Alan,
My short answer is: I don't know, but I hope that the LWPC resources that
Paul has (a) made available and (b) applied, will allow valuable learning in
this area. The work of Watt, Wait et al in this area was far from finished
when (in the 1970s) effort quickly shifted elsewhere, and the number of
people now familiar with the shrinking VLF knowledge base from that era is
small. On the other hand, phase measurements in that era were coarse (no
PLLs; microsecond clock jitter) and access to basic simulation resources was
limited; so I view Paul's demonstration of accessible comparison between
accurate phase measurements and values from mature modeling tools as a very
encouraging indicator of potential for renewed progress.
In that vein, some comments related to diurnal phase bumps:
Diurnal phase reversals (as in bumps, or as in ramps immediately after the
main diurnal transition for example) may be (Davies pg. 382) "...due to
reflections from different D layers (or) ... interference between multiple
rays or modes". The phase effects of multiple mode (multiple ray) paths are
considerably dependent on distance, even at distances greater than 10Mm.
At ~ 5Mm (NAA-Todmorden), the basic shape of the diurnal phase plot would
generally be described as trapezoidal, but varies considerably from month to
month, and bumps/phase-reversals also vary considerably. An intriguing
example (GBR-Boulder) of variation in the basic diurnal characteristic is
shown in Chilton, 1964
(http://ftp.rta.nato.int/public//PubFullText/AGARD/AG/AGARD-AG-74///AGARD-AG
-74.pdf) (original document page 264, Fig 3): the manner in which the
diurnal phase plot shapes of non-adjacent months pair is counterintuitive at
first glance, makes more sense if you scan frames in month-order, and is an
illustration of the multi-mode effects that also affect phase reversal /
phase bumps. With LWPC would be possible (but time consuming) to identify
which modes, terminator effects and D-layer height values are operative in
the phase bumps seen in the NAA-Todmorden plots provided by Paul; I'm
guessing that with continued application of the resources demonstrated by
Paul that this knowledge will gradually assimilate.
73, Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Alan Melia
Sent: Thursday, January 9, 2014 3:22 PM
To: [email protected]
Subject: LF: Re: VLF Terminator Phase Bumps
Jim I'd have to think about that it is a very long path....its possible too
much of the path is in darkness, so the effect at the terminator is washed
out ??
Alan
G3NYK
----- Original Message -----
From: "hvanesce" <[email protected]>
To: <[email protected]>
Sent: Thursday, January 09, 2014 9:55 AM
Subject: LF: VLF Terminator Phase Bumps
> Alan,
>
> I took a quick look for some examples of VLF terminator bumps (not
> prevalent
> in a random sample) and the first one I found was NPM - Farnborough (from
> Hampton - 1964); note some qualitative and quantitative similarities with
> Paul's measured phase values.
>
> 73, Jim AA5BW
>
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