones in the Western North Pacific in October, 2020

摘要: 利用多年高分辨率气象要素场资料，完整阐述了一次台风群发时其附近气象要素场和大尺度环流异常情况，综合考虑台风群发时的多种环境变量和大尺度环流的共同作用，并阐明其各自对台风群发的影响机制。此外，使用GPI (Genesis Potential Index)作为定量的指标来衡量台风生成可能性，通过计算个别气象要素异常对GPI的贡献来确定本次台风群发事件中的最大环境影响因素，同时使用大气向外长波辐射表征热带大气季节内振荡的活跃程度。研究发现：2020年7~10月是一次典型的MJO对流传播事件，自印度洋、孟加拉湾一带自西向东传播，2020年10月份传播到南海以及西北太平洋海域。本文认为MJO对流传播和拉尼娜事件共同造成了2020年10月份西北太平洋地区的环境异常，进而导致台风群发事件的产生。

Abstract: Using high-resolution meteorological element field data for many years, this article fully describes the meteorological element field and large-scale circulation anomalies near a typhoon cluster. It comprehensively considers the combined effects of multiple environmental variables and large-scale circulation during a typhoon cluster, and clarifies their respective impact mechanisms on the typhoon cluster. In addition, GPI (Genesis Potential Index) is used as a quantitative indicator to measure the possibility of typhoon formation. The maximum environmental impact factor in this typhoon cluster event is determined by calculating the contribution of individual meteorological element anomalies to GPI. At the same time, atmospheric outward long-wave radiation is used to characterize the activity level of intraseasonal oscillations in the tropical atmosphere. The study found that July-October 2020 was a typical MJO convective propagation event that spread from the Indian Ocean and the Bay of Bengal from west to east, and spread to the South China Sea and the northwest Pacific Ocean in October 2020. This article believes that MJO convective propagation and La Nina events jointly caused environmental anomalies in the northwest Pacific region in October 2020, which in turn led to the occurrence of a typhoon cluster event.