Seasonality and regionality of the Madden-Julian oscillation and convectively coupled equatorial waves

Abstract

This study examines seasonal and regional variations in the amplitudes of convectively coupled equatorial waves (CCEWs), including Madden-Julian oscillation (MJO) and tropical depression (TD) disturbances. The climatological seasonal variations of the n = 1 equatorial Rossby (ERn1) wave are similar to those of the MJO over the Indian Ocean and the central Pacific. The antisymmetric components of CCEWs (mixed Rossby gravity, n = 0 eastward inertial gravity, and n = 2 westward inertial gravity waves; MRG, EIGn0, and WIGn2 waves, respectively) show similar seasonal cycles over the central Pacific with peaks during boreal summer and fall. CCEW amplitudes are also examined as a function of the MJO phase. The activities of all CCEWs except for the MRG wave are significantly enhanced in the convectively mature phase of the MJO over the Indian Ocean, whereas the amplitude peak of the Kelvin and WIGn1 (ERn1 and TD) waves shifts from the mature phase over the Indian Ocean to the convectively developing (decaying) phase of the MJO over the western and central Pacific. The MRG wave has an amplitude maximum in the decaying phase over the Indian Ocean, and the peak shifts to the preceding phase of the MJO over the Pacific Ocean.