| 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. |