Influence of Clouds on Solar UV

Abstract

In 1801 Johann Ritter discovered non-ionizing, electromagnetic, ultraviolet (UV) radiation (Diffey, 1982) and the effect of clouds on solar UV radiation has been studied as early as the 1930s (e.g. Buttner, 1938), with the most recently published work based on 2 years of continuous UV measurements in Germany (Schwander et al., 2002). Figure 4–1 illustrates the effect of clouds on UV radiation during 1 year of continuous daily erythemal UV measurements from both satellite and ground-based sensors, in this case the satellite-based total ozone mapping spectrometer (TOMS) and ground-based Biometer instrument, both at Toowoomba, Australia (27.6°S, 151.9°E, 693 m above sea level). The effect of clouds can be seen by the general decrease of the UV levels from the clear-sky levels (i.e. the maximum envelope of the data points). Differences between the effects by clouds on UV levels, as measured by satellite versus ground-based, is discussed later in the chapter.