Articles | Volume 24, issue 4
https://doi.org/10.5194/npg-24-645-2017
https://doi.org/10.5194/npg-24-645-2017
Research article
 | 
19 Oct 2017
Research article |  | 19 Oct 2017

Kinematic parameters of internal waves of the second mode in the South China Sea

Oxana Kurkina, Tatyana Talipova, Tarmo Soomere, Ayrat Giniyatullin, and Andrey Kurkin

Abstract. Spatial distributions of the main properties of the mode function and kinematic and non-linear parameters of internal waves of the second mode are derived for the South China Sea for typical summer conditions in July. The calculations are based on the Generalized Digital Environmental Model (GDEM) climatology of hydrological variables, from which the local stratification is evaluated. The focus is on the phase speed of long internal waves and the coefficients at the dispersive, quadratic and cubic terms of the weakly non-linear Gardner model. Spatial distributions of these parameters, except for the coefficient at the cubic term, are qualitatively similar for waves of both modes. The dispersive term of Gardner's equation and phase speed for internal waves of the second mode are about a quarter and half, respectively, of those for waves of the first mode. Similarly to the waves of the first mode, the coefficients at the quadratic and cubic terms of Gardner's equation are practically independent of water depth. In contrast to the waves of the first mode, for waves of the second mode the quadratic term is mostly negative. The results can serve as a basis for expressing estimates of the expected parameters of internal waves for the South China Sea.

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Short summary
Large internal waves may be a great danger to offshore structures. The breaking of such waves may strongly modify the seabed. Their core properties depend on how temperature and salinity vary in the water column. These variations are represented by three vertical locations and four coefficients of the relevant equation. We established how these seven quantities vary in the South China Sea for waves of the second mode (which create compressions or expansions of the intermediate water layer).