Impacts of Low‐Level Jets on Moisture Transport to the Pantanal, Brazil

Abstract

Moisture transport from the tropics to the subtropics by the low‐level jets (LLJs) east of the Andes crosses the Pantanal region, located in the Upper Paraguay River Basin (UPRB), a biome strongly dependent on remote moisture sources. This study investigates the climatological contribution of these LLJs to moisture transport into the UPRB and their influence on regional precipitation. For this purpose, LLJs and Lagrangian moisture transport were objectively identified in reanalysis data for the 1980–2018 period. The LLJs present a seasonal transition from predominantly nocturnal during summer to all‐day occurrence in autumn, while in winter and spring they are mostly active from night to morning. Four LLJs with higher LLJ intensity and frequency east of the Andes were selected and named according to their latitude: J4N (4° N–70° W), J15 (15° S–65° W), J19 (19° S–60° W) and J31 (31° S–64° W). The LLJ moisture source regions contribute considerably to moisture inflow into the UPRB, with the highest contribution (63.5%) occurring between austral summer and spring. The J15 and J19 regions showed the strongest impacts; on LLJ days, the UPRB acts as a moisture sink for J15 moisture sources, while J19 acts both as a moisture sink for UPRB and a moisture source for the La Plata Basin. The net moisture contribution from J15 and J19 results in an average increase of 0.08 mm day −1 over the UPRB. Additionally, UPRB precipitation increased by at least 30% during LLJ events in J15 in austral summer, reaching up to 50% in autumn. The J15 moisture source region is highly correlated with interannual and low‐frequency variabilities of precipitation in UPRB. These findings underscore the importance of incorporating LLJ indices in future assessments of extreme events in the Pantanal.

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