Global warming weakens Maritime Continent barrier effect on MJO propagation

Abstract As the Indo-Pacific warm pool expands in a warming climate, the probability of an MJO event successfully propagating through the Maritime Continent (MC) is projected to increase by 29.3% by the late 21st century under the SSP5-8.5 scenario. This enhanced propagation is facilitated by a zonal asymmetry in moistening during warm pool expansion. Moisture increases more rapidly over equatorial zone compared to off-equatorial regions over the western-central Pacific, near the east expanding boundary of the warm pool. As a result, the moistening rate preceding MJO convection, which is linked to the intensified equatorward moisture gradient, outpaces the growth rate of MJO amplitude, which depends on total column moisture there. This differential establishes more favorable thermodynamic conditions for eastward propagation of MJO events from the MC into the western Pacific under global warming. By the end of the century, the emergence frequency of MJO convection over the western Pacific is projected to rise by 36%. In consequence, the intraseasonal variations of precipitation extremes induced by the large-scale MJO convection over the western Pacific may become more pronounced in future climate scenarios.