Robust responses of the MJO to extreme climate changes

Robust responses of the MJO to extreme climate changes

 

Here we ask how the Madden-Julian Oscillation (MJO) responds to climate changes, and if any of the MJO theories can explain this response. To address these questions, we simulate the MJO in a wide range of climates by using the superparameterized (SP) community atmosphere model (CAM). In each simulation, we force the SPCAM with uniformly distributed SSTs—no zonal and meridional SST gradients, and different simulations are forced by different SSTs, ranging from 1^oC to 35^oC. According to our simulation results (Fig. 1), we find 1) the MJO can exist over SSTs as cold as 1^oC; 2) the strength of the MJO increases with global warming; 3) the wavenumber of the MJO decreases from 7 in the coldest climate to 1 in the warmest climate. These findings challenge the traditional view of the MJO—that it is a wavenumber 1-2 phenomenon and can only exist over warm SSTs. The latter two findings confirm the theoretical prediction of Yang and Ingersoll (2014, GRL, A theory of the MJO horizontal scale). This suggests that the Yang and Ingersoll model might have already captured the essential MJO physics.