Development processes of the Tropical Pacific Meridional Mode

Mechanisms for the spatio-temporal development of the Tropical Pacific Meridional Mode (TPMM) are investigated using a coupled ocean-atmosphere model and observations. In both observations and the model, this meridional mode displays decadal variations and is most pronounced in spring and early summer. The model simulation suggests that once SST anomalies in the subtropical northeastern Pacific are initiated, say by northeasterly trade wind variability, perturbations evolve into a merdional dipole in 2-3 months. A wind-evaporative-SST feedback causes a southwestward propagation of initial subtropical SST anomalies, while anomalous equatorial upwelling helps form the southern lobe of the meridional dipole. The TPMM development is a fast process (a few months) and depends on the seasonal cycle.