Seasonal variation of speed and width from kinematic parameters of mode‐1 nonlinear internal waves in the northeastern East China Sea

Abstract

Abstract To better understand the statistical and theoretical characteristics of nonlinear internal waves (NLIWs) in the broad continental shelf of the northeastern East China Sea (ECS), historical hydrographic data collected over 50 years between 1962 and 2011 are analyzed to calculate monthly climatology. Based on KdV and extended KdV models under the two‐layer approximation (i.e., mode‐1 NLIWs), the monthly climatology for propagating speed and characteristic width is constructed, ranging from 0.8 to 1.2 m s −1 and from O(10 2 ) to O(10 3 ) m, respectively. The result is consistent with a few previous in situ observations in the region. When NLIWs originating in the southeastern slope area approach the shallower regime (northwestward propagation), they propagate more slowly with neither break nor extinction, but with a shorter width, since both the Iribarren and Ostrovsky numbers are small ( I r ≪ 0.45 and O s ≪ 1, respectively). Limitations of the two‐layered KdV‐type models are discussed (e.g., an importance of mode‐2 waves) in the context of occasional extension of the low‐salinity Changjiang Discharged Water onto the area, which implies distinct effects on the kinematic parameters of NLIWs in the ECS.