Crossing to Alaska.

KL7L is a station that I always think is in a very interesting place in terms of HF propagation. 

Overnight, I ran WSPR at 14MHz, using 1W from the vertical delta loop. 

This is the plot of all the spots from 19:38UT 14/05/2018 to 07:50UT 15/05/2018:

The appearance and very sharp peak of signal at around 06:30UT is quite interesting. It is exquisitely linked to sunset at KL7L.  Here's the picture as my signal peaks at 06:36UT in Alaska:

And as the strong peak falls away at 06:44UT, less than a quarter of an hour later:

I've been thinking a fair bit about the likely propagation path for this event.  My transmitter has been in daylight for some hours at 06:30UT, although it's clear from the overall signals received here that the D layer is not yet strongly formed.  In fact, we are just before the point where DX signals vanish and local signals come to dominate.

At the same time, it's the sunset period in Alaska, and the D layer will be weakening rapidly.  At the moment, during the depths of solar minimum, the Lyman alpha radiation is fairly low, too. 

Is there a component of long path propagation?  I'm not sure.  The duration of the peak signal is similar in length to that seen in UK-VK long path propagation, roughly 20 - 30 minutes.  If it was just D layer weakening, then perhaps the peak signal might last considerably longer, given that KL7L evenings are now constant and quite strong twilight.

Any thoughts?  Please post a comment!