Large‐scale atmospheric circulation control of summer extreme hot events over China

Abstract

A large‐scale high air temperature event in China during July 2017 is examined using observational reanalysis data. Based on this case study, summer extreme hot events (EHEs) over China are classified into five types using the self‐organizing map (SOM) method. The five EHE types include those over northeast China (NEC type), northwest China (NWC type), north China (NC type), mid‐eastern China (MEC type) and south China (SC type). All types are associated with sustainable anticyclones (EHE anticyclones). Composite analysis shows that the EHE anticyclone in northern China (corresponding to the NEC, NWC and NC types) is primarily formed by downstream wave train propagation from upstream blocking, while EHE anticyclone formation in southern China (corresponding to the MEC and SC types) is driven by the joint action of downstream wave train propagation and westward movement of the western Pacific subtropical high. Moreover, the upstream blocking and downstream EHE anticyclone embedded in the wave train play important roles in maintaining the wave train. The upstream blocking acts as an energy source for downstream EHE anticyclone intensification and leads to EHE formation, with the intensified zonal wind at certain latitudes affecting the wave train propagation direction. This finding indicates that the upstream blocking with intensified zonal wind at certain latitudes may serve as an indicator for the prediction of EHE anticyclones over China. As a consequence of the persistent EHE anticyclone, the land surface is primarily warmed by enhanced shortwave radiation through reduced regional cloud cover. For the NWC and NC types, heating of the lower atmosphere takes place via the sensible heat flux; whereas, for the NEC, MEC and SC types, the main heating terms are the latent heat flux, sensible heat flux and upward longwave radiation.

Atmospheric blocking events: a review

“…[59][60][61][62][63][64][65] Some of these blocking events and episodes have even become mass casualty events recently, especially for the nations of Eurasia in 2003 12 and again in 2010, 66 as well as being the underlying cause of ecological disasters, such as large forest fires or adverse agricultural impacts. [67][68][69][70] There are indicators that the recent heat and drought of northern Russia and Siberia have been associated with blocking, including the measurement of 38 °C (100 °F) in Verkhoyansk on June 20, 2020 (see the University of Missouri blocking archive 71 ). However, a wide range of other types of extreme weather events have been attributed to the blocking environment, such as cold waves, 46,47,63,[72][73][74][75] extreme precipitation and flooding, 76,77 summer season thunderstorm activity, 78 blizzards, 79,80 as well as having an impact on the weather for entire seasons.…”

Influence of Large‐Scale Circulation Patterns on Compound Dry and Hot Events in China

“…Sun et al., 2017; W. Wang et al., 2015; W. Wei et al., 2015; L. X. Zhang & Zhou, 2015; Zhu et al., 2015). Hot events are generally accompanied by quasi‐stationary anticyclonic systems, which could enhance insolation (and adiabatic subsidence) and suppress moisture convergence and precipitation system (M. Y. Li et al., 2020). These anticyclonic systems can be driven by wave train propagation and/or movements of WPSH depending on regions.…”

Large‐scale circulation features responsible for different types of extreme high temperatures with extreme coverage over South China

“…Located in the tropical–subtropical region, South China is influenced by the East Asian summer monsoon and various circulation systems at different latitudes, such as the WPSH, westerly jet stream, tropical cyclones (TCs) and mid‐high‐latitude wave train (Ding and Chan, 2005; Yang and Sun, 2005; Fang and Jian, 2011; Wang et al ., 2016). Previous studies have investigated the circulation anomalies leading to the EHT over South China (e.g., Chen and Lu, 2015; Wang et al ., 2017; Li et al ., 2020). Luo and Lau (2017) pointed out that the EHT over South China are caused by an anomalous anticyclone centred over South China, which is related to the westward movement of the WPSH.…”