西双版纳热带季节雨林辐射长期变化特征

  目的  太阳辐射是森林生态系统最主要的能量来源，同时是影响森林生态系统区域气候与环境的最重要因素之一。探讨森林辐射长期变化特征，以期为气候变化、热带地区森林生产力、辐射能量平衡的研究以及辐射模型的建立和验证等建立研究基础。  方法  利用西双版纳热带季节雨林14年（2003—2016）辐射实测数据，对不同时间尺度的辐射各分量变化特征及其占总辐射的比率进行了比较分析。  结果  西双版纳热带季节雨林的总辐射、净辐射、反射辐射、大气逆辐射和林冠向上长波辐射的年平均值分别为:5 268.8、3 151.5、513.8、12 468.6、13 299.3 MJ/m2。总辐射的年际变化呈波动上升趋势，相反，净辐射的年际变化呈显著下降趋势；受大气状况的影响，大气逆辐射的年际变率较大，导致有效辐射的年际变率较大，而林冠向上的长波辐射年际变率较小；受研究区域特殊天气、季节性雾的影响，大气逆辐射日变化曲线在干季呈双峰型，雨季呈单峰型；在不同时间尺度上，林冠向上的长波辐射高于大气逆辐射，表明热带季节雨林林冠是大气的一个热源。净辐射占年总辐射的比率在60%左右，年际变化呈显著下降趋势，反射辐射和有效辐射占年总辐射的比率变化不大；净辐射占总辐射比率在昼间高，清晨和傍晚低，日变化曲线呈倒U型，反射辐射和有效辐射占总辐射的比率在昼间低，清晨和傍晚高，日变化曲线呈U型。  结论  西双版纳热带季节雨林辐射除受到太阳活动、云量和水汽等因子的影响外，还受区域小气候的影响，如季节性落叶和季节性雾。研究森林辐射特征的长期变化，对于气候变化研究、气候模型验证和森林生产力研究等具有重要意义。 

Long-term variation characteristics of radiation in the tropical seasonal rainforest in Xishuangbanna,southwestern China

Objective]Solar radiation is the main source of energy and also one of the most important influencing factors affecting the local and regional climate and environment of forest ecosystem.However,long-term changes of radiation data are needed to focus on climate change research.Exploring the long-term characteristics of solar radiation of forest is very important to establish a research foundation for climate change,tropical forest productivity,radiation energy balance,and the establishment and verification of radiation models.In order to explore the long-term changes of radiation characteristics of tropical seasonal rainforest in Xishuangbanna of southwestern China,the observation of ground based long-term radiation had been conducted.Method]The characteristics of the ratio of various components to solar radiation had been explored in a tropical seasonal rainforest in Xishuangbanna on different time scales from 2003 to 2016.Result]The multi-year mean annual values of total radiation,net radiation,reflected radiation,atmospheric invers-radiation and upward canopy long-wave radiation were:5268.8,3151.5,513.8,12468.6,13299.3 MJ/m²,respectively.The inter-annual variation of global radiation showed a fluctuating upward trend,whereas the net radiation fluctuates showed a downward trend,and a significant decrease in the proportion of global radiation.The inter-annual variability of atmospheric invers-radiation was higher due to the different atmospheric conditions were mainly affected,which resulting in a large inter-annual variability of the effective radiation.Whereas the inter-annual variability of upward canopy long-wave radiation was lower,indicating that the canopy long-wave radiation of tropical seasonal rainforest was not changed too much.The diurnal variation curve of atmospheric inverse-radiation was bimodal in the dry season and unimodal in the rainy season.On different time scales,the upward long-wave radiation from the forest canopy was higher than the atmospheric inverse-radiation,indicating that the tropical seasonal rainforest canopy was a heat source for the atmosphere.The ratio of net radiation to Comment annual global radiation was about 60%,and the inter-annual variation showed a significant downward trend.The ratios of reflected radiation and effective radiation to annual global radiation were relatively stable.The ratio of net radiation to global radiation was high during the daytime but low at dawn and dusk,which showed an inverted U-shaped curve.The ratios of reflected radiation and effective radiation to total radiation were lower during the daytime and higher at dawn and dusk,which showed U-shaped curves.Conclusion]In addition to being affected by general factors such as solar activity,cloud cover and water vapor,the radiation of Xishuangbanna tropical rainforest is also affected by regional climates,such as seasonal defoliation and seasonal fog weather.The study of long-term changes in forest radiation characteristics have great significance for climate change research,climate model verification and forest productivity research.