Summer upper-level jets modulate the response of South American climate to ENSO

• Published in: Climate Dynamics
• Main Authors: Collazo, Soledad, García-Herrera, Ricardo, Barriopedro, David
• Other Authors: European Commission, orcid:
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2023
• Subjects: El Niño-Southern Oscillation | Extreme temperatures | Multiparametric characterization | South American summer climate | Subtropical and polar front jet | Weather regimes; Argentina; Pacific; South Atlantic Ocean
• Online Access: http://hdl.handle.net/10261/342345; https://doi.org/10.1007/s00382-023-06955-9; https://api.elsevier.com/content/abstract/scopus_id/85172089559

The upper-level jet stream is a critical element of atmospheric circulation, driving synoptic systems and extreme weather events. This study analyzes the impact of upper-level jets on South American (SA) summer temperature and precipitation under different El Niño-Southern Oscillation (ENSO) phases. Using the ERA5 reanalysis dataset from 1979 to 2022, we perform a daily multiparametric characterization of the jet stream, considering its spatial and temporal discontinuities. Besides latitude and intensity, we find that the departure and number of branches of the subtropical jet (STJ) and the longitudinal extent of the Pacific branch of the polar front jet (PFJ) are needed for their description. An additional parameter is required to characterize the STJ due to its absence on around 40% of summer days over SA. Moreover, we observe distinct long-term changes in PFJ parameters across different ocean basins. Three synoptic weather types (WTs) of the upper-level zonal wind are identified: normal conditions, a prominent STJ pattern, and a PFJ-only pattern. The latter pattern is associated with anticyclonic anomalies at 500 hPa in the South Atlantic Ocean and an active SA Convergence Zone, which favors clear skies and warm (wet and cold) conditions in southern SA (Brazil). Consistently, the probability of experiencing warm spells in central Argentina is increased more than twofold. Finally, we detect that the temperature anomalies associated with the WTs are independent of the ENSO phase. However, ENSO modulates the frequency of the WTs: during La Niña (El Niño), the PFJ-only (prominent STJ) pattern is more common. This work was supported by the SAFETE project, which has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 847635 (UNA4CAREER). Peer reviewed