Magnetic methods, surface

Abstract

The shape, strength and variations of the Earth’s magnetic field, have been studied over 500 years. Starting from measurements, repeated in time, at different places on earth, a model of the Earth’s magnetic field, in space and time has been built up. Magnetic observatories are places where long time series of accurate measurements of the magnetic field are made, analysed and disseminated to institutions and persons seeking this information. Variations in different period ranges provide information about diverse processes, affecting the magnetic field. Short period variations (~min, hr) are indicative of disturbances in the magnetosphere caused by the Sun’s corpuscular streams and magnetic fields, medium-term variations (~day, year) describe effects of the sun’s radiation and long-term variations (~year, decade, century) provide insights into the nature of the Earth’s internal magnetic field, its origin, and modification in the Earth’s outer core (secular varia-tion). Closely spaced measurements on the Earth’s surface are used in studies for resource exploration, tectonics and mapping the formation of the oceanic crust. The form of the Earth’s magnetic field is defined every five years, collating all available measurements as the IGRF. This also provides estimates of secular variation. The vast quantity of data collected about spatial and temporal variations of the Earth’s magnetic field, has resulted in increasingly accurate models of processes on the Sun, in space and on and within the Earth.