How to filter out extra-tropical variabilty to highlight the structure of the Semiannual Oscillation using just multiple linear regression.
Some time ago, with a Journal Club I’m part of (shout-out to Go stratospheric!), we read “Representation of the equatorial stratopause semiannual oscillation in global atmospheric reanalyses” (Kawatani et al. 2020), a paper about the Semiannual Oscillation (SAO). One figure (Figure 1) piqued our interest. The SAO is supposed to be a characteristic of the tropical stratosphere and be… you know… semiannual. But in Figure 1, the more sticking feature is extra-tropical and with an annual cycle.