Service International des Indices Géomagnétiques
International Service of Geomagnetic Indices

AE, AU, AL, AO indices

AE, AU, AL, AO time resolution: 1 minute (UT) interval
unit: nT
Available 1-hour (UT) interval: from 1957 to 1965 (only AE); from 1966 to 1975

1-minute (UT) interval: 1975 (only AE and AL); from 1978 to June 1988;
March 1989; from 1990 onwards
Type of index Auroral index horizontal component disturbances
Purpose To monitor the magnetic signature of the eastward and westward auroral electrojets in the Northern hemisphere.
Network Made of 12 observatories in the Northern auroral zone.
(see list of actual and previous AE magnetic observatories)
Derivation The magnetograms of the horizontal components from the AE stations are superimposed (*): the upper envelope defines the AU index, and the lower envelope define the AL index; then AE = (AU - AL) and AO = (AU + AL)/2.

(*) More specific and detailed information may be found on the WDC for Geomagnetism - Kyoto website devoted to AE.
ISGI Collaborating Institute WDC for Geomagnetism - Kyoto, Japan
IAGA endorsed IAGA Bulletin 27, 1969, p.123, resolution 2
Origin of name Name "AE" came from "Auroral Electrojet"
Historical references • Davis, T. N., and M. Sugiura (1966) - Auroral electroject activity index AE and its universal time variations, J. Geophys. Res., 71, 785-801, doi:10.1029/JZ071i003p00785.