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Changes in Earth's magnetic field on a time scale of a year or more are referred to as secular variation. Over hundreds of years, magnetic declination is observed to vary over tens of degrees. [13] The animation shows how global declinations have changed over the last few centuries. [34] The direction and intensity of the dipole change over time.
The rate of reversals in the Earth's magnetic field has varied widely over time. Around , the field reversed 5 times in a million years. In a 4-million-year period centered on , there were 10 reversals; at around , 17 reversals took place in the span of 3 million years.
The magnetic field of a magnetic dipole has an inverse cubic dependence in distance, so its order of magnitude at the earth surface can be approximated by multiplying the above result with (R outer core ⁄ R Earth) 3 = (2890 ⁄ 6370) 3 = 0.093 , giving 2.5×10 −5 Tesla, not far from the measured value of 3×10 −5 Tesla at the equator.
This image shows magnetic declination, or the angle between magnetic and geographic north, according to the World Magnetic Model released in 2025. Red is magnetic north to the east of geographic ...
NASA's Solar Dynamics Observatory scientists used computer models to generate a four-day, time-lapse view of the sun's changing magnetic field. The field lines are more concentrated in regions ...
The coolest of these, 2MASS J10475385+2124234 with a temperature of 800-900 K, retains a magnetic field stronger than 1.7 kG, making it some 3000 times stronger than the Earth's magnetic field. [18] Radio observations also suggest that their magnetic fields periodically change their orientation, similar to the Sun during the solar cycle. [19]
Vasil and his team developed new models of the interaction between the sun’s magnetic field and the flow of plasma, which varies at different latitudes during an 11-year cycle.
Geomagnetic secular variation refers to changes in the Earth's magnetic field on time scales of about a year or more. These changes mostly reflect changes in the Earth's interior, while more rapid changes mostly originate in the ionosphere or magnetosphere. [1] The geomagnetic field changes on time scales from milliseconds to millions of years.