New Insights into the South American Low Level Jet from RELAMPAGO Observations

Abstract

The Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) campaign produced unparalleled observations of the South American Low-Level Jet (SALLJ) in Central Argentina with high temporal observations located in the path of the jet and near rapidly growing convection. The vertical and temporal structure of the jet is characterized using 3-hourly soundings launched at two fixed sites near the Sierras de Cordoba (SDC), along with high-resolution reanalysis data. Objective SALLJ identification criteria are applied to each sounding to determine the presence, timing, and vertical characteristics of the jet. The observations largely confirm prior results showing that low-level jets (LLJs) most frequently come from the north, occur overnight, and peak in the low levels, though LLJs notably peaked higher near the end of longer duration events during RELAMPAGO. This study categorizes LLJs into short-lived events that appear to follow a diurnal cycle and long-lived events that are more elevated and lack a clear diurnal cycle. All observed LLJs appeared to be, at least partially, synoptically driven with evidence of subsynoptic scale processes clearer in the short-lived events. Importantly, evidence of both boundary layer processes and large-scale forcing were observed during short-lived cases, but in long-lived cases, the synoptic forcing was dominant. Lastly, higher levels of moisture and larger convective coverage east of the SDC occurred near the end of the long-lived LLJ periods.