Effect of Downward Shortwave Radiation Difference on the Surface Radiation Balance of Meadow Grassland

Abstract

Based on the 20%， 40%， 60% and 80% quantiles of the daily cumulative energy of downward shortwave radiation， the four-component radiation observation data observed by the Haibei Animal Husbandry Experimental Station of China Meteorological Administration from September 2014 to December 2020 were divided into five groups.The influence of difference in downward shortwave radiation on the radiation balance of meadow grassland has been analyzed， which provided a basis for clarifying the changes and causes of radiation balance under different sunlight conditions.The results show that the downward shortwave radiation energy in the whole year is 8192.9 MJ·m-2·a-1， which can be theoretically received under the condition of abundant sunlight.Under normal sunlight， it is only 80% of that in the condition of abundant sunlight， while this proportion is only 40% under the condition of less sunlight.The downward shortwave radiation received by the surface under different sunlight conditions showes a very significant logarithmic increase trend in the same month， and the difference between the groups exceeds the difference between different season.There are also large differences between the groups of upward shortwave radiation and atmospheric longwave radiation.However， the upward shortwave radiation increases with the increase of solar radiation， due to the change of air humidity and cloudiness， while the atmospheric longwave radiation decreases with the increase of solar radiation.The variation of surface longwave radiation under different sunlight conditions is small， and does not exceed 3%.Although the difference in surface longwave radiation is not significant between the three sunlight conditions， due to the small amount of downward shortwave radiation received under the condition of less sunlight， the surface longwave radiation is 3.4 times more than the downward shortwave radiation， while it is only 1.4 and 1.7 times under the other two lighting conditions.As the increase of sunlight， the net shortwave radiation received by the surface increases， and the net longwave radiation also increases.Therefore， the energy absorbed by the radiation under different sunlight conditions accounts for 36% to 39% of the downward shortwave radiation energy received in each case.In addition， the difference of sunlight conditions also affect the linear regression model between downward shortwave radiation and net total radiation.The coefficient of determination and slope of the relationship model are the smallest under the condition of less sunlight.The coefficient of determination of the relationship model are above 0.85 for both normal and abundant sunlight.However， the slope is 1 when the sunlight is normal， while the slope is 0.87 when the sunlight is abundant.

Keywords

• four-component radiation
• differences in downward shortwave radiation
• meadow grassland
• radiation balance