| The essential ecosystem parameters to Hydrological simulation models、 process models and biophysical models. In the long-term evolution of the Earth’s climate system, changes due to in Earth’s orbit caused by the amount of solar radiation. This change in the amount of solar radiation has a very significant impact on climate change, agricultural production and people’s daily lives. With the Earth Sciences and Ecology expanding scale, solar radiation is becoming increasingly important. Both the estimation of agricultural production potential and study on solar energy projects are based on the total solar radiation day. Loess Plateau hilly region is important to restore vegetation and ecological agriculture construction Northwest of China. Solar radiation is the energy infrastructure in the area of crop growth and vegetation restoration. It can be the scientific basis to research on the features with spatial and temporal variability of solar radiation resource in Loess Plateau with Hilly Areas, to establish a mathematical model of solar radiation law in its area, then estimate the total amount of solar radiation days in order for the future research in the area of climate changes, agricultural activities and the effective utilization of solar energy. This paper includes the following three aspects:1. Spatial-temporal distribution of solar radiation characteristicsIn this paper, 2005--2014 years solar radiation data is used to analyze variability on time scales of the reflected radiation、 the net radiation、 photo- synthetically active radiation、 ultraviolet radiation、total radiation in the year、 quarter、month and day in the Loess Plateau with hilly areas. On year-time scale, it has uneven distribution on the total radiation, reflected radiation, net radiation, photo-synthetically active radiation, ultraviolet radiation. Due to various factors such as cloudiness, precipitation, air condition, etc. in the region, its solar radiation significantly different in different years. On season、 month and day time scale, different changes in the solar elevation angle of the sun’s rays lead to different optical path length, which results in different variations of aerosol particles, air molecules and water vapor and other absorbing materials and scattering volume. The last integrated result is a different solar elevation angle, a different distribution of solar radiation. Mainly the distribution of solar radiation in the summer and fall more than that winter and spring, so the seasonal changes match its climate change characteristics.2. The correlation of overall radiation between the reflected radiation, net radiation, photo-synthetically active radiation, ultraviolet radiation, sunshine hours.By Pearson correlation analysis to study the total radiation and the reflected radiation, net radiation relevance, photo-synthetically active radiation, ultraviolet radiation, sunshine duration, correlation between net radiation, photo-synthetically active radiation, ultraviolet radiation with the total radiation is higher as a whole, which reach the two-sided test at the 0.01 level basically. The correlation coefficient of net radiation and global radiation up to 0.986, 10-year average correlation coefficient of 0.900 or more, the correlation coefficient of photo-synthetically active radiation and the total radiation up to 0.996, 10-year average correlation coefficient of 0.930 or more. The total radiation and sunshine hours in the day, month, quarter, time scales tested were correlated extremely positive. In the day time scales, the correlation coefficient is between 0.887 ~ 0.990; in the month time scale, the correlation coefficient is between 0.739 ~ 0.939; in the quarter, the correlation coefficient is between 0.653 ~ 0.976. The total radiation and sunshine correlation at day time scale are high in the region as a whole, which is over 0.887, and 0.01-level significantly correlated. Therefore, the establishment of model-based estimates of total daily sunshine hours of solar radiation, use of fitting high precision estimation model calculates the total radiation, and then by the total radiation and the reflected radiation, net radiation, photo-synthetically active radiation, ultraviolet radiation significant correlation to calculate reflected radiation, net radiation, photo-synthetically active radiation, ultraviolet radiation.3.The estimate model of total daily solar radiation1) Empirical model: use modified AP equation and substitute into the region’s astronomical and geographical factors(latitude, solar declination, hour angle, Integrated Day, etc.) to estimate the local solar radiation. But this model needs more parameters, a little cumbersome, only applies to short time scale.2) Regression Model: take sunshine time as the independent variable, the total daily solar radiation as the dependent variable to make the linear regression respectively、quadratic regression、cubic regression、exponential regression、logarithmic regression and l At last, exponential model was found the best, the coefficient of determination was 0.921, the mean-square root error(RMSE) was 2.45.To validate the models, and the average percentage error(MPE) was 3.89%, it was found the preferred model. In order to further improve the accuracy of the estimate, to establish the estimation models in different months through monthly, to verify the results of statistical indicators: mean deviation(MBE) was 0.084, and the mean percentage error(MPE) was 1.778%.3) Gaussian model: Gauss function to fit the characteristics of solar irradiance, and then fitting equation integrating the time of sunrise and sunset time interval can be calculated, mean square root error(RMSE) was 24.17. In fact, to validate the model, and the average percentage error(MPE) 1.778% scatter fitting a curve was very close to the ideal model for 1: 1 lines. To establish the parameters of the model requires fewer variables and high fitting accuracy, Gaussian model has better accuracy and applicability. |
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