Fig. 2
From: Morphology of tropical mesospheric echoes observed by VHF radar
Percentage occurrence of echoes categorized with echoes occurring for 5–20 minutes (T1), 20 to 40 minutes (T2), and more than 40 minutes (T3), observed during the different seasons, (a) winter, (b) spring equinox, (c) summer and (d) fall equinox. The percentage occurrence shown on the bottom (top) axis is for T1 (T2 and T3), respectively.