Interannual changes in the variability of tropical Pacific instability waves

Using the global ocean assimilation data, interannual changes in the variability of the tropical instability wave (TIWV) of the in the tropical eastern Pacific are analyzed. The dominant patterns of TIWV are computed by the principal component analysis (PCA). The first PCA mode of TIWV (PCA1) is identified as an asymmetric pattern with the maximum loadings in the far eastern equatorial Pacific at 4°N, and the second PCA mode (PCA2) does a symmetric pattern with the maximum loadings at the equatorial eastern Pacific. PCA1 is dominated by the 2-4 year periods and mainly driven by the baroclinic instability, which is modified by the intensity and distribution of the cold tongue temperature. On the other hand, PCA2 varies with the dominant period of about 5 years, and it is mainly induced by the barotropic instability determined by the mean current distribution. Furthermore, the temporal variations of each mode are seasonally phase-locked as like El Nino does.