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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.
Changes that predate magnetic observatories are recorded in archaeological and geological materials. Such changes are referred to as paleomagnetic secular variation or paleosecular variation (PSV). The records typically include long periods of small change with occasional large changes reflecting geomagnetic excursions and reversals. [38]
The International Geomagnetic Reference Field (IGRF) is a standard mathematical description of the large-scale structure of the Earth's main magnetic field and its secular variation. It was created by fitting parameters of a mathematical model of the magnetic field to measured magnetic field data from surveys, observatories and satellites ...
The secular variation of a time series is its long-term, non-periodic variation (see Decomposition of time series).Whether a variation is perceived as secular or not depends on the available timescale: a variation that is secular over a timescale of centuries may be a segment of what is, over a timescale of millions of years, a periodic variation.
Produced soon after acquisition, 98% of the differences between QDD and definitive data (X-north, Y-east, Z-down) monthly mean values should be less than 5nT. QDD are intended to support field modelling activities during the modern satellite survey era, providing extra constraints on, for example, models of the field secular variation.
The model consists of a degree and order 12 spherical harmonic expansion of the magnetic scalar potential of the geomagnetic main field generated in the Earth's core. [2] Apart from the 168 spherical-harmonic "Gauss" coefficients, the model also has an equal number of spherical-harmonic secular variation coefficients predicting the temporal ...
The Earth's field is roughly like a tilted dipole, but it changes over time (a phenomenon called geomagnetic secular variation). Mostly the geomagnetic pole stays near the geographic pole , but at random intervals averaging 440,000 to a million years or so, the polarity of the Earth's field reverses.
The largest magnetospheric-ionospheric current variations, resulting in the largest external magnetic field variations, occur during geomagnetic storms and it is then that the largest GIC occur. Significant variation periods are typically from seconds to about an hour, so the induction process involves the upper mantle and lithosphere. Since ...