Distinct mechanisms of Korean surface temperature variability during early and late summer

Abstract

Several climate factors were identified that affect the surface air temperature (SAT) variations in Korea during summer (June-July-August). Korean summer SAT variation exhibits remarkable differences between early summer (June) and late summer (July and August). On one hand, the significant warming trend during early summer is primarily influenced by the global-scale trend that is manifested in East Asia. The residual variability, obtained by removing warming trend from total SAT, represents Korean SAT variability independent of the global-scale trend. This residual variability is closely related to the meridional dipole-like air temperature structure between Korea and northeastern China, which is largely controlled by the atmospheric circulations over East Asia. However, this atmospheric structure does not originate from the remote oceanic forcing such as sea surface temperature (SST) variability over Pacific. During late summer, on the other hand, the Korean SAT is dominantly regulated by the atmospheric variability, which is closely related to the Pacific SST variability, while the contribution of global warming signal is insignificant. The SST anomalies in the central to eastern tropical Pacific lead to a dipole-like atmospheric circulation from the tropics to East Asia, which modulates SAT in Korea. These results imply that the Korean SAT variability during early and late summer has different sources. That is, both the global-scale trend and atmospheric variability over the East Asia should be considered in monitoring Korean SAT during early summer, whereas the SST variability in the central to eastern tropical Pacific needs more attention during late summer.