Heatwave and Blocking in the Northeastern Asia: Occurrence, Variability, and Association

Abstract

The spatiotemporal variation and characteristics of heatwave in Northeastern Asia are investigated on both a grid basis and an event basis. We find that persistent, extensive, and intense heatwave has become more frequent during the last four decades. Such trend is found significantly correlated with the increase of temperature. The association between heatwave and blocking is also analyzed using two leading blocking indices, examining 500-hPa geopotential height (TM index) and vertically averaged potential vorticity anomaly (PV index), respectively. A discrepancy between blocking climatology of TM index and PV index is exhibited, with the former displaying two high-frequency zonal bands at the north and south regions, while the latter only showing one high frequency band in the north. However, grid-based concurrence analysis using the two blocking indices agreeably suggests that blocking favors the occurrence of heatwave, especially in the north region where blocking often occurs. We further explicitly investigate their temporal association with time lags, which has not been done before in the literatures. It reveals that heatwave mostly occurs after or on the onset day of blocking and ends after or at the end of blocking. It indicates that blocking is more of a favorable environmental condition to trigger heatwave than maintain it. Lastly, the impact of blocking on the characteristics of heatwave events is explored on an event basis using a 3-D spatiotemporal object model. Blocking-related heatwave events are more likely to be more persistent, extensive, and intense than unrelated events.