Comparing the impact of cloudiness on carbon dioxide exchange in a grassland and a maize cropland in northwestern China

Yang, Bai; Wang, Jian; Zhang, Baocheng; Zhang, Zhihui; Liang, Junwu

doi:10.1007/s11284-012-0930-z

Cited by 29 publications

(36 citation statements)

References 30 publications

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“…Therefore, to determine the diffuse component of total PAR, we followed the methods derived by Spitters et al (1986) and Reindl et al (1990) which have been widely used in the literature (Gu et al, 1999;Jing et al, 2010;Zhang et al, 2010;Bai et al, 2012). The calculation is performed deriving the diffuse PAR radiation from the following formulation (Spitters, 1986):…”

Section: Methods To Derive Total and Diffuse Parmentioning

confidence: 99%

“…Since no direct observations of cloud cover were made at K34 or RBJ, measurements of global solar radiation at the surface to assess the presence or absence of clouds were used (Gu et al, 1999;Oliveira et al, 2007;Zhang et al, 2010;Bai et al, 2012). The critical step in this approach is identifying what is a "clear-sky" day in order to establish a basis for comparison with cloudy or partly cloudy days.…”

Section: Procedures For the Quantification Of Aerosol And Cloud Effectmentioning

confidence: 99%

“…When clear-sky irradiance is not available, sky conditions can be described in terms of the "clearness index", kt, defined as the ratio of solar radiation received at the surface to the solar irradiance at the top of the atmosphere (TOA). For a given solar elevation angle, small kt values indicate an increase in the cloud coverage and/or aerosol loading, while higher values indicate more clear-sky conditions (Gu et al, 1999;Zhang et al, 2010;Bai et al, 2012). Mathematically, the clearness index can be expressed by…”

Section: The Definition Of the Clearness Indexmentioning

confidence: 99%

“…The clear days selected by the method of Gu (1999) were compared with the clear-sky days from satellite observations (GOES10) and it was found that about 70 % of the number of clear days selected by GOES10 were also selected by the method of Gu (1999). Two patterns for clear mornings and afternoons were assumed (Gu et al, 1999;Zhang et al, 2010;Bai et al, 2012): (1) kt should increase smoothly with the solar zenith angle, cos(z), and (2) the relationship between clear-sky kt and cos(z) must form an envelope in the lumped scatterplot of kt against cos(z). The following steps and procedures were employed to find kt * : First, values of kt were plotted against time during the day.…”

Section: Defining Clear Skies Conditionsmentioning

confidence: 99%

“…The changes in the observed NEE relative to NEE with clear skies were used to determine the percentage effect of aerosols and clouds on the NEE ( %NEE). The %NEE was calculated by the following relationship (Bai et al, 2012;Gu et al, 1999;Oliveira et al, 2007):…”

Section: Determination Of Nee On Clear-sky Daysmentioning

confidence: 99%

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The effect of atmospheric aerosol particles and clouds on net ecosystem exchange in the Amazon

et al. 2014

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Abstract. Carbon cycling in the Amazon is closely linked to atmospheric processes and climate in the region as a consequence of the strong coupling between the atmosphere and biosphere. This work examines the effects of changes in net radiation due to atmospheric aerosol particles and clouds on the net ecosystem exchange (NEE) of CO 2 in the Amazon region. Some of the major environmental factors affecting the photosynthetic activity of plants, such as air temperature and relative humidity, were also examined. An algorithm for clear-sky irradiance was developed and used to determine the relative irradiance, f , which quantifies the percentage of solar radiation absorbed and scattered due to atmospheric aerosol particles and clouds. Aerosol optical depth (AOD) was calculated from irradiances measured with the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor, onboard the Terra and Aqua satellites, and was validated with ground-based AOD measurements from AERONET (Aerosol Robotic Network) sun photometers. Carbon fluxes were measured using eddy covariance technique at the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) flux towers. Two sites were studied: the Jaru Biological Reserve (RBJ), located in Rondonia, and the Cuieiras Biological Reserve at the K34 LBA tower (located in a preserved region in the central Amazon). Analysis was performed continuously from 1999 to 2009 at K34 and from 1999 to 2002 at RBJ, and includes wet, dry and transition seasons. In the Jaru Biological Reserve, a 29 % increase in carbon uptake (NEE) was observed when the AOD ranged from 0.10 to 1.5 at 550 nm. In the Cuieiras Biological Reserve, the aerosol effect on NEE was smaller, accounting for an approximate 20 % increase in NEE. High aerosol loading (AOD above 3 at 550 nm) or high cloud cover leads to reductions in solar flux and strong decreases in photosynthesis up to the point where NEE approaches zero. The observed increase in NEE is attributed to an enhancement (∼ 50 %) in the diffuse fraction of photosynthetic active radiation (PAR). The enhancement in diffuse PAR can be done through increases in aerosols and/or clouds. In the present study, it was not possible to separate these two components. Significant changes in air temperature and relative humidity resulting from changes in solar radiation fluxes under high aerosol loading were also observed at both sites. Considering the long-range transport of aerosols in the Amazon, the observed changes in NEE for these two sites may occur over large areas in the Amazon, significantly altering the carbon balance in the largest rainforest in the world.

