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LF: D-Layer and Propagation

To: [email protected]
Subject: LF: D-Layer and Propagation
From: "Roelof Bakker" <[email protected]>
Date: Tue, 13 Jan 2015 21:35:57 +0100
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Hello Alan,

I have been given your article "A possible way of Forecasting good Radio Propagation conditions on 136kHz" a good thought over. Generally speaking the Kyoto Dst figures are a good indicator for LF reception in the NDB band (200kHz - 520kHz). I have used these to good effect the last couple of years.
What has puzzled me is that after a solar disturbance propagation from
NDB's in northern Canada is restored much quicker than from stations at a
lower latitude.
The last weeks the sun has been eruptive and T/A propagation has been
about the worst as I remember.
Since two days propagation is getting better, but only for Canadian NDB's
above about 50 degrees north.
Last night, I heard 21 Canadian NDB's of which the majority is located
above 55 degrees north. Also one NDB from the north bank of Alaska was
heard.
At the same time nothing was heard from latitudes below 48 degrees. This
also applies to Canadian and USA NAVTEX transmissions on 518 kHz. It has
also been quite some time since there has been WSPR reception from USA
stations in Europe.
It is clear that long haul (aural) reception of Canadian NDB's above 48
degrees north has been excellent, whilst reception below this latitude has
been nil.
In your article you state "My observations, confirmed by reference to
professional papers on the subject, suggest that there is an excess of
absorbing ionisation in the D-layer, through which night-time signals must
pass before being returned earthwards by refraction in the lower boundary
of the E-layer. This absorbing D-layer ionisation seems to remain for some
time after the geomagnetic conditions recover."
In winter the daily build up of the D-Layer is much weaker at higher
latitudes. This might be the reason that the effects of absorbing
ionisation due to solar disturbances lasts not as long as at lower
latitudes.
Best regards,
Roelof Bakker, PA0RDT

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