Fig. 1From: Seasonal variations of nighttime D-region ionosphere in 2013 solar maximum observed from a low-latitude stationExample of spectrograms showing the tweek events on 22 February 2013 at 0:30 LT (a), 13 March at 2:00 LT (b), and 15 May 2013 at 2:30 LT (c)Back to article page