PNNL

Abstract

This study documents the spatial and temporal distribution of the South American low-level jet (SALLJ) and quantifies its impact on the convective environment using a 6.5-month convection-permitting simulation during the Remote Sensing of Electrification, Lightning, And Mesoscale/Microscale Processes with Adaptive Ground Observations and Clouds, Aerosols, and Complex Terrain Interactions (RELAMPAGO-CACTI) campaigns. Overall, the simulation reproduces the observed SALLJ characteristics in Central Argentina near the Sierras de Córdoba (SDC), a focal point for terrain-focused upscale growth. SALLJs most frequently occur in the summer with maxima to the northwest and east of the SDC and minima over the higher terrain. The majority of SALLJ periods began earlier to the west than to the east of the SDC and were most frequent overnight, consistent with prior observations suggesting SALLJ links to upper-level trough propagation and diurnal processes. SALLJ periods often have higher amounts of low-level moisture and instability compared to non-SALLJ periods, with these impacts accumulating over time when the SALLJ is present and lingering after it disappears. SALLJ periods are not consistently characterized by an increased magnitude of wind shear over any particular layer (even when accounting for SALLJ height) but do have shear vectors oriented in a more N-S direction compared to non-SALLJ periods, which could favor upscale growth. A case study is shown where the SALLJ influenced both the magnitude and direction of wind shear concurrent with convective upscale growth near the SDC. This study highlights the complex relationship between the SALLJ and its impacts during periods of widespread convection.