Geomagnetic secular variation

Geomagnetic secular variation is the changes in the <a href="/facts/Earth%2527s_magnetic_field/73G36wmx">Earth's magnetic field</a> on time scales of about a year or more. These changes mostly reflect changes in the <a href="/facts/Internal_structure_of_Earth/678dYXU7">Earth's interior</a>, while more rapid changes mostly originate in the <a href="/facts/Ionosphere/mT9tTBE5">ionosphere</a> or <a href="/facts/Magnetosphere/BXzgPoPy">magnetosphere</a>.
The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the <a href="/facts/Ionosphere/mT9tTBE5">ionosphere</a> and <a href="/facts/Magnetosphere/BXzgPoPy">magnetosphere</a>, and some changes can be traced to <a href="/facts/Geomagnetic_storms/4rD8DSlm">geomagnetic storms</a> or daily variations in currents. Changes over time scales of a year or more mostly reflect changes in the Earth's interior, particularly the iron-rich <a href="/facts/Outer_core/1U5pw3La">core</a>. These changes are referred to as <a href="/facts/Secular_variation/55wVcxuE">secular variation</a>. In most <a href="/facts/Scientific_modelling/aNyvIyUQ">models</a>, the secular variation is the amortized time <a href="/facts/Derivative/7Ito70Dh">derivative</a> of the magnetic field 
 
 
 
 
 B
 
 
 
 {\displaystyle \mathbf {B} }
 
, 
 
 
 
 
 
 
 
 B
 
 ˙
 
 
 
 
 
 {\displaystyle {\dot {\mathbf {B} }}}
 
. The second derivative, 
 
 
 
 
 
 
 
 B
 
 ¨
 
 
 
 
 
 {\displaystyle {\ddot {\mathbf {B} }}}
 
 is the secular acceleration.

Geomagnetic secular variation open-in-new

Geomagnetic secular variation