Long-term changes in atmospheric circulation, earth rotation rate and north–south solar asymmetry

Abstract

Earlier studies have demonstrated a relation between long-term changes in the Earth's rotation rate and the prevalence of zonal or meridional types of circulation. The results, however, have been confined to the 20th century and to the Northern hemisphere. In the present paper we compare the long-term changes in the length of the day (LOD) and the temperature contrast between the equator and the pole in the Northern and the Southern hemispheres as an indirect measure for the zonality of the atmospheric circulation. In the 20th century in the Northern hemisphere we find a high negative correlation between the rotation rate and the equator/pole temperature contrast, while in the 19th century the correlation is positive. For the Southern hemisphere, the situation is opposite. The correlation changes when the North–South asymmetry of solar activity also changes sign. The decadal changes in LOD are shown to be related to the changes in the North–South asymmetry of solar equatorial rotation rate supposedly induced by planetary-driven changes in the angular momentum of the solar system, with both quantities showing pronounced periodicities and high squared coherence at 47 years. It is hypothesized that decadal changes in LOD are driven by core-mantle coupling processes regulated by solar wind transferring solar magnetic fields and angular momentum modulated by planetary influences. The atmospheric circulation in the Northern and Southern hemispheres is found to be different not only on decadal time-scales but also in the 11-year solar cycle, and different in even and odd cycles. While long-term changes in geomagnetic activity closely follow sunspot activity changes, the correlation between the two in the 11-year cycle has been decreasing in the last century with the increase of the North–South solar activity asymmetry which modulates also the asymmetry of galactic cosmic rays flux considered a candidate mediator between solar activity and climate.