[CQ-Contest] What happened on 10m?

[Carl K9LA]

Propagation enthusiasts,

In a message to this reflector on 14 December, N7DF hypothesized that 
the cause of the good conditions on Sunday of the 10m contest was due to 
the interplanetary magnetic field (IMF) turning south around 0300 UTC on 
the Sunday of the contest.

The southward-turning of the IMF appears to have resulted in minimal 
impact to the Earth's environment. This can be seen in the K-index data. 
The K-index at several stations was running at 0 prior to the IMF 
turning southward, and it jumped to only 1 in the 0600-0900 UTC period. 
I'm not even sure the southward-turning of the IMF was the cause of the 
K-index jumping to 1, as similar jumps from 0 to 1 were seen prior to 
Sunday.

An inspection of several ionosondes in North America and Europe that had 
data (Wallops Island in Virgina, Millstone Hill in Massachusetts, and 
Rome) shows no F2 region enhancement on Sunday. So I think it's safe to 
rule out an F2 region mechanism (at least in the areas of those ionosondes).

What does show up in the ionosonde data is evidence of sporadic E, which 
isn't surprising since December is a good month for sporadic E. In fact 
sporadic E was showing up prior to Sunday, so I doubt that the 
southward-turning IMF had anything to do with this, either.

In summary, I believe the good conditions on Sunday of the 10m contest 
were simply due to sporadic E (as correctly pointed out, in my opinion, 
by others - for example, N0JK), and didn't have much (if anything) to do 
with the IMF turning southward. That's my story and I'm sticking to it - 
and it's based on my understanding of the processes in the ionosphere 
and a review of ionosonde data.

Carl K9LA