Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Dynamic, thermodynamic and energetic controls on tropical precipitation

Auteur : Rossi, Stefano

Université de soutenance : Universität Innsbruck

Grade  : Master of Science in Environmental Meteorology 2022

Résumé
Tropical precipitation is primarily organized in a narrow band around the equator, the so-called Intertropical Convergence Zone, which shifts meridionally throughout the year. Previous studies have argued that shifts of the ITCZ in response to different forcings are controlled by dynamic, thermodynamic and energetic constraints. Here we investigate if and to what extent one of these proposed theories works better than the other both globally and in individual oceanic sectors. We use reanalysis monthly data from ERA5 and compute ITCZ predictors based on the different theories. Thermodynamic theories show good predictive skills in all situations, and in particular when considering the global zonal mean. Precipitation in homogeneous oceans like the East Pacific and the Atlantic regions, which tends to have bottom heavy vertical velocity profiles is better predicted by dynamic variables. This happens also during Northern Hemisphere Summer, when rainfall is strong and confined in the NH. Energetic theories work better for non homogeneous sectors, characterized by specific phenomena such as the South Pacific Convergence Zone (West Pacific) and the South Asian monsoon (Indian). Finally, results from reanalysis data are compared with those from selected model output in the CMIP6 archive. The comparison indicates that reanalysis and models show similar patterns in the solstice seasons, but much larger deviations around the equinoxes, when the ITCZ transitions across the equator from one Hemisphere to the opposite one.

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