Figure 2

Values of EEJ strength and corresponding Lomb-Scargle periodograms for the year 2006. (a) Hourly binned daily values of EEJ strength and (b) their corresponding normalized Lomb-Scargle periodograms are presented. This type of binned daily values average out the gravity waves with periods less than 1 h. Moreover, they show periods that are dependent on local time (like solar tides). Also, as the larger scale planetary waves modulate these local-time dependent tidal waves, the periodogram spectral power is a direct measure of the interaction strength between tidal and planetary waves. Dashed lines in the right panel represent the 90% significance levels. Here, one can note a systematic variation of statistically significant periodicities with respect to local time for the wave periods between 11 and 20 days (i.e., the quasi-16-day periods are present here at all the local times).