| The thesis is composed of five chapters.The concepts of solar radiation, photosynthetically active radiation (PAR) and ultraviolet radiation are given in Chapter 1. The purposes and structures of this research are also included in this chapter.A comparison between measured and modeled clear-sky surface solar irradiance data is discussed in Chapter 2. Based on the surface measured direct-normal and diffuse irradiance data under clear sky in 12 days, the optical properties of aerosols and columnar water vapor retrieved from Cimel, and columnar ozone observed by Dobson in IAP Observing Station, Xianghe, three radiative transfer models (MODTRAN, 6S, SBDART) are used to calculate the direct-normal and diffuse surface solar irradiance, then comparisons between measured and modeled irradiance are made. It is shown that modeled and measured direct-normal irradiance are in good agreement. While the modeled mean diffuse irradiance is larger than the measurement by 3% ~ 5% and about 80% to 90% model estimates are higher than the corresponding measurements. The difference between our results with reports in literatures is that our model overestimates are lower than their reports and our model estimates are less than the measurements in some cases (about 10% - 20%). There should be some space to improve the agreement of modeled and measured diffuse irradiance if the estimates of aerosol optical properties and other model inputs are improved. The instruments used to measured solar irradiance, their performances and calibration methods, quality controls of observing data, cloud screen methods and so on are also introduced briefly in this section.Photosynthetically active radiation (PAR) is an important energy source of photosynthesis for green plants. In Chapter 3, based on the 15 months solar radiation data from Oct. 2004 to Dec. 2005 in IAP Observing Station, Xianghe, the diurnal variation characteristics of the ratio of PAR to global radiation (PAR/R_s) in different seasons are shown. A least square regression fit is usedto calculate the relationship between PAR and Rs in different months, and the ratio ranges from 1.808 to 2.048 uE J"1, with an annual mean value of 1.948 uE JT1. The ratio decreases from the largest to the smallest as season changes from summer to winter. The ratio is between 1.893 and 2.048 uE J'1 and changes from 2.003 to 2.385 uE J"' under clear and overcast sky respectively. A new parameterized method for calculating the instantaneous PAR is given and it shows higher accuracy in PAR modeling than traditional method, which calculating PAR from global radiation based on fixed annual mean PAR/RS value. At last, the regional differences among Xianghe, Taihu and Ejina regions on PAR daily gross, hourly gross and instantaneously extreme high values are analyzed.A discussion of ultraviolet radiation is the main content of Chapter 4. Based on the measured radiation data from Oct. 2004 to Dec. 2005, the diurnal variation of the ratio (UV/Rs) are shown and the differences of the ratio in different months, seasons and under clear and overcast sky are analyzed. It shows that the monthly variation of the ratio is between 3.3% and 4.3%, and the ratio changes from 3.8% to 4.5% and between 3.4% and 5.9% under clear and overcast sky respectively. The relationship between UV and relative optical mass and the relationship of hourly UV versus global and diffuse solar radiation are discussed. It indicates that the ratio of UV to diffuse radiation and the ratio of diffuse radiation to global radiation can be fit very well by an exponential equation. At last, the differences between Xianghe and Taihu regions on UV daily gross, hourly gross and instantaneously extreme high values are analyzed.A summary of this research and some conclusions are given in Chapter 5. Some issues for further study are indicated.
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