Abstract
This study examines the influence of the Atlantic Multidecadal Oscillation (AMO) on the Choco Low-level Jet (CJ) variations during the 1983–2016 period. Considering the September–November (SON) 925 hPa zonal wind index in the CJ core, a significant breakpoint occurs in 1997 with larger values after 1997. The changes in the CJ and Caribbean Low-Level Jet (CLLJ), and their related ocean-atmospheric patterns and impacts on precipitation over Colombia were analyzed considering separately the 1983–1996 and 1998–2016 periods, which overlap the cold and warm AMO phases, respectively. During the 1998–2016 period, the negative sea surface temperature (SST) anomalies in the tropical Pacific Ocean and the positive ones in the Caribbean Sea and Tropical North Atlantic (TNA) strengthen the CJ and weaken the CLLJ, and moisture is transported into Central and Western Colombia increasing the rainfall there. Our results indicate that part of the CJ strengthening after 1997 was due to a higher percentage of intense CJ events coinciding with La Niña events during the warm AMO and cold Pacific Decadal Oscillation (PDO) background. However, the AMO-related SST and sea level pressure (SLP) variations in the TNA seem to be more crucial in modulating the CJ and CLLJ intensities, such that CJ is weakened (intensified) and CLLJ is intensified (weakened) before (after) 1997. As far as we know, the relations of the CJ and CLLJ intensities to the AMO phases were not examined before and might be useful for modeling studies.
Highlights
Northwestern South America (SA) has a complex atmospheric dynamics modulated by several factors such as the Intertropical Convergence Zones (ITCZ) of the Atlantic and Pacific Oceans, moisture transport from the Amazon Basin, the trade winds, and the local topography characterized by threeAtmosphere 2020, 11, 174; doi:10.3390/atmos11020174 www.mdpi.com/journal/atmosphereAtmosphere 2020, 11, 174 branches of the Andes in Colombia
Indices are significantly and negatively correlated with a correlation of −0.69 (Figure 3c). These results indicate that the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO) backgrounds after 1997 contribute to strengthen the Choco Low-Level Jet (CJ), and those before 1997, to weaken the CJ
The CJ intensification and the consequent moisture flow towards Colombia are associated with a regional east–west cell that weakens the trades in the extreme eastern equatorial Pacific (Figure 7b)
Summary
Northwestern South America (SA) has a complex atmospheric dynamics modulated by several factors such as the Intertropical Convergence Zones (ITCZ) of the Atlantic and Pacific Oceans, moisture transport from the Amazon Basin, the trade winds, and the local topography characterized by three. Kayano et al [40] discussed the negative relation of the SST anomaly pattern in the Atlantic and Pacific Oceans in a multidecadal time scale in terms of the low-frequency backgrounds associated with the AMO and the Pacific Decadal Oscillation (PDO), such that the warm AMO (WAMO) phase relates to the cold PDO (CPDO) phase and the cold AMO (CAMO) phase relates to the warm PDO (WPDO) phase. They showed that these backgrounds affect the interannual climate variability.
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