## 3 Tidal Characteristics of DS0 and DW2  
### Altitude-Time Variations  
Amplitudes and phases of the non-migrating diurnal tide, DS0, extracted from COSMIC, CMAM30, and ERA temperature data over the equator during 2006 to 2010 are shown in Figure 1. The amplitudes observed in COSMIC are small, varying from 0.6 to 0.9 K,and observed intermittently from 35 to 40 km. Above 40 km, the amplitudes are almost negligible. In CMAM30 and ERA, on the other hand, significant amplitudes greater than 0.6 K are seen above 5-10 hPa. The year-to-year variations are consistent within these datasets in both amplitude and phase. There is a seasonal variation with maxima during the month of August and minima during the month of October. Amplitudes of 1 K are observed during August 2006, 2008, and 2009 in both CMAM30 and ERA at altitudes above 3 hPa. The amplitudes are comparatively smaller in 2007. These features are absent in COSMIC. However, the phase variations are highly consistent among all three datasets above 30 km/10 hPa.  
Figure 2 shows the variability in DS0 amplitudes and phases over 65\({}^{\circ}\) N similar to Figure 1. Significant variability is observed in COSMIC during the boreal winter. Tidal amplitudes of 1 to 2 K are observed from 25 to 40 km in small bands varying periodically over scales of less than a month. In CMAM30 and ERA, short-term variations, albeit with small amplitudes, are also seen during the boreal winters. During the winters of 2008-2009 and 2009-2010, these amplitudes are slightly larger. Earlier studies have shown that non-stationary, i.e., changing SPW1 amplitudes can alias into DS0 and DW2 components [13; 14; 30]. [PERSON] [37] has shown that SPW1 varies with similar periodicities from 30 to 120 days. The DS0 amplitudes observed in Figure 2 in COSMIC, thereby, appear to arise due to aliasing. The phases in CMAM30 and ERA, although highly consistent and similar, do not provide any useful information as the amplitudes are very small.  
Figure 1: Amplitudes and phases of DS0 tide over equator from COSMIC observations, CMAM30, and ERA-interim reanalysis datasets using \(\pm\)10 days window.  
Amplitudes and phases of the DW2 tide extracted from COSMIC, CMAM30 and ERA temperature data over the equator are shown in Figure 3. Similar to DS0, the variability of DW2 in COSMIC temperatures is intermittent and observed between 30 and 40 km. In CMAM30 and ERA, regular variations with a winter maximum are seen above 5 hPa. CMAM30 amplitudes at 2 hPa are 1 K, and ERA amplitudes are larger and reach values of 2 K. Further, in ERA data, DW2 shows occasional peaks during summers indicating a semi-annual variation superimposed on an annual variation. DW2 phase variations of CMAM30 and ERA are similar and comparable with that of COSMIC.  
Figure 4 shows the variability of DW2 amplitudes and phases over 65\({}^{\circ}\) N. Similar to DS0, the variations in DW2 amplitudes also appear to be affected significantly by aliasing. Amplitudes of 0.8 to 1 K are observed in COSMIC temperatures from 25 to 40 km during boreal winters as striations vary periodically over scales of less than a month and are probably due to aliasing, as seen in the case of DS0 [13; 14; 30]. DW2 amplitudes are almost absent over 65\({}^{\circ}\) N in CMAM30 and ERA temperature data. Phases of DW2 over 65\({}^{\circ}\) N do not provide any information in any of the datasets.  
Figure 2: Amplitudes and phases of DS0 tide over 65\({}^{\circ}\) N from COSMIC observations, CMAM30, and ERA-interim reanalysis datasets using \(\pm\)10 days window.  
Figure 4: Amplitudes and phases of DW2 tide over 65\({}^{\circ}\) N from COSMIC observations, CMAM30, and ERA-interim reanalysis datasets using \(\pm\)10-day window.  
Figure 3: Amplitudes and phases of DW2 tide over equator from COSMIC observations, CMAM30, and ERA-interim reanalysis datasets using \(\pm\)10-day window.