The Geomagnetic Indices Bulletin is a one page sheet containing the magnetic indices Kp, Ap, Cp, An, As, Am and the provisional aa indices. The bulletin is published monthly.

The geomagnetic aa index provides a long climatology of global geomagnetic activity using 2 antipodal observatories at Greenwich and Melbourne- IAGA Bulletin 37, 1975 p. 128

Geomagnetic Range index using data from multiple observatories - Mayaud 1948

This file is comprised of the variation one minute values of the geomagnetic components X, Y and Z. These data were calculated by the Air Force Geophysics Laboratory magnetometer network during the years 1978-1983. The values are variation values and should not be used in looking at absolute values of the geomagnetic components.

Report on the status of world wide geomagnetic observatories

The NOAA National Centers for Environmental Information (formerly National Geophysical Data Center) receives, on a monthly basis, indices that are based on the data from two approximately antipodal observatories in England and Australia. The AA-indices are available from 1868 to present.

A full description of the indices Kn, Ks, Km is given in a monography,"Indices Kn, Ks et Km, 1964-1967", edited in 1968 by the Centre National de la Recherche Scientifique, 15 quai Anatole, France, 75007 Paris, which contains these indices for 2964-1967 while the International Association of Geomagnetism and Aeronony (IAGA) Bulletin NO. 39 contains those for 1959-1963. Yearly computations of these data are published in the series of IAGA Bulletin No.32. All of them are available in digital form at the appropriate World Data Center. Briefly, the three-hourly indices Kn and Ks for the Northern and Southern Hemispheres respectively are derived from the K indices of observatories approximately well distributed in latitude and in longitude. The indices are standardized according to the distances of the stations to the auroral zones. The stations are arranged in groups representing a longitude sector in one of the hemispheres (5 in the Northern Hemisphere, 4 in the Southern). The observatories currently in use are: MGD-Magadan, EYR-Eyrewell, PET-Petropavlovsk, LAU-Lauder, MMB-Memambetsu, CAN-Canberra, POD-Podkammenaya Tunguska, SVE-Sverdlovsk, GNA-Gnangara, NGK-Niemegk, KGL-Kerguelen, CZT-Crozet, HAD-Hartland, HER-Hermanus, OTT-Ottawa, AIA-Argentine Island, FRD-Fredericksburg, NEW-Newport, VIC-Victoria, TUC-Tucson The mean standardized K of each sector is converted into an equivalent amplitude and the weighted (in longitude) averages and these amplitudes are converted back into Kn and Ks. Km is derived in the same way from am, the average of an and as. Indices an, as and am are expressed in gammas (one gamma equals one nanoTesla) and correspond to the magnetic activity level (as it can be inferred from K indices 0 at an invariant magnetic latitude of 50 degrees. Indices Kn, Ks and Km are expressed in the same units as Kp. Values published in these reports are only provisional because in some months all observatories used in each longitude sector have not sent K indices at the right time and because K indices of Antarctic Stations have be rescaled at the end of each wintering.

Three orthogonal flux-gate magnetometer elements, (spinning twin fluxgate magnetometer prior to GOES-8) provide magnetic field measurements in three mutually perpendicular components: HP, HE and HN. HP is perpendicular to the satellite's orbital plane. HE lies parallel to the satellite-Earth center line and points earthward. HN is perpendicular to both HP and HE, and points westward for GOES-4 and earlier satellites, and eastward for later spacecraft. The Synchronous Meteorological Satellites (SMS-1 and SMS-2) and the Geostationary Operational Environmental Satellites (GOES-1, GOES-2, etc.) all carry on board the Space Environment Monitor (SEM) instrument subsystem. The SEM has provided magnetometer, energetic particle, and soft X-ray data continuously since July 1974. Geosynchronous satellites have an unobstructed view of the sun for all but the few dozen hours per year when the Earth eclipses the sun. You can identify these intervals as gaps in the X-ray data near satellite local midnight in March-April, and September-October. The volume of these data makes it impossible to issue a guarantee as to the quality of each and every data point. Users should be suspicious of 'spikes' in the data and attempt to correlate them with other sources before assuming that they represent the space environment. The time of these observations has not been corrected for the down-link and preprocessing delay which is within 1 - 5 seconds.

The NOAA National Centers for Environmental Information (formerly National Geophysical Data Center) maintains an active database of worldwide geomagnetic observatory data to further the understanding of Earth magnetism and the Sun-Earth environment.Historically, magnetic observatories were established to monitor the secular change (variation), of the Earth's magnetic field, and this remains one of their most important functions. This generally involves absolute measurements sufficient in number to monitor instrumental drift and to produce annual means. Over 70 countries operate more than 200 observatories worldwide. The magnetic observatory data are crucial to the studies of secular change, investigations into the Earth's interior, navigation, communication, and to global modeling efforts. In addition to the continuously operating magnetic observatories, many countries make measurements at temporary magnetic stations (known as repeat stations), over a period of days every 5 - 10 years.The Earth's magnetic field is described by seven parameters. These are declination (D), inclination (I), horizontal intensity (H), vertical intensity (Z), total intensity (F) and the north (X) and east (Y) components of the horizontal intensity. By convention, declination is considered positive when measured east of north, inclination and vertical intensity positive down, X positive north, and Y positive east. The magnetic field observed on Earth is constantly changing.

The NOAA National Centers for Environmental Information (formerly National Geophysical Data Center) receives, on a monthly basis, Q indices from Sodankyla. These data are available from July 1957 to the present. Sodankyla indices are the most complete records of Q indices that NCEI has. The archive also contains Q indices from 15 other observatories. The Q index is a measure of geomagnetic activity assigned by high latitude (geomagnetic latitude > 58 degrees) geomagnetic observatories for each 15 minute interval. The index is designed to study auroral and ionospheric phenomena over a time scale smaller than that possible with KP. The Q scale is loosely logarithmic, with possible values from 0 to 11.