Topband: auroral zone and pmaps
Fri, 28 Dec 2001 22:22:36 -0500
Steve VE6WZ said:
> My point is, aurora absorption is a very REAL thing.......what
> other phenomena could explain the almost constant 160m blackout
> punctuated by only brief flashes of propagation?
In addition to auroral absorption, another "oh, shoot" exists with
auroral activity. Intense discrete auroral forms can be an indication of
significantly increased electron densities - along with the resulting
gradients that can cause refraction/reflection of our RF to where we
don't want it to go.
I've never experienced the conditions VE6WZ sees in Calgary, but those
of us at somewhat lower latitudes (I'm in northeast Indiana) do see
interesting things happening with the auroral zone - and they may not
all be bad.
Those pmap pictures referenced by W4ZV, et al, only tell us where
visible aurora is likely to occur (low energy precipitating electrons).
What we don't really know is where the more intense ionization is that
can impact our RF (generally it's at the equatorward and poleward edges
of the auroral oval). The auroral oval superimposed on the pmap is a
canned picture based on the auroral activity level assigned from the
satellite measurement of estimated power input to the polar region -
it's not even a real-time photo.
Indeed, what's happening in the auroral zone is quite dynamic. And it
depends on whether we're talking about early evening local time (quiet
arcs with little absorption), around midnight local time (bright active
regions with rapid and strong increases in absorption), or the early
morning hours local time (broad diffuse regions with strong, slowly
I recently submitted a short article to The Low Band Monitor showing a
pmap and the corresponding visible aurora photo taken from another
satellite that shows the auroral zone may not be that formidable - at
least in the evening hours local time with Kp = 4. It appears that our
RF could sneak under (as suggested by Oler and N4XX in their CQ article
a while back) or perhaps even through gaps in the intense discrete
auroral forms. The intense discrete auroral forms could also explain the
often-reported skewing effect. As a side note, this intense ionization
appears to give us the very selective auroral-E propagation to the
Scandinavian countries on the higher bands in the late afternoon and
early evening hours (like the 15m spot I saw today on Packet from
California to Norway around 0100 UTC).