The Dynamics and Variability of the South American Low-Level Jet (SALLJ)

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The South American Low-level Jet (SALLJ) flows southward along the eastern slopes of the Andes, with its maximum wind speed about a mile above the surface. The jet is a key component of the climate of South America as it brings moisture from the tropical Atlantic to inland regions of the continent. It also contributes to the formation of mesoscale convective systems (MCSs) and the extreme weather they produce. In many ways the SALLJ is analogous to the Great Plains low-level jet (GPLLJ) that flows northward along the eastern side of the Rockies and brings moisture from the Gulf of Mexico to the breadbasket of the plains. But research on the GPLLJ dates back to at least the 1950s while the SALLJ was not extensively documented until the 1980s. Also, most of the research on the SALLJ is focused on the central Andes, from southern Peru to Paraguay (on the east side), and the extension of the SALLJ into Columbia and Venezuela was not documented until 2010. The distinction between the central and northern Andes is significant, as the two regions differ in their climate, large-scale circulation regimes, and connections to climate modes like El Nino.Here the Principal Investigators (PIs) conduct a comprehensive examination of the SALLJ, including both the northern and central Andes. Preliminary work by the PIs shows a strong difference in seasonality between the SALLJ between two regions, with relatively muted seasonality in the central Andes but a distinct summer minimum in the north. This difference prompts the PIs to hypothesize that different mechanisms could be involved in the northern Andes, where factors such as the strength and position of the North Atlantic Subtropical High could be relevant. A further issue is the impact of variability in the northern branch on the central branch. These issues are explored through examination of meteorological data and numerical simulations using two climate models (CESM2 and ECHAM6).The work has broader impacts due to the impact of SALLJ variability on water resources and extreme weather over inland South America. The PIs work with partners at the Brazilian National Center for Monitoring and Early Warning of Natural Disasters to develop tools for monitoring and forecasting SALLJ activity and extreme precipitation. The PIs also conduct local outreach through seminars on climate variability, climate change, and their socioeconomic impacts, presented during their department's Geography Awareness week. The project supports a PhD student and a postdoctoral research associate, thereby providing support and training to the next generation of researchers in this area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.