Modulation of the MJO intensity over the equatorial western Pacific by two types of El Niño

Abstract

The modulation of the Madden–Julian Oscillation (MJO) intensity by eastern Pacific (EP) type and central Pacific (CP) type of El Nino was investigated using observed data during the period of 1979–2013. MJO intensity is weakened (strengthened) over the equatorial western Pacific from November to April during EP (CP) El Nino. The difference arises from distinctive tendencies of column-integrated moist static energy (MSE) anomaly in the region. A larger positive MSE tendency was found during the convection developing period in the CP MJO than the EP MJO. The tendency difference is mainly caused by three meridional moisture advection processes: the advection of the background moisture by the intraseasonal wind anomaly, the advection of intraseasonal moisture anomaly by the mean wind and the nonlinear eddy advection. The advections’ differences are primarily caused by different intraseasonal perturbations and high-frequency activity whereas the background flow and moisture gradient are similar. The amplitudes in the intraseasonal suppressed convection anomaly over the central Pacific is critical in modulating the three meridional moisture advection processes. The influences on the central Pacific convection anomaly from seasonal mean moisture in two types of El Ninos are discussed.