[Seminar on June 30] The Role of Diabatic Heating on Mid-latitude Rossby Waves and Its Response to Climate Change


Dr. Lei Wang

Harvard University

10am, June 30, 2018

Room 319, Building 40, IAP


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.

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