Interannual Variability of Winter Sea Level Induced by Local Atmospheric Forcing in the NorthEast Asian Marginal Seas (NEAMS): 1993-2017

MyeongHee Max Han1, SungHyun Nam1, Yang-Ki Cho1, Hyoun-Woo Kang2, Kwang Young Jeong3 and Eunil Lee4, (1)Seoul National University, School of Earth and Environmental Sciences, Seoul, South Korea, (2)Korea Institute of Ocean Science and Technology, Ocean Climate Prediction Center, Busan, South Korea, (3)Korea Hydrographic and Oceanographic Agency, Research Div., Busan, South Korea, (4)Korea Hydrographic and Oceanographic Agency, Busan, South Korea
Significant interannual variability of winter (November and December) sea level on top of the long-term rising of regional sea level, is investigated in the NorthEast Marginal Seas (NEAMS) that consist of the Yellow and East China Sea (YECS) and East Sea (ES, also referred as Sea of Japan). Sea level observed from satellite altimetry commonly shows large interannual variations (standard deviation: 39.85 mm) with long-term rising trend (3.88 mm/yr) from 1993 to 2017 in winter, yielding years of high (Period H) and low (Period L) sea level anomalies (Period H: 1999, 2000, 2003, 2004, 2015, and 2016 vs Period L: 1993, 1995, 2005, 2013, 2014, and 2017). The interannual winter sea level anomalies in the NEAMS are correlated with patterns of the East Asian winter monsoon (northwesterly or southeastward wind stress and atmospheric pressure at the sea level); stronger (weaker) southeastward wind stress in the southern Okhotsk Sea (OS) than the southern ES with higher (lower) atmospheric pressure between the two marginal seas, e.g., area around the Soya Strait, during the Period H (Period L). Horizontal convergence (divergence) in the NEAMS associated with positive (negative) sea level anomaly is induced during the Period H (Period L) by decreased outflow from the ES through the Tsugaru Strait and Soya Strait (decreased inflow into the ES through the Korea Strait and YECS via the shelf intrusion) due to increased southwestward Ekman transport linked to enhanced southeastward wind stress in the southern OS (southern ES). Multiple regression analysis of wind stress anomalies in the southern ES and OS on the winter NEAMS sea level anomaly provides significantly high skills with r-squared of 0.49 and p-value less than 0.0006. The winter NEAMS sea level anomaly, well predicted by atmospheric pressure anomaly in the Soya Strait (correlation coefficient of 0.62 with p-value less than 0.0010), has significant (0.41 with p-value less than 0.0433) correlation with the North Pacific Gyre Oscillation (NPGO) among several climate indices. This study highlights important roles of local (monsoonal) atmospheric forcing in winter sea level variability in the NEAMS.