Publications

Bilbao, J.; Roman, R.; Miguel, A. (2014). Turbidity coefficients from normal direct solar irradiance in Central Spain. ATMOSPHERIC RESEARCH, 143, 73-84.

Abstract
Atmospheric turbidity causes attenuation of solar radiation reaching the earth's surface under a cloudless sky. The Angstrom turbidity coefficient and the aerosol optical thickness, AOD550, were obtained from 10-minute direct normal solar irradiance measurements recorded in a rural area of Castilla y Leon region, Spain, from July 2010 to December 2012. During the study period, the diurnal variation of the mean monthly 10-minute turbidity coefficient increased in early morning, remained with fluctuations around noon, and increased or diminished in the evening, near sunset. The monthly turbidity coefficient shows an annual cycle with minimum values in winter and maximum values in summer, varying between 0.04 in winter and 0.16 in summer. The frequency distribution of 10-min Angstrom turbidity coefficient on cloudless days shows that 0.65% of values are below 0.02, 84.50% between 0.02 and 0.15, and 14.85% above 0.15. Comparing at solar noon AOD550nm retrieved from MODIS (MODerate resolution Imaging Spectroradiometer on-board the Terra satellite) with those estimated from direct normal solar radiation measurements shows a good correlation coefficient of 0.78, although MODIS values are lower than estimated ones. High turbidity situations were investigated depending on the season and air-mass origin; the results show that they might be attributed to aerosol dust from the Sahara desert. The most significant high turbidity situations were investigated on base of wind at 700 mb and air-mass origin; the result shows that this might be attributed to aerosol dust from the Sahara desert. (C) 2014 Elsevier B.V. All rights reserved.

DOI:
10.1016/j.atmosres.2014.02.007

ISSN:
0169-8095; 1873-2895