UV-B AND UVI MEASURED AND CALCULATED IN VALLADOLID, SPAIN.

1. UV-B AND UVI MEASURED AND CALCULATED IN VALLADOLID, SPAIN. P.Salvador, J. Bilbao, A. de Miguel and A. Perez-Burgos Department of Applied Physics, University of Valladolid, Science Faculty. Prado de la Magdalena s/n, Valladolid, 47005, Spain 983.42.31.33, pasalgo@fa1.uva.es 1 Goals 3 Results and Discussion Figure 1 shows that the maximum of ozone measured with the spectrometer TOMS by the NASA was reached in January (496 DU) and the maximum of UVB in June (47.2 kJm-2day-1). The difference between the maximum of ozone (usually at February) and the maximum in UVB four month later (usually in June) is due to the wind of the stratosphere, (Vilaplana, 2004). It has been made a classification of the days following the clearness of the atmosphere. The clearness index is given by the expression: The spectral range corresponding to wavelenghts between 280 and 315 nm is called the UVB. The UVB radiation only represents a 5 % of the UV radiation (Miguel 2005) and a 0.5% of the solar radiation (Leun, 1993) The UVI is a dimensionless index and one unit equals 25 mWm-2 of erythemal radiation. The aim of this work is to give a description of the variation of UVB, ozone and UVI in Valladolid, Spain and validate a model developed by our research group called CIBA_1.2. Figure 1: Daily values of UVB (280-315nm) and ozone between 2002 and 2005. where Dh is the horizontal diffuse hourly irradiance, In the normal incidence direct hourly irradiance, Z the zenith angle and k a constant equal to 1.041 for Z in radians (Perez 1990). It have been found 34 clear days with a clearness index higher than 12 at solar noon. The model CIBA_1.2 has been tested during the 34 days. The results for the ten clearest days can be seen in Figure 2. The main caracteristics of that days and the MBE, RMSE and the percentage of error at the solar noon are shown in Table 1. 2 Methods The measurements were recorded by a Yankee UVB-1 sensor mounted in the C.I.B.A. (Low Atmosphere Research Center). The geographical coordinates of the place are: 42º 1’ North latitude, 4º 32’ West longitude and 832 m above sea level. Figure 2: Hourly UVB (Wm-2) measured and calculated by CIBA_1.2 in Valladolid for ten clear days. Table 1: Main characteristic of ten clear days. Ozone, Pressure, Temperature, Relative Humidity, Mean Bias Error, Root Mean Square Error and percentage of error at solar noon. Fig.I Yankee UVB-1 sensor. The input parameters: surface pressure, humidity and air temperature at ground level were measured and recorded at CIBA station and ozone daily column values were obtained from TOMS by NASA. In the Figure 3 we can see the evolution of UVI at solar noon between 2002 and 2005. The values reached are smaller than 10. The highest value is 9.3. These results obtained by UVB-1 with the conversion factor given by Vilaplana (0.12 Wm-2volt-1) are in concordance with the values calculated by CIBA_1.2. 4 Conclusions The lag between the maximum of ozone and the maximum UVB is four months separated. The percentage difference between measured and evaluated UVB is 8.3%, at solar noon in the clearest days. The highest value of UVI between 2002 and 2005 at solar noon is 9.3. Figure 3: UVI measured values in CIBA at solar noon and calculated values in the period 2002 to2005. Fig.II CIBA measurements solar station. References Bird, R. E. and Riordan, C.,A simple solar spectral modeling for direct normal and diffuse horizontal irradiance. Solar Energy. 32,461-471, 1984. Gueymard, C.A., Parametrized Transmitance Model for Direct Beam and Circumsolar Spectral Irradiance. Solar Energy. 71 nº5, pp. 325-346. 2001. Leun, J.C. and Gruijl, F.R., Influences of Ozone Depletion on Human and animal Health. UV-B radiation and ozone depletion, edited by Manfred Tevini., pp. 95-125, Lewish Publishers, 1993. Miguel, A.H., J.Bilbao, P.Salvador, A study of UV total solar irradiation at a rural area of Spain, Solaris 2005 2ndJoint Conference,Athens (Greece), 32-3, May 2005. Edit. Hellenic Illumination Committee. Perez, R., Ineichen, P., Seals, R., Modeling daylight availability and irradiance components from direct and global irradiance. Solar Energy, vol. 44, No. 5, pp. 271-289, 1990. S.I.R.S.A. 1998. “Manual de usuario, Sensor de radiación ultravioleta, modelo UVB-1.” sirsa@sirsa.es. Vilaplana, J.M., Medida y análisis del ozono y de la radiación solar ultravioleta en el Arenosillo-INTA, Huelva. Tesis Doctoral. Universidad de Valladolid. 2004. WMO, Report of the WMO meeting of experts on UV-B measurements, data quality and standardization of UV indices, Les Diablerets, Switzerland, 1994. 6th Workshop on ULTRAVIOLET RADIATION MEASUREMENTS Davos, Switzerland, 20-21 October 2005 Acknowledgments The authors gratefully acknowledge the financial support extended by the Spanish Science and Technology Ministry under the Project: REN2003-04522/CLI.