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Fig. 5 | Earth, Planets and Space

Fig. 5

From: Planetary-scale MLT waves diagnosed through multi-station methods: a review

Fig. 5

Spectral periodic table (SPT) as an analogy of the periodic table of elements. The left panel was wrapped from a frequency cross spectrum, so that spectral peaks in the same column share the same origin, one wave and its interactions with different migrating tides (see He et al. 2021b). For example, spectral peaks indicated by the red vertical lines, termed the red family, can be explained as either a Q2DW [\(\frac{1}{\text {50h}}\),3] or its secondary waves (SWs) through interactions with different migrating tides, while the spectral peaks indicated by the blue vertical lines can be explained as another Q2DW [\(\frac{1}{\text {41h}}\),4] and its SWs. Noted that the SPT might not be completed and can be extended to include more rows, in analogy to the potential extension of the periodic table of elements. The magenta arrow denotes increasing frequency 0\(<f<\)3.5 cpd, indicating how the cross spectrum is wrapped into the table. In each row of the table and from left to right, \(\delta f:=|\frac{f}{\text {1cpd}}-\lfloor \frac{f}{\text {1cpd}}\rceil |\), namely, the absolute spectral frequency difference to the nearest tidal frequency \(\lfloor \frac{f}{\text {1cpd}}\rceil\), increases from 0 to 0.5 cpd. The current figure is adjusted from Figure 1 in He et al. (2021b)

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