Department of Geomagnetism

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Dynamo or Gyroscope?

Written by : Alexandra Marsenić | Published in: Geomagnetic field |

 

  • Why are  the planetary and astrophysical magnetic fields prevailingly dipolar?
  • Why  is rotation of the cosmic body necessary for their existence?
  • What causes their time changes?
  • What causes their deflection from rotational symmetry?
  • Can the notion of a free-charge gyroscope explain their existence?

 

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Spatial and temporal variations of the geomagnetic activity

Written by : Vladimir Pohanka | Published in: Geomagnetic field |

Spatial and temporal variations of the geomagnetic activity as seen by an observer from outer space

 

Vladimír Pohánka and Fridrich Valach

 

The magnetic field which is observed by the geomagnetic observatories located on the Earth's surface (let us call it the geomagnetic field) is not invariable. It shows temporal as well as spatial variations. To understand these variations, one must consider some knowledge about the sources of the magnetic field - there are several of them:

 

(1) The main part of the geomagnetic field is produced in the molten, liquid and highly conductive Earth's core. Here the relevant processes are described by the physical theory which is called magnetohydrodynamics. This field changes slowly, the corresponding time scales are years, centuries, even millenia.

 

(2) Another source of the geomagnetic field is presented by magnetic rocks in the Earth's crust, for instance by well known magnetite. Neither this component of the geomagnetic field can change quickly.

 

(3) Finally,certain part of the observed geomagnetic field originates in the near-Earth space environment. It is generated by current systems flowing in the conductive part of the Earth's atmosphere - ionosphere; for instance, complex systems of electric currents exist in auroral regions. Important are also the magnetic fields that are caused by electric currents in magnetosphere - both in inner magnetosphere and in the distant magnetospheric tail. The processes in the near-Earth space environment are very dynamic and they are driven by explosive processes that take part in the solar atmosphere and in the
interplanetary space (e.g. coronal mass ejections and co-rotating interactive regions).

 

These changes of the geomagnetic field may seriously affect the life on the Earth: in the past, the violent changes of the geomagnetic field already inflicted a lot of damage. Examples are wide-area failures of the electricity supply lasting for hours; these were caused by melting the windings in saturated transformers by geomagnetically induced currents (GICs). Reported were also fires at telegraphic stations that were set by the GICs. For our modern society, which is immensely dependent on the vulnerable technological systems, the extreme magnetic storms represent the hazard that might cause even more severe damage.

 

We are not able to see the above mentioned temporal and spatial changes of the geomagnetic field by own eyeball. We can just directly see auroras, which are related to these changes indirectly. The aim of this short paper is to visualise the Earth magnetic field and its changes over the whole Earth surface.