Doc, is that what we in CB referred to as "skip"?
No...."the "skip" phenomenon is the radio signal bouncing off of ionized layers in the atmosphere, and is confined to frequencies that are typically below 30 MHz (the CB band is around 27 MHz if I recall). Transmissions above 30 MHz are not reflected, and continue to pass through the atmosphere into space, under normal conditions (there are some exceptions). The level of atmospheric ionization varies with the level of sunspot activity, and exists in 11-year cycles......we are coming out of a solar "minimum" right noiw, so "skip" propagation is limited to frequencies much lower than 30 MHz, the higher the level of sunspot activity, the greater the critical atmospheric ionization, and the higher the frequency radio signals that will "skip". This is why CB'ers will sometimes have "skip" and sometimes not, depending on the level of sunspot activity.
"Tropospheric Ducting" is caused by the collision of a warm humid air mass with a cold humid air mass, which sometimes forms a "tube or duct" where radio signals that are above the frequency that can be reflected off the ionosphere can travel for sometimes great distances. The principle is nature creating a form of "waveguide" which is the mechanical method by which radio signals all the way up into the microwave spectrum are transmitted to antennas. The best examples of waveguide use is in radar installations, and microwave ovens. It is essentially a rectangular resonant hollow tube through which the radio energy passes.
The presence of high concentrations of water droplets in humid air masses creates a "surface", which if formed into a tube by convergence of warm and cold air masses, simulates a "pipe" through which the VHF and UHF radio signals can travel, instead of escaping into space as they would normally do.
The physics of RF propagation is a rather complex science, and can be sometimes hard to explain, and conceptualize.......I hope I've answered your question.......
doc