The influence of clouds on surface UV erythemal irradiance

Alados-Arboledas, L.; Alados, I.; Foyo-Moreno, I.; Olmo, F.J.; Alcántara, A.

doi:10.1016/s0169-8095(03)00027-9

Cited by 85 publications

(47 citation statements)

References 36 publications

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“…A more general method consists of finding the degree of the polynomial closest to the experimental data by means of a potential regression. This method has been used by other authors (Thiel et al, 1997;Alados-Arboledas et al, 2003). These results suppose an overcast sky transmissivity (C T of 8) of 50% according to the linear regression and of 40% according to the quadratic and the potential ones.…”

Section: Cloud Modification Factor In Relation To Total Cloudinessmentioning

confidence: 99%

“…For this, the information routinely registered in most meteorological stations is used: cloud type and amount, expressed in terms of fractional cloud coverage in oktas, which are usually recorded in a 3-hourly database. This kind of approach has been followed in previous studies (Ilyas, 1987;Frederick and Snell, 1990;Frederick et al, 1993;Blumthaler et al, 1994Blumthaler et al, , 1996Thiel et al, 1997;Kuchinke and Núñez, 1999;Grant and Heisler, 2000;Josefsson and Landelius, 2000;Alados-Arboledas et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Influence of cloudiness over the values of erythemal radiation in Valencia, Spain

Esteve

Marı́n

Tena

et al. 2009

Intl Journal of Climatology

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The influence of cloudiness over experimental UV erythemal radiation (UVER) has been studied. This influence has been analysed considering total cloudiness and low clouds. The measurements of cloudiness correspond to the daily values registered at 13 : 00 GMT at the Meteorological Centre of Valencia, which is part of the State Agency of Meteorology of Spain (AEMET). The UVER measurements were made using a YES UVB-1 radiometer located on the roof terrace of the Physics Faculty at the Burjassot Campus, Valencia (latitude 39.508°, longitude −0.418°, 60 m above sea level). First, a statistical analysis of cloudiness at 13 : 00 GMT in Valencia was carried out, confirming that the situation is mainly clear skies or very few clouds. Next, the influence of cloudiness on experimental UVER values was analysed, for both total cloudiness and low clouds. The experimental UVER values decrease as cloudiness increases for all solar zenith angles (SZA), and this reduction increases with the zenith angle. Next, the cloud modification factor (CMF) has been defined to reduce the influence of the zenith angle and ozone over the UVER. In order to quantify the relationship between CMF and the degree of cloudiness in oktas, linear, quadratic and potential regressions for both total cloudiness and low clouds have been calculated. Transmissivity due to total cloudiness and for overcast skies reaches 40%. On the other hand, the analysis of the influence over the zenith angle shows that CMF reduces as the zenith angle increases in the case of both total cloudiness and low clouds. With regard to the low cloud CMF, the results are comparable to those proposed by the COST-713 Action "UV-B Forecasting" for partially cloudy or cloudy skies (70% and 50%, respectively). Finally, the relationship between the CMF and the clearness index (k T ) has been analysed, as both parameters are simple indicators of cloudiness. It has been proved that such relationship is close to unity for zenith angles in the mid-range, while the CMF is greater than k T for lower SZA and is less than k T for high SZA, which indicates a certain dependence of these two parameters on the zenith angle.

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Section: Cloud Modification Factor In Relation To Total Cloudinessmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence of cloudiness over the values of erythemal radiation in Valencia, Spain

Esteve

Marı́n

Tena

et al. 2009

Intl Journal of Climatology

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“…It can be seen that the annual solar cycle (driven by astronomical factors) and the total ozone annual cycle explain the sinusoidal evolution of the UVI values. In addition, the figure shows significant day-to-day variability which is mainly associated with changes in the cloud cover (Alados-Arboledas et al, 2003b). These short-term UVI changes are also affected by the day-to-day fluctuations of the aerosol load (di Sarra et al, 2002) and the total ozone column (Antón et al, 2008).…”

