[DX] Can anyone explain this?

[Dave Shrader]

I'm not a propagation specialist, so my opinions are subject to several
options: they are/may be valid, they may be partially correct, or I'm
totally off the wall!!

With that disclaimer stated I'll guess at some qualitative physics.

In the transition zone between daylight and darkness the ionization
levels of the atmosphere are dynamically changing. 

In the daylight zone there is moderately high ionization deep into the
atmosphere and the ionization intensity is decreasing as a function of
time, sun angle and high altitude [200,000 feet] molecular dynamics. In
the dark zone low altitude ionization is recombining, continuity
equations, as a function of time and the motion of the F layer. The
ionization density is moving to a higher altitude.

So, the density of the ionization is changing as a function of
daylight/darkness, sun activity, altitude. This creates a boundary layer
of varying ionization that is moderately wide, moderately high, and
quite dynamic. In the dynamic region where this is happening the
divergence and gradient [curl] of the ionization levels [technical terms
for the variation[s] of ionization] create a reflective three
dimensional boundary between daylight and darkness. This boundary layer
revolves around the earth as one component of 'grey line' propagation.

In fifteen minutes the full transition from daylight to darkness occurs.
While you are in this fifteen minute window you will have short periods
of propagation along the ionization gradient.

Hope this summary meets your needs.

>From a simple engineer who worked for several years on ionization
effects in media other than the atmosphere.

Deacon Dave, W1MCE
 
FireBrick wrote:
> 
> My software logging also provides a gray line display.
> I was trying to work Myanmar on 15 cw. Pretty weak.
> I looked at the gray line screen and advanced the time but due to the sun's
> location there was no time that both I and XZ were both in twilight at the
> same time.
> But.
> There was a time, approx 1800Z that we would both be equidistant from the
> gray line.
> What I mean is that the amount of time before I was in twilight was just
> about equal to the amount of time after dawn in XZ.
> 
> So for the heck of it, I checked and sure enough, as that time approached
> the XZ signal rose to s2, peaked, and then dropped back down as I approached
> twilight. The opening was short, maybe 10-15 minutes.
> 
> I will check this out again when I can.
> But my question to you is...
> What is the reason for this?
> 
> -----------------------------------------------------
> You May be a CheeseHead if: You decided to have a picnic this summer because
> it fell on a  weekend.
> -----------------------------------------------------
> 
> Bill H. in Chicagoland
> w9ol@billnjudy.com
> www.billnjudy.com
> http://files.billnjudy.com
> 
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