Observational Study on the downward solar radiation at the sea surface in the Western Pacific

In situ observation of downward solar radiation in the Western Pacific were carried out with voluntary merchant ships for five years from autumn 1990 through autumn 1995. Daily means of the short wave radiation were computed from the observed solar radiation. Then, the effects of shadows of the ship's superstructures on the observed radiation were corrected if needed. A 5-year average of short wave radiation along the main sea-lanes in the Western Pacific was calculated based on the observed daily mean solar radiation. Maximum values of 270-280 Wm^-2 are found around 15°-20°N in May and June, while those of 290 Wm^-2 are observed south of 18°S in November and December along the lanes. Small annual variations are found in the equatorial region. Annual mean values at the equator are about 230 Wm^-2 between New Guinea and Indonesia, and 200 Wm^-2 east of New Guinea. The 5-year average of short wave radiation was compared with the climatologies given in previous studies. We have concluded that some of results of previous studies are significantly underestimated.