Fig. 1
From: A minimum in the latitude variation of spread-F at March equinox
Sample ionograms showing spread-F at a Okinawa (26.3° N, 127.6° E; 15.3° N mag. lat.) and b Yamagawa (31.2° N, 130.6° E; 21.2° N mag. lat.) on 05 April 2002 (Ap = 4) and c Kokubunji (35.7° N, 139.5° E; 26.5° N mag. lat.) and d Wakanai (45.4° N, 141.7° E; 36.5° N mag. lat.) on 17 March 2003 (Ap = 42) in Japan. Spread-F is range type at Okinawa and Yamagawa (low latitudes) and frequency type at Kokubunji and Wakanai (mid latitudes)