Characteristics of radiation flux of coniferous and broadleaved mixed forest in low subtropical China

The distribution characteristics and relationship of radiation flux,including downwelling shortwave radiation(R_Sd),upwelling shortwave radiation (R_Su),downwelling longwave radiation(R_Ld) and upwelling longwave radiation(R_Lu) of coniferous and broadleaved mixed forests in low subtropical China,were analyzed.The major results were as followings: the average daily radiation flux was R_Lu(36.34 MJ/(m²·d))＞R_Ld(32.43 MJ/(m²·d))≫R_Sd(12.46 MJ/(m²·d)) ＞ R_Su(0.98 MJ/(m²·d)).The variation coefficient(CV) of long wave radiation flux was obviously less than that of shortwave radiation flux.When the waves of radiation were the same,the CV of upwelling was less than that of the downwelling.All of the monthly gross radiation flux fluctuated in single apex in a year,except R_Ld.The average diurnal processes of R_Sd and R_Su presented peak type curves,however the processes of R_Ld and R_Lu presented wave curves.In the output of radiation flux in 2003,R_Lu was the largest(80.7%) and the percentage of R_Su was only 2.2%.These indicated that R_Lu was more important than R_Su,which was considered as the most important part of output radiation.The average daily short radiation reflected that coefficient(η) was 8.3%.The dominant factors of η in different temporal scales were varied.In longer temporal-scales as monthly, there existed good correlation between R_n and R_Lu,while there existed good correlation between R_n and R_Sd in short temporal-scales(≤1 d).It seemed that the shorter the temporal-scale was,the better the correlation was.It indicates that it is very important to emphasize the temporal-scale when researching the relationship of the radiation flux.