In a special experiment an ionogram was recorded for each of 32 beams so that the full 360 degree azimuth range could be monitored. 32 ionograms from one run of the experiment were processed to produce Figure 13. The figure shows a map of the highest propagating frequency at about 7am local time. High propagation frequencies, which are colour-coded red, correspond to a stronger ionosphere in that direction away from Alice Springs. The figure shows that radio wave propagation to the east is much stronger than propagation to the west.
Sunlight ionises the upper atmosphere, which strengthens the ionosphere to the east.
To the west, however, the depleted night-time ionosphere shows much reduced propagation. In effect this figure shows sunrise in the ionosphere. Figure 12 shows strong propagation between 10000 km and 12000 km. Figure 13 shows a similar propagation map but from an hour later. The result is almost uniform propagation conditions as a function of azimuth.