Changes in the magnetic field of the Earth
(the field intensity and its elements) in time under the influence of various factors are called
geomagnetic variations. Geomagnetic variation is the difference between the observed magnitude of the intensity
magnetic field and its average value over any long period of time, for example, a month or a year.
Long-term observations of the magnitude of the magnetic field intensity by the world network of observatories
made it possible to classify time variations of the field.
It is customary to distinguish four types of magnetic variations: secular, annual, daily and magnetic disturbances.
Secular variations of the magnetic field, apparently connected with the processes inside the Earth, occur during prolonged
periods of time in tens and hundreds of years and lead to significant changes in the average annual elements of terrestrial
Annual variations are changes in mean monthly values of itensity
magnetic field. They are characterized by a small amplitude (tens of nT).
Daily variations are associated with solar and lunar day changes in the intensity of the geomagnetic field due to
changes in solar activity. The maximum of variation is reached in the daytime and at the confrontation of the Moon.
Annual and daily variations are smooth, periodic, unperturbed variations.
Their intensity increases from the equator to the poles, reaching 200 nT.
In addition to unperturbed variations, there are perturbed variations, which include nonperiodic impulse variations,
magnetic storms. The perturbed variations are associated with irregular processes in the solar wind and on the Sun,
affecting the ionosphere and the magnetosphere of the Earth.
The World Data Center for Solar-Terrestrial Physics has an extensive archive of data on magnetic
field of the Earth, obtained by the world network of geomagnetic observatories and stations and in analytical centers.
Minute Values of Geomagnetic Field Elements
Hourly Mean Values of Geomagnetic Field Elements
Annual Mean Values of the Magnetic Field Elements