Fig. 2
From: A minimum in the latitude variation of spread-F at March equinox
Statistics of occurrence, onset time and duration of spread-F at b Okinawa, c Yamagawa, d Kokubunji and e Wakkanai in March to April 2002; black bars indicate range type spread-F, and red bars indicate frequency type spread-F. a Daily mean magnetic and solar activity indices (Dst and F10.7)