Re: LF: Daytime 29.499 kHz

["Markus Vester" <markusvester@aol.com>]

Paul,

 

thanks very much, these are impressive plots. Some time ago Peter Schnoor had posted similar annual graphs for 75 kHz http://lf-radio.de/misc/hbg/chart_all.png and 135.43 kHz http://df3lp.de/misc/hga22/, but yours are the first I have seen for low frequencies.

 

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

From: Paul Nicholson

Sent: Saturday, March 08, 2014 11:29 AM

To: rsgb_lf_group@blacksheep.org

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
--

From: Paul Nicholson

Sent: Saturday, March 08, 2014 12:54 AM

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
--