Search results
Results From The WOW.Com Content Network
Secular variation is sometimes called secular trend or secular drift when the emphasis is on a linear long-term trend. The term is used wherever time series are applicable in history , economics , operations research , biological anthropology , and astronomy (particularly celestial mechanics ) such as VSOP (planets) .
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 .
The semi-analytic planetary theory VSOP (French: Variations Séculaires des Orbites Planétaires) is a mathematical model describing long-term changes (secular variation) in the orbits of the planets Mercury to Neptune.
A prominent feature in the non-dipolar part of the secular variation is a westward drift at a rate of about 0.2° per year. [35] This drift is not the same everywhere and has varied over time. The globally averaged drift has been westward since about 1400 AD but eastward between about 1000 AD and 1400 AD. [37]
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 weaker variations are the Earth's magnetic map. Within these weaker areas the local directions and intensities change gradually (secular variation). A compass does not point to the true North Pole but to a direction that is a function of the North Magnetic Pole and the local secular variation to yield a magnetic declination.
, the trend component at time t, which reflects the long-term progression of the series (secular variation). A trend exists when there is a persistent increasing or decreasing direction in the data. The trend component does not have to be linear. [1]
Apart from the 168 spherical-harmonic "Gauss" coefficients, the model also has an equal number of spherical-harmonic secular variation coefficients predicting the temporal evolution of the field over the upcoming five-year epoch.