Carl Luetzelschwab, K9LA had some comments about
SSNe, or Effective Sunspot Numbers, and the T-Index. He continues with more
comments below, through the end of this bulletin. Carl begins, "In the January 6 Bulletin, I said the T Index and SSNe were
similar methods that give a better picture of what the ionosphere is doing
"now." Both represent an effective sunspot number based on real-time
sounding of the F2 region critical frequency. Let's look at the basic
difference between SSNe and the T Index.
"SSNe is calculated from a worldwide set of ionosondes at geomagnetic
latitudes lower than 50 degrees. The SSNe plot also shows the RMS %
difference between the foF2 values used to derive SSNe and foF2 calculated
from the model using that SSNe as input. This parameter typically runs
about 20% or so - if it exceeds 30% this indicates that the global
ionosphere is departing more from the model expectation than usual. And if
it exceeds 50%, buyer beware!
"The T Index is calculated from 14 ionosondes in the Australian sector. The
regional maps (Australasia, Europe, and North America) show the difference
between the predicted monthly T Index (which is in tabular format at
www.ips.gov.au/HF_Systems/6/4/1) and the current observed hourly conditions
in the desired region.
"Which one is best to use? That's a tough call, but I'd personally give the
edge to SSNe for global predictions as it is based on worldwide data.
"To reiterate from the January 6 Bulletin, neither gives us a daily model
of the ionosphere. But both do allow you to assess whether the current
conditions are generally equal to, better than, or worse than the median
value from your propagation prediction program when using the heavily
averaged smoothed sunspot number (or smoothed solar flux).
"Thanks to Jim Secan of Northwest Research Associates in Tucson for
information on SSNe and for forwarding the T Index information from Garth
Patterson at IPS."
