Interannual Variability of Near‐Inertial Energy in the South China Sea and Western North Pacific

Interannual variability of surface mixed‐layer near‐inertial energy (NIE, representing the intensity of near‐inertial waves) in the South China Sea and western North Pacific (WNP) is investigated using satellite‐tracked surface drifter data set. It is found that NIE in the study region correlates negatively with El Niño‐Southern Oscillation (ENSO) with a correlation coefficient of R = −0.44 and a time lag of 5 months, mainly because the variation of local wind stress lags behind El Niño by 4 months. By separating summer and winter seasons, the correlation is significantly improved. The summer NIE correlates positively with El Niño (R = 0.62), since tropical cyclones over the WNP tend to be stronger and longer‐lived during the El Niño developing phase. The winter NIE correlates negatively with El Niño (R = −0.65), since the winter monsoon is weakened by the ENSO‐related WNP anomalous anticyclone. This is the first time that interannual variability of NIE is studied by direct current velocity observations.