Preliminary Study On The Variability Of The Pacific Ocean And One Of Its Formation Mechanisms

Observations and air-sea models indicate that decadal to interdecadal variabilities exist in the Pacific Ocean. In the North Pacific, the decadal variability is expressed as PDO (Pacific Decadal Oscillation). In 1976-1977, there is a climate "Regime Shift" in the Pacific Ocean. So tar oceanographers and meteorologists have not come to agreement about the physical mechanism of this decadal fluctuation.This paper has analyzed the temporal and spatial patterns of PDO on the basis of some variable data from JED AC, NCEP/NCAR and COADS, and also discussed the effect of zonal wind to PDO, coming to the conclusion that the local wind stress in the North Pacific is a positive feedback to the PDO.Based on the above analysis, a nonlinear air-sea coupled model is constructed to analyze the formation and development mechanism of the decadal variability in the Pacific Ocean. There are indications that, in the midlatitude, the Sverdrup transport resulted from the zonal wind anomaly plays an important role to the heat budget in the high and low latitude. The difference in temperature between high and low latitude is a key factor to sustain this zonal wind anomaly in the midlatitude. When this difference is great to some extent, owing to the non-linearity in the air-sea coupled system, the zonal wind in midlatitude will jump from one state to another, which in turn effects the heat storage in the high and low latitude. Thus there will be a discontinuous oscillation in this coupled system. Therefore, decadal oscillation can also be formed by itself in the midlatitude of the Pacific Ocean. This formation mechanism isalso available in the Atlantic Ocean. Besides, the above analysis suggests that the upper layer heat storage variability in 10?N-20?N is not entirely resulted from the subduction water originated in the north.The decadal variability in the tropical Pacific shares some common characteristics with the North Pacific. There also exist anomalous signals similar to the PDO period of more than 20 years. There is a good positive correlation between NINO3 index and PDO index. The east and the west tropical Pacific Ocean are positively and negatively correlated to the anomaly of the upper layer heat storage in the Kuroshio and Oyashio Extension, respectively. Air-sea model and data analysis also show that a decadal variability of the upper layer storage exists in the low latitude, which is negatively correlated to that in the high latitude. The anomaly of the upper layer heat storage in the low latitude may affect the equatorial easterly wind and results in the decadal anti-phase oscillation of the upper layer heat storage in the tropical Pacific Ocean. The negative correlation of the anomaly of the heat storage in the eastern Pacific may also probably come from the modulation of ENSO. So the origination of this oscillation in the tropical Pacific may be in the midlatitude. In addition, the upper heat storage and the thermocline in the tropical Pacific also contain the westward signals of 10-year period.