Atmospheric circulation types controlling rainfall in the Central American Isthmus
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Fecha
2022
Tipo
artículo original
Autores
Sáenz Soto, Fernán
Hidalgo León, Hugo G.
Muñoz, Angel G.
Alfaro Martínez, Eric J.
Amador Astúa, Jorge Alberto
Vázquez Aguirre, Jorge Luis
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Resumen
Rainfall mechanisms in the Central American Isthmus are controlled by complex
physical interactions across spatial and temporal scales, which are reflected on the
dynamics of atmospheric circulation patterns affecting the region. However, physical mechanisms and their relationships with thermodynamic distributions connected to overturning circulations remain elusive. Here, a set of six recurrent daily
atmospheric patterns, or weather types (WT), is defined using a k-means++ clustering algorithm on standardized fields of Convective Available Potential Energy
(CAPE) and winds at 925, 850, and 200 hPa. The relationships between these
weather types, their temporal characteristics, and anomalous distributions of
moisture flux divergence, equivalent potential temperature (saturated and
unsaturated), and observed rainfall are used to describe physical processes
controlling the latter, for all seasons. Regional observed rainfall is analysed
from a set of 174 automatic stations from all countries from Mexico to
Panama. By modulating vertically integrated moisture fluxes, these weather
types, and the different climate drivers linked to them, control the temporal
and spatial rainfall characteristics in the region, especially over the Pacific
side of the isthmus. During some stages of the regional rainy season,
described by two weather types, thermal anomalies in convective quasiequilibrium characteristic of the upward branch of the Hadley cell force
westerly flow over Central America, enhancing rainfall. While during other
stages, the enhancement of the trades and the displacement of convection
to the ITCZ area over the eastern tropical Pacific, characteristic of the midsummer drought, diminishes rainfall. This study sets the stage for a better
understanding of the mechanistic relationship between these weather types
and rainfall characteristics in general, like onset, demise, and duration of
rainy seasons. Hence, these results can inform process-based model diagnostics aiming at bias-correcting climate predictions at multiple timescales
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CENTRAL AMERICA, WEATHER, PRECIPITATION, Convection patterns