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