Section: Experimental Uv Indexmentioning

confidence: 98%

Influence of the calibration on experimental UV index at a midlatitude site, Granada (Spain)

et al. 2011

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Abstract. The ultraviolet index (UVI) is the most commonly used variable to inform about the level and potential harmful effect of ultraviolet (UV) radiation reaching the Earth's surface. This variable is derived from the output signal of UV radiometers applying conversion factors from calibration methods. This paper focused on the influence of the use of two of these methods (called one-step and two-steps methods) on the experimental UVI measured by a YES UVB-1 radiometer located in a midlatitude station, Granada (Spain) for the period 2006-2009. In addition, it also analyzes the deviation from the UVI values obtained when the manufacturer's calibration factors are applied. For this goal, a detailed characterization of the UVB-1 radiometer from the first Spanish calibration campaign of broadband UV radiometers at the "El Arenosillo" INTA station in 2007 was used. In addition, modeled UVI data derived from the LibRadtran/UVSPEC radiative transfer code are compared with the experimental values recorded at Granada for cloud-free conditions. Absolute mean differences between measured and modeled UVI data at Granada were around 5% using the onestep and two-steps calibration methods, indicating an excellent performance of these two techniques for obtaining UVI data from the UVB-1 radiometer. Conversely, the application of the manufacture's calibration factor produced a large overestimation (∼14%) of the UVI values, generating unreliable alarming high UVI data in summer. Thus, the number of days with an extreme erythemal risk (UVI higher than 10) increased up to 46% between May and September at Granada. This percentage reduced to a more reliable value of 3% when the conversion factors obtained with the two-steps calibration Correspondence to: M. Antón (mananton@unex.es) method are used. These results evidence the need for a sound calibration of the broadband UV instruments in order to obtain reliable measurements.

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“…The short-term variability of the UV radiation reaching the Earth's surface is mainly controlled by changes in the cloud cover [1,2]. Thus, cloudiness variability often masks the effects of ozone changes, and it may reduce, cancel or even reverse the expected UV increase related to the reduction in ozone amount [3].…”

Section: Introductionmentioning

confidence: 99%

Study of UV cloud modification factors in Southern Patagonia

Wolfram¹,

Orte²,

Salvador³

et al. 2017

AIP Conference Proceedings

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How large and how long are UV and total radiation enhancements? AIP Conference Proceedings 1810, 110002 (2017) ewolfram@gmail.comAbstract. Anthropogenic perturbation of the ozone layer has induced change in the amount of UV radiation that reaches the Earth's surface, mainly through the Antarctic ozone hole, making the ozone and ultraviolet (UV) radiation two important issues in the study of Earth atmosphere in the scientific community. Also the clouds have been identified as the main modulator of UV amount in short time scales and produce the main source of uncertainty in the projection of surface UV level as consequence of projected ozone recovery. While clouds can decrease direct radiation, they can produce an increase in the diffuse component, and as consequence the surface UV radiation may be higher than an equivalent clear sky scenario for several minutes. In particular this situation can be important when low ozone column and partially cloud cover skies happen simultaneously. These situations happen frequently in southern Patagonia, where the CEILAP Lidar Division has established the Atmospheric Observatory of Southern Patagonia, an atmospheric remote sensing site near the city of Río Gallegos (51º55'S, 69º14'W). In this paper, the impact of clouds over the UV radiation is investigated by the use of ground based measurements from the passive remote sensing instruments operating at this site, mainly of broad and moderate narrow band filter radiometers. We analyzed the UV Index obtained from a multiband filter radiometer GUV-541 (UVI) [Biospherical Inc.] installed in the Observatorio Atmosférico de la Patagonia Austral, Río Gallegos, since 2005. Cloud modification factors (CMF, ratio between the measured UV radiation in a cloudy sky and the simulated radiation under cloud-free conditions) are evaluated for the study site. The database used in this work covers the period 2005-2012 for spring and summer seasons, when the ozone hole can affect these subpolar regions. CMF higher than 1 are found during spring and summer time, when lower total ozone columns, higher solar elevations and high cloud cover occur simultaneously, producing extreme erythemal irradiance at ground surface. Enhancements as high as 25% were registered. The maximum duration of the enhancement was around 30 minute. This produces dangerous sunbathing situations for the Río Gallegos citizen..

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The influence of clouds on surface UV erythemal irradiance

Cited by 85 publications

References 36 publications

Influence of cloudiness over the values of erythemal radiation in Valencia, Spain

Influence of cloudiness over the values of erythemal radiation in Valencia, Spain

Influence of the calibration on experimental UV index at a midlatitude site, Granada (Spain)

Study of UV cloud modification factors in Southern Patagonia

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