Topband: Enhanced electron recombination

[Robert Brown]

Tom-
 
Good to hear from you again.  As for your comments, one or two
corrections.  First, I was talking about paths going across the
geographic polar cap as the longitudes (East Coast and Mongolia)
differ by close to 180 degrees.  It would seem inescapable that
signals from the East Coast would go northward and on crossing the
polar cap, they would come down from a northerly direction in
arriving at Mongolia.  Any other directions would involve rather
unusual circumstances that should be identified and explained, if
possible.
 
My discussion was for the JT DXpedition around the equinox and
assumed a low level of geomagnetic/auroral activity, say Kp=1+ or
so.  Moreover, the dawn-dusk direction went across the auroral
oval at a local time about 6 hours different than the local time
of maximum auroral activity (midnight at Alaskan longitudes).  So
the level of auroral activity in that region would be a minimum
and the ionosphere would be supported mainly by its weak sources
(starlight, galactic cosmic rays and solar UV scattered by the
geocorona).
 
Under those circumstances, the enhanced electron recombination due
to the O+ ion chemistry in ionospheric electric fields could
reduce signal absorption and skewing in the region, making it more
likely that signals could go across the center of the polar cap.
But if auroral activity were greater than that level, all bets are
off as the enhanced electron recombination is relatively modest in
magnitude and can't compete with electron production from any
greater auroral electron influx.
 
So I had a limited agenda in my discussion but one that is still
important when it comes to paths across the polar caps, say in
long-path situations.
 
As for the other situations you mentioned, I am at a loss to
respond in detail as dates, times and geomagnetic details are
lacking.  But as I said in my QEX article at the end of last year,
160 meter propagation involves signals undergoing refraction,
scattering of some type or auroral reflections.  I cannot come up
with any other mechanisms to advance 160 meter signals so it
would seem to me that any of your observations of skewed paths
would have to be explained in those terms.
 
Ionospheric refraction is gradual and efficient, scattering is
largely isotropic in direction and thus quite can be very
inefficient in advancing signals while auroral reflections are
sort of a "wild card", dependent in strength and direction on the
level of auroral activity and potentially accompanied by heavy
absorption.  But those are the choices that you have to explain
your observations of skewed paths.
 
Given the report of a skewed path, the sort of questions I always
have are "what happened and where?" In the past you have always
been good about identifying auroral events and I appreciate that.
As for your SW and SE paths, I have already given my views on
those in the QEX article and will not repeat them here.
 
73,
 
Bob, NM7M