Listening to AA7FV

Since AA7FV told me he was receiving the strongest spots he'd ever seen on WSPR at 14MHz, I've been taking more of an interest in what's going on.

Last night, the signal reached a new record, with two spots at -2dB SNR from 2W into a large rhombic antenna at AA7FV.  My antenna is a vertical delta loop in quiet conditions.

The pattern of the spots, when plotted out, looks like this. Y scale is SNR in dB:

The pattern, which comes to an abrupt halt after the 00UT spot, clearly trends upwards from a fairly low SNR in my local early evening, peaking strongly in the period 22-00UT.

I've noticed this kind of thing many times before, and the timing appears to be related to the passing of magnetic midnight at roughly mid-Atlantic longitudes:

Situation at peak spot strength.  Image NOAA.

The great circle path between AA7FV and myself is thus:

Great circle path.  Image: Google.

The path, if it is the same as the great circle path (which may not be the case) from AA7FV goes straight into the magnetic midnight sector where it finds a quiet conditions aurora between Greenland and Iceland, although the signal enters the overall auroral oval much earlier, over the northern extremities of Quebec.

It is possible, perhaps even likely, that the AA7FV signal takes more of a tangential path to the aurora that may then skew its path towards the UK.  This is very difficult to demonstrate, but has certainly ben noted in abundance in the scientific literature, where up to 100 degree deviations from the great circle path have been determined.

Superficially, this seems to suggest that some form of enhanced ionisation exists in this auroral zone that considerably boosts the signal strength over what it would be without it.  This occurs repeatedly from night to night, so the link with the auroral oval seems strong, especially as the signal vanishes soon after my local midnight.

As always, any informed insights welcome under comments!