AE Availability

For years 1957 through 1964, hourly AE indices were derived at the Geophysical Institute, University of Alaska and the NASA Goddard Space Flight Center from hand-scaled hourly average values.

Indices for 1965 were derived at NASA from 2.5-minute digitized values.

For years 1966 through 1974, AE and related indices were derived at NGDC from 2.5-minute digital values scaled by semi-automatic machines from analog magnetograms.

Beginning in 1975, NGDC produced the indices with one minute resolution and included data collected by digital magnetometers.

There is a break in the indices for years 1976 and 1977.

Indices for 1978 and later years are produced at WDC-C2 for Geomagnetism (Kyoto, Japan).

In general, the indices AE, AO, AU and AL from 1966 onwards are reasonably consistent and were derived from data of the same network of Northern Hemisphere observatories.