Newsletter No.3 July-1998@

Figure 1

In order to know the seas along the coast of Japan, we have to know the whole of the Pacific, because all the environmental phenomena are linked through the seas. At first we start to move the GCM (General Circulation Model), by using the Nest model, and to zoom resolving power of phenomena up for the surrounding area of Japan. Figure 1 shows the rise of sea surface with the contour lines in unit of 10 cm, by running 10 years of annual average wind and heat on the surface of the Pacific. A sub-tropical circulation system with Kuroshio as a central configuration can be seen clearly. As approaching to the equator, so the effect of the earth rotation becomes small, and a gradient of sea surface extends toward east-west direction, corresponding to the trade wind system. We can see the existence of the north equatorial current, the equatorial anti-current, the equatorial current and the south equatorial current. As the present model is not considered with the existence of sea ices, the model is thought not to be expressed exactly at the high latitude, such as the Sea of Okhotsk and the Behring Sea. Yet, the average circulation systems are well reproduced, from the view point of the whole Pacific.

The above results are obtained by covering the lattice of the unit 0.5 degree ( about 60km) in longitude and latitude. Next we save these results in hard disk in computer. Using these data, we investigate the sea near Japan. Figure2 shows the result using the model with resolving power of three times both in longitude and latitude ( about 20km). With this model, the configuration of the ground is depicted more realistically than in Figure1. By this fact, the currents flowing on these configuration are also supposed to be more realistic. Such being the case, it is a feature of Nest model that as the mesh of model becomes smaller, new phenomena, which have not be seen by a coarse model, would be appeared. In Figure 2, the aspect of Kuroshio is seen more realistically than in Figure l. For example, we can see generation of maelstroms of cold and warm water with meandering after flowing off Choshi. This example is the result of 800 days calculation, and a model do not reach a stable one. So I think the aspect of the result may change hereafter. At present I intend to use Nest model( newly input parameters) with three stages. It is hoped that we can show the result with lattice interval of about 5 km in near future. In addition I will make hindcast for 97-98 El Nino, the largest one in our history, using this high resolution Nest model, and investigate how the seas surrounding Japan were affected at that time, by comparing the satellite data and observed records along the Japanese Coast.

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