Impact of the 11-yr Solar Activity on the QBO in the Climate System

The QBO (quasi-biennial oscillation) in the climate system, with a mean cycle-length slightly above or below 2 years, is studied in a simple forced dynamical system. The fundamental cause of the quasi-biennial periodicity of the QBO is nonlinear resonance of the system to the seasonal forcing that is modulated by the 11-yr solar cycle. For a given nonlinearity, the cycle-length and the amplitude of the QBO depend on the intensity of both the unmodulated seasonal cycle and the 11-yr solar cycle, which may be one of the reasons why the QBO properties in climate vary with time and space.