Investigating the convectively coupled MRG and EIG n=0 continuum

Space-time spectrum analysis of tropical cloudiness data show strong evidence that convectively coupled Mixed Rossby-Gravity (MRG) and n=0 Eastward Inertia-Gravity (EIG0) waves occur primarily along the Western/Central Pacific Ocean. In agreement with linear shallow water theory, these observations based on spectral filtering also show that MRG and EIG0 cloudiness patterns are antisymmetric with respect to the equator and they propagate coherently with the tropospheric flow towards the west and east, respectively, and with periods between 3-5 days. In contrast to the spectral approach, in this talk it is shown that while empirical orthogonal functions (EOF) of 2-6 bandpass filtered cloudiness data along the tropical Pacific Ocean also suggest an antisymmetric pattern, the leading EOF implies a poleward propagating oscillation, with the associated tropospheric flow moving to the west and with a 3-5 day period. These two views are then rectified by applying an independent approach based on a tracking method to asses tropical convection organization. It is shown that on average 2/3 of MRG and EIG0 events develop independently of one another and 1/3 of the events overlap in space and time. This analysis also shows that MRG and EIG0 cloudiness fields tend to propagate meridionally away from the equator, as in the EOF results. The tracking approach demonstrates that while the lack of zonal propagation implied from the EOF analysis is due to the interference between eastward and westward propagating convectively coupled disturbances, the poleward propagation is confirmed based on the typical trajectory of the disturbances. In addition, it is shown that the westward propagation of the circulation associated with the cloudiness patterns is consistent with the expected theoretical behavior of MRGs and EIG0s.