Separating the diffuse and direct component of global radiation and its implications for modeling canopy photosynthesis Part I. Components of incoming radiation

Spitters, C.J.T.; Toussaint, Hervé; Goudriaan, J.

doi:10.1016/0168-1923(86)90060-2

Cited by 507 publications

(252 citation statements)

References 10 publications

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“…The detailed explanations about the calculation of the total PAR can be found in Zhou et al (1996) and Ji et al (1993). To determine the diffuse component of the total PAR, Spitters et al (1986) proposed the following relationship:…”

Section: Total Par and Diffuse Parmentioning

confidence: 99%

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

et al. 2010

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Abstract. 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 CO 2 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 CO 2 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 CO 2 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 CO 2 uptake and light use efficiency of vegetation occur with the clearness index of about 0.37 and lower air temperature. Under other sky conditions, CO 2 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 CO 2 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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Section: Total Par and Diffuse Parmentioning

confidence: 99%

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

et al. 2010

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“…where a is plant canopy albedo (assumed constant at 0.15), p is the ratio of energy in the PAR to shortwave wavebands (0.5 [Spitters et al, 1986]), f PARi is the monthly average fraction of incident radiation intercepted by the canopy and f Si is average shortwave irradiance per month (W m À2 ). Sellers et al [1992] established from theoretical and empirical evidence a linear relationship between f PAR and the ''simple ratio'' (s) of near infrared to visible reflectances at the canopy surface.…”

Section: A22 Canopy Light Absorptionmentioning

confidence: 99%

Steady state turnover time of carbon in the Australian terrestrial biosphere

Barrett¹

2002

Global Biogeochemical Cycles

119

127

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[1] The turnover time of terrestrial carbon was estimated using a multiobjective parameterization method that combined data sets of plant production, biomass, litter and soil-C observations in the calibration of a C-cycle model for the Australian continent (VAST1.1; Vegetation and Soil carbon Transfer). The method employed a genetic algorithm to minimize model-data deviations and maximize consistency between estimated model parameters and all available data. Based on the parameterization, the turnover time of biosphere C for Australia was estimated to be 78 years which is longer than global C-turnover estimates (of 26-60 years) due entirely to slower turnover of C in the upper 20 cm of soil. Turnover times of litter and deeper soil-C were similar to global values. By splitting total C in the upper 20 cm between labile and nonlabile fractions (based on published data) the turnover time of the labile pool was at least 44 years which is still longer than global estimates (9-25 years). Longer C-turnover in Australian surface soils was attributed to (1) limited soil moisture slowing decomposition more than net primary production, (2) frequent fires leading to a large fraction of nonlabile charcoal C in soil, and (3) strong adsorbing capacity for organic-C in these highly weathered soils. It was found that >89% of the C flux to the atmosphere from decomposition of organic matter originated from fine litter, coarse woody debris and the upper 20 cm of soil in all biomes.

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“…The two conductances are then combined in parallel to obtain the total surface vapor conductance of the canopy. The applicable values of Q p used for calculating g S for the two classes of leaves are modeled from observed incident radiation using the approach described by Spitters et al [1986]. L cdoy values are calculated using the following equation, which assumes a spherical distribution of leaves within the canopy:…”

Section: Transpiration Model and Canopy Conductance Submodel Configurmentioning

confidence: 99%

Quantitative comparison of canopy conductance models using a Bayesian approach

Samanta

Clayton

Mackay

et al. 2008

Water Resources Research

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[1] A quantitative model comparison methodology based on deviance information criterion, a Bayesian measure of the trade-off between model complexity and goodness of fit, is developed and demonstrated by comparing semiempirical transpiration models. This methodology accounts for parameter and prediction uncertainties associated with such models and facilitates objective selection of the simplest model, out of available alternatives, which does not significantly compromise the ability to accurately model observations. We use this methodology to compare various Jarvis canopy conductance model configurations, embedded within a larger transpiration model, against canopy transpiration measured by sap flux. The results indicate that descriptions of the dependence of stomatal conductance on vapor pressure deficit, photosynthetic radiation, and temperature, as well as the gradual variation in canopy conductance through the season are essential in the transpiration model. Use of soil moisture was moderately significant, but only when used with a hyperbolic vapor pressure deficit relationship. Subtle differences in model quality could be clearly associated with small structural changes through the use of this methodology. The results also indicate that increments in model complexity are not always accompanied by improvements in model quality and that such improvements are conditional on model structure. Possible application of this methodology to compare complex semiempirical models of natural systems in general is also discussed.

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Separating the diffuse and direct component of global radiation and its implications for modeling canopy photosynthesis Part I. Components of incoming radiation

Cited by 507 publications

References 10 publications

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

Steady state turnover time of carbon in the Australian terrestrial biosphere

Quantitative comparison of canopy conductance models using a Bayesian approach

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Separating the diffuse and direct component of global radiation and its implications for modeling canopy photosynthesis Part I. Components of incoming radiation

Cited by 507 publications

References 10 publications

The effects of clouds and aerosols on net ecosystem CO&lt;sub&gt;2&lt;/sub&gt; exchange over semi-arid Loess Plateau of Northwest China

The effects of clouds and aerosols on net ecosystem CO&lt;sub&gt;2&lt;/sub&gt; exchange over semi-arid Loess Plateau of Northwest China

Steady state turnover time of carbon in the Australian terrestrial biosphere

Quantitative comparison of canopy conductance models using a Bayesian approach

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Resources

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The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China

The effects of clouds and aerosols on net ecosystem CO<sub>2</sub> exchange over semi-arid Loess Plateau of Northwest China