Bruce K1FZ said: "I have noticed that there appears to be a link between the start of an aurora and long path 160 meter openings."
Others have noted this interesting effect. The only physical tie between the two that I'm aware of is that a spike in the K index can initially improve the electron density valley that is above the E region peak in the nighttime ionosphere, resulting in a better chance of ducting. This comes from a paper by Zhang and Kamide in JGR in 2004 (they just reported their results, but didn't tie it to amateur radio propagation - heck, they might not even be aware of amateur radio!). I'm not saying this is exactly what happens, just that it *may* explain the link between the start of an aurora and long path 160 meter openings. As for the echoes that started this thread and aurora, one respondent wondered about the velocity of propagation of the RF slowing down due to a back scatter mechanism. Ionosondes report virtual height (not true height) because they assume the speed of light for the vertical incident RF. But as the RF goes up in the ionosphere, the group velocity decreases as the index of refraction approaches zero. If these echoes are of Earthly origin, then the appropriate plasma frequency could decrease the group velocity and contribute to the echo mechanism. Just speculation. Having said all this, right now I think Andy G4PIQ's comments are most appropriate for the echoes - unless there is some data and physical mechanism that says otherwise. Of course this is the problem with many of these unusual occurrences - we don't have enough relevant data with respect to the ionosphere or whatever - just observations of an interesting happening. Carl K9LA _________________ Topband Reflector Archives - http://www.contesting.com/_topband