SOLAR ACTIVITY & HF PROPAGATION

The Sun–Earth Interconnect Since the late 1800s, it was noted solar activity affected telegraphic lines, and later, radio communications. However,
there was no scientific proof for this link. From the 1920s onward, radio amateurs clearly correlated HF propagation and the MUF to the solar cycle. But again, there was no scientific proof. Astronomers and physicists knew there was a sun–earth connection, but without direct observational data, it remained an un proven scientific theory.

The scientific proof did not come until quite recently – basically, the space age – when we got our first look at the sun from outside our protective atmosphere. In the 1970s, the Voyager spacecrafts were the first to confirm the existence of the solar wind. It was not until Skylab that increases in radiation and the solar wind were linked to solar flares, and coronal mass ejections (CME) were first detected. The sun-earth interconnect finally became a scientific fact.

More at http://www.qrparci.org/mambo/pdf/FDIM81.pdf