A seasonal climatology of UV reflectivity for southern South America

Abstract

A seasonal climatology for the Lambertian equivalent reflectivity (LER) in ultraviolet (UV) for southern South America is introduced. The study region was limited by 10° and 60°S and by 100° and 30°W; the data set spanned the period 1978–2015. Features of the seasonal means and of the quarterly (Q) and the interannual (IA) variabilities for each season were ascribed to atmospheric and oceanic processes of local, regional, or global origin which lead to the formation or maintenance of clouds. Shifts in the Q and IA time series were detected, most notably in the early 1990s. Linear trends were also estimated. The largest positive and negative trends in the Q time series were found along the Peruvian Andes (PA) (3.20 reflectivity units [RU] decade−1) and east of the Chapada Diamantina (CD) and the Serra do Espinhaço (SE) in Brazil (−1.40 RU decade−1), respectively. The largest positive and negative trends in the IA time series were found in PA (6 RU decade−1, summer) and east of CD and SE (−2.50 RU decade−1, spring), respectively. The linkages between UV LER and regional or global circulation indices were also studied. The largest relationships were found with the Dipole Mode Index on a Q basis and with the Southern Oscillation Index on an IA basis in winter.