Destabilization of the Madden-Julian Oscillation in Present and Future Climates

A weak temperature gradient (WTG) balance framework is used to investigate the destabilization of the Madden-Julian Oscillation (MJO) in SP-CESM and ERA-interim. It is shown that the strength and vertical structure of intraseasonal variations in large-scale vertical moisture advection can be accurately diagnosed from apparent heating. The role that various apparent heating processes (e.g. radiative heating, microphysical processes) play in driving large-scale vertical moisture advection is assessed, and their individual contributions to the destabilization of the MJO examined. The reduction of longwave radiative cooling during the enhanced convective phase is shown to play a crucial role in allowing the ensemble cloud population to further grow moisture anomalies associated with the MJO. The WTG balance framework is then applied to a 4×CO2 simulation of SP-CESM, in which a marked increases in MJO activity occurs. The role that changes in the static stability, the vertical moisture gradient, and the strength of the radiative feedback may play in increasing MJO activity is discussed.