Responses of net ecosystem exchanges of carbon dioxide to changes in cloudiness: Results from two North American deciduous forests
Responses of net ecosystem exchanges of carbon dioxide to changes in cloudiness: Results from two North American deciduous forests
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DOI：
10.1029/1999jd901068
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发表时间：
1999-12-27
影响因子：
4.4
通讯作者：
Black, TA
中科院分区：
文献类型：
--
作者：
Gu, LH;Fuentes, JD;Black, TA
我们分析了来自加拿大北方白杨林和温带混交林的半小时二氧化碳通量测量值，以检验云对森林碳吸收的影响。结果表明，云层的存在持续且显著地增加了两种森林在晴朗天空下的二氧化碳净生态系统交换（NEE）。这种增强随云量、太阳仰角的不同而不同，在两种森林之间也存在差异。对于白杨林，在太阳仰角20°~ 25°区间，峰值增强幅度约为30%，在太阳仰角55°~ 60°区间，峰值增强幅度约为55%。对于混交林，太阳仰角30°~ 35°区间的峰值增强幅度在60%以上，65°~ 70°区间的峰值增强幅度在30%左右。平均太阳仰角bbb20°时，白杨林和混交林的NEE最大，辐照度分别为晴空辐射的78%和71%。目前这两个地点的一般气候模式允许进一步增加云量，以增强它们的碳吸收。我们发现，这两种森林都能承受由云量增加引起的太阳辐射的大幅减少（白杨林为53%，混交林为46%），而不会降低它们的碳吸收能力。我们认为，多云条件下碳吸收的增强是与云存在相关的多种环境因素相互作用的结果。
We analyzed half-hourly tower-based flux measurements of carbon dioxide (CO2) from a boreal aspen forest and a temperate mixed deciduous forest in Canada to examine the influences of clouds on forest carbon uptake. We showed that the presence of clouds consistently and significantly increased the net ecosystem exchanges (NEE) of CO2 of both forests from the level under clear skies. The enhancement varied with cloudiness, solar elevation angles, and differed between the two forests. For the aspen forest the enhancement at the peak ranged from about 30% for the 20 degrees-25 degrees interval of solar elevation angles to about 55% for the 55 degrees-60 degrees interval. For the mixed forest the enhancement at the peak ranged from more than 60% for the 30 degrees-35 degrees interval of solar elevation angles to about 30% for the 65 degrees-70 degrees interval. Averaged over solar elevation angles >20 degrees, the aspen and mixed forests had the maximal NEE at the irradiance equivalent to 78 and 71% of the clear-sky radiation, respectively. The general patterns of current shy conditions at both sites permit further increases in cloudiness to enhance their carbon uptake. We found that both forests can tolerate exceedingly large reductions of solar radiation (53% for the aspen forest and 46% for the mixed forest) caused by increases in cloudiness without lowering their capacities of carbon uptake. We suggest that the enhancement of carbon uptake under cloudy conditions results from the interactions of multiple environmental factors associated with the presence of clouds.