Diurnal variation of precipitation in the warm season (June-September) in Japan is described by using data at 1,234 stations on an automated rain-gauge network. Local precipitation and widespread precipitation are separately analyzed. Diurnal variation of thunderstorm frequency is also described by use of data at 85 observatories. Local precipitation and thunderstorms exhibit a pronounced maximum between 1500 and 1800 local time in the inland areas. Time of maximum differs by a few hours according to regions and local topography. On the other hand, 0300-0600 maxima prevail at maritime stations on islands and peninsulas, except for the Nansei Islands where a 1200-1500 maximum occurs at relatively large islands. Widespread precipitation shows a pervasive signal of weak maximum in early to middle morning, except that a maximum tends to occur around noon over the Nansei Islands.
The effect on the Pacific and Indian Oceans of the radioactive fallout have been systematically studied by the present authors for many years. In this study, the content and distribution of 137Cs, plutonium isotopes (238Pu, 239Pu, 240Pu and 241Pu) and americium (241Am) which is a decay product of 241Pu on the Southern Ocean surface are reported. Water samples were collected south of Australia and New Zealand in 1977-1978. Above radioactive nuclides were precipitated from a large amount of sea water on board and brought back to the land laboratory. 137Cs was coprecipitated with ammonium phosphomolybdate. Plutonium and americium were coprecipitated with magnesium hydroxide. The determination of 137Cs was done by gamma-spectrometry. For plutonium and americium, alpha-spectrometry was used after the separation of these nuclides from a bulk of magnesium hydroxide precipitate by using ion exchange resin method. The result of determination showed that content of 137Cs ranged from 0.02 to 0.15pCil-1, 239+240Pu from 0.2 to 2.5×10-4pCil-1, 241Am from 0.2 to 0.5×10-4pCil-1. The ratio of 238Pu to 239+240Pu was 20 to 160%. The comparison between these results and those previously obtained in the Pacific and Indian Oceans will be done.