2019年南海夏季风爆发特征及其与10~25 d ISO的关系

Characteristics of South China Sea summer monsoon onset in 2019 and its relationship with 10-25 d intraseasonal oscillation

使用NCEP/NCAR再分析资料对2019年高度场、OLR场和风场进行了环流分析,计算假相当位温、西南风和垂直风切变等物理量,并且使用Lanczos滤波器滤波后进行分位相讨论了ISO与2019年南海夏季风爆发的关系。结果表明,2019年南海夏季风爆发的日期为5月6日,其爆发偏早。在5月6日后具体特征表现为:200 hPa高空急流范围扩大,强度增强;副热带高压不断东撤,南海地区不再盛行西南风;850 hPa上南海地区盛行西南风且对流大面积爆发;假相当位温随高度变化的特征显示出对流增强的趋势。为了探讨2019年南海夏季风爆发与ISO的关系,进一步研究发现2019年存在10~25 d大气季节内振荡。一方面,ISO有利于2019年爆发时间偏早,另一方面,南海夏季风爆发后从孟加拉湾—印度洋东部低频对流多次随时间向东北传播,经历发展—最强—减弱—抑制—最弱—恢复的6个阶段,有利于南海地区偏西风增强以及对流活动的爆发维持,使得其爆发强度增强。

The NCEP/NCAR reanalysis data was used to perform a circulation analysis on the 2019 height field,OLR field and wind field and was used to calculate the physical quantities such as pseudo-equivalent temperature,southwest wind and vertical wind shear.Then,the Lanczos filter was used to filter the phase and discuss the relationship between ISO and the 2019 South China Sea summer monsoon onset.Results show that the date of the 2019 South China Sea summer monsoon onset is May 6,and its outbreak is too early.The specific characteristics after May 6 are as follows:200 hPa upper level jet range is expanded and its strength is enhanced;the subtropical high continues to withdraw eastward,and the southwest wind no longer prevails in the South China Sea;southwest wind prevails in the South China Sea area at 850 hPa and convection breaks out in large areas;the characteristic that the potential pseudo-equivalent temperature changes with altitude shows the trend of convection enhancement.In order to discuss the relationship between the 2019 South China Sea summer monsoon onset and ISO,further research reveals that there are 10-25 days of intraseasonal oscillations in 2019.On one hand,ISO is conducive to the early outbreak of 2019.On the other hand,after the outbreak,low-frequency convection from the Bay of Bengal-East Indian Ocean propagated to the northeast many times over time,going through six stages of development-strongest-weakening-suppression-weakest-recovery.It is conducive to the enhancement of the westerly wind in the South China Sea and the maintenance of the outbreak of convective activities,which increases its outbreak intensity.