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 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 High Definition Geomagnetic Model (HDGM) is a global, high resolution model of the Earth's geomagnetic main and crustal field, providing magnetic field values (total field, dip, and declination) at any point above or below the Earth's surface. Well planners can use HDGM to compute magnetic reference values at any point, as well as easily integrate HDGM into their directional drilling software. HDGM is updated annually to correctly model secular changes in the geomagnetic field.

The High Definition Geomagnetic Model (HDGM) is a global, high resolution model of the Earth's geomagnetic main and crustal field, providing magnetic field values (total field, dip, and declination) at any point above or below the Earth's surface. Well planners can use HDGM to compute magnetic reference values at any point, as well as easily integrate HDGM into their directional drilling software. HDGM is updated annually to correctly model secular changes in the geomagnetic field.

The High Definition Geomagnetic Model (HDGM) is a global, high resolution model of the Earth's geomagnetic main and crustal field, providing magnetic field values (total field, dip, and declination) at any point above or below the Earth's surface. Well planners can use HDGM to compute magnetic reference values at any point, as well as easily integrate HDGM into their directional drilling software. HDGM is updated annually to correctly model secular changes in the geomagnetic field.

The High Definition Geomagnetic Model (HDGM) is a global, high resolution model of the Earth's geomagnetic main and crustal field, providing magnetic field values (total field, dip, and declination) at any point above or below the Earth's surface. Well planners can use HDGM to compute magnetic reference values at any point, as well as easily integrate HDGM into their directional drilling software. HDGM is updated annually to correctly model secular changes in the geomagnetic field.

The High Definition Geomagnetic Model (HDGM) is a global, high resolution model of the Earth's geomagnetic main and crustal field, providing magnetic field values (total field, dip, and declination) at any point above or below the Earth's surface. Well planners can use HDGM to compute magnetic reference values at any point, as well as easily integrate HDGM into their directional drilling software. HDGM is updated annually to correctly model secular changes in the geomagnetic field.

Report on the status of world wide geomagnetic observatories

The NOAA National Centers for Environmental Information (formerly National Geophysical Data Center) receives magnetograms from over 200 geomagnetic observatories. The Center archives data from 1867 to the present, however the primary holdings are from 1957 to the present. The archives contain over 5,000 reels of 35 mm microfilm copies of magnetograms. Magnetograms are records obtained from an instrument known as a magnetometer which is designed to measure small variations in the components of the geomagnetic field. There are two types of magnetometers, the La Cour and the Ruska. The magnetogram consists of one or more (usually 3) variometers, one for each element usually D, H, Z (less common X, Y, Z) and a recorder. The standard magnetogram usually has all three components recorded simultaneously on one sheet of paper. In addition to the 3 traces, reference lines (baselines) are recorded. The baselines are used in absolute calibration of the magnetogram. The normal recording speed is 20 mm/hour with the drum turning once in 24 hours.

The World Magnetic Model is the standard model used by the U.S. Department of Defense, the U.K. Ministry of Defence, the North Atlantic Treaty Organization (NATO) and the International Hydrographic Organization (IHO), for navigation, attitude and heading referencing systems using the geomagnetic field. It is also used widely in civilian navigation and heading systems. The model is produced at 5-year intervals, with the current model expiring on December 31, 2029. The current model WMM2025 is produced jointly by the NCEI and the British Geological Survey (BGS). The model, associated software, and documentation are distributed by NCEI on behalf of US National Geospatial-Intelligence Agency and by BGS on behalf of UK Defence Geographic Centre.