Dr. Lei Wang

Harvard University

10am, June 30, 2018

Room 319, Building 40, IAP

Abstract

Precipitation and storm track activity in the Southern Hemisphere feature a remarkable 20-30 day periodicity known as Baroclinic Annular Mode. While it is well-documented that the jet stream will shift poleward in a warming climate, the change of coherent modes of Rossby waves remains unknown. We finds a robust increase of intra-seasonal 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. This work identifies that both the increase of diabatic heating and the enhancements of the waveguide effects as candidate mechanisms.
In this presentation, I will demonstrate idealized modeling results to explain the main cause of the increase. Evidence suggests both the increase of moisture can effectively contribute to the intensification of the intra-seasonal variability, which implies a more predictable baroclinic annular mode in the Southern Hemisphere in a warmer climate. This finding serves as a stimulus for future studies to unveil the role of changing diabatic heating on the intra-seasonal variability in the mid-latitudes.