Figure 7. Correlation between (a) the primary part of the leading principal component and Niño3.4 represented by the three-month running means of SSTA (0 represents the corresponding DJF mean of SSTA variation, and the negative and positive running means represent the previous and following months considered at the middle point, respectively); and (b) is the same as (a) but for the secondary component. (c) and (d) are similar to (a) and (b), but for the tropical Indian Ocean (TIO) index. The shading presents statistical significance at the 95% confidence level.