Doubling of SSW occurrence due to stronger MJO as expected in a warmer climate.
As the Sudden Stratospheric Warming (SSW) was observed to be led by specific phase of Madden-Julian Oscillation (MJO)  , and the MJO was predicted to get stronger under a global warming scenario , we started thinking of the behind mechanism of the MJO-SSW teleconnection and the changes in a future warmer climate.
We first validated the MJO-SSW teleconnection by showing that the Arctic stratospheric temperature fluctuate with the MJO phase significantly.
The message deliverer is the large-scale waves excited by the MJO forcing. Shown below is a hovmoller plot of the meridional component of wave activity flux, where the northward propagation of the flux is clear in both WACCM and Idealized dry core model. The signal seems to be halted and noisy around 30N, possibly due to the interaction with the jet there, which turned out to be a key process determining the SSW response (will discuss later).
In response to a stronger MJO forcing as expected in a warmer future climate , the Arctic stratosphere is warmed by over 4K, the polar night jet is weakened by over 3m/s and the SSW frequency almost doubles, in both a Held-Suarez type idealized model and the Whole Atmospheric Community Climate Model (WACCM).