The Earth's magnetic field is generated by electric currents in the molten outer core, and affected by local variations in the mantle and crust. Above the surface, fluctuations of magnetospheric and ionospheric origin are increasingly significant and are impacted by the solar wind. The magnetic field protects us from cosmic radiation and the atmosphere from erosion by the solar wind.
Understanding geomagnetic fields is critical to compass navigation. The direction of magnetic north does not correspond to the geographic north, and a correction (magnetic declination or variation) is required to convert from one to the other.
The direction of the magnetic field vector varies with position and time (the Earth's magnetic poles shift over time). Scientists around the world are studying this variation to improve our understanding of it, and ability to predict changes.
The World Magnetic Model (WMM) is scientific software that calculates magnetic declination, inclination, and intensity at a particular time and position. It is based on data measured by dedicated satellites as part of the SWARM mission and by the ground based observatories of the INTERMAGNET network. It is relied upon throughout the world for navigation, mineral exploration, atmospheric and space science.
The Ap geomagnetism index is used to measure the overall level of geomagnetic activity on Earth. It is derived from the Kp index, which quantifies disturbances in the Earth's magnetic field caused by solar wind and other solar activities.
The official values for the Ap index, along with other related geomagnetic activity indices such as the three-hour Kp index, are calculated by the GeoForschungsZentrum Helmholtz Centre in Potsdam, Germany.
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