Tropical Pacific Ocean SST and velocity observations are used to construct NINO3 and NINO4 area average, 20-year long interannual time series of local and advective convergences of thermal energy. The variability of the sum of these observed convergences in each region is balanced by the vertical convergence of thermal energy due to the latent surface flux (86% in NINO3; 84% in NINO4). The latitude scale of the El Nino SST anomalies is shown to be equal to the ratio of the poleward mean speed of water parcels to the time scale at which thermal energy is given back to the atmosphere by a negative SST feedback through latent heat flux anomaly. Simultaneous observations and analyses of velocity and SST underscore the importance of the time-mean, wind-driven, poleward circulation in the establishment of the patterns of El Nino/SST anomalies directly north and south of the Pacific equator.
Niiler, P., D. K. Lee, and J. Moisan. 2004. "Observed mechanisms of El Nino SST evolution in the Pacific." Journal of Marine Research 62, (6). https://elischolar.library.yale.edu/journal_of_marine_research/62