The Distribution Characteristic And Mechanism Of Intraseasonal Oscillations In Global Oceans

Analysis of the Sea Level Anomaly (SLA) from satellite altimeter and OFES, and Sea Surface Temperature (SST) from TMI shows that the dominant intraseasonal oscillations in the ocean have latitudinal distribution characteristic. The frequency of the most energetic SSH variability decreases polarward. For example, the variability with period around 1 month dominates at the latitudinal band centered along 7°N(S). The variability with period around 2 months dominates at the latitudinal band centered along 14°N(S). The most energetic latitudinal bands move polarward to 20°N(S) for 3-month period variability, to 26°N(S) for 4-month period variability, and to 32°N(S) for 5-month period variability. In each latitudinal band, the dominant-frequency signal usually contributes more than 40% to the total power spectrum of the intraseasonal variability. Based on the linear Rossby wave theory, through vertical eigenmode decomposition method and WKB approximation method, using the WOA01 temperature and salinity data, the first baroclinic Rossby radius of deformation and the critical periods of the first baroclinic Rossby wave are calculated. The results show that the intraseasonal oscillations dominate at the latitudinal band centered along the isolines of the corresponding first baroclinic Rossby wave's critical periods. The two-dimension Fourier Transform of SLA proves that the intraseasonal oscillations basically accord with the dispersive relation of the first baroclinic Rossby wave. Analysis of 31 tidal stations in the ocean indicates that most of the tidal stations'peak-spectrum frequency is nearly identical to the stations'critical frequency at which the latitudinal group velocity of Rossby wave becomes zero.To further prove that the dominant intraseasonal oscillations in the oceans are first baroclinic Rossby wave with zero group velocity, several numerical experiments are designed based on the 1.5-layer reduced gravity model. These experiments are as follows: firstly, to check whether the 1.5-layer numerical model could reproduce the latitudinal distribution characteristic of dominant intraseasonal oscillations in Pacific Ocean; the lateral friction's impact on the latitudinal distribution characteristic of intraseasonal oscillations is analyzed. Secondly, the nonlinear term's impact on the latitudinal distribution characteristic of dominant intraseasonal oscillations is analyzed. Finally, the first baroclinic Rossby wave's critical periods in the model are changed by choosing different reduced gravitational acceleration and the initial value of upper layer's thickness; through analyzing the SLA of these experiments, whether the distribution of dominant intraseasonal oscillations change when the first baroclinic Rossby wave's critical periods change is tested. The results of these experiments reveal that the 1.5-layer model could well reproduce the latitudinal distribution of intraseasonal oscillations in Pacific Ocean; the nonlinear term in the model has little impact on the latitudinal distribution of dominant intraseasonal oscillations; when the first baroclinic Rossby wave's critical periods change, the latitudes where the dominant intraseasonal oscillations center along also change; and the dominant intraseasonal oscillations are in good agreement with the first baroclinic Rossby wave's critical periods.The work in this thesis proves that the dominant intraseasonal oscillations in global oceans are the first baroclinic Rossby wave with zero group velocity through data analysis, numerical simulation and formula deduction for the first time, which strongly supports the conclusion that the first baroclinic Rossby wave with zero group velocity is the main mechanism of latitudinal distribution of dominant intraseasonal oscillations in the oceans. This work also explains the power spectrum peak at the first baroclinic Rossby wave's critical periods at the island tidal station.