Maps for the N _m F₂ winter anomaly intensity distribution from Pavlov and Pavlova (2012) (a)–(c) and from the RO measurements (d)–(f), as well as the longitudinal variation of the N _m F₂ winter anomaly intensity averaged at 40–60° geographic latitudinal bands based on the RO data (g)–(i). Panels (a, d, g) correspond to low solar activity; (b), (e), (h) correspond to moderate solar activity; and (c), (f), (i) display high solar activity. White color on panels (d)–(f) shows the regions, for which the winter/summer ratio is less than 1. Bold gray curves (a)–(f) are the geomagnetic equator and ±15° geomagnetic latitudes.