The effects of clouds and aerosols on net ecosystem CO2 exchange over semi-arid Loess Plateau of Northwest China
The effects of clouds and aerosols on net ecosystem CO2 exchange over semi-arid Loess Plateau of Northwest China
复制标题
云和气溶胶对西北半干旱黄土高原生态系统CO2净交换的影响
DOI：
10.5194/acp-10-8205-2010
复制
发表时间：
2010-01-01
影响因子：
6.3
通讯作者：
Wang, T.
中科院分区：
文献类型：
--
作者：
Jing, X.;Huang, J.;Wang, T.
利用兰州大学半干旱气候与环境观测站的观测资料，研究了云和大气气溶胶对黄土高原半干旱地区陆地碳循环的影响。分析了生长中期（7 - 8月）白天（太阳仰角大于50A度）CO2净生态系统交换（NEE）与漫射辐射、云量和气溶胶光学深度（AOD）的变化关系。结果表明，在半干旱区，云对草地（LAI值较小）的CO2吸收有显著影响，与森林和作物覆盖区有很大不同。冠层的光饱和度较低，约为434.8 W m（-2）。因此，在光学厚云的阴天条件下，CO2吸收量随着clearclearindex（地球表面接收的总太阳辐射与平行于地球表面的地外辐照度之比）的增加而增加，植被的CO2吸收量和光利用效率在clearclearindex约为0.37、气温较低时达到最大值。在其他天空条件下，CO2吸收量随云量的增加而减少，但由于PAR弥散分数的增加，光利用效率提高。此外，在多云条件下，CO2 NEE的变化也是多种环境因素（尤其是气温）相互作用的结果。与其对太阳辐射变化的响应相反，碳吸收对AOD的增加表现出轻微的负响应。半干旱草原与森林、农田响应差异的原因可能是冠层建筑结构的差异。
The impacts of clouds and atmospheric aerosols on the terrestrial carbon cycle at semi-arid Loess Plateau in Northwest China are investigated, by using the observation data obtained at the SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) site. Daytime (solar elevation angles of larger than 50A degrees) net ecosystem exchange (NEE) of CO2 obtained during the midgrowing season (July-August) are analyzed with respect to variations in the diffuse radiation, cloud cover and aerosol optical depth (AOD). Results show a significant impact by clouds on the CO2 uptake by the grassland (with smaller LAI values) located in a semi-arid region, quite different from areas covered by forests and crops. The light saturation levels in the canopy are low, with a value of about 434.8 W m(-2). Thus, under overcast conditions of optically thick clouds, the CO2 uptake increases with increasing clearness index (the ratio of global solar radiation received at the Earth surface to the extraterrestrial irradiance at a plane parallel to the Earth surface), and a maximum CO2 uptake and light use efficiency of vegetation occur with the clearness index of about 0.37 and lower air temperature. Under other sky conditions, CO2 uptake decreases with cloudiness but light use efficiency is enhanced, due to increased diffuse fraction of PAR. Additionally, under cloudy conditions, changes in the NEE of CO2 also result from the interactions of many environmental factors, especially the air temperature. In contrast to its response to changes in solar radiation, the carbon uptake shows a slightly negative response to increased AOD. The reason for the difference in the response of the semi-arid grassland from that of the forest and crop lands may be due to the difference in the canopy's architectural structure.