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Long-term studies of air / sea temperatures at Oki-no-Tori Sima

 

Iwao Nakano, Hidetoshi Fujimori and Junichi Kimura*

Japan Marine Science and Technology Center

*Present affiliation : Shin-Nippon Meteorogical & Oceanographical Consultant Co., Ltd.

 

Oki-no-Tori Sima (20°25'N, 136゜05'E) is the southernmost place in Japan and surrounded all over by coral reef. There is no significant land mass within the reef. Thanks to this natural condition, it is possible to observe the pure oceanic weather. The tidal observation at Oki-no-Tori Sima (Sato, 1994) was started by Hydrographic Department of Marine Safety Agency in 1987. The observation of oceanic weather was also started by JAMSTEC and the Ministry of Construction in 1988. The record of the atmospheric pressure drew the clear atmospheric tide with the peak-to-peak amplitude of 3 hPa.

Time series of the air and water temperature clearly showed the monthly mean air temperature of March had a year-to-year fluctuation. The temperature in 1993 is 0.5℃ lower than that in 1994 and other years. In 1996, the temperature of March was higher than that in 1993 even though the winter in 1996 was more severe than those years and there remained the lingering snow until early July. This cause is not explained by a local heating at Oki-no-Tori Sima. But it is well understood by the large scale heating, i. e. going north of a warm water originated from the warm water pool.

On the other hand, the summer of Japan seemingly depended on how far the warm water intrudes in the Sea of Japan. In case that the intrusion reached off the Central Japan in the Sea of Japan, the summer is as hot as that in 1994. But in case of no intrusion, it was as cool as that in 1993.

The warm water of SST 26℃ passes Oki-no-Tori Sima and goes north normally in late March. But this timing of passing seemed to be controlled by SST of the tropical zone or warm water pool at that time. There is a strong relation between how the warm water intrudes in the Sea of Japan and when the warm water passes Oki-no-Tori Sima. The latter can be monitored with the air and water temperature at Oki-no-Tori Sima as Trenberth (1994) pointed out that changes in tropical Pacific SSTs lead SSTs in the north Pacific by three months. This scenario may allow us to predict the state of summer in Japan three months before.

 

 

 

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