Fig. 3

Same as Fig. 2 but showing the local time dependence of echoes occurring for 5–20 minutes (T1), 20 to 40 minutes (T2), and more than 40 minutes (T3) at 65–70 km (R1), 70–80 km (R2), and 80–85 km (R3), observed during the different seasons. The seasonal average for each combination is also shown (black line) as a reference.