Clemens,

Not necessarily; two possibilities come immediately to mind: trapped surface
wave and a change in the modal interference pattern (from phase changes due
to ice and/or frozen soil, a change in ionospheric height, or a quantitative
change in polarization processes).

My thoughts on this topic come mainly from the literature, so I could be
missing important pieces. On the other hand I found nothing in Watt's book,
AGARD, Wait, Thomson or others on the side of substantially lower VLF losses
in winter, just higher.

I will keep an eye open for other examples of stronger signals in winter,
and it will be a pleasure to learn the mechanisms of each of them. I'll
begin by trying LWPC (with appreciation to Paul) on the path that you
described; and I will pass along any findings of interest. Thank you for the
example.

73,  Jim AA5BW


-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Clemens Paul
Sent: Sunday, March 9, 2014 4:15 AM
To: [email protected]
Subject: RE: LF: Daytime 29.499 kHz

Jim,

I use to receive SAQ from Grimeton on 17,2kHz here in southern Germany in
winter always significantly stronger (I really mean signal strength, not
SNR) than in summer.
Distance is a bit less than 1Mm, path is virtually completely over land.
Is this a contradiction to the material you've presented in your posting?

73
Clemens
DL4RAJ  

>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of hvanesce
>Sent: Sunday, March 09, 2014 9:37 AM
>To: [email protected]
>Subject: RE: LF: Daytime 29.499 kHz