This study conducted to investigate the relationship between residual currents and weather conditions in the western coast of Anmyeon-do, Korea, during spring of 2016. To analyze the multi-layered current meter data and the same period surface atmosphere data for 32 days from April 15 to May 17, 2016 at two stations near Kkotji beach in Anmyeon-do. The observed current records are summarized with descriptive statistics and the tidal characteristics are identified with harmonic analysis. In addition to the overpowering straight back and forth motions, a slight rotational pattern is observed at the ST01, while a predominantly straight Northtward-Southward oscillations are detected at ST02, aligned with the nearby coastlines. The residual currents converge (diverge) between ST01 and ST02 followed by the sea level increase (decrease) between the two stations. The complex correlation analysis reveals that the residual currents significantly correlate with abrupt surface wind fluctuations due to extratropical cyclones.
The drivers of residual current are the periodic variations of longshore winds and the local bottom topography. The non-tidal residual currents and the concurrent surface atmosphere data are jointly analyzed. Using various methods, such as complex correlation, complex EOF, cross correlation and spectral analysis, I present the spatial patterns of such dynamical events occurring synchronously in the both stations as well as the surface atmosphere. The characteristics of each mode of residual currents and surface wind vectors were confirmed through complex EOF. The first mode of residual current (R1) accounted for 46.8% of the total variation and the second mode (R2) accounted for 24.9%. I assume that R1 is wind-induced component in the longshore direction and R2 is bottom friction-induced component in the opposite direction of R1. Both the modes significantly correlate with the first wind mode (W1, longshore wind) of a few hours prior. Our spectral analysis suggests that the significant periods of the major modes of surface winds and residual currents match well to each other at about 1.6 days and 4 days per cycle.