Recent Changes in the Low-Level Jet along the Subtropical West Coast of South America

Abstract

Surface winds along the subtropical west coast of South America are characterized by the quasi-weekly occurrences of low-level jet events. These short lived but intense wind events impact the coastal ocean environment. Hence, identifying long-term trends in the coastal low-level jet (CLLJ) is essential for understanding changes in marine ecosystems. Here we use ERA5 reanalysis (1979–2019) and an objective algorithm to track anticyclones to investigate recent changes in CLLJ events off central Chile (25–43 °S). Results present evidence that the number of days with intense wind (≥10 ms−1), and the number and duration of CLLJ events have significantly changed off central Chile in recent decades. There is an increase in the number of CLLJ events in the whole study area during winter (June-July-August; JJA), while during summer (December–January–February; DJF) a decrease is observed at lower latitudes (29–34 °S), and an increase is found at the southern boundary of the Humboldt system. We suggest that changes in the central pressures and frequency of extratropical, migratory anticyclones that reach the coast of South America, which force CLLJs, have played an important role in the recent CLLJ changes observed in this region.

High-Frequency Variability of the Surface Ocean Properties Off Central Chile During the Upwelling Season

“…Examination of individual maps revealed a high degree of coherence among them lending support to the use of the composite maps. The SLP field at the time of maximum alongshore wind stress at POSAR (Figure 11A) shows the SPA centered at its climatological position during summer (about 35 • S, 85 • S) and with normal strength (∼1025 hPa) but bulging toward the southern coast of South America in connection with a migratory high-pressure cell that has moved from the South Pacific Ocean toward the continent in the last few days (Aguirre et al, 2021). This evolution is consistent with the gradual increase in SLP recorded by POSAR in the early stages of the upwelling events (e.g., Figure 7C).…”

Global horizontal irradiation: spatio-temporal variability on a regional scale in the south of the Pampeana region (Argentina)

“…This center is a cell detachment of the semi-permanent South Pacific anticyclone. From this action center, other smaller anticyclones called migratory are periodically detached and enter Argentine territory moving towards the east to later join the South Atlantic Anticyclone (Alessandro 1998;Aguirre et al 2021). Each of the positions of the migratory anticyclones will define particular weather conditions and wind directions (Celemín 1984).…”

“…8 Stationary and migratory anticyclones scheme in the southern area of South America. (Aguirre et al 2019;2021) analyzed the average density of anticyclones in the Southern Hemisphere. Aguirre et al (2021) documented the difference between the density of the 2000-2019 decade and the first decade of the data (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988).…”

“…(Aguirre et al 2019;2021) analyzed the average density of anticyclones in the Southern Hemisphere. Aguirre et al (2021) documented the difference between the density of the 2000-2019 decade and the first decade of the data (1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988). The authors found that during summer an increase in migratory anticyclone density was noticeable around 40° S, while a slight decrease was observed between 27° S and 38° S. Nevertheless, minor changes in density of migratory anticyclones were found during winter.…”

Spatio-Temporal Variability of Hydroclimatology in the Upper Cauca River Basin in Southwestern Colombia: Pre- and Post-Salvajina Dam Perspective

“…The data have been regrouped into a regular latitude-longitude grid of 0.25 • and are available for monthly averaged data on pressure and individual levels https://cds.climate.copernicus.eu/cdsapp#!/search?type=dataset (accessed on 17 May 2021). This reanalysis has been used in recent studies of extreme event trends associated with climate variability and climate change [58][59][60], surface wind speed, and variability in the South American region [61,62], and land-atmosphere interactions [63].…”