The dependence of global and diffuse PAR radiation components on sky conditions at Athens, Greece

Jacovides, C.P.; Tymvios, Filippos; Assimakopoulos, Vasiliki D.; Kaltsounides, N.A.

doi:10.1016/j.agrformet.2007.01.004

Cited by 88 publications

(69 citation statements)

References 39 publications

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“…The ratio between PAR and SW downward irradiance varies between 0.41 and 0.43; these values are in agreement with measurements of this ratio at other Mediterranean sites (Jacovides et al, 2007). relative maxima and minima (although measurements every 10 min under sample the oscillation) are in phase with the maxima of the aerosol optical depth.…”

Section: Observationssupporting

confidence: 74%

Estimate of surface direct radiative forcing of desert dust from atmospheric modulation of the aerosol optical depth

2013

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Measurements carried out on the island of Lampedusa, in the central Mediterranean, on 7 September 2005, show the occurrence of a quasi-periodic oscillation of aerosol optical depth, column water vapour, and surface irradiance in different spectral bands. The oscillation has a period of about 13 min and is attributed to the propagation of a gravity wave able to modify the vertical structure of the planetary boundary layer, as also confirmed by satellite images. The wave occurred during a Saharan dust event. The oscillation amplitude is about 0.1 for the aerosol optical depth, and about 0.4 cm for the column water vapour. The modulation of the downward surface irradiances is in opposition of phase with respect to aerosol optical depth and water vapour column variations. The perturbation of the downward irradiance produced by the aerosols is determined by comparing the measured irradiances with estimated irradiances at a fixed value of the aerosol optical depth, and by correcting for the effect of the water vapour in the shortwave spectral range. The direct radiative forcing efficiency, i.e., the radiative perturbation of the net surface irradiance produced by a unit of optical depth aerosol layer, is determined at different solar zenith angles as the slope of the irradiance perturbation versus the aerosol optical depth. The estimated direct surface forcing efficiency at about 60° solar zenith angle is −(181 ± 17) W m⁻² in the shortwave, and −(83 ± 7) W m⁻² in the photosynthetic spectral range. The estimated daily average forcing efficiencies are of about −79 and −46 W m⁻² for the shortwave and photosynthetic spectral range, respectively

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Section: Observationssupporting

confidence: 74%

Estimate of surface direct radiative forcing of desert dust from atmospheric modulation of the aerosol optical depth

2013

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“…BEIS3.14 and MEGAN2.02 used values of 4.6 and 4.55 µmol photons per Joule, respectively. The WRF-AQ version of MEGAN2.1 uses different conversion factors for direct (4.0 µmol photons per Joule) and diffuse light (4.6 µmol photons per Joule) based on observations reported by Lizaso et al (2005) and Jacovides et al (2007).…”

Section: Above Canopy Environmentmentioning

confidence: 99%

The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1): an extended and updated framework for modeling biogenic emissions

et al. 2012

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Abstract. The Model of Emissions of Gases and Aerosolsfrom Nature version 2.1 (MEGAN2.1) is a modeling framework for estimating fluxes of biogenic compounds between terrestrial ecosystems and the atmosphere using simple mechanistic algorithms to account for the major known processes controlling biogenic emissions. It is available as an offline code and has also been coupled into land surface and atmospheric chemistry models. MEGAN2.1 is an update from the previous versions including MEGAN2.0, which was described for isoprene emissions by Guenther et al. (2006) and MEGAN2.02, which was described for monoterpene and sesquiterpene emissions by Sakulyanontvittaya et al. (2008). Isoprene comprises about half of the total global biogenic volatile organic compound (BVOC) emission of 1 Pg (1000 Tg or 10 15 g) estimated using MEGAN2.1. Methanol, ethanol, acetaldehyde, acetone, α-pinene, β-pinene, t-β-ocimene, limonene, ethene, and propene together contribute another 30 % of the MEGAN2.1 estimated emission. An additional 20 compounds (mostly terpenoids) are associated with the MEGAN2.1 estimates of another 17 % of the total emission with the remaining 3 % distributed among >100 compounds. Emissions of 41 monoterpenes and 32 sesquiterpenes together comprise about 15 % and 3 %, respectively, of the estimated total global BVOC emission. Tropical trees cover about 18 % of the global land surface and are estimated to be responsible for ∼ 80 % of terpenoid emissions and ∼ 50 % of other VOC emissions. Other trees cover about the same area but are estimated to contribute only about 10 % of total emissions. The magnitude of the emissions estimated with MEGAN2.1 are within the range of estimates reported using other approaches and much of the differences between reported values can be attributed to land cover and meteorological driving variables. The offline version of MEGAN2.1 source code and driving variables is available from http://bai.acd.ucar.edu/MEGAN/ and the version integrated into the Community Land Model version 4 (CLM4) can be downloaded from http://www.cesm. ucar.edu/.

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“…To date, estimation of PAR has almost totally focused on estimation of incident PAR flux on the ground surface and above the vegetation canopy directly from the ground-based global solar radiation. However, when light penetrates the air, it is affected by several atmospheric processes such as Rayleigh scattering, water vapor and ozone absorption, and aerosol loadings (Misson et al 2005;Jacovides et al 2007). Apparently, as a counterpart of the incident PAR, the lost PAR energy ratio (LPR) in the atmosphere is much more directly related with absorption processes than the incident PAR.…”

Section: Introductionmentioning

confidence: 99%

“…Even though PAR is extremely important, it is often not measured in most meteorological stations around the world; therefore, it has to be estimated from the commonly measured global solar radiation (R S ). As a result, PAR is usually estimated with other measured variables as follows, using one of three approaches: (a) the fractional energy of PAR to global solar radiation (fE; Kvifte et al 1983;Papaionnou et al 1993;Udo and Aro 1999;Mõttus et al 2001;Tsubo and Walker 2005), (b) the fraction of photon flux/energy conversion of PAR (fFEC; Alados et al 1996;Aro 1999, 2000;Alados et al 1996;Alados and Alados-Arboledas 1999;Al-Shooshan 1997;Finch et al 2004;Jacovides, et al 2004Jacovides, et al , 2007, or (c) the PAR photon flux density (PPFD;McCree 1966;Papaionnou et al 1993;Alados et al 1996;Jacovides et al 2004). Such processes were driven by different quantitative methods (McCree 1972;McCartney 1978;Udo and Aro 1999), and each method has its positive and negative attributes.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of photosynthetic photon flux density (PPFD) and estimates in coastal northern California

Smith

Jacovides

et al. 2010

Theor Appl Climatol

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The dependence of global and diffuse PAR radiation components on sky conditions at Athens, Greece

Cited by 88 publications

References 39 publications

Estimate of surface direct radiative forcing of desert dust from atmospheric modulation of the aerosol optical depth

Estimate of surface direct radiative forcing of desert dust from atmospheric modulation of the aerosol optical depth

The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1): an extended and updated framework for modeling biogenic emissions

Dynamics of photosynthetic photon flux density (PPFD) and estimates in coastal northern California

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