Changes in the Hadley cell descending branch and its impact on long-term precipitation variability in soutwestern Sout America

ELIZABETH B. NARANJO TAMAYO; MYRIAM KHODRI; MAXIMILIANO VIALE; VÁLERIE DAUX; JUAN A. RIVERA; JULIÁN VILLAMAYOR; GABRIEL ARNOULD

San Francisco

Congreso; AGU 2019; 2019

Theclimate and its variability along the Cordillera de Los Andes, fromthe subtropics to latitudes around 45°S, is influenced by differentlarge-scale atmospheric and oceanic forcings, which have beendocumented mainly in variables such as temperature and precipitation.For instance, a centennial decreasing trend has been observed inprecipitation records estimated from tree ring widths from theAltiplano area to northern Patagonia. These declining trends inprecipitation were associated to an increase in the frequency ofdroughts , fostering the occurrence of a mega-drought along theCentral Andes (between 30° and 40°S). In this region, the climateis strongly affected by the descending branch of the Hadleycirculation. This global circulation plays a key role in determiningthe location of the subtropical dry zones, which are important notonly for the hydrological cycles but also for the global energybudget of the Earth?s climate system. Recent studies suggest thatthe Hadley circulation is expanding poleward approximately 0.2 ° perdecade in each hemisphere since 1979. However, limited evidences andhigh uncertainties exist when considering longer time periods andabout its impacts on precipitation changes in subtropics.Thepurpose of this investigation is to study the long-term changes inthe position of the descending branch of the Hadley cell surroundingSouth America, by describing the changes in the semipermanentSoutheasternPacific High(SPH) position. Reanalysis and observations during the 20thcentury and the first part of the 21stcentury were used to calculate metrics that quantify movement in thepoleward boundary of the Hadley cell and its impacts onprecipitation. Monthly time series of meridional stream function(ψ500)and the latitude of maximum sea level pressure (SLP) over theSoutheastern Pacific Ocean were considered, as well as some indicesfor describing the SPH intensity, SPH latitude and SPH longitude.Based on precipitation records between 25° and 45°S, the linksbetween the observed trends in precipitation and the changes in theHadley cell were explored, and results will be discussed in thispresentation. p { margin-bottom: 0.25cm; direction: ltr; color: #000000; line-height: 115%; orphans: 2; widows: 2 }p.western { font-family: "Calibri", sans-serif; font-size: 11pt; so-language: es-AR }p.cjk { font-family: "Calibri", sans-serif; font-size: 11pt; so-language: zh-CN }p.ctl { font-family: "Times New Roman", serif; font-size: 11pt; so-language: ar-SA }