Note: Heavy (dark) lines are for the current 27-day Bartel rotation; light lines are for the last rotation.
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 SWPC) and is based on the URSI-88 model.
The Australian Space Weather Services (SWS) 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 Bureau of Meteorology Space Weather Services organization in Sydney, AU, as reported in their Daily Solar and Geophysical Report.
References for the SSNe and T indexes are as follows:
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