An improved equation for estimating diurnal atmospheric radiation near the surface in Japan

It is important to evaluate precisely whether observational data that include screen-level air temperatures could be affected by the environment around meteorological surface observation stations. It is well known that atmospheric radiation (downward long-wave radiation) from the atmosphere and clouds affects the temperature of the ground as well as observational air temperature data, but there are few stations that observe atmospheric radiation. Therefore, various formulas have been proposed and developed to estimate the atmospheric radiation under clear sky conditions that use air temperature and water vapor pressure; these are used in earth surface models to estimate average hourly thermal energy budgets in the planetary boundary layer. It is necessary to verify whether the formulas are applicable for recent data in Japan, because these formulas were developed with data collected at local observation stations during specific periods. In this study, the accuracy of the familiar formulas used for estimation of diurnal atmospheric radiation under clear sky conditions was evaluated. Results from the formulas were compared with observational data from five stations, namely Sapporo, Tateno (Tsukuba), Fukuoka, Ishigaki Island, and Marcus Island, at which renovated solar and infrared radiation observations commenced on 31 March 2010. It was found that there were noticeable differences between observations and calculations as well as their seasonal variations. Therefore, the coefficients of Brutsaert (1975), which are comparatively theoretical, were adjusted to fit the regional meteorological conditions. The new Brutsaert-type formulas caused the differences