What SunSpot Number indices should be used.
*** New 12/29/2016 ***
NOAA has changed how they put out the Ionospheric indices that are used in the NTIA/ITS HF Propagation Models.
Let's see how long this works.:)
The SunSpot Number (SSN) used by these HF prediction programs should be what is called
R12 - the Smoothed SunSpot Number
Unfortunately R12 is no longer computed. But R13 is:
R13 - the Smoothed SunSpot Number
For past values, use
Historical Smoothed SSN (1749-2016) Indices
For predicted values, use SMOOTH SSN from
table. Provided by Australia.
Make sure you scroll down and look at the graph.