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Effective Sunspot-Number Indices


Note: Heavy (dark) lines are for the current 27-day Bartel rotation; light lines are for the last rotation.

NOTE: If you are looking for the observed sunspot number derived from optical observations of the sun, you've been miss-routed.
This link provides a comparison of the effective SSN shown on this page to the observed solar sunspot number.

The effective sunspot number (SSNe) index is defined as that SSN which will return a zero average-error between foF2 values generated from a model (to which the SSNe is input) and a set of foF2 observations. The NWRA SSNe (solid lines on the plot) is generated by Northwest Research Associates, Inc., using mid-latitude foF2 observations from a single day as input (provided by the NOAA NCEI) and is based on the URSI-88 model.

The T index (dashed lines) is similar to the SSNe index in concept, although it is calculated using a different algorithm. The index plotted here is the daily value valid for the Australian sector calculated by the Australian Space Weather Services (SWS) organization, Sydney, AU, as reported in their Daily Solar and Geophysical Report. (See references below)

References for the T index are as follows:

  • Turner, J.F., The development of the ionospheric index T, IPS Series R Report, R11, June, 1968.
  • Caruana, J., The IPS monthly T index, Solar-Terrestrial Predictions, Proceedings of a workshop at Leura, Australia October 16-20, 1989, Vol 2, pp 257-263, 1990.
  • Wilkinson, P.J., Predictability of ionospheric variations for quiet and disturbed conditions, J. Atmosph. Terr. Phys., 57, 1469-1481, 1995.

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