Hello all:
Note the good information on propagation from W3LPL. This could be
helpful to know in the upcoming ARRL DX contests and CQ WPX SSB. It
appears that conditions to Europe will likely favor us in the south for
a change.
73,
John, K4BAI.
-----Original Message-----
From: pvrc-admin@mailman.qth.net [mailto:pvrc-admin@mailman.qth.net] On
Behalf Of Frank Donovan
Sent: Friday, February 06, 2004 1:44 PM
To: pvrc
Cc: k3zo@arrl.net; k3na; k3rv
Subject: [PVRC] 40 meter night time propagation
Fred,
I enjoyed reading your propagation articles in the PVRC bulletin.
I thought I'd take advantage of this icy morning to explain in
some detail the ionosperic process that causes the loss of direct-
path propagation to Europe and Japan.
We often experience brief European openings on 40 meters at night
as the solar flux drops as we approach solar cycle minimum.
This same phenomenon also causes the sudden loss of propagation
on the higher bands as night-time arrives over the north Atlantic
and north Pacific. It also causes the disappearance of our sunrise
opening o Japan on 20 meters.
The loss of propagation that often (but not always) impacts north
Atlantic and north Pacific night-time propagation is caused by an
electron depletion region in the F layer ionosphere known as the
mid-latitude trough. The mid-latitude trough is primarily a night-
time phenomenon that occurs almost exclusively during the winter
and the equinoxes. Summer occurences are very rare.
The pole-ward wall of the mid-latitude trough is bounded by
the low-latitude boundary of the auroral region. The width of
the mid-latitude trough is typically five degrees or more, extending
towards the equator from its pole-ward boundary with the aurora.
During the night, the equator-ward edge of the mid-latitude
trough steadily drifts to lower latitudes. The mid-latitude trough
disappears by re-ionization when the sun rises over that part
of the ionosphere.
During the onset of increased geo-magnetic activity, the low-latitude
edge of the auroral region rapidly shifts towards the equator.
Consequently, the entire mid-latitude trough also shifts toward lower
latitudes and propagation to Europe and Japan is likely to fail
completely.
What does this mean for upcoming ARRL DX contests?
40 meter propagation to Europe on 40 meters will be best during
the hours near our sunset. Propagation to northern Europe will
fade away within an hour or two after sunset, and only the southern
tier of Europe may be workable by as early as 0100Z. Europe will
often fade away by 0200Z, except for skew paths toward the south-
east and south. On many (but not all) nights, propagation will
return briefly during the hours near European sunrise, as the mid-
latitude trough is re-ionized by the sun. Propagation to Europe
will last longer into the night in North Carolina and Virginia than it
does in New Hampshire and Massachusetts. Similarly, 15 meters
will lose propagation to Europe shortly after European sunset,
and 20 meters will lose propagation to Europe soon thereafter.
On paths to Japan, direct path 40 meter propagation towards the
northwest is unlikely except for a very brief period at 0800Z
(Japanese sunset) and during the hour so around 1130-1230Z
(our sunrise). During the remaining hours, propagation to Japan will
be over the familiar (to 40 meter DXers) southwest skew path.
On 15 and 20 meters, evening openings to Japan will be brief,
beginning shortly after 2130Z (sunrise in Japan) , and failing shortly
on 15 meters after our sunset and soon afterwards on 20 meters.
The morning 20 meter direct path openings to Japan we've become
used to on 20 meters during high sunspot years will be only a distant
memory as the mid-latitude trough kills that path during the
Japananese night-time hours.
As we approach solar minimum, we should be prepared for
shorter openings over the north Atlantic and north Pacific paths.
Knowledge of propagation phenomenon will be more of a strategic
advantage than during the high sunspot cycle, as openings become
more fleeting. Operators who are aware of these patterns will be
less likely to be disappointed by missed opportunities.
73!
Frank
W3LPL
donovanf@erols.com
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