Oceanic Response to the Atmospheric Freshwater Flux

Using MIT OGCM forced with atmospheric freshwater flux (evaporation minus precipitation, E-P) from GPCP and SSM/I, the oceanic response and its physical mechanisms are studied.

As shown in Fig.1a, the mean anomaly of E-P between 1989 and 2000 relative to 1988 is about 75 cm/year in the subtropics of the North and South Pacific, and about -75 cm/year in the tropics of the Pacific.

Forced by the E-P anomaly shown in Fig. 1a, the anomaly of ocean temperature between 0 and 50 m is simulated and shown in Fig. 1b. The temperature decreases by about 0.2C in the tropics between 20S and 15N, by about 0.2C north of 30N and west of 170W, and by about 0.8C east of Australia. In the mean time, the temperature increases by about 0.6C along the latitudinal belt of 20N and along the western coast of the North America, and by about 1.0C in the subtropics of the South Pacific.

Our question is: Can we understand these temperature anomalies?

First, vertical mixing will generally become weak when precipitation increases (negative E-P as shown in Fig. 1a), therefore the temperature near the surface should increase, which is opposite to the result of our simulation.

Secondly, the South Equatorial Current will become weak when precipitation increases more in the central and western Pacific than in the eastern Pacific (refer to Fig. 1a). This will result in a reduction of cold advection from the western coast of Peru and the temperature in the tropical Pacific should increase, which can not explain the cooling in our simulation either.

Our current work is to explain the reason why we have such a distribution of temperature anomaly.