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Date: Sat, 8 Mar 2014 00:55:54 -0700
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Subject: RE: LF: Daytime 29.499 kHz
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Paul,

Thanks for making the 12-month plot of NAA - Todmorden diurnal amplitude
(and for the effort that went into a year of quality data capture).

After Markus mentioned the broad midday maximum I searched the home library
for the definitive empirical model (monthly/diurnal), and found strong
empirical support for: "it depends" (frequency, water, latitude, path
length, path orientation, path direction...). I couldn't find much agreement
between seemingly similar cases, so I had begun to search narrowly for a
monthy/diurnal amplitude of NAA-eastward when you sent your plot; thanks!

Is your relative amplitude axis in intensity or power? I assumed intensity
because you have sometimes given amplitude in Tesla. If that's the case,
your ~ March 7th data seems to show 9 "night-only" hours at roughly* 11dB
above the 15 "day-somewhere" hours; with the middle of the broad daytime
maximum only ~ 8dB below night amplitude (i.e. perhaps indicating around
10dB SNR at 1500 UT for Bob and Markus?). 

* (eyeball averaging night colors and day colors)   

If I'm interpreting correctly, then a typical 24-hour period in July looks
like 2 "night-only" hours (at slightly better transmission than March),
followed by two sunrise peak-nulls and a gradual rise to (at midday) ~ 6dB
below night amplitude; and several hours of July daytime (each 24 hours) at
only 6dB below March nighttime amplitude.  

Regarding the year-round outlook: I'm having trouble finding (in your NAA
diurnal plot) when the path would be closed for Bob, Paul, Markus et al:
Except for the two or three sunrise interference nulls and two or three
sunset interference nulls (about 30 minutes each), and on the basis of 15dB
to 25dB March TA SNR reports, I don't see a time, day or night, year-round,
when the path would not  be open for Bob, Paul, Markus et al.  Am I missing
something?

On a related topic:
In the course of my initial search today, I found and cross-indexed about a
dozen particularly good papers and textbook sections in this subject area
(monthly diurnal VLF amplitude as a function of frequency, latitude, path
length, path orientation, path direction, land/water and other factors).
Most are empirical; I included only a few (best of) analytical and
computational (LWPC and FDTD) studies because the analytical/computational
work is not very mature for immediate purposes. If anyone's interested I
will post or e-mail papers and/or links to papers, and citations from the
texts. 

I hope I read your plot correctly; if so this could be an interesting year.

73,  Jim AA5BW


-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Paul Nicholson
Sent: Friday, March 7, 2014 4:54 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Daytime 29.499 kHz


Plot of variation of NAA diurnal amplitude for year 2013.

  http://abelian.org/vlf/tmp/naa_2013a.png

Dark areas are where NAA was off.  White areas are when my equipment was
down.

--
Paul Nicholson
--