| The Photo-synthetically Active Radiation (Qp), defined as the wavelength band of400nm to700nm, can be used of plant photosynthesis. It is the formation base of biological dry matter.PAR can control the speed of the Terrestrial biological photo-synthesis, that can directly impact on plant growth, development, production and product quality, and PAR also affect the material and energy exchange between surface and atmosphere, such as the carbon cycle, nutrient cycle, water cycle and thermal cycle.The characteristics of Photo-synthetically Active Radiation in Lhasa and Haibei in the Tibetan Plateau were analyzed based on long-term in-situ measurements of surface radiation data from Chinese Ecosystem Research Network. Observation data from2005-2010are used to investigate the temporal variability of Qp. Then, an estimation equation of Lhasa and Haibei was established. The main results are as follows:(1) Qp shows the similar seasonal and diurnal features as those observed for broadband global radiation (Rs).In Lhasa, the annual mean of the daily values of Rs and Qp are20.2MJ·m-2and37.2mol·m-2,16.2MJ·m-2and30.2mol·m-2. Qp showed a trend of decreasing year by year(2) The high values of Rs and Qp both appeared in June and the low values appeared in January in Lhasa.Their maximum and minimum values are25.4MJ·m-2and14.0MJ·m-2,48.7mol·m-2and25.2mol·m-2, respectively. The high values of Rs and Qp both appeared in May or June and the low values appeared in January in Haibei.Their maximum and minimum values are22.1MJ·m-2and42.2mol·m-2,10.1MJ·m-2and16.8mol·m-2. The analysis of the hourly values also revealed a diurnal pattern, with higher values around noon and lower values around sunrise and sunset.(3) The PAR fraction (Qp/Rs) ranged from1.3mol·MJ-1(inter)-3.2mol·MJ-1(summer) with an annual mean value of1.89mol·MJ-1and1.88mol·MJ-1. It showed a trend of decreasing year by year showing a trend of decreasing year by year. The seasonal variation between summer and winter is more obvious. The seasonal Qp/Rs value in winter is10.6%and9.6%lower than that in summer. The hourly values also revealed a diurnal variation with high value around sunrise and sunset, low value around noon. Both Rs and Qp present the trend of diminishing. A lookup table of PAR fraction is count from6:00to18:00, that from January to December during2005to2010.This lookup table can be applied to agriculture and ecology, that in order to estimate biomass.(4) An estimation equation of Lhasa and Haibei was established based on analyzing the temporal variability of Qp and its dependence on the clearness index and solar zenith angle. The relative deviation is about4.49%and5.76%respectively. |
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