The expanding tropics impact on central Andes precipitation

JUAN A. RIVERA; MYRIAM KHODRI; VÁLERIE DAUX; JULIÁN VILLAMAYOR; ELIZABETH B. NARANJO TAMAYO

Vienna

Congreso; EGU2019; 2019

The central Andes have undergone a drying trend over the last decades with adverse socioeconomiceffects throughout the south of Argentina and Chile. The long-term precipitation variability in this regionhas been associated with modes of sea surface temperature (SST) and atmospheric circulation variabilityacting at decadal-to-multidecadal timescales, such as the Interdecadal Pacific Oscillation and theSouthern Annular Mode. More recently, the drying long-term trend of precipitation in central Andes hasalso been linked to a poleward expansion of the Hadley Cell (HC) in the Southern Hemisphere (SH)over the last decades. In previous works several possible causes of the HC expansion have beenproposed, involving both external forcing (e.g., greenhouse gases and ozone depletion effects) andinternal climate variability (e.g., SST and atmospheric modes). In this work the relationship between the HC extent in the SH and the precipitation variability in centralAndes at decadal-to-multidecadal timescales is evaluated. For the analysis historical simulations of theAtmospheric Model Intercomparison Project phase 6 (AMIP6) of the IPSL-CM6A-LR model are used. TheHC expansion in the SH is characterized using the zonal mean meridional mass streamfunction at 500hPa to identify the mechanisms involved in the link with precipitation. The principal modes of decadal-to-multidecadal climate variability affecting the HC extent are also identified and characterized to detectthe causes and dynamical processes that explain the HC expansion and the central Andes drying trendover the last decades.