Striking evidence, in addition to spread F, for field-aligned electron density irregularities is commonly observed on postsunset Alouette 2 topside sounder ionograms recorded near perigee (500 km). This evidence is provided by distinctive signal returns from sounder-generated Z mode waves. At low latitudes these waves become guided in wave ducts caused by field-aligned electron density irregularities and give rise to strong long-duration echoes. At high latitudes, extending well into the polar cap, transmitted Z mode waves (and stimulated electrostatic waves at the plasma frequency and trapped ordinary mode echoes) produce a series of vertical bars on the ionogram display as the satellite traverses discrete field-aligned density structures. Within 15° dip latitude of the dip equator, Z mode wave ducts were encountered on about one third of the ionograms sampled; beyond 75° invariant latitude, vertical bar phenomena were encountered on more than three fourths of the ionograms sampled.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.