Influence of the solar cycle and QBO modulation on the Southern Annular Mode

Abstract

Influence of the 11‐year solar cycle and the stratospheric equatorial Quasi‐Biennial Oscillation (QBO) on the Southern Annular Mode (SAM) in late winter/spring is examined through the analysis of combined reanalysis data of ECMWF. It is found that the signal is strongly affected by both the solar cycle and the QBO. Regarding the effect of the solar cycle, the signal extends to the upper stratosphere and persists into the following summer in years with high solar activity, but it is restricted to the troposphere and disappears very quickly in years with low solar activity. For the QBO, the signal extends to the upper stratosphere in late winter/spring but disappears in the following summer in QBO‐west years. On the other hand, the signal extends vertically as the time evolution and tends to persist into the following summer in QBO‐east years. When both the solar cycle and the QBO are considered, the effects from the solar cycle dominate and those from the QBO work as linearly superimposed factors. Role of ozone on the solar cycle and QBO modulation is also discussed.