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Section: Methods To Derive Total and Diffuse Parmentioning

confidence: 99%

Section: Procedures For the Quantification Of Aerosol And Cloud Effectmentioning

confidence: 99%

Section: The Definition Of the Clearness Indexmentioning

confidence: 99%

Section: Defining Clear Skies Conditionsmentioning

confidence: 99%

Section: Determination Of Nee On Clear-sky Daysmentioning

confidence: 99%

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The effect of atmospheric aerosol particles and clouds on net ecosystem exchange in the Amazon

et al. 2014

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Impact of Sky Conditions on Net Ecosystem Productivity over a “Floating Blanket” Wetland in Southwest China

Shao,

Liu,

et al. 2023

Adv. Atmos. Sci.

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Water and carbon dioxide fluxes over an alpine meadow in southwest China and the impact of a spring drought event

et al. 2015

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Based on the eddy covariance measurements from June 2011 to December 2013, the seasonal variations and the controls of water and CO2 fluxes were investigated over an alpine meadow in Lijiang, southwest China. The year 2012 had the largest total precipitation among years from 2011 to 2013 (1037.9, 1190.4, and 1066.1 mm, respectively). A spring drought event occurred from March to May 2012, and the peak normalized difference vegetation index (NDVI) in 2012 was the lowest. Throughout the whole year, net radiation (Rn), vapor pressure deficit, and air temperature (Ta) were the primary controls on evapotranspiration (ET), and R n is the most important factor. The influence of R n on ET was much more in the wet season (R(2) = 0.93) than in the dry season (R(2) = 0.28). In the wet season, the ratio of ET to equilibrium ET (ETeq) (0.92 ± 0.14; mean ± S.D.) did not show a clear seasonal pattern with NDVI when the soil water content (SWC) was usually more than 0.25 m(3) m(-3), indicating that ET could be predicted well by ETeq (or radiation and temperature). On half-hourly and daily scales, photosynthetic active radiation (PAR) and air temperature were the main meteorological factors in determining the net ecosystem production (NEP). The seasonal trends of NEP were closely related with the change of NDVI. The integrated NEP in the 2012 wet season (157.8 g C m(-2) year(-1)) was 19.5 and 23.8 % lower than in the 2011 and 2013 wet season (207.0 and 196.1 g C m(-2) year(-1)). The mean ET/ETeq for each of the wet seasons from 2011 to 2013 was 0.88. The 2012 spring drought and its reduction in NDVI decreased the total NEP significantly but had little effect on the total ET in the wet season. The different response of NEP and ET to the spring drought was attributed to the high SWC and small vapor pressure deficit during the wet season.

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Comparing the impact of cloudiness on carbon dioxide exchange in a grassland and a maize cropland in northwestern China

Cited by 29 publications

References 30 publications

The effect of atmospheric aerosol particles and clouds on net ecosystem exchange in the Amazon

The effect of atmospheric aerosol particles and clouds on net ecosystem exchange in the Amazon

Impact of Sky Conditions on Net Ecosystem Productivity over a “Floating Blanket” Wetland in Southwest China

Water and carbon dioxide fluxes over an alpine meadow in southwest China and the impact of a spring drought event

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