Causes of Interannual Variation of Summer Mean Alongshore Current Near the East Coast of Korea Derived From 16‐Year‐Long Observational Data

Abstract Interannual variation in the summer surface current near the east coast of Korea was analyzed using long‐term (~16 years) time series measurements. Significant interannual variations in the summer alongshore current, which have a magnitude comparable to that of the climatological summer mean (equatorward) current, were observed. Positive anomalies (more poleward) occurred during 2001, 2009, 2010, and 2014; negative anomalies (more equatorward) occurred during 2002, 2006, and 2012. A linear combination of equatorward propagating coastal‐trapped waves, forced primarily by remote winds off the Russian coast, and an upwelling/downwelling response to local wind forcing, though contribution of the latter is not as significant as that of the former, successfully reproduced (46%) the observed anomalies in the alongshore current (correlation coefficient of 0.68). The influence of cross‐shore movement of the poleward flowing offshore current explains 35% of the total variance in the interannual anomalies of the alongshore current (correlation coefficient of 0.59), yielding less equatorward or slight poleward current near the coast in 2001 and 2009 with onshore movement of the offshore current. The combined effects of wind and offshore current explain ~72% (correlation coefficient of 0.85) of the anomalies in the alongshore current observed during summer near the east coast of Korea, providing significant implications for interannual current dynamics near the midlatitude western boundary.