Solar flare observed
On 31 March 2001 the effect of a major solar flare was observed on HF (shortwave) propagation. Having had advance warning of an enormous sunspot, noaa 9393 and the likelihood of interference with HF (short wave radio) propagation I set the chart recorder to observe the signal strength from the BBC relay in South Africa on 6190 kHz.
This is the NOAA record of the solar X ray flare at 11:00+ utc that day:
# Edited Events for 2001 Mar 31
#
#Event Begin Max End Obs Q Type Loc/Frq Particulars Reg#
#-------------------------------------------------------------------------------
6850 + 1100 1112 1131 GO8 5 XRA 1-8A M2.1 2.8E-02 9393
As you can see region 9393 of the sun produced a large X ray flare between 1100 and 1131 UTC to magnitude M2.1 . And here is the printout from the chart recorder:
Another strong flare was recorded on April 2nd 2001
The explanation is that the x-ray flare from the sun disturbs the earth's ionosphere and so prevents it from reflecting the HF signal. When the flare stops, the ionosphere takes a little time to recover but eventually the signal is reflected again.