Paul,

With each piece of data (your NAA/WH2XBA 3-day amplitude below) this becomes
more interesting. 

Summarizing some previous discussion and thoughts:
NAA amplitude and phase are stable and repeatable night to night (amplitudes
stable and repeatable within +/- 1dB across 3 nights).
On two successive nights WH2XBA amplitudes are reduced and less stable (less
stable even after normalizing amplitude stability for SNR), and are
accompanied by premature, fast phase swings (2-hour transitions) of ~120
degrees.   
If I think of ionosphere, oscillator phase, long-path ground effects,
antenna and weather, my thoughts are slightly biased toward antenna and
perhaps some secondary weather/temperature effect on the antenna, as you and
Bob had considered.

I'm glad that you noticed premature and fast 120 degree phase swings on
successive nights, in contrast to stable phase on a (relatively) nearby
path. That is intriguing  on its own, especially in the absence of
indicators in the Dst and other indices. 

Much appreciation to Bob, yourself and others for making these questions
possible.

73,   Jim

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Sunday, March 9, 2014 12:44 PM
To: [email protected]
Subject: Re: LF: Daytime 29.499 kHz


Jim wrote:

 > was the quick phase change of 120 degrees  > corrected prior to
integration?

I'm plotting the signal in 20 minute integrations so there isn't much loss
due to the phase change.

We had about 120 deg phase change on the night of 6th/7th but it took 6
hours, not 2.

Here I plot three nights of opera alongside NAA for comparison of amplitudes

  http://abelian.org/vlf/tmp/29499_140309b.gif

--
Paul Nicholson
--