Summer Onset in Northern East Asia: Feature, Mechanism and Variability

Summer in the East Asian monsoon region is characterized by heavy rainfall and high temperature. Its onset, depicted and/or airflow as well surface air temperature, has been documented. However, onset of summer season rarely addressed northern Asia (NEA) around edge monsoon. This study investigates feature, mechanism, variability NEA based on ERA-5 reanalysis dataset for 1979–2020. Results show that, climatology, occurs pentad 31 when spring-to-summer warming process decelerated at highest rate. The change rate mainly attributed to a decrease diabatic heat, mostly sensible temperature advection plays small role. After summer, regional low-level northwesterly winds are weakened, local cyclonic low forms. latter, coupled with southerly south, advects more moisture into increases rainfall. Furthermore, threshold 17 °C, climatological mean 31, was proposed depict NEA. Based threshold, year-to-year timing revealed, ranging from 29 (late May) 34 (middle June), standard deviation 1.2 pentads. It advanced 0.6 pentads, average, after late 1990s. provides new method objectively quantify Asia, which thermodynamically explainable may help us monitor different latitudes topography.