In this paper, the char acteristics of Photo synethically active Radiation ( PAR) and the ratio of the PAR to global radiation ( ηQ ) are analyzed and studied by using the observation solar spectral radiation and meteorological data in Xidatan at the northern boundary of Tibetan Plateau permaf rost regions in 2005. The results show that diurnal variation of PAR is larger at noon than that in morning and evening, similar to the daily variation trend of Q. The PAR shows a single peak and changes smoothly on clear days. Oppositely, it is instability and less in value in the cloudy days than that on clear days. T he PAR is larger in spring and summer than that in autumn and winter. T he maximum of PA R occurs in May and the minimum occurs in December. T he ηQ is larger on cloudy day than that on clear day . T he daily variat ion of ηQ is smaller at noon than that in morning and evening.The annual variation o f ηQ shows a bimodal type and varies between 1. 75 mol•MJ-1 and 1. 96 mol•MJ-1 . The annual average of ηQ is 1. 88 mol•MJ-1 . A t last, the climatological calculation means of the photosynthetically active radiation for this region are put forward. |
Introduction
