<P> The positions of the magnetic poles can be defined in at least two ways: locally or globally . The local definition is the point where the magnetic field is vertical . This can be determined by measuring the inclination . The inclination of the Earth's field is 90 ° (downwards) at the North Magnetic Pole and - 90 ° (upwards) at the South Magnetic Pole . The two poles wander independently of each other and are not directly opposite each other on the globe . They can migrate rapidly: movements of up to 40 kilometres (25 mi) per year have been observed for the North Magnetic Pole . Over the last 180 years, the North Magnetic Pole has been migrating northwestward, from Cape Adelaide in the Boothia Peninsula in 1831 to 600 kilometres (370 mi) from Resolute Bay in 2001 . The magnetic equator is the line where the inclination is zero (the magnetic field is horizontal). </P> <P> The global definition of the Earth's field is based on a mathematical model . If a line is drawn through the center of the Earth, parallel to the moment of the best - fitting magnetic dipole, the two positions where it intersects the Earth's surface are called the North and South geomagnetic poles . If the Earth's magnetic field were perfectly dipolar, the geomagnetic poles and magnetic dip poles would coincide and compasses would point towards them . However, the Earth's field has a significant non-dipolar contribution, so the poles do not coincide and compasses do not generally point at either . </P> <P> Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the solar wind . This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second . They carry with them a magnetic field, the interplanetary magnetic field (IMF). </P> <P> The solar wind exerts a pressure, and if it could reach Earth's atmosphere it would erode it . However, it is kept away by the pressure of the Earth's magnetic field . The magnetopause, the area where the pressures balance, is the boundary of the magnetosphere . Despite its name, the magnetosphere is asymmetric, with the sunward side being about 10 Earth radii out but the other side stretching out in a magnetotail that extends beyond 200 Earth radii . Sunward of the magnetopause is the bow shock, the area where the solar wind slows abruptly . </P>

Which is the most important source of electromagnetic waves for earth