17 Mar Midday Boundary-Layer Collapse in the Altiplano Desert: The Combined Effect of Advection and Subsidence
| Título | Midday Boundary-Layer Collapse in the Altiplano Desert: The Combined Effect of Advection and Subsidence |
| Autor | Francisca Aguirre, Jordi Vilá-Guerau, Reinder Ronda, Felipe Lobos, Francisco Suárez, Oscar Hartogensis |
| Línea (s) | Recursos Críticos |
| Año de publicación | 2023 |
| Revista | Boundary-Layer Meteorology |
| Palabras claves | |
| Resumen | 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 (≈−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 ≈−4 K h−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 ≈8×10−5 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. |
| Doi | https://doi.org/10.1007/s10546-023-00790-5 |
| Autor de correspondencia | Francisco Aguirre – Correa, faguirre2@uc.cl |