Comparison for the Characteristics and Mechanisms of Independent Daytime, Nighttime, and Compound Heatwaves Over Yangtze-Huaihe River Basin

With the growing need to fully understand the characteristics of daytime and nighttime heatwaves under the global warming, an overall investigation has been conducted distinctly separating and comparing independent daytime, nighttime, and day-night compound heatwaves over China. The findings reveal that the Yangtze-Huaihe River basin (YHRB) suffers from the most frequent compound heatwaves, which also exhibit a significant rise in both frequency and intensity during 1961–2020. Focused on the regional heatwaves over YHRB, independent daytime and compound heatwaves are mostly related to the atmospheric systems at middle and lower levels, including strengthened and westward western North Pacific subtropical high (WNPSH) and the Pacific-Japan/East Asia—Pacific (PJ/EAP) pattern, which benefits the sunny weather and downdrafts over YHRB. On the other hand, independent nighttime and compound heatwaves are influenced by the synoptic systems at higher levels, including northward and cyclonic meandering East Asian subtropical jet (EASJ), strengthened and eastward South Asian high (SAH), and positive phase of circumglobal teleconnection (CGT) pattern accompanied with cloudy weather and strengthened downward longwave radiation over north YHRB. Our findings would help improve the understanding of the mechanisms underlying various types of heatwaves and better respond to them.