## 4 Discussion
The black contours show the wavelet power at a confidence level of 99% with respect to a white noise background [44]. In this figure also, in all panels, the periods at 50 and 100 days are highlighted using horizontal dashed lines to aid the eye. Unlike in DW2, the short-term variability in DS0 in the stratosphere (10 hPa) is weak. One hundred-day variability is seen from September 2008 to September 2009. The annual oscillation is very prominent. At 1 hPa, 50-day variability is seen from mid-2006 to almost end of 2007, similar to DW2. Higher up, at 0.0007 hPa, significant variability is seen at periods from 40 to 100 days at the end of 2006, summer of 2007, beginning of 2008, and winter of 2008-2009 as well. This also is similar in many ways to the variability seen in DW2. Detailed investigation of the Figures 9 and 10 shows that variability in SPW1 amplitude in the high-latitude stratosphere is occasionally similar to that in DS0 and DW2 amplitudes in the equatorial high-altitude, i.e, the MLT region\(\longrightarrow\)50-day period in the winter of 2006-2007, \(\sim\)100-day period in the beginning of 2008, and 70-day period in the beginning of 2009. At other occasions, such as during the summer of 2007, and at periods less  
Figure 10: Wavelet power spectrum of average amplitude of DS0 over \(\pm 20^{\circ}\) at (**a**) 0.0007 hPa, (**b**) 1 hPa and (**c**) 10 hPa, (**d**) wavelet power spectrum of SPW1 amplitude over 65\({}^{\circ}\) N at 10 hPa extracted from CMAM30 temperature data. than 50 days, variabilities seen in DS0 ad DW2 are not observed in SPW1 amplitude (the variabilities in SPW1 amplitude over the Southern Hemisphere at 65\({}^{\circ}\) S are also verified (not shown here), and no similarities are seen). We thereby conclude that this is supporting evidence that part of the variability of DS0 and DW2 in the equatorial MLT region during winter could be attributed to non-linear interactions, while variability over significant durations otherwise, particularly during summers, remains unexplained. A simple correlation analysis is performed between DS0 and DW2 amplitudes over the equator from 2006 to 2010 and that of SPW1 in the high-latitude stratosphere to investigate this further. In Figure 11, panel (a) shows the correlation between amplitudes of high-latitude stratospheric SPW1 with equatorial DS0, panel (b) shows the correlation between equatorial DS0 at 10 hPa with equatorial DS0 at all altitudes, panel (c) shows the correlation between amplitudes of high-latitude stratospheric SPW1 with equatorial DW2, and finally, panel (d) shows the correlation between equatorial DW2 at 10 hPa with equatorial DW2 at all altitudes. Equatorial DW2 has a very good correlation with high-latitude stratospheric SPW1, particularly near the stratopause and in the MLT region. Simultaneously, the correlation of DW2 in the MLT is also good with that in the lower altitudes over the equator. This indicates that DW2 in MLT is influenced via non-linear interactions by SPW1 from high latitudes as well as other sources from below. In the case of equatorial DS0 in the MLT region, its correlation with high-latitude stratospheric SPW1 does not appear to be significant but is large and positive in the lower mesosphere. The correlation is also reasonably good with itself from the lower altitudes. This shows that both DS0 and DW2 also have a source in the equatorial lower atmosphere and could probably be explained as the global oscillations from classical tidal theory [1; 2; 3]. The anti-symmetric nature of their global structures also supports this argument. Figure 11: Correlation between amplitudes of (**a**) high-latitude stratospheric SPW1 with equatorial DS0, (**b**) equatorial DS0 at 10 hPa with equatorial DS0 at all altitudes, (**c**) high-latitude stratospheric SPW1 with equatorial DW2, (**d**) equatorial DW2 at 10 hPa with equatorial DW2 at all altitudes.