CLIMATOLOGICAL ESTIMATION OF THE MONTHLY NORMALS OF THE LONGWAVE RADIATION BALANCE OF THE ATMOSPHERIC BOUNDARY LAYER IN JAPAN

Abstract

This study defines the air layer between the ground and the 850 mb surfaces as the climatological atmospheric boundary layer, according to Kayane (1965). The monthly normals of the longwave radiation balance of the atmospheric boundary layer for 82 weather stations in Japan were estimated from the monthly normals off surface weather elements, with an aid of an experimental formula as follows _??_ where B is the longwave radiation balance of the atmospheric boundary layer, a StefanPoltzman constant, T surface air temperature in K, e surface water vapor pressure in mb and ii total fractional cloudiness. The coefficient dij is given in Table 1. This formula was introduced recently by the author (Nakagawa, 1979) after parameterization of theoretical computations with surface weather elements. The radiation map was drawn for each month based on estimated values. The results obtained are summarized as follows : The atmospheric boundary layer in Japan everywhere loses the heal due to the longwave radiation transfer, except for the northern Japan Sea coast region during winter, and the annual total cooling ranges from 8 kly/year on the Japan Sea side to 18 kly/year on the Pacific Ocean side of the Mainland. The distributionn of the monthly longwave radiation balance of the atmospheric boundary layer in Japan can be divided into two types, the winter and the summer ones. The winter type of distribution is characterized by the remarkable spatial differences in the cooling, especially by the sharp contrast between the Japan Sea and the Pacific Ocean sides. On the other hand, the characteristic of the summer type is that the distribution shows a general uniformity over the whole area of Japan, and that the form of the isolines is very simple. The distribution of the annual total is, therefore, characterized by the winter type because of its remarkable spatial differences and the long duration of its occurence. Both the occurences and the exchange of the two types of distribution seem to be due to the contrary patterns of the annual variations in the longwave radiation balance of the atmospheric boundary layer between the Japan Sea and the Pacific Ocean sides. Then, in the present study, harmonic analysis of the monthly normals of the longwave radiation balance of the atmospheric boundary layer was used to investigate its seasonality in Japan. The variance of the longwave radiation balance of the atmospheric boundary layer was large along the Japan Sea coast but small along the Pacific Ocean coast. It ranged from 616 ly2/day2 at Fukaura to 24 ly2/day2 at Owase. The first three harmonics proved sufficient to account for most of the variance in Japan. Mapping of the results revealed the first harmonic as the most important component in the whole area of Japan, especially on the Japan Sea side, with a winter minimum of the longwave radiation cooling. The importance of the first harmonic, with a late spring minimum, decreased and the second and the third harmonics were important comparably in the Kanto district and its neighborhood. The second harmonic increased also in western Kyushu. Along the Pacific Ocean coast region south of Poso peninsula, the importance of the third harmonic was greater than that of the second one. According to the pattern of the annual variation in the monthly longwave radiation balance of the atmospheric boundary layer, the Japan Islands were divided into eight types of climatic provinces.