Maps for the winter anomaly intensity in TEC for quiet geomagnetic conditions (a–c) and for a moderate geomagnetic disturbance (3 < K _p ≤ 6, K _p-1 ≤ 3; d–f) at different levels of solar activity: −90 s.f.u. (a, d), −120 s.f.u. (b, e),−200 s.f.u. (c, f). Panels (g–i) show the longitudinal variations in the TEC winter anomaly intensity averaged in the 40–60° geographic latitude bands for quiet (solid lines) and disturbed (dashed lines) geomagnetic conditions. White domains on panels (a–f) correspond to 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.