The upper limit of 'ionospheric propagation' varies with what important feature of the sun?

Question

And how does it affect the propagation of radio signals?

part of my physics HW that I couldn't find the answer to XD Thank you in advance if you can help me :)

Answer 1

look here

http://www.radio-electronics.com/info/pr...

http://www.pgh-net.com/oes/prop-main.htm...