RADIO WAVE PROPAGATION

Radio Signal "Skip"
Sky Wave vs. Ground Wave


The solar sunspot cycle averages eleven years; sometimes it's as short as
eight, or as long as fifteen years to encompass the minimum to maximum,
back to minimum appearance of sunspots on the face of the sun.
Sunspots are distinguished from solar flares. The occurrence of solar flares
is more sporadic. Solar flares are unpredictable phenomena which
can completely prevent HF propagation due to a
sudden rise in electromagnetic bombardment.

The sun, like any star, radiates electromagnetic ("EM") radiation,
and sunspots are special foci of EM generation. These emissions range from
the lowest (VLF radio frequencies below the commercial AM radio band), to
the highest (Gamma rays). In particular, Ultraviolet, X, and Gamma rays
rain down on earth's upper atmosphere and collide with the oxygen and
nitrogen atoms floating there. These high speed collisions
knock electrons free, a process referred to as "ionization." The
atmospheric level where ionization occurs is accordingly labeled the
"ionosphere." The ionosphere has three main subdivisions/layers, D, E,
& F, with the E and F layers having further subdivisions.

When solar sunspots or / and flares are at maximum or highly active, HF
(shortwave) band radio propagation is inhibited due to excessive radiation
bombardment and the resultant over-ionization. However, slightly more than
usual levels of radiation are instrumental in permitting DX signals to skip,
because the free ions refract radio waves.

Solar Wind #1

Solar Wind #2