Analysis of Coefficients for Net Longwave Radiation Formula and Albedo

Abstract

For a region with no direct measurements of net radiation, net longwave radiation is estimated using air temperature, relative humidity, sunshine duration by FAO’s or Penman’s formula, and net shortwave radiation is estimated using solar radiation and albedo. However, the coefficients of these formulas were determined by foreign meteorological data, not the Japanese ones. This paper describes that the coefficients are determined on daily and hourly data based on the three national research institutes in Japan. The coefficients are determined by optimization procedure from measured longwave radiation at the three sites as possible as reproducing the longwave radiation by the formula. As a result, the coefficients have a difference in region by region; therefore, the coefficients should be determined principally for an individual region. By limiting the period to the crop growing season (April to October) that has a snowfall region, the estimation accuracy of the formula was remarkably improved. In the analysis of albedo based on the above materials, the effect of the hourly changes of the albedo on shortwave radiation shows about 0.20 during the crop growing season, excluding the snow season.