Comment on “Record solar UV irradiance in the tropical Andes, by Cabrol et al.”

Recently Cabrol et al. (2014), hereafter C14, reported measurements of the UV Index (UVI) reaching 43.3 at a high altitude location in the Andes (Licancabur; 22.5◦ S, 67.5◦ W, 5917m a.s.l.). This value is much larger than those previously reported from other high altitude tropical locations. For example, UVI maxima reported for Mauna Loa (19.5◦ N, 155.6◦ W, 3397m a.s.l.) (Bodhaine et al., 1997; McKenzie et al., 2001), La Paz, Bolivia (16.5◦ S, 68.1◦ W, 3420m a.s.l.) (Zaratti et al., 2014), and Chile’s northern Atacama Desert (Chajnantor Plateau; 23.0◦ S, 67.8◦ W, 5100m a.s.l) (Cordero et al., 2014) are less than 26. The large UVI values measured by C14 are surprising because they would simultaneously require atmospheric conditions—specifically low total ozone amounts and cloud enhancements of UV-B radiation—that are extremely unlikely if not impossible (Seckmeyer et al., 2010). An alternative explanation of the results of C14 is that the large reported UV-B changes stem from instrument problems or data analysis issues, as will be discussed later. There are two important reasons why these measurements should be questioned and re-examined more closely: