On 8 Jul 2010 at 12:00, Alan Melia wrote:

> See a QST article by the late Bob Brown NM6M around 2000 (I can't find
> the reference) which describes the illumination at the dawn edge of the
> ionosphere from underneath which creates an intensely absorbing
> condition. As the intensity increases with solar elevation and the
> illumination is from above the attenuation actually decrease

You mean:

Bubbles in the Ozone Layer - Bob Brown NM7M (not NM6M)
QST December 1999 p44-46

Have just downloaded it from the ARRL Members Only Archive
http://p1k.arrl.org/pubs_archive/97434

73 Dave G3YMC

http://www.davesergeant.com