Solar magnetic field and the correlation between sunspot activity and Earth atmospheric parameters

Sun is the main energy source in the vicinity of the Earth. The terrestrial atmosphere is governed by the energy it receives from the Sun. Many studies during the last two centuries have demonstrated correlations between solar activity and atmospheric parameters.  The problem is that these correlations, even if highly statistically significant, are not stationary. They may strengthen, weaken, disappear, and even change sign depending on the time period.

In earlier studies it has been found that the sign of the correlations in the Northern hemisphere depends on the prevailing large-scale atmospheric circulation. According to the Vangengeim–Girs classification, there are three main forms of atmospheric circulation: W (zonal or westerly), C (meridional), and E (easterly) for the Atlantic–Eurasian sector, as well as three similar forms: Z, M1, and M2 for the Pacific–American sector. It has been also found that the reversals of the correlations between solar activity and atmospheric parameters is preceded by (or coincides with) the turning points in the evolution of the large-scale circulation forms and mainly of the meridional forms C and M1.

The epochs of large-scale circulation are in turn affected by the stratospheric polar vortex (a large-scale circulation pattern in the stratosphere which develops during polar winter), so the changes in circulation epochs may be associated with the changes in the state of the vortex which can affect the troposphere-stratosphere interaction via planetary waves. If the zonal wind velocity in the vortex exceeds a critical value, planetary waves propagating upward can be reflected back to the troposphere. Under a weak vortex, planetary waves propagate to upper atmospheric levels. Both the circulation epochs and the state of the vortex have cyclic variations with a period of about 60 years.

Two types of solar activity agents are supposed to influence the state of the polar vortex: solar UV irradiance, and energetic particles, mostly electrons, which are trapped in the Earth’s magnetosphere and during geomagnetic disturbances are accelerated and precipitate into the atmosphere. They are related to the two components of the solar magnetic field which is the basis of solar activity. These two components have opposite effects on the stratospheric polar vortex. Here we demonstrate that the relative variations of these two components are in antiphase and oscillate with a period of about 60 years, ultimately determining the correlations between sunspot activity and atmospheric parameters.