Observation And Theoretical Study Of Ocean Fluctuations And Offshore Eddies

The planetary Rossby wave, the circuit of / signals, the long-term transport of tidal current in the East China Sea, the Yellow Sea and the Bohai Sea, and the upwelling structure of cold votex are focused based on T/P data analysis, numerical modeling and ocean dynamics analysis respectively. The main achievements are as follows,1. Based on TOPEX/Poseidon (T/P) and ERS-1 and -2 satellite altimeter data between October 1992 and December 2000, high frequency oscillations with periods less than 150 days are analyzed and their spatial distributions are described. We analyze the ratio, instead of the energy itself, of the energy corresponding to certain frequency band from Power Spectrum relative to the total energy in the 20-143d range. The results show that the period of the most energetic oscillations in this band increases with latitude from about one month near the tropics to about four months near 30°, in agreement with the latitudinal dependency of the phase speed of westward propagating long Rossby waves, which dominate the variability in those latitudes. As a result, the global spatial distributions of the period of the dominant oscillations are largely zonal, with relatively small differences between different ocean basins. It suggests that the oscillations with periods around 60d are mainly associated with planetary Rossby waves except the often regarded as tidal aliasing especially near 30°N(S).2. Based on the same T/P altimeter dataset, the circuit of /signals are studied. 1)In cases, positive Sea Level Anomally (SLA hereafter) signals propagate eastward from equatorial West Pacific to East Pacific. After reaching the coast area, the signals go to pole directions along the east Pacific boundary and continuously generate westward planetary Rossby waves. The strength of the Rossby waves is the strongest near 10°N in the period of , it suggests that an signal circuit bounded with equator and 10°N exits. The other signal circuit bounded with equator and 10°S also exits, but it is weak compared with the former. Westward signals mainly in the channels centered 5°N and 7°S respectively. Westward seasonal signals mainly in the three channels centered 6°N,10°N and 8°S. 2) Two kinds of signals, fast and slow, transport information from east Pacific to West Pacific at the same latitude. The phase speed of slow one with wave length of 700－800km is consistent with that of planetary Rossby wave. The basin scale signals propagate so fast that it should be the ocean response to air anomally. 3. Based on high resolution POM model, the tidal wave including K1,O1,M2 and S2 , of the East China Sea, the Yellow Sea and the Bohai sea is simulated. To select the initial surface points at 5′× 5′as tracer, the main results are as follows: 1) the long-term lagrangian transport of the tracers can form belt structure, i.e. the tracer density is high along the belts and low between two adjacent belts. The Quenggang is the center of the radioactive belts. 2) From the distribution of the annually averaged tidal transport velocity, the East China Sea absorbs water from the West Pacific through Japan island chain and drains off water through the Taiwan Strait and Tsushima Strait. In the Yellow Sea, tide induced long-term velocity is anticlockwise. In Bohai, two anticlockwise structures appear. In general speaking, the exchange between the Yellow Sea and the Bohai Sea is very weak. 3) We find that the time step should be less than 10 minutes to follow the lagrangian transport based on Eularian velocity, otherwise the accumulated error can not be neglected.4. From recent two times of comprehensive investigations, we find the peaks of nutrients locate off the cold votex center, and infer that the upwelling in the mesoscale cold eddy emerges a ringlike structure. The strongest upwelling region is not located in the centre of the eddy, but in the place being certain distance from the centre. Meanwhile, these observed results are also explained from dynamics.