On the left, a sequence of observations from the EB040 ionosonde, including ionograms for 23:00:01 UT, 23:05:01 UT, and 23:10:01 UT. On the right is a sequence of ionograms from AT138. These ionograms are for times 21:00:00 UT, 21:05:00 UT, and 21:10:00 UT. In the ionograms, red points represent O-polarised echoes and green points represent X-polarised ones. Other colours indicate oblique reflections. All panels show ranges from 80 km to 800 km on the vertical axis and frequencies from 0.0 MHz to 6.0 MHz on the horizontal axis. The echoes in the EB040 ionograms starting around 3 MHz and above 440 km are the oblique trace received from the EA036 transmissions, while those at ranges above 600 km are the oblique signals from DB049.