Topband: Topband Angle changes at sunrise/sunset

[btippett@alum.mit.edu (Bill Tippett)]

I wrote:

>I also would be interested in any explanations for why TOA's 
apparently change from low to high angles at sunrise...but the 
same is not usually true for sunset.

        Bob NM7M sent the following explanation for this:

"As for the changes in angle at sunrise, and the lack at sunset,
that has to do with the E->W motion of ionosphere layers.  At
sunrise, ionospheric layers are tilted downward or lowered as the
sun rises, refracting signals downward at steeper angles, while at
sunset layers are raised slightly as the sun sets, with little
effect on angles.
 
This is most striking with dawn enhancements and discussed nicely
in VE7DXR's articles where he uses the motion of transverse plasma
frequency contours from the PropLab Pro program to show the
tilting."

        Thanks Bob...I had not seen that explanation before!

                                                73,  Bill  W4ZV