Synoptic control of the spatiotemporal variability of fog and low clouds under ENSO phenomena along the Chilean coast (17°-36° S)

Abstract

The northern and central coasts of Chile have an extensive semi-permanent layer of stratocumulus clouds that produce fog on land, a crucial resource for water-stressed areas. This study examines the spatio-temporal variability of fog and low clouds (FLC) across four climatic zones (17°S-36°S) characterized by arid conditions. Our analysis aims to elucidate the relationship between FLC patterns and the El Niño-Southern Oscillation (ENSO) phenomenon based on 25 years (1998–2022) of GOES satellite images. The variability of FLC shows a marked, although spatially asymmetric, seasonal cycle, with a subtle positive trend in the long-term. Our results suggest that the presence of FLC is controlled by the strength of the thermal inversion (correlation coefficient, r = 0.7), which, in turn, depends on the sea surface temperature (SST) and the subsidence. Specifically, FLC patterns are controlled by SST in the north (r = −0.9) and by subsidence intensity in the south (r = 0.9). Furthermore, our analysis indicates a potential link between ENSO and FLC, which alters the SST-subsidence equilibrium. At 20°S, warm phases of ENSO lead to increased FLC during the summer and decreased FLC during the winter. Conversely, at 30°S, warm phases result in decreased FLC during the summer and increased FLC during the winter. However, during cold phases, this trend is reversed. At 20°S, FLC decreases in summer and increases in winter, while at 30°S, FLC increases in summer and decreases in winter. In summary, our study offers a novel perspective on understanding the large-scale dynamics associated with FLC frequency along the central and northern coasts of Chile, including FLC underlying mechanisms and the long-term influence exerted by ENSO on the phenomenon.