Geomagnetic Secular Variation and its Changes, 1942.5 to 1962.5

Four centuries of geomagnetic secular variation from historical records

We present a new model of the magnetic ­ eld at the core{mantle boundary for the interval 1590{1990. The model, called gufm1, is based on a massive new compilation of historical observations of the magnetic ­ eld. The greater part of the new dataset originates from unpublished observations taken by mariners engaged in merchant and naval shipping. Considerable attention is given to both correcti...

Dynamic responses of the Earth’s outer core to assimilation of observed geomagnetic secular variation

Assimilation of surface geomagnetic observations and geodynamo models has advanced very quickly in recent years. However, compared to advanced data assimilation systems in meteorology, geomagnetic data assimilation (GDAS) is still in an early stage. Among many challenges ranging from data to models is the disparity between the short observation records and the long time scales of the core dynam...

Changes in cosmic ray cut-o rigidities due to secular variations of the geomagnetic ®eld

An analytical expression is derived for the cuto€ rigidity of cosmic rays arriving at a point in an arbitrary direction, when the main geomagnetic ®eld is approximated by that of an eccentric dipole. This expression is used to determine changes in geomagnetic cuto€s due to secular variation of the geomagnetic ®eld since 1835. E€ects of westward drift of the quadrupole ®eld and decrease in the e...

Fractal Analysis for Geomagnetic Secular Variations

Forward and adjoint quasi-geostrophic models of the geomagnetic secular variation

We introduce a quasi-geostrophic model of core dynamics, which aims at describing core processes on geomagnetic secular variation timescales. It extends the formalism of Alfvén torsional oscillations by incorporating non-zonal motions. Within this framework, the magnetohydrodynamics takes place in the equatorial plane; it involves quadratic magnetic quantities, which are averaged along the dire...