Contribution Assessment of Northern Hemispheric Atmospheric Circulations to Korean Mid-Summer Surface Warming by the Atmospheric Nudging Experiment

Anomalous surface warming in Korea has been explained by the high-pressure anomaly accompanied by the vertical sinking motion and weakening of westerlies at the exit of the East Asian Jet. The large-scale circulations linked to this high pressure over East Asia are characterized by the low pressure over the Arctic (AC) and the high pressure over Western Europe (WE), East Asia, and the North Pacific (NP). To assess the contribution of these circulation anomalies to the hot summer in Korea, the four nudging experiments (AC, NP, AC + NP, and WE) are applied to the simulations with 50 different initial conditions in July. As a result, the most similar patterns on local and hemispheric scales are found in the AC + NP nudging experiment. However, the near-surface response in the AC + NP is still weak, and its center shifts to the north compared to the observed, which is induced by the weaker diabatic contribution for the downward motion in the nudging experiment. Using the quasi-geostrophic omega equation, we find that the simulated radiative feedback process is not sufficient to build up the large-scale subsidence with the short nudging period. Despite this limitation, AC + NP well simulates the coherent sinking motion and high-pressure system near Korea by the vorticity advection associated with the upper-level westerlies. It implies that the contribution of the North Pacific circulation (a downstream region) should also be considered to reasonably simulate the East Asia surface warming along with those in the upstream regions.