Characteristics of Intense Convection in Subtropical South America as Influenced by El Niño–Southern Oscillation

Abstract

El Niño–Southern Oscillation (ENSO) is known to have teleconnections to atmospheric circulations and weather patterns around the world. Previous studies have examined connections between ENSO and rainfall in tropical South America, but little work has been done connecting ENSO phases with convection in subtropical South America. The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) has provided novel observations of convection in this region, including that convection in the lee of the Andes Mountains is among the deepest and most intense in the world with frequent upscale growth into mesoscale convective systems. A 16-yr dataset from the TRMM PR is used to analyze deep and wide convection in combination with ERA-Interim reanalysis storm composites. Results from the study show that deep and wide convection occurs in all phases of ENSO, with only some modest variations in frequency between ENSO phases. However, the most statistically significant differences between ENSO phases occur in the three-dimensional storm structure. Deep and wide convection during El Niño tends to be taller and contain stronger convection, while La Niña storms contain stronger stratiform echoes. The synoptic and thermodynamic conditions supporting the deeper storms during El Niño is related to increased convective available potential energy, a strengthening of the South American low-level jet (SALLJ), and a stronger upper-level jet stream, often with the equatorward-entrance region of the jet stream directly over the convective storm locations. These enhanced synoptic and thermodynamic conditions provide insight into how the structure of some of the most intense convection on Earth varies with phases of ENSO.

Study of a Mesoscale Convective Complex associated with the coupling between jets in South America

“…Similar behavior was found by Sortais et al (1993). According to Bruick et al (2019), in El Niño years there is a more intense LLJ and ULJ, generating deeper storms at the tropical inlet of the jet stream.…”

The combined influence of ENSO and PDO on the spring UTLS ozone variability in South America

“…Ferreira et al 2003;Montini et al 2019), modifying the transport of heat and moisture from the tropics to the subtropics of South America (Fernandes and Rodrigues 2018;Montini et al 2019). These changes in circulation alter the strength and location of deep convection (Bruick et al 2019), and precipitation anomalies over the Amazon, and over subtropical and southeast South America (e.g. Ropelewski and Halpert 1987).…”

“…During the austral spring and summer deep convective clouds associated with mesoscale convective systems (MCSs) in South America are capable of reaching the tropopause (Gettelman et al 2002). These MCSs are strongly modulated by atmospheric variations on synoptic-to-interannual time scales (Ferreira et al 2003;Zipser et al 2006;Salio et al 2007;Mulholland et al 2018;Bruick et al 2019).…”

“…Ozone is the most important greenhouse gas controlling temperatures in the upper troposphere-lower stratosphere (Forster and Shine 1999). El Niño events are known to enhance deep convection on interannual timescales over subtropical South America (Bruick et al 2019). However, little is known about the importance of convective processes on tropopause circulation in this region and implications for the tropopause boundary on interannual to decadal timescales.…”

“…This is accomplished by examining spatial and temporal patterns of UTLS ozone based on reanalysis during the austral spring (September-November, SON). Mechanisms explaining patterns of UTLS ozone SON anomalies and relationships between ENSO and PDO are further examined with focus on regions where ENSO teleconnections are strongest (Ropelewski and Halpert 1987;Grimm 2003Grimm , 2004Gonzalez et al 2017;Bruick et al 2019).…”