Which of the following types of propagation is most commonly associated with occasional strong signals on the 10-, 6-, and 2-meter bands from beyond the radio horizon?
Why Sporadic E happens when patches of intensely ionized material form in the E region, about 60 to 70 miles up, and reflect signals that would normally pass straight through. Because the ionization is very dense, it can bend frequencies far above the usual MUF, which is why it shows up as sudden, strong openings on 10, 6 and even 2 meters. Typical hops run roughly 500 to 1400 miles, and the openings come and go over minutes to hours, most often in late spring and early summer.
Watch out D region absorption is the opposite effect: the lowest ionospheric layer soaks up energy on the lower HF bands during daylight rather than returning signals. Gray-line propagation is an HF enhancement along the sunrise/sunset terminator, not a VHF phenomenon.
6 meters is the Magic Band, and the magic is sporadic E. Think E for Excitement on 10/6/2.