Amplitudes of SD, SD
, and Q16 (a-h). The amplitudes of the semi-diurnal (SD; thin continuous lines), semi-diurnal envelope (SDenvelope; thick continuous lines), and quasi-16-day (Q16; dashed) periods in the EEJ strengths are shown along with the correlation coefficient (R) between SDenvelope and quasi-16-day wave amplitudes. One can note that there is a good correlation between these two parameters for the three strong major warming years 2006, 2009, and 2013 (R values are 0.78, 0.85, and 0.79, respectively). This signifies that during the strong SSW events, the interaction between semi-diurnal and quasi-16-day waves is stronger.