Contrasting Circulation Patterns of Dry and Humid Heatwaves Over Southern China

Heatwaves pose severe threats to human health, especially those combining heat and humidity. Here, we use dry- and wet-bulb temperatures as indicators to classify dry and humid heatwaves in southern China and distinguish their different mechanisms. We find that both dry and humid heatwaves are accompanied by an eastward extension of the South Asian high, a westward extension of the western North Pacific subtropical high, and a low-level anticyclonic anomaly. The major differences between dry and humid heatwaves are that these anomalies are more widespread albeit weaker and shift more southward for humid than dry heatwaves. Consequently, dry heatwaves are associated with drastically increased temperature and decreased relative humidity, while humid heatwaves are accompanied by relatively weaker but more expanded temperature increases and stronger increases in humidity. Understanding the differences between dry and humid heatwaves and their origins advances our knowledge of heatwaves which can better mitigate their detrimental effects.