This entity is created by currents of (*) molten iron inthe outer core, in accordance with the geodynamo theory, and the interaction of this entity with particles in the solarwind causes the aurora borealis.
Fluctuations in one component of this entity are given by the K-index. Simple models of this entity areaccurate for low values of the McIlwain L-parameter, but at higher L-shells a model like the one named forTysganenko are needed. Secular variation in this entity includes 0.2 degree westward drift. Isogonic lines areareas where the declination of this entity is invariant. This entity is created by currents of (*) molten iron inthe outer core, in accordance with the geodynamo theory, and the interaction of this entity with particles in the solarwind causes the aurora borealis. For 10 points, name this entity which measures around 30 microteslas at the surfaceof our planet.
Fluctuations in one component of this entity are given by the K-index.
Earth's magnetic field [or magnetosphere]