On Fri, 15 Dec 2006 09:08:09 -0500, "C. J. Clegg"
wrote:

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?

Here is an ionogram from the station in Canberra this morning about
1.5 hours before sunrise.

http://www.vk1od.net/lost/ionogram.gif

Note the E layer at 100km height, very well established. It is so
intense, that there are multiple E - earth - E - earth "reflections".
You can see the F layer above it, and f0F2 looks between 2 and 3MHz.

(I believe that the existence of such a strong E layer before sunrise,
and the height in the 90km to 100km range characterise sporadic E.)

Sometimes the E layer reflection is so intense, that there isn't a
hint of the F layer. I don't know how they assess f0F2 under those
conditions, but they still produce the statistics.

I think you may be reading more accuracy into the maps than is safe.

As for "normally affecting higher frequencies", here you can see the
ionsonde discovering the Es layer at up to about 10MHz. When you take
into account oblique paths of a couple of thousand km or more, the Es
here with critical frequency up to about 10MHz should reflect 50MHz
ok. Now exploitation of that depends on such a patch of Es in the
right place, angled the right way, between two stations attempting
communication. There have been some big openings on 6m here in the
last week or so, not huge, just the seasonal openings typical around
the solstices.

Owen
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