Space-time spectral analysis was applied to 17 years of twice daily, northern hemisphere sea-level pressure grids. The results for each individual year were compared with values of sea surface temperature averaged over a large region in the tropical Eastern Pacific Ocean. This comparison revealed a positive correlation between the ocean temperature and the pressure variance at the zonal scales and frequencies generally associated with the gravest, westward propagating, zonal wave number 1, symmetric normal-mode Rossby wave (i.e., the (1,1) mode). Variations in the surface temperature in the tropical Pacific are known to be accompanied by large changes in the distribution of tropical precipitation; thus the present results suggest that latent heat release may be a major excitation mechanism for the (1,1) Rossby normal mode.