Bill,
Thanks for the posting. I was pleased to see your remarks referred to
magnetic activity.
I have consistently argued that skewing is due to ionization along a path
and the most frequent source of ionization above the normal levels in the
ionosphere is from aurora disturbances. Their geophysical signature is
elevated K- and A-indices, particularly from high latitude
magnetometers. Thus, in suggesting times for good, undisturbed DXing, I
have cited days with low K-sums on the Meanook Magnetometer in Canada.
The extent of auroral ionization increases with high levels of
disturbance and the IGY was a time when much of this was noted, eg.g.,
Xrays from auroral electrons detected by University of Minnesota physicists
over Minneapolis. So it is not surprising that skewing or lateral
deviations are observed on northerly paths during times characterized by
high K-values.
To see what is going on, it is helpful to have a mapping capability, such
as found in MINIPROP PLUS or DXAID (out of Canada). Those programs show
clearly the great-circle paths and whether they come close to auroral
latitudes. The DXAID program is particularly good as the auroral zones
in its displays are sensitive to the level of disturbance, through
K-values, and are based on the same NOAA/NASA type of data that is found
on the Internet.
Just as consistently as I have argued FOR skewing during magnetic
disturbances, I have argued AGAINST it during times of geomagnetic quiet
(K=0) shown by high latitude magnetic observations. The solar wind is
always blowing by, jiggling high latitude field lines, but the levels of
auroral electron influx vary greatly and at low K-values, there is little
ionization overhead (judging from high latitude riometer data). So high
latitudes have to be considered "home base" for additional ionization and
effects, whether absorption or skewing, of Top Band signals.
I should add that ray-tracing shows that there will be modest skewing of
a "natural origin" when paths approach the terminator. The lateral
deviation is small, a degree or two, and away from the terminator. So
any signals approaching the terminator are deviated away from it, into
regions where the electron density gradient across the path is very small
compared to that around the terminator. So once out of the influence of
the terminator, they are no longer deviated and follow a new great-circle
path.
Before taking off my "white coat", let me say that I am interested in the
physical processes which affect propagation so do not try to engage me
with any sort of discussion of "paranormal events" or metaphysical
views. As I have often said, we have been playing radio for almost 100
years. We ought to get some of these things right lest our legacy be
viewed as trivial by those who follow.
73,
Bob, NM7M
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