The influence of the Andes mountains on the South American low‐level flow

Abstract

[1] A dry, hydrostatic, three-dimensional primitive equation model is used to evaluate the mechanical effect of the Andes mountains on the South American low-level flow (LLF). The model simulations reproduce the evolution of a baroclinic wave over the continent under winter and summer conditions. In both seasons as a consequence of the interaction between the basic flow and the Andes, northerly LLF was reproduced east of the Andes which resembles the main characteristics of the observed flow. Moreover, seasonal changes of cyclone activity have a significant impact on the location of maximum LLF and its alignment, which exhibits a NW-SE orientation during winter and more meridional orientation in the warm season.

Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods

“…For example, Wang and Fu (66) showed that the intensity of the SALLJ is predicted by the intensity of westerly flow across the Andes at 700 hPa. Likewise, models suggest that as westerlies shift southward over the lower topography of the southernmost Andes the trajectory of the SALLJ becomes more southerly (64).…”

“…Here we use the term "Chaco Jet" interchangeably with SALLJ, considering it to be a particularly strong episode of the SALLJ with deeper southward penetration (62). The SALLJ is primarily caused by a trough of low pressure that forms on the eastern side of the Andes in response to the setup of baroclinic wave trains over high topography (63)(64)(65). Baroclinic waves are changes in upper atmosphere air pressure (<500 hPa) that emanate from the south Pacific and are magnified as the westerlies interact with the orographic barrier of the Andes (64,66,67).…”

“…The SALLJ is primarily caused by a trough of low pressure that forms on the eastern side of the Andes in response to the setup of baroclinic wave trains over high topography (63)(64)(65). Baroclinic waves are changes in upper atmosphere air pressure (<500 hPa) that emanate from the south Pacific and are magnified as the westerlies interact with the orographic barrier of the Andes (64,66,67). The intensity and orientation of the SALLJ are thus sensitive to the strength and latitude of the westerly flow and the height and width of Andean topography where the westerlies cross the Andes (Fig.…”

Spatial Variation in the Temporal Resolution of Subtropical Shallow-Water Molluscan Death Assemblages

“…The works of Paegle (1998), Saulo et al (2000Saulo et al ( , 2007, Salio et al (2002), Campetella and Vera (2002) and Marengo et al (2004) discuss how this northerly flow, after being constrained by the eastern slope of the Andes, often exhibits throughout the year a low-level jet structure (LLJ,~17°S), with its core at about 1 km above the ground.…”

Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability

“…Silva Dias (2000) has also suggested that the position of the jet, its intensity and diurnal cycle may be substantially altered by the impact of latent heating in the central Brazilian Amazon basin. On submonthly timescales the frontal passages and the South Atlantic Convergence Zone (SCAZ) activity Vera et al, 2002;Campetella and Vera, 2002) may modulate the SALLJ. For example, when moisture flux into southeastern South America via the low-level jet is strong, SACZ convection is weaker than normal (Sugahara et al, 1994;Liebmann et al, 1999).…”