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Paul,
There seems to be a wealth of information in there.
Generally there is more day (blue) than night (orange), presumably due
to longer days at high altitudes. In June, the geometrical shift
between eariest sunrise and latest sunset (Analemma) is quite obvious.
Some singular features like outages and SIDs
seem to be a bit smeared out, looks like you have applied some
averaging over consecutive.
BTW I'm wondering how you generate these
a-posteriori plots, are you continuously saving all raw data from your
VLF loops? If I get the numbers right, two channels with 96 kHz
samplerate would deliver about a terabyte per month - you must
have accumulated a neat stack of harddisks ;-)
Best 73,
Markus
Sent: Saturday, March 08, 2014 11:29 AM
Subject: Re: LF: Daytime 29.499 kHz
Yes Jim the 'z' scale is
proportional to amplitude (flux
density), not power.
I completely
agree with your interpretation of the plot -
- The nighttime
window doesn't quite close and even
in high summer we
still have couple of useful hours.
- In compensation for the short
night, the daytime propagation
improves: better and
longer, and by July, midday levels
are about 6dB below the
March nighttime.
We should consider 'midday' to be relative to the center
of the path.
For comparison, NAA for two more years
http://abelian.org/vlf/tmp/naa_2012a.png
http://abelian.org/vlf/tmp/naa_2011a.png
Looks
pretty repeatable year to year.
As Alan mentioned, the midday 'dome' is a
feature of most long
range diurnals. For example, NAU (Aguada) at
40.8 kHz for
2012 and 2013
http://abelian.org/vlf/tmp/nau_2012a.png
http://abelian.org/vlf/tmp/nau_2013a.png
Path
length to NAU is 6740km, NAA is 4672km.
Going eastwards, TBB (Bafa,
Turkey) on 26.7 kHz range 2883km
http://abelian.org/vlf/tmp/tbb_2013a.png
shows
that it's not just an east-to-west feature.
During flares, the signal is
always enhanced which confirms
that the dome improves with
ionisation.
The midday dome is essentially D-layer propagation.
D-layer is
formed by solar radiation (mostly nitric oxide ionised by
Lyman
alpha) with a reflection height of around 70km. At night
this
layer dissipates and reflection occurs from the E-layer at
95 km or
thereabouts. Away from midday we have a mixture of
the two, with
E-layer reflections being attenuated by passage
through a partially formed
D-layer.
The D layer is a good reflector when fully formed but
being
lower, more hops are required to cover a path.
--
Paul
Nicholson
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Sent: Saturday, March 08, 2014 12:54 AM
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
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