On Fri, 28 Dec 2001, Tom Rauch wrote:
> It would be interesting to see, in non-jargon English, a description
> of (or debate about) what people who study the ionosphere think is
> going on.
>
> A back and forth exchange in some moderated forum would be
> enlightning!
so here is my contribution to the exchange:
Friends in Radio Land -
Like you, I have seen a number of complaints or words of praise
for propagation in recent days. As one who used the Meanook
K-sums to suggest a "Christmas Present" in the form of good
propagation on Top Band, I feel obliged to add a few words to
the discussion, words of explanation.
The K-sums need no apologies but the spottiness of propagation
does. In that regard, I could turn to my recent publication in
QEX, "160 Meter Propagation: Unpredictable Aspects", and cite the
various factors that I listed. Surely, among the many there, the
culprits could be found. But I would single out two, the filling
of the electron density valley above the E-region by the higher
levels of solar activity and unsettled meteorological conditions
of the sort we have been experiencing.
The filling of the electron density valley was mentioned in the
April 2001 issue of the Low Band Monitor and a graph presented to
show the problem for solar max as compared to solar min. The
raising of the bottom of the valley, largely by scattering of
solar UV by the geocorona into the dark hemisphere, then serves
to reduce the probability of signal ducting at low-and mid-latitudes,
making propagation on DX paths in those regions less stable.
As for meteorological factors, those have not been established to
everyone's satisfaction but on general principles, one can expect
the inclination or tilts of ionospheric regions to be affected by
turbulent winds, particularly at the altitudes where Top Band
signals are propagated. With the unsettled conditions we recently
experienced at low altitudes, it does not take any great stretch
of the imagination to think the situation is unsettled also up
around 100 km or so. That would serve to reduce the scale-size of
atmospheric regions when it comes to their coherent motions and
affect the direction or inclination of DX ray paths in their
refraction. In a nutshell, propagation paths would be spottier
or more broken up than in quieter conditons.
I would leave it to Tom, KN4LF, to comment further on the factors
of meteorological origin; he's the meteorologist, not me. It just
seems to me that both the solar and terrestrial weather contribute
to the strange propagation experienced recently. Now that the
winter solstice has passed, the effect of the solar wind will
increase again. The question becomes which factor will be the
dominant one in the days ahead. Stay tuned!
73,
Bob, NM7M
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