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192Re: [dxatlas] 90-day SSN data for HamCAP

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  • Pete Smith
    Apr 9, 2005
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      [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
      calculated in
      ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SUNSPOT_NUMBERS/sunspot.predict. It
      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
      http://www.nwra-az.com/spawx/comp.html 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
      particular context.

      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:

      >I 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.
      >73, Bill
      >Yahoo! Groups Links
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