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ISSN 1006-9895

CN 11-1768/O4

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淮南森林冠层辐射传输过程的特征
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中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室LASG

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41575092,2018YFC1506600


Characteristics of solar radiation and radiative transfer of a forest canopy in Huainan, China
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State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics LASG,Institute of Atmospheric Physics,Chinese Academy of Sciences

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    摘要:

    本文利用淮南森林观测站2018年7月1日至2019年6月30日冠层辐射观测,分析了淮南栎树森林下垫面冠层内外辐射变化特征。结果表明:1)从春季到夏季,栎树冠层之上向下的太阳短波辐射增加,到冬季逐渐减少。从早春开始,由于叶片生长增多冠层中间和冠层之下向下的太阳短波辐射下降,从秋季到冬季树叶凋落其向下的太阳辐射增加,与冠层之上的变化趋势相反;对于向上的短波辐射,无论冠层之上、冠层中间还是冠层之下,随季节的变化都与向下的短波辐射相似,只是数值小很多。2)冠层之上、冠层中间和冠层之下向下长波辐射随时间的变化从春季逐渐开始增大至夏季达到最大,随后逐渐减小并在冬季达到最小;就空间变化而言,冠层中间和冠层之下的向下长波辐射值比冠层之上的辐射值高,使得冠层对长波辐射的振幅增大,晴空条件最高可达1.3倍。3) 淮南森林区冠层之上(距地面25m)年平均反照率为0.14,比中国北方地区(350N)温带季风气候区(混交林为主)反照率的整体水平低0.01,表明淮南的森林茂密、灌丛更多些。4)冠层上部分和整层的短波辐射透射率主要受叶片的影响。夏季,冠层的短波透射率平均为0.1。到了冬天,叶子凋落,透射率增加并趋于一个平稳的波动。冠层的短波辐射吸收率在夏季最高,秋季逐渐降低,随着叶子凋落在冬季迅速减小,趋于一常值。

    Abstract:

    Forest canopy as an active interface between vegetation and environment transmits energy by reflecting, absorbing and transmitting solar radiation by leaves. The radiation above, within and below the forest canopy is very important in the energy balance, water and carbon cycle. Its variation with season and distribution within forest canopies is few studied in Huainan area. Using the data of total radiation measured at Huainan forest observation station from 1 July 2018 to 30 June 2019, the temporal change characteristics of solar radiation above the Sawtooth Oak canopy, and the spatial distribution and transfer of solar radiation through the canopy were analyzed, and also the albedo, transmittance and absorptance of the canopy were given. The results show that: (1) The downward shortwave radiation above the Sawtooth Oak canopy increases from spring to summer, then decreases gradually to winter. But the downward shortwave radiation within and under the canopy demonstrate a different trend with smaller value. It decreases from the early spring and increases from autumn to winter as opposite to that above the canopy. Concerning the upward shortwave radiation, whether above, within or under the canopy, the seasonal variation pattern is the same as the downward one, but the value is much smaller. (2) The downward longwave radiation above, within and under the canopy gradually increases with time from spring to summer, then decreases gradually and reaches the minimum in winter; in terms of spatial change, the radiation value of longwave within and under the canopy is higher than that above the canopy, which enhances longwave radiation and can be as large as 1.3 times under clear skies. (3) The annual average albedo above the canopy in Huainan forest area is 0.14, which is 0.01 lower than that in the temperate monsoon climate area (mainly mixed forest) in northern China (350N), indicating that the forest is denser in Huainan. (4) The shortwave radiation transmittance of the upper part and the whole canopy is mainly affected by the leaves. In summer, the average shortwave transmittance of the whole canopy (τ) is 0.1. But in winter, the leaves wither and fallen, the transmittance increases and tends to a stable fluctuation. The absorptance of shortwave radiation in the canopy was the highest in summer and decreased gradually in autumn, and decreased rapidly in winter as the leaves withered, tending to a stable fluctuation. These results could be useful for validating layered radiative transfer and photosynthesis models and for further study the energy, water and carbon cycle of the forest ecosystem.

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  • 收稿日期:2019-12-18
  • 最后修改日期:2020-04-09
  • 录用日期:2020-04-21
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