Atmospheric circulation types controlling rainfall in the Central American Isthmus

Abstract

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 areu s e dt od e s c r i b ep h y s i c a lp r o c e s s e s 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.

Spatiotemporal variability of the rainy season in the Yucatan Peninsula

“…Mexico's National Meteorological Service (SMN, in Spanish) maintains the national climatological database for Mexico, integrated into the Climate Computing project (CliCom). This project consists of a quality‐controlled data set using Climate Computing software developed by the United Nations Organization and incorporated into the data set by Dunn et al (2020) (Sáenz et al, 2023). Observations at each of the 5459 meteorological stations in the country are recorded daily at 0800 LST (local standard time).…”

Do changing circulation types raise the frequency of summertime thunderstorms and large hail in Europe?

“…The clustering analysis was performed using the k-means procedure of MacQueen (1967). Weather patterns of single days were assigned to the cluster to which the Euclidean distance was lowest (Zhang and Villarini 2019, Zhang et al 2022, Saenz et al 2023. To accurately determine the final number of regimes, we employed a two-step procedure.…”

Central America urgently needs to reduce the growing adaptation gap to climate change

“…Reviews of these climate precursors can be found in and Maldonado et al (2016). In Sáenz et al (2023), an analysis of the atmospheric circulation types controlling rainfall in Central America is presented. Table 1 summarizes the characteristics of a non-exhaustive list of mesoscale to large-scale mechanisms acting in the region.…”

“…Observational climate data across Central America vary largely by country (Sáenz et al, 2023). However, even in areas with better coverage, it is sparse and often contains large gaps in time series.…”