Geomagnetic Hourly Averages from world wide observatories

Geomagnetic variation data with 2.5 minute resolution

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Geomagnetic 10 second data provides high temporal resolution of geomagnetic variations

Geomagnetic One Minute Means from world wide observatories

Geomagnetic Range index using data from multiple observatories - Mayaud 1948

Report on the status of world wide geomagnetic observatories

These data are vector and scalar component values of the Earth's magnetic field for 2004 recorded at the Boulder Magnetic Observatory in Colorado. Vector values are measured using 3 mutually orthogonal fluxgate magnetometer sensors. The scalar value of the total magnetic field is recorded with a proton precession magnetometer. All values are calibrated with measurements of the absolute value of the geomagnetic field using a DI-Flux magnetometer. The data are numerically filtered to prevent aliasing, and quality controlled during processing. Longer period values of the field, including hourly, daily, monthly, and annual means are derived from the 1-minute data.

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.

This file is comprised of absolute mean hourly values of the geomagnetic components D, H and Z or X, Y and Z. These values, on magnetic tape, are available from approximately 220 of the 400 worldwide observatories which have ever operated. Most of the values were hand-scaled from the analog recordings (magnetograms) and were added to the file via punched cards. From some observations, for more recent years, there are means of values recorded directly on magnetic tape from digital magnetometers at various sample rates, for example, each minute. The accuracy of these data varies but is generally good, particularly for the more recent years. Approximately 60 observation-years of these data are added to the files each year.