Cycle 24: The Continuing Deviation Between the Sunspot Number and F10.7 Activity Indices
Ken Tapping [Ken.Tapping@nrc-cnrc.gc.ca], National Research Council, D.R.A.O., Penticton,
BC, Canada
Cycle 24 is marked by a continuing deviation between the sunspot number and 10.7cm solar
radio flux indices which is unique since 1947. It reflects a decline in photospheric activity
compared with that seen in the chromosphere and corona. The comparison to date indicates we
are at or very close to the activity maximum. The deviations suggest two things: firstly that the
Sun is doing something different, perhaps similar to previous periods of extended low activity,
and secondly, that there is a need for a certain care in how we rate sunspot number (and F10.7)
based proxies when modelling historical irradiances.