[With apologies to readers of the VOACAP list, who are joining this in
mid-thread, I feel that Bill and I are floundering fairly far out of our
depth in this discussion that began on the dxatlas list. The question
began as what SSN to use in Ham Cap, a simplified front end for
VOACAP. HamCAP comes with a table of predicted international SSNs, but can
also link with IonoProbe, which downloads daily SSNs from the SEC. VE3NEA,
the author of Ham Cap, prefers the SEC numbers, but the variance from the
international SSns is considerable, with the SEC number typically running
much higher. Any advice appreciated!]
Bill, there's some apples and oranges, or something going on
here. IonoProbe gets its numbers from the Joint USAF/NOAA Solar and
Geophysical Activity Summary. Here's a sample:
"SGAS Number 099 Issued at 0245Z on 09 Apr 2005
This report is compiled from data received at SWO on 08 Apr
A. Energetic Events
Begin Max End Rgn Loc Xray Op 245MHz 10cm Sweep
B. Proton Events: None
C. Geomagnetic Activity Summary: The geomagnetic field was quiet.
D. Stratwarm: Not Available
E. Daily Indices: (real-time preliminary/estimated values)
10 cm 088 SSN 056 Afr/Ap 005/004 ...."
Ionoprobe's retrospective record of these reports shows March 12 (chosen
randomly) with a SSN of 67, versus 42 on the table you cite. March 18 is
37 versus 25, and so on.
I have no idea what the explanation is, though I do note that there is
another table, ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SUNSPOT_NUMBERS/2005
, which gives the numbers just for this year to date and states that
"Values are preliminary after Dec 2004."
There is an interesting explanation of how various sunspot numbers are
seems clear from this explanation that the international sunspot number is
a highly-massaged, worldwide average number that does not become final for
some months after the date of observation. By contrast, the number cited
in the SGAS is the SEC's every-six-hour figure, and must be based strictly
on its own observations. An interesting graph at
speaks to this. To quote from the
" This plot illustrates the differences between the "real" sunspot number
(SSN), which is calculated from optical observations of the sun, a sunspot
number derived from the 10.7cm solar radio flux (SSNf), and a sunspot
number derived from fitting an ionospheric model to ionospheric
measurements. All of these indices are used as inputs to models of the
ionosphere for use in communications-performance predictions - this plot
shows that they don't always agree as to what the SSN should be in that
Note: The F10.7-derived SSN (SSNf) is calculated from the 10.7cm solar
radio flux (the Penticton Radio Observatory noon value) using the following
F10.7 = 63.74 + 0.727*SSNf + 0.000895*SSNf**2
So, where does this leave us? Where it left me, frankly, is wondering why
we use sunspot numbers at all, rather than solar flux and A/K indices, or
at least the SSNf, which would be closer to the values Bill cited than to
the current high value of optically-observed SSN. On the other hand, Alex
argues that results from using the lower SSNs seem to run consistently low
in terms of predicted vs. observed S/R ratio.
It would be interesting to pass this discussion over to the VOACAP list and
see what the gurus there, particularly including Greg Hand and George Lane,
think of it. In fact, I have done that, and it will be interesting to see
what comes of it.
73, Pete N4ZR
At 09:12 AM 4/9/2005, bill_w4zv wrote:
> > Maybe the logic of
> > the calculation has an error somewhere in its data collection.
>Definitely so. The current 90 day average (1 Jan 05 - 31 Mar 05) is
>28.4 using this data:
>I don't have IonoProbe, but it must have a problem if the 47 number
>Pete quoted for the IonoProbe calculation is correct. Anyhow, now I
>know what to use and will probably just go with the NOAA forecast
>which seems to be fairly accurate at this stage of the cycle.
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