Evaporation Driven by Atmospheric Boundary Layer Processes over a Shallow Saltwater Lagoon in the Altiplano

Abstract

Observations over a saltwater lagoon in the Altiplano show that evaporation E is triggered at noon, concurrent to the transition of a shallow, stable atmospheric boundary layer (ABL) into a deep mixed layer. We investigate the coupling between the ABL and E drivers using a land-atmosphere conceptual model, observations, and a regional model. Additionally, we analyze the ABL interaction with the aerodynamic and radiative components of evaporation using the Penman equation adapted to saltwater. Our results demonstrate that nonlocal processes are dominant in driving E. In the morning, the ABL is controlled by the local advection of warm air (similar to 5 K h(-1)), which results in a shallow (<350 m), stable ABL, with virtually no mixing and no E (<50 W m(-2)). The warm-air advection ultimately connects the ABL with the residual layer above, increasing the ABL height h by similar to 1 km. At midday, a thermally driven regional flow arrives to the lagoon, which first advects a deeper ABL from the surrounding desert (similar to 1500 m h(-1)) that leads to an extra similar to 700-m h increase. The regional flow also causes an increase in wind (similar to 12 m s(-1)) and an ABL collapse due to the entrance of cold air (similar to-2 K h(-1)) with a shallower ABL (similar to-350 m h(-1)). The turbulence produced by the wind decreases the aerodynamic resistance and mixes the water body releasing the energy previously stored in the lake. The ABL feedback on E through vapor pressure enables high evaporation values (similar to 450 W m(-2) at 1430 LT). These results contribute to the understanding of E of water bodies in semiarid conditions and emphasize the importance of understanding ABL processes when describing evaporation drivers.