Interannual variability of mid‐summer heat wave frequency over the Sichuan Basin

Abstract

AbstractHeat waves generally hit the Sichuan Basin (SCB) in summer, especially in July and August. This study investigates the interannual variability of mid‐summer heat wave frequency (HWF) over the SCB. The leading mode of the SCB mid‐summer HWF, which explains 48% of the total variance, exhibits an uniform spatial pattern and an increasing trend. This leading pattern mainly dominated by two factors: the mid‐to‐upper‐level height anomalies over western Europe and tropical convection anomalies. On one hand, the mid‐level height anomalies over western Europe could affect the HWF over most parts of the SCB by inducing an eastward‐propagating atmospheric teleconnection wave train to northeastern Asia, which causes a northwestward shifted western North Pacific subtropical high, leading to significant subsidence anomalies over the SCB, hence induces less cloudiness and below‐normal precipitation in‐situ. Consequently, there are increased surface solar radiation and decreased soil moisture over the region, favouring the occurrence of HWs there. On the other hand, the enhanced Philippine Sea convection and suppressed tropical eastern Indian Ocean convection excite an anomalous lower‐tropospheric cyclone dominant over the western North Pacific and southern China, which could weaken the transport of water vapour from the tropic oceans to the northeastern SCB and then contributes to decreased precipitation, favouring a higher HWF.