影响日本海夏季海洋热浪事件的主要大气环流型及其可能机理

Dominant atmospheric circulation patterns influencing summer marine heatwaves in the Japan/East Sea and their underlying mechanisms

摘要:

基于1982—2023年NOAA第二版最优插值海温数据和ERA5大气再分析资料,探究了夏季日本海海洋热浪事件形成的主要原因及其可能机理。结果表明,夏季日本海海洋热浪发生时,日本海处于深厚高压系统控制之下,云量偏少,海表吸收更多的短波辐射,使得海温上升。根据日本海海洋热浪事件发生时的大气环流,基于大气遥相关指数将海洋热浪分类,得到影响日本海夏季海洋热浪的主要大气环流型,即受纬向的欧亚型遥相关(Eurasian teleconnection pattern,EU)和经向的东亚-太平洋型遥相关(East Asia-Pacific teleconnection pattern,EAP)波列共同作用,主要表现为欧亚大陆中高纬地区上空纬向“+-+”波列,东亚经向上“-+-”波列,正位势高度异常中心位于日本海上空。日本海海洋热浪开始前15 d起乌拉尔山地区的土壤湿度持续异常偏干,以及前6 d起菲律宾以东洋面的异常降水活动,是造成该大气环流型的主要原因。采用线性斜压模式(linear baroclinic model,LBM)的数值模拟验证了此结论。

Abstract:

In recent decades,the increasing frequency and intensity of marine heatwaves (MHWs) have posed a growing threat to marine ecosystems.The Japan/East Sea (JES),located in East Asia,has experienced frequent summer MHW events;however,the dominant atmospheric drivers and associated mechanisms remain incompletely understood.Using the NOAA Optimum Interpolation Sea Surface Temperature (OISST,version 2) dataset and ERA5 atmospheric reanalysis data for the period 1982—2023,this study identifies summer MHWs in the JES and investigates the primary atmospheric circulation patterns and physical mechanisms responsible for their development.The results indicate that summer MHWs in the JES are predominantly associated with a deep anomalous high-pressure system.This circulation pattern reduces total cloud cover,enhances downward shortwave radiation at the sea surface,and consequently leads to pronounced sea surface temperature warming.Treating all MHWs as a homogeneous category obscures the influence of atmospheric circulation;therefore,MHWs were further classified based on large-scale circulation characteristics.Using atmospheric teleconnection indices,the dominant circulation pattern influencing summer MHWs in the JES was identified.This pattern features a zonal “+-+” wave train over the Eurasian continent and a meridional “-+-” wave train over East Asia,with a positive geopotential height anomaly centered over the JES.Approximately 15 days prior to MHW onset,anomalously dry soil moisture conditions are observed in the Ural Mountains,while enhanced precipitation activity occurs over the ocean east of the Philippines about six days before onset.These anomalies act as key precursors contributing to the development of the dominant circulation pattern.To verify this mechanism,idealized heat sources were imposed in a linear baroclinic model,with one heat source centered at the 1.0σ level over the Ural Mountains and another at the 0.45σ level over the ocean east of the Philippines.The model simulations successfully reproduce the formation of a positive potential height anomaly center over the JES,supporting the proposed physical mechanism.These findings provide important insights into the formation mechanisms of summer MHWs in the JES and offer valuable guidance for their monitoring and prediction.