Topband: 160 Mid Winter Lull
k4kyv at hotmail.com
Sat Nov 25 18:01:27 EST 2006
Over the years I have noticed that the better conditions on 160m often occur
between early November and late December. Propagation sometimes goes into
the doldrums after Xmas and through the end of February, even if noise
levels are low during this period. More than once, I recall a weather front
moving through sometime between Xmas and New Year's, and the the static
stayed with us for the rest of the season. We may be enjoying right now
the best conditions on the band that we'll see the entire season.
Someone brought to my attention a couple of web pages that may help explain
"D Region Mid Winter Absorption Anomaly - A period of increased MF radio
wave absorption at high and mid latitudes occurring in mid winter and is
associated with sudden stratospheric warming and the Quasi Biennial
Oscillation (QBO). You may notice that most of your good DX contacts are in
the fall and spring. This is due to the D Region Mid Winter Absorption
Anomaly. (See definition #17. Sporadic-D (Ds) Absorption & Wave Guiding).
(See definition #19. Sudden Stratospheric Warming (STRATWARM ALERT)."
The relation between ionospheric winter anomalies and solar wind:
"There are two different winter anomalies. A small one that appears in
connection with ionization at relatively low latitudes in the bottom of the
D-region of the ionosphere. There, the electron densities in the winter
happen to be less than should be expected. On the other hand, the classic
winter anomaly is present when in the winter the upper D-region, again at
relatively low latitudes, has more ionization than should be expected. Both
these effects are due to the slant compression of the geomagnetic field
produced by the solar wind in the winter season (which is, of course, the
summer season when reference is made to events in the other hemisphere)."
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