Using the ocean assimilation data, the interannual variation of the tropical instability waves (TIWV), especially in the tropical eastern Pacific Ocean has been analyzed. The interannual variation of TIWV is strongly phase-locked to seasonal cycle. This seasonality is related to the intensity of the cold tongue. Thus, the maximum variability of TIWV is associated with the La Nina period when the cold tongue is fully developed. While during the El Nino the TIWV has been suppressed. The meridional thermal flux by the TIWV in the ocean mixed layer is negatively correlated to the tropical eastern Pacific sea surface temperature anomalies, inferring the negative feedback effect with respect to ENSO development. The effect of the TIWV is incorporated into the two-stripped down version of the ENSO model. From the model results, it is found that the asymmetric characteristics of ENSO can be caused by the asymmetric thermal heating by the meridional heat flux due to the TIWV.