2.3.1 spase://CNES/NumericalData/CDPP-AMDA/Indices/Ground_Based/ground-based-aa aa aa IAGA-endorsed magnetic activity index 2018-01-16T11:00:00Z Index which purpose is to measure the amplitude of global geomagnetic activity during 3-hour intervals normalized to geomagnetic latitude ±50°. aa was introduced to monitor geomagnetic activity over the longest possible time period. ISGI website at EOST; License: CC BY-NC https://creativecommons.org/licenses/by-nc/4.0/ spase://CNES/Person/Aude.Chambodut TechnicalContact IAGA geomagnetic indices http://isgi.unistra.fr/indices_aa.php spase://CDPP/Repository/CDPP/AMDA Online Open AMDA at CDPP http://amda.cdpp.eu Text ISGI/UNISTRA spase://CNES/Instrument/CDPP-AMDA/Indices/Ground_Based MagneticField 1975-01-01T00:00:00Z 2019-01-21T21:00:00Z PT3H Earth.NearSurface aa aa nT Aa Aa Daily Mean of aa nT