Local evaporation controlled by regional atmospheric circulation in the Altiplano of the Atacama Desert

Abstract

We investigate the influence of regional atmospheric circulation on the evaporation of a saline lake in the Altiplano (also known as the Andean Plateau) region of the Atacama Desert. For that, we conducted a field experiment in the Salar del Huasco (SDH) basin (135g km east of the Pacific Ocean), in November 2018. The measurements were based on surface energy balance (SEB) stations and airborne observations. Additionally, we simulate the meteorological conditions on a regional scale using the Weather Research and Forecasting Model. Our findings show two evaporation regimes: (1) a morning regime controlled by local conditions, in which SEB is dominated by the ground heat flux (∼0.5 of net radiation), very low evaporation (LvE < 30 Wm-2) and wind speed <1 ms-1; and (2) an afternoon regime controlled by regional-scale forcing that leads to a sudden increase in wind speed (>15 ms-1) and a jump in evaporation to >500 Wm-2. While in the morning evaporation is limited by very low turbulence (u∗∼0.1 ms-1), in the afternoon strong winds (u∗∼0.65 ms-1) enhance mechanical turbulence, increasing evaporation. We find that the strong winds in addition to the locally available radiative energy are the principal drivers of evaporation. These winds are the result of a diurnal cyclic circulation between the Pacific Ocean and the Atacama Desert. Finally, we quantify the advection and entrainment of free-tropospheric air masses driven by boundary layer development. Our research contributes to untangling and linking local- and regional-scale processes driving evaporation across confined saline lakes in arid regions.