Sq variation

In geophysics, Sq-Variation (often also Sq-Gang ) denotes the fluctuation of the horizontal intensity of the earth's magnetic field over the course of the day. Their contribution can only be separated when the sun is calm, hence the name sq: solar-quiet . It has its origin in the magnetic fields that create the plasma currents in the ionosphere.

If the horizontal component of the local magnetic field (i.e. the magnetic field at the measuring station) is plotted over time in a diagram , the Sq-pace around the local noon shows up as a clear deviation of the otherwise largely constant amount of the horizontal intensity. The fluctuations depend on the season and the geomagnetic latitude . They are in the order of magnitude of a maximum of ± 50nT, i.e. on average significantly less than 0.1% of the earth's magnetic field.

root cause

At noon , the sun's rays hit the earth at the steepest angle. The UV component of the radiation therefore intensifies the ionization in the terrestrial ionosphere to a particular degree at noon (TEC). This also significantly increases the portion of the earth's magnetic field induced by the ionosphere, which can be clearly seen in a measurement of the horizontal component of the field. The declination of the magnetic field and the vertical component, however, remain unchanged.

The amplitude of the Sq variation is width dependent.

Differentiation from other effects

The Sq variation is a periodic effect with a smooth curve. This clearly distinguishes it from disturbances in the ionosphere . The dependence of the variation on the latitude is also atypical for other disturbances of the earth's magnetic field.

literature

• FH Hibberd: The geomagnetic Sq variation - Annual, semi-annual and solar cycle variations and ring current effects . Journal of Atmospheric and Terrestrial Physics, 1985