UV and global solar radiation in Łódź, Central Poland

Abstract

AbstractWith the overall aim of quantifying urban atmospheric effects on different parts of the solar spectrum, a multi year analysis of data collected at Łódź was undertaken. UV (290–400 nm) and global solar radiation measured by means of a Kipp and Zonen CUV3 radiometer and a Kipp and Zonen CM11 pyranometer in the center of Łódź between 1997 and 2001 are analysed. The mean annual sum of global and UV solar radiation equaled 3710.8 MJ m−2 and 154.1 MJ m−2, respectively. The minimum monthly total of solar energy occurred in December (48.7 M Jm−2—global; 2.1 MJ m−2—UV); however, the maximum monthly total occurred atypically in May (620.9 MJ m−2—global; 25.3 MJ m−2—UV). UV clearness index (Kuv) is approximately half of the clearness index of the global solar radiation, indicating greater attenuation of that part of the spectrum (Kuv 0.14 in December to 0.26 in May). A linear regression model was fitted to the daily values of UV and global (g) solar irradiation (Duv = a + Dgb). The slope coefficient b and the coefficient of determination equal 0.039 and 0.98, respectively. Cloudiness exerts an important control on the solar radiation flux at the ground level and for the relation between UV and global solar radiation. The convective clouds caused an increase of global and UV solar irradiance by about 10–20% compared to clear days, the enhancement resulting from reflections. On clear days, UV comprises 3.3–4% of global solar irradiance (10‐min values) on average, while during cloudy weather it increases to 8%. The results presented have implications for understanding the radiative transfer of UV and global solar radiation in the atmosphere over an urban area and the influence of clouds on transmission of solar radiation flux. Copyright © 2009 Royal Meteorological Society