Variability of regional atmospheric moisture over Northern South America: patterns and underlying phenomena

We evaluate the spatio-temporal variability of atmospheric moisture in northern South America. The spatial structure of moisture is discussed in seasonal and interannual time scales. We combine the principal component analysis of moisture flux divergence and the physical information flow to measure the relative influence of global climate phenomena in the leading modes of regional variability. Our results highlight the inherent complexity of spatial structure in this region due to the interaction of the Tropical Andes, the regional circulation changes related to the annual migration of the ITCZ, the low-level jet structures of regional atmospheric transport and the moisture transport from surrounding marine areas. Modes of variability related to oscillations in the tropical and extratropical Atlantic and Tropical Pacific are the most important sources of variability underlying the regional atmospheric moisture. To emphasize ENSO related variability, we propose a seasonal state classification index that unambiguously classifies the local evolution of precipitation in El Niño and La Niña years, showing the occurrence of marked differences in local moisture content in each of these phases.