Analysis Of Pacific Ocean Circulation And Its Response To Global Warming

A dual nested Hybrid Coordinate Ocean Model(HYCOM) and a sensitivityexperiment that increases the net heat flux were used to simulate the climaticallyPacific Ocean current system and the impact of the oceanic dynamical process toglobal warming.Oceanic circulations have important impacts on the hydrological elements andthermohaline conditions of the world’s oceans. They have great influences on theglobal climate. The Pacific gyre is the most important component of the globaloceanic circulations. Global warming and the attendant series of abnormal change ofthe ocean and the atmosphere are the frontier and hot issue of oceanographic research.It is of great significance to explore the current structure and its response to the globalwarming using numerical simulations.Modelled results were compared with ADCP in situ measurements and previousstudies. It was shown that the model has fine capacity in simulations: modelledcurrent structure and its temporal variation near the origin of the Kuroshio are similarto that of the ADCP measurements; the westerly shoaling core of the EquatorialUndercurrent and the undercurrent’s source water were reproduced; simulated currentfield of the Kuroshio and current discharge at Lombok Strait are well consistent withobservations.The annually mean current field in the Pacific was constructed with the modelingresults, and quantitative analysis was conducted based on the qualitative analysis inthe first place. The source and replenishment of the major currents were discussed:the source of the South Equatorial Current comes from the Peru Current and the upwelling of the Equatorial Undercurrent; the Equatorial Undercurrent originatesfrom the return flow of the New Guinea Coastal Current; the eastern boundarycurrents in the north Pacific has a relatively narrow flow range in the surface layerand a wider range in the subsurface layer; the Subtropical Countercurrent features atwo-core or even multiple-core structure in both hemispheres. The seasonal variationof the current was analyzed: the source of the North Equatorial Countercurrent inwinter and spring differs that in summer and autumn; the surface layer of the NorthEquatorial Countercurrent features seasonal disappearance; the westwardsintermediate layer of the Equatorial Current only exists in autumn and west of theinternational date line; there is a noticeable seasonal discrepancy of the current fieldin the west Pacific, comparing that in summer and autumn with that in winter andspring.In the sensitivity experiment that increases the net heat flux, it was found that theoceanic dynamical process causes the spatial inhomogeneity of the increase oftemperature in the Equatorial Pacific, and there exists a weakest pathway of theincreasing temperature along the equator region, from the sub-surface layer of thewestern Pacific to the surface layer of the eastern Pacific. That the temperatureincrease is the weakest in the eastern equatorial Pacific is likely to have to do with theEquatorial Undercurrent, however, the deepening of the pycnocline in the easternPacific and the increase of vertical heat transport are important reasons for theweakest temperature increase in the surface layer and the relatively strongtemperature increase in the sub-surface layer of the eastern Pacific. The discharge ofthe Equatorial Undercurrent has been increasing. The velocity of the equatorialsurface current increases east of the150°W meridian, whereas it decreases west of it.The variation of the horizontal heat transport that caused by the velocity change iscorrelated with the spatial distribution of SST anomaly.Under the impact of the subtropical cell, the water mass that has the weakesttemperature increase in the equatorial eastern Pacific surface layer moves poleward to the subtropical region, where it sinks between20°-30°N. When sinking to thepycnocline, the water mass enters the equatorial region via a branch of a sub-surfaceadvective current, where it merges with the Equatorial Undercurrent, forming a loopin which the temperature increase in minimum. This implies that in the circumstanceof global warming, the subtropical cell is pivotal to the transport of the water massthat has the weakest temperature increase.