The influence of the Atlantic multidecadal oscillation on the eastern Andes low-level jet and precipitation in South America

Charles Jones,Leila M V Carvalho

doi:10.1038/s41612-018-0050-8

Abstract

The South America low-level jet (SALLJ) on the eastern slopes of the Andes is a unique climatological feature in the continent. The SALLJ transports large amounts of moisture and controls the spatiotemporal variability of precipitation in southeast South America. This study shows a remarkable influence of the Atlantic Multidecadal Oscillation (AMO) on decadal-to-multidecadal variability of the SALLJ. The results show a consistent pattern in which active SALLJ days during negative AMO phases are associated with negative precipitation anomalies over northern Amazon and the Atlantic Intertropical Convergence Zone (ITCZ). Increased cross-equatorial flow over northwestern South America combined with the outflow associated with the atmospheric subsidence over the negative precipitation anomalies enhances northerly winds along the eastern slopes of the Andes and Amazon. This atmospheric circulation response, which is more prevalent in the austral winter, intensifies the SALLJ. In the exit region of the SALLJ over southern Brazil, Uruguay and northern Argentina, an anomalous low-level cyclonic circulation is associated with enhanced precipitation. The influence of the AMO on the SALLJ is consistent with paleo-proxy studies showing multidecadal changes in precipitation over the La Plata River drainage basin. The analysis shows that secular trends reinforce the SALLJ and precipitation patterns. Moreover, the study highlights the importance of natural variability (i.e., decadal-multidecadal variations) occurring within long-term trends in the mean state, possibly associated with global warming, and significant changes in the SALLJ and precipitation over South America.

Highlights

Climate variability and change in South America affect millions of people and impact water resources, agriculture, economic activity, human health, ecosystems and biodiversity1–5_ENREF_1
The South America low-level jet (SALLJ) is a key component of the climate in South America and this study investigated the variability of the low-level jet on decadal-to-multidecadal time scales
The negative Atlantic Multidecadal Oscillation (AMO) phase during November 1965–August 1996 and positive phase during September 1924–October 1965 were associated with multidecadal regimes of high and low SALLJ activity, respectively

Summary

Introduction

Climate variability and change in South America affect millions of people and impact water resources, agriculture, economic activity, human health, ecosystems and biodiversity1–5_ENREF_1 In this context, the South American Monsoon System (SAMS) plays a central role in determining the climate of the continent.[3,6,7,8,9,10] In addition, the South America low-level jet (SALLJ) on the eastern slopes of the Andes is a distinctive component in such variability[11,12,13]; the SALLJ transports large amounts of moisture, induces the formation of mesoscale convective systems and determines the spatiotemporal variability of precipitation in southeast South America.[14,15,16] Unlike the boreal summer lowlevel jet on the east of the Rocky Mountains in North America, the SALLJ is present year-round exhibiting intraseasonal-tointerannual variations.[11,17].

Methods

Results

Conclusion