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aσ indices

Indices
aσDawn , aσNoon , aσDusk ,
aσMidnight		 time resolution: 3-hour (UT) interval
unit: nT
 
Available From 1959 onwards
 
Type of index K-derived in 4 Magnetic Local Time sectors
 
Purpose To provide a characterization of local geomagnetic activity in 4 longitudes sectors and possible hemispheric discrepancies
 
Network based on the am network
(see list of actual and previous am magnetic observatories)
 
Derivation In each MLT sector, the K scaled for each station, are averaged, and the result is converted into amplitude using mid-class amplitudes for (K=9 lower limit) = 500 nT.
4 indices are thus calculated: aσDawn (03–09 MLT), aσNoon (09–15 MLT), aσDusk (15–21 MLT), and aσMidnight (21–03 MLT)
 
ISGI Collaborating Institute EOST, Strasbourg, France
 
IAGA endorsed No. aσ are test indices mainly devoted for academic research
 
Main references • Chambodut, A., A. Marchaudon, M. Menvielle, F. El-Lemdani and C. Lathuillere (2013) - The K-derived MLT sector geomagnetic indices, Geophys. Res. Lett., 40, 4808-4812, doi:10.1002/grl.50947.
 
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