Browsing by Author "Ronda, Reinder"

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    Evaporation driven by Atmospheric Boundary Layer Processes over a Shallow Salt-Water Lagoon in the Altiplano
    (2024) Hartogensis, Oscar; Aguirre Correa, Francisca; Suárez Poch, Francisco Ignacio; Lobos Roco, Felipe Andrés; Ronda, Reinder; Vilà-Guerau de Arellano, Jordi
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    Evaporation Driven by Atmospheric Boundary Layer Processes over a Shallow Saltwater Lagoon in the Altiplano
    (2024) Aguirre-Correa, Francisca; De Arellano, Jordi Vila-Guerau; Ronda, Reinder; Lobos-Roco, Felipe; Suarez, Francisco; Hartogensis, Oscar
    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.
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    Midday Boundary-Layer Collapse in the Altiplano Desert: The Combined Effect of Advection and Subsidence
    (2023) Aguirre Correa, Francisca; De Arellano, Jordi Vila-Guerau; Ronda, Reinder; Lobos Roco, Felipe Andrés; Suárez Poch, Francisco Ignacio; Hartogensis, Oscar; CEDEUS (Chile)
    Observations in the Altiplano region of the Atacama Desert show that the atmospheric boundary layer (ABL) suddenly collapses at noon. This rapid decrease occurs simultaneously to the entrance of a thermally driven, regional flow that causes a rise in wind speed and a marked temperature decrease. We identify the main drivers that cause the observed ABL collapse by using a land-atmosphere model. The free atmosphere lapse rate and regional forcings, such as advection of mass and cold air as well as subsidence, are first estimated by combining observations from a comprehensive field campaign and a regional model. Then, to disentangle the ABL collapse, we perform a suite of numerical experiments with increasing level of complexity: from only considering local land-atmosphere interactions, to systematically including the regional contributions of mass advection, cold air advection, and subsidence. Our results show that non-local processes related to the arrival of the regional flow are the main factors explaining the boundary-layer collapse. The advection of a shallower boundary layer (approximate to -250 m h(-1) at noon) causes an immediate decrease in the ABL height (h) at midday. This occurs simultaneously with the arrival of a cold air mass, which reaches a strength of approximate to -4 Kh(-1) at 1400 LT. These two external forcings become dominant over entrainment and surface processes that warm the atmosphere and increase h. As a consequence, the ABL growth is capped during the afternoon. Finally, a wind divergence of approximate to 8 x 10(-5) s(-1) contributes to the collapse by causing subsidence motions over the ABL from 1200 LT onward. Our findings show the relevance of treating large and small-scale processes as a continuum to be able to understand the ABL dynamics.