What SunSpot Number indices should be used.

NOAA has changed how they put out the Ionospheric indices that are used in the NTIA/ITS HF Propagation Models. This will try to explain what indices to use.

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• The SunSpot Number (SSN) used by these HF prediction programs should be what is called R12 - the Smoothed SunSpot Number.
• NGDC used to have it linked in this table.
• That was last updated May 15, 1999.
• George Lane says to use: ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SUNSPOT_NUMBERS/sunspot.predict for compatibility with VOACAP.
• SEC also maintains SunSpot data with slightly different numbers under Solar Cycle Progression.
  • For past values, you must use the Recent Solar Indices table.
    • The proper column in this table is Smoothed RI
  • For predicted values, you must use the Predicted Indices table.
    • The proper column in this table is SunSpot Number Predicted
  • You will notice that the Predicted table is about 6 months behind the current date. That is because it takes that long for the smoothed SunSpot Number to become permanent.
• I questioned someone at SEC as to what was the difference between SEC's and NGDC's sunspot predictions, and here is his response.
• Note: We cannot control the content nor accessibility of the NOAA web pages.

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