Estimating Cloud Type from Pyranometer Observations

Duchon, Claude E.; O’Malley, Mark S.

doi:10.1175/1520-0450(1999)038<0132:ectfpo>2.0.co;2

Cited by 79 publications

(76 citation statements)

References 15 publications

(15 reference statements)

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“…Previous studies in the Amazon have shown that the background AOD, due to atmospheric natural conditions, is about 0.1 at 550 nm. There are few models assessed in the literature for the calculation of S 0 (Ricchiazzi et al, 1998;Duchon and O'Malley, 1999). In this study, we chose to employ an algorithm for clear-sky irradiance that would include the intrinsic characteristics of local conditions in the Amazon.…”

Section: Procedures For the Quantification Of Aerosol And Cloud Effectmentioning

confidence: 99%

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: Procedures For the Quantification Of Aerosol And Cloud Effectmentioning

confidence: 99%

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

et al. 2014

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“…The pyranometer detects these circumstances, but integrates the whole sky and therefore does not provide the relevant information in the direction of the Sun alone. An automatic determination of cloud type is possible with these data (Duchon & O'Malley 1999), however, which would be interesting to combine in a future work with the information on aerosols provided by PAPS.…”

Section: The Pps Pyranometer and Solar Radiation Monitoringmentioning

confidence: 99%

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

Meftah

Corbard

Irbah

et al. 2014

A&A

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Context. For the past thirty years, modern ground-based time-series of the solar radius have shown different apparent variations according to different instruments. The origins of these variations may result from the observer, the instrument, the atmosphere, or the Sun. Solar radius measurements have been made for a very long time and in different ways. Yet we see inconsistencies in the measurements. Numerous studies of solar radius variation appear in the literature, but with conflicting results. These measurement differences are certainly related to instrumental effects or atmospheric effects. Use of different methods (determination of the solar radius), instruments, and effects of Earth's atmosphere could explain the lack of consistency on the past measurements. A survey of the solar radius has been initiated in 1975 by Francis Laclare, at the Calern site of the Observatoire de la Côte d'Azur (OCA). Several efforts are currently made from space missions to obtain accurate solar astrometric measurements, for example, to probe the long-term variations of solar radius, their link with solar irradiance variations, and their influence on the Earth climate. Aims. The Picard program includes a ground-based observatory consisting of different instruments based at the Calern site (OCA, France). This set of instruments has been named "Picard Sol" and consists of a Ritchey-Chrétien telescope providing full-disk images of the Sun in five narrow-wavelength bandpasses (centered on 393.37, 535.7, 607.1, 782.2, and 1025.0 nm), a Sun-photometer that measures the properties of atmospheric aerosol, a pyranometer for estimating a global sky-quality index, a wide-field camera that detects the location of clouds, and a generalized daytime seeing monitor allowing us to measure the spatio-temporal parameters of the local turbulence. Picard Sol is meant to perpetuate valuable historical series of the solar radius and to initiate new time-series, in particular during solar cycle 24. Methods. We defined the solar radius by the inflection-point position of the solar-limb profiles taken at different angular positions of the image. Our results were corrected for the effects of refraction and turbulence by numerical methods. Results. From a dataset of more than 20 000 observations carried out between 2011 and 2013, we find a solar radius of 959.78 ± 0.19 arcsec (696 113 ± 138 km) at 535.7 nm after making all necessary corrections. For the other wavelengths in the solar continuum, we derive very similar results. The solar radius observed with the Solar Diameter Imager and Surface Mapper II during the period 2011-2013 shows variations shorter than 50 milli-arcsec that are out of phase with solar activity.

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“…However, most of the studies related to cloudiness have focussed on the analysis of only short-wave radiation measurements [3,4] and scarce research on the complete effect of clouds on the different wavelengths has been conducted. Thus, studies dealing with the simultaneous effect of cloudiness on the solar and on the terrestrial radiation are needed to improve the understanding of the absorption, scattering and emission processes suffered by solar and terrestrial radiation in presence of clouds.…”

Section: Introductionmentioning

confidence: 99%

Effect of cloudiness on solar global, solar diffuse and terrestrial downward radiation at Badajoz (Southwestern Spain)

Sánchez¹

2012

Opt. Pura Apl.

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ABSTRACT:Among all the components participating in the Earth radiation balance, clouds exhibit a large uncertainty in their characterization and quantification, partially due to their complex interaction with radiation. Although they play a key role attenuating and controlling the solar radiation and absorbing, scattering and emitting infrared radiation, their description is still very poor and more detailed studies are demanded. In order to contribute to that aim, simultaneous measurements of solar global irradiance, solar diffuse irradiance and downward infrared irradiance on a one-minute basis were performed at a radiometric station located in the Campus of the University of Extremadura in Badajoz (Spain). In this study the information provided by solar irradiance and its partitioning direct-to-diffuse, and by downward infrared irradiance is compared for some particularly interesting cases of study: cloud-free, partially cloudy and overcast. It is noted that infrared radiation does not exhibit the variability shown by the global solar radiation and directdiffuse partition in the different conditions analysed. The results emphasize the joint use of measurements of solar and infrared radiation which positively contribute to achieve a thorough description of the cloudiness field.

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Estimating Cloud Type from Pyranometer Observations

Cited by 79 publications

References 15 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

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

Effect of cloudiness on solar global, solar diffuse and terrestrial downward radiation at Badajoz (Southwestern Spain)

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