Abstract:
The variation of photosynthetically active radiation (
Qp) and ratio of
Qp to broadband solar radiation (
Rs) at Sanjiang in Northeast China were analyzed on the basis of in situ data measured during 2005-2011. The results indicate that the seasonal and diurnal variation of
Qp are similar to those of
Rs. The daily values of
Qp range from 0.11 to 60.47 mol m
-2, with an average annual value of 23.76 mol m
-2. The daily values of
Qp/
Rs range from 1.52-2.07 mol MJ
-1, with an average annual value of 1.91 mol MJ
-1. The seasonal variation of
Qp/
Rs is similar to that of
Qp.
Qp and
Qp/
Rs reach a maximum in summer and a minimum in winter. An estimation equation for
Qp was established on the basis of the optical air mass, clearness index, and
Qp data measured in 2011. Evaluation of the results shows that this estimation equation can be used to calculate historical
Qp data with a relative error within 5.7%.