Extreme April cold surges associated with slowest water temperature evolution in the Yellow Sea in 2020

Severe cold surges occurred over northeast Asia in April 2020. The cold weather caused the record-breaking slow warming of water evolution during the spring of 2020 and the delayed and suppressed spring bloom in the Yellow Sea, which are identified in the Socheongcho Ocean Research Station within the northeastern basin of the Yellow Sea. Although previous studies have pointed out that dipole atmospheric circulation over Siberia and the East Sea rendered this unprecedented retardation event, a dynamic process for inducing this dipole atmospheric circulation still has not been addressed. Here we show that the atmospheric dipole pattern is the mixed wave train and blocking type. The wave train induces the vorticity forcing of western/central Russia and propagates southeastward toward the East Sea, almost similar to the East Atlantic/Western Russia teleconnection affecting the weather over Eurasia. The blocking days over Siberia remarkably increase in 2020. This Siberian blocking frequency seems related to the meandering westerly wind in the high latitude. The wave train pattern mainly contributes to forming the dipole atmospheric circulation during normal years; however, the blocking pattern is more major process in generating the dipole circulation for the extreme cold surge of 2020.