Large-scale circulation features responsible for different types of extreme high temperatures with extreme coverage over South China,International Journal of Climatology

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Large-scale circulation features responsible for different types of extreme high temperatures with extreme coverage over South China
International Journal of Climatology ( IF 3.5 ) Pub Date : 2021-07-02 , DOI: 10.1002/joc.7283
Wenting Lin ₁ , Ruidan Chen _{1,

2} , Zhiping Wen _{3,

4} , Wei Chen ₅

Affiliation

This study classifies the summer extreme high temperatures (EHT) over South China into Day-EHT, Night-EHT and Mixed-EHT (corresponding to EHT with extreme coverage only in daytime, only at night and both in daytime and at night) and compares their associated circulation patterns. All types of EHT are associated with the intensification and expansion of western Pacific subtropical high (WPSH). Concurrently, anomalous subsidence occurs over South China, which reduces the cloud cover and favours daytime warming. However, different types of EHT feature different circulation configurations. Day-EHT are influenced by the northwestward-extending WPSH and tropical cyclones, manifesting an abnormal anticyclonic-cyclonic pair. Anomalous northeasterly winds dominate over South China, which cause lower humidity and faster heat dissipation and thus the EHT disappear at night. Night-EHT are related to the westward-extending WPSH and intensified East Asian westerly trough, presenting a subtropical anticyclonic anomaly and a mid-latitude cyclonic anomaly. Anomalous southwesterly and northerly flows meet around South China, favouring more water vapour convergence in situ. The above-normal humidity results in smaller amplitude of cloud cover reduction and weaker daytime warming compared to Day-EHT, but favours heat maintenance and Night-EHT. Moreover, the mid-high-latitude wave train preceding Day-EHT (Night-EHT) lies more northward (southward) with the upstream high-pressure anomaly occurring around the Ural Mountains (Caspian Sea). Mixed-EHT combine the anomalies for Day-EHT and Night-EHT and weak humidity anomaly occurs over South China, thus the daytime EHT could persist until night albeit cools down slightly. These distinguished features indicate that different types of EHT should be considered separately for better forecast and projection of EHT.

中文翻译：

华南地区极端覆盖不同类型极端高温的大尺度环流特征

本研究将华南夏季极端高温（EHT）分为Day-EHT、Night-EHT和Mixed-EHT（对应极端覆盖仅在白天、仅在夜间、白天和夜间都有极端覆盖的EHT）并比较它们相关的流通模式。所有类型的EHT都与西太平洋副热带高压（WPSH）的增强和扩张有关。同时，华南地区出现异常沉降，减少了云量，有利于白天变暖。但是，不同类型的 EHT 具有不同的循环配置。Day-EHT受西北偏副高和热带气旋影响，表现为反气旋-气旋对异常。异常的东北风在华南地区占主导地位，这会导致较低的湿度和更快的散热，因此 EHT 在夜间消失。夜间EHT与西伸副高、东亚西风槽增强有关，呈现亚热带反气旋异常和中纬度气旋异常。异常的西南偏北气流在华南周围汇合，有利于更多的水汽就地汇聚。与Day-EHT相比，高于正常的湿度导致云量减少幅度较小，白天变暖较弱，但有利于热量维持和夜间EHT。此外，Day-EHT（Night-EHT）之前的中高纬波列更偏北（向南），上游高压异常发生在乌拉尔山脉（里海）周围。混合 EHT 结合了 Day-EHT 和 Night-EHT 的异常，华南地区出现了弱湿度异常，因此白天 EHT 可以持续到晚上，尽管略有降温。这些显着特征表明，为了更好地预测和预测 EHT，应分别考虑不同类型的 EHT。

更新日期：2021-07-02

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