JMA commenced observations of direct solar radiation in 1932 using a silver-disk pyrheliometer. The number of observation locations increased up to 79 (including overseas locations) in 1938; the locations were restructured twice after World War II and from 1972 observations were carried out at 14 locations including the stations at Okinawa, which reverted to Japan that year. In October 2007, the observations converged to four locations.
From 31 March 2010, JMA observes not only direct radiation but also diffuse radiation and long-wave downward radiation using a precise radiation observing system at five locations: Sapporo, Tsukuba, Fukuoka, Ishigakijima and Minamitorishima (Table 220.127.116.11).
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