Observational Analysis of the SALLJ During the RELAMPAGO Campaign

The intense observational period of the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign took place east of the Andes in Central Argentina during November-December 2018. The overarching goal of the campaign was to study convective lifecycle near the Sierras de Córdoba (SDC), a topographic feature east of the Andes. Our objective is to determine how terrain-initiated deep convection grows rapidly upscale to form MCSs and which large-scale and mesoscale factors contribute to the observed convective lifecycle.

Of particular interest to this study is the South American Low-Level Jet (SALLJ), a ribbon of fast moving air in the lower levels of the atmosphere oriented north-south that lies to the east of the Andes and brings moisture from the Amazon southward to Central Argentina. Low Level Jets (LLJs) are known to advect heat and humidity rapidly from one region to another and therefore greatly alter the thermodynamic (e.g., instability) and dynamic (shear, convergence) environments. It has been hypothesized that the SALLJ plays a role in sustaining the long-lived convection near the SDC, but sparse data means the SALLJ is not well characterized.

RELAMPAGO produced unparalleled observations of the SALLJ in Central Argentina with high temporal observations at two fixed sites near the SDC, located both in the path of the jet and near rapidly growing convection. Using 3-hourly soundings launched at these two sites during the campaign, along with high-resolution reanalysis from the European Centre for Medium-Range Weather Forecasts (ERA5), this study aims to improve our understanding of the SALLJ. Criteria for objectively identifying the SALLJ in Central Argentina will be presented, and these criteria will be used to describe the vertical and temporal structure of the jet observed during RELAMPAGO. Between the two stations analyzed, differences in occurrence, max wind speed height, strength, and most common wind direction of LLJs identified were found, possibly related to latitude and influence of terrain. From a broader view, the SALLJ appears to exhibit characteristics of both a nocturnal LLJ and a more synoptically forced “low-level jet stream”. To investigate these differences further, two distinct elevated LLJ cases that were followed by serial upscale growth of convection near the SDC will be presented along with a synoptic analysis using ERA5 data.