Assimilating The Vertical Diffusivity Coefficient Of The South China Sea By The Adjoint Data Assimilation Method

The vertical diffusivity coefficient of the South China Sea is studied by the adjoint data assimilation method in this thesis. The satellite data SST and the harmonic constant of M2, S2, Kb 0, extracted from TOPEX/POSEIDON satellite altimeter are used in data assimilation. So the average of the vertical diffusivity coefficients of the South China Sea in the thermocline in January, April, July, October, 1997 are2.2 10-4/m2s-1, 7.8 10-5m2s-1 , 1.0 10-4m2s-1 , 1.0 10-4m2s-1 respectively.A two layer numerical model is given which includes vertical integration equation, momentum equation, temperature equation, and its adjoint equations to study the vertical diffusivity coefficient. Some ideal experiments are made in ideal district in order to test the feasibility of the model. The assimilated result is quite same to the real vertical diffusivity coefficient, which suggests that the numerical model is feasible.Based on this, the numerical model is used in the South China Sea. The upper thermocline is the first level, and the rest is the second level.The initial values Kv of assimilation is 2.0xl(T4/?1s'~l and the time window of assimilation is 1 month. The vertical diffusivity coefficients Kv in January, April, July, October, 1997 are studied respectively. Theresult is same as the fact that the vertical diffusivity coefficient is large near the coastline and the vertical diffusivity coefficient is small in the interior. The vertical diffusivity coefficient assimilated in January is larger and the possible reason is that the vertical mixing of the South China Sea is stronger in winter and there is a cool eddy in winter in the South China Sea.