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Journals - Author Instructions

In conventional mathematical notation, an italic letter with a subscript generally denotes a variable taken at or with reference to some condition (indexed by the subscript). Thus, R om , the subscript m appearing here in the same way as for other single italic variables, would be the correct notation for, say, observed resonance, optical radius, etc. ApJ generally prefers to set two-letter abbreviations roman (not italic) within equations, to distinguish them from strings of variables: thus EM for emission measure is set roman so it is not misread as "energy times mass." We have adopted the roman abbreviations Ro, Ra, Re for Rossby, Raleigh, and Reynolds numbers (and so for other named variables), as being most consistent with our general notation and least prone to misreading. Then, following conventional notation, magnetic Reynolds numbers are set Re