A Robust Increase of the Intraseasonal Periodic Behavior of the Precipitation and Eddy Kinetic Energy in a Warming Climate

Abstract

Precipitation and storm track activity in the Southern Hemisphere feature a remarkable 20 to 30-day periodicity known as baroclinic annular mode. In climate model projections following the representative concentration pathway 8.5 scenario, this work finds a robust increase of intraseasonal variability of the precipitation and density-weighted eddy kinetic energy at the 20–30 day frequency range by 25% and 20%, respectively, in austral summer toward the end of the century, despite small changes in seasonal-mean quantities at corresponding latitudes. These results suggest that a warming climate can feature a stronger dynamical organization of the 20–30 day periodicity by the moist baroclinic waves. For austral winter, the weak 20–30 day periodicity in the current climate becomes a prominent mode of quasiperiodic variability toward the end of the century in these model projections. This work identifies both the increase of diabatic heating and the enhancements of the waveguide effects as candidate mechanisms.