The Madden-Julian Oscillation in a warmer world

Abstract

Global warming's impact on the Madden-Julian Oscillation (MJO) is assessed using one of the few models capable in reproducing its key features. In a warmer climate predicted for the end of the century, the MJO increases in amplitude (by ~30%) and frequency, showing a more circumglobal propagation tendency. The MJO spatial extent becomes enhanced, deeper, and more zonally extended but meridionally confined. A stronger vertical tilting structure in diabatic heating, moisture, and convergence fields is seen. Our findings indicate that these changes result from an intensification of the frictional wave-conditional instability of the second kind mechanism via the coupling of dynamical and thermodynamic response to the warming. The warming and moistening of the mean state contribute to the enhanced deep convective heating, driving a stronger-forced Kelvin wave-like perturbation. This reinforces the frictional low-level convergence, leading to larger shallow convective heating and therefore to a faster development and enhancement of the deep convection in the MJO.