Markus,
Thanks
for the DHO diurnal plot.
It?s
a memorable image, with interesting symmetries.
I
remain hopeful of finding or making a model that qualitatively represents VLF
amplitude and phase diurnals for a substantial percentage of cases. This would
be very helpful in preparing for DX, QRP and other
activities.
Thomson
has done some great work in this area (VLF diurnals). I was surprised to find
that he reverted (prior to 2011) to Wait?s 2-parameter ionospheric reflection
model (using h and beta*, and adjusting them empirically), instead of using LWPC
or ModeFinder (which he mentions require more knowledge of ionospheric
parameters than is currently available: http://www.physics.otago.ac.nz/space/Thomson_LongPath_paper_JGR_2011.pdf
; I thought Paul might also find this point interesting)
To
make matters more interesting, Han (http://people.ee.duke.edu/~cummer/reprints/132_Han11_JGR_DaytimeDRegionSharpness.pdf
) recently showed considerable and substantial disagreement (qualitative
and quantitative) between beta* parameters values derived (empirically) by a
number of expert sources including Thomson. Han?s findings are well-summarized
on the last page of his paper. The kind of discrepancies shown by Han seem (to
me) suggest a lot of work remaining on the way to good diurnal amplitude and
phase models. Among the four expert sources on D-region beta cited by Han, there
were three different findings on the polarity of the change in beta with zenith
angle: decreasing beta with increasing zenith angle (1 of 4), increasing
beta with increasing zenith angle (2 of 4), relatively constant beta with
increasing zenith angle (1 of 4); not to mention considerable disagreement
between the four sources in magnitude of sensitivity of beta to zenith angle.
All of this is clearly summarized on the last page of the
paper.
I
thought you might find the paragraph above interesting because it shows a
significant gap in the understanding of some basics that affect (at some
distances and on some days) whether VLF daytime signal strength increases or
decreases. In his conclusion, Han describes the magnitude of disagreement
in derived values for beta as surprising. He suggests that the two-parameter
model may not be sufficient (a circumstance that Thomson hoped to avoid, see
above)
On
a related topic, Han?s method of deriving beta (using broadband signals) is
interesting and appears to have substantial merit, but I?m guessing that the
available broadband sources used by Han (sferics) come with their own issues in
this type of measurement.
I
think I can end on a light note: if you have a chance to look at one figure and
one paragraph in this paper by Volland: http://nvlpubs.nist.gov/nistpubs/jres/68D/jresv68Dn2p225_A1b.pdf
, Adobe Reader page 4 (document page 228), including Figure 3 and the paragraph
including ?A remarkable exception from this
rule has been observed in Lindau (Germany), Figure 3 shows two successive daily
phase variations of GBR? Such phase inversions are rare??, I
think you may find something interesting, odd or even humorous.
* (D-region electron density sharpness)
Regards,
Jim
