On Fri, 15 Dec 2006 08:09:45 +0000, Owen Duffy wrote:

You missed my point, it isn't so much as the exact location of the
virtual midpoint, but is there an ionosound measureing that point, or
is the map constructed by interpolating measurements from just a small
number of ionsondes, and is the interpolation sound?

Oh, OK, I get it.

I have no idea. I use the map at http://solar.spacew.com/www/fof2.html
and I don't know how they get the information they use to build that map.

Sporadic E does not depend on sunlight, it is one of the mysteries of
Es.

Doesn't sporadic E normally affect the higher frequencies, 15 meters and
above, rather than the lower frequencies around 75 meters?