Seasonal Variation of Speed and Width of Nonlinear Internal Waves in the Northern East China Sea

To better understand statistical and theoretical characteristics of nonlinear internal waves (NLIWs) on the broad continental shelf in the East China Sea (ECS), historical hydrographic data collected bi-monthly on the shelf over 50 years from 1962 to 2011 are analyzed. Based on three different models (KdV, eKdV, and BO equation) under two-layer approximation, monthly mean seasonal climatologies of propagating speed and characteristic width of NLIWs are constructed, ranging from 0.8 to 1.2 m/s and from O(10²) to O(10³) m, respectively. Such prediction is consistent with observations previously conducted in the region during summer (July and August). As approaching the shallower regime (northwestward), NLIWs propagate slower with shorter width without breaking and extinction of NLIWs, evaluated with Iribarren number and Ostrovsky number. Limitations of two-layered KdV-type models are discussed (e.g. potential importance of 2nd-mode waves) in the context of occasional extension of low salinity Changjiang Discharged Water (CDW) in the region.