Figure 3

The contour plots of periodograms of EEJ and TEC in the years 2005 to 2013. Contour plot of the Lomb-Scargle periodograms corresponding to all the local times as shown in Figure 2b is presented in subplot a[1]. Similarly, periodograms of EEJ in the left panel (a) and TEC in the right panel (b) for the observation durations in the years 2005 to 2013 are shown. The spectral powers are normalized with respect to their respective 90% significance level values. The color bar represents the strength/relative power of the significant periods, and all the periods with relative power greater than approximately 0.6 (dark green) are above 90% significance level. It should be noted that during the major warming cases in 2006, 2009, and 2013, both the EEJ and the EIA crest region station, Diego Garcia, show strong quasi-16-day periodicities.