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| Titel |
The effects of clouds and aerosols on net ecosystem CO2 exchange over semi-arid Loess Plateau of Northwest China |
| VerfasserIn |
X. Jing, J. Huang, G. Wang, K. Higuchi, J. Bi, Y. Sun, H. Yu, T. Wang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 17 ; Nr. 10, no. 17 (2010-09-02), S.8205-8218 |
| Datensatznummer |
250008745
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| Publikation (Nr.) |
 copernicus.org/acp-10-8205-2010.pdf |
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| Zusammenfassung |
| 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 50°) 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. |
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