Massive solar flare disrupts worldwide HF radio communication

Hams worldwide were having a great time today in the CQ WW SSB Contest (2014.10.25) on HF until about 17:00 UTC when a massive X-class solar flare caused radio blackout worldwide.  The sound of all the HF bands closing down was remarkable.  The only HF communication remaining active was via ground wave propagation.  The HF radio blackout started to lift about 18:30 UTC with the re-opening of the 10m and 12m bands and then the other bands over time.

X-class solar flare erupting 2014.10.25
Photo by NASA/SDO

Massive X3.1 Class Solar Flare 2014.10.24
Photo by NASA/SDO

So what does X3.1 solar flare mean?  Solar flares are classified as A, B, C, M or X according to the peak flux in watts per square meter (W/m2) X-rays near Earth, as measured on the GOES spacecraft.

Classification	Peak Flux Range picometre (W/m2)
A	< 10−7
B	10−7 - 10−6
C	10−6 - 10−5
M	10−5 - 10−4
X	10−4 - 10−3
Z	> 10−3

Within each class there is a linear scale from 1 to 9.n (apart from X), so an X2 flare is twice as powerful as an X1 flare, and is four times more powerful than an M5 flare.  X class flares up to X28 have been recorded.

Good DX and 73, NJ2X