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Auroral Electrojet (AE, AL, AO, AU) - A Global Measure of Auroral Zone Magnetic Activity

Metadata Updated: September 16, 2022

The AE index is derived from geomagnetic variations in the horizontal component observed at selected (10-13) observatories along the auroral zone in the northern hemisphere. To normalize the data a base value for each station is first calculated for each month by averaging all the data from the station on the five international quietest days. This base value is subtracted from each value of one-minute data obtained at the station during that month. Then among the data from all the stations at each given time (UT), the largest and smallest values are selected. The AU and AL indices are respectively defined by the largest and the smallest values so selected. The symbols, AU and AL, derive from the fact that these values form the upper and lower envelopes of the superposed plots of all the data from these stations as functions of UT. The difference, AU minus AL, defines the AE index, and the mean value of the AU and AL, i.e. (AU+AL)/2, defines the AO index. The term "AE indices" is usually used to represent these four indices (AU, AL, AE and AO). The AU and AL indices are intended to express the strongest current intensity of the eastward and westward auroral electrojets, respectively. The AE index represents the overall activity of the electrojets, and the AO index provides a measure of the equivalent zonal current.

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License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Date September 18, 2015
Metadata Created Date September 16, 2022
Metadata Updated Date September 16, 2022
Reference Date(s) January 1, 1976 (publication)
Frequency Of Update asNeeded

Metadata Source

Harvested from NGDC STP Indices

Additional Metadata

Resource Type Dataset
Metadata Date September 18, 2015
Metadata Created Date September 16, 2022
Metadata Updated Date September 16, 2022
Reference Date(s) January 1, 1976 (publication)
Responsible Party DOC/NOAA/NESDIS/NCEI > National Centers for Environmental Information, NESDIS, NOAA, U.S. Department of Commerce (Point of Contact)
Contact Email
Guid gov.noaa.ngdc.stp.indices:G00584
Access Constraints Use Constraints: None, Access Constraints: No Constraints
Bbox East Long 180.00
Bbox North Lat 90.00
Bbox South Lat -90.00
Bbox West Long -180.00
Coupled Resource
Frequency Of Update asNeeded
Harvest Object Id 9bb8ac07-dc70-4bd1-abf4-eb6110b867da
Harvest Source Id 8fcc91fb-3399-4b06-abea-b4dadb7df9b7
Harvest Source Title NGDC STP Indices
Licence While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by any errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.
Metadata Language eng; USA
Metadata Type geospatial
Old Spatial {"type": "Polygon", "coordinates": [[[-180.0, -90.0], [180.0, -90.0], [180.0, 90.0], [-180.0, 90.0], [-180.0, -90.0]]]}
Progress underDevelopment
Spatial Data Service Type
Spatial Reference System
Spatial Harvester True
Temporal Extent Begin 1957-01-01

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