MAJOR MAGNETIC STORMS 1868-2005 ACCORDING TO THE AA* CRITERIA For a plot of sunspot number and aa Yearly Indices 1868-2005, see ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/AASTAR/aasspot.gif A simple global index of magnetic activity is produced in France from the K indices of two nearly antipodal magnetic observatories in England and Australia. ... Daily average AA may be derived similarly to Ap. ... An AA* index has been derived that is the counterpart of Ap* but is available for a longer span of years. ...