Is the variability of ENSO due to frequency modulation by the long term variation in solar activity?

The spectral content of the El Nino Southern Oscillation (ENSO) is broad and complex, a characteristic shared by other climate variables. Spectral analysis of ENSO in different time intervals demonstrated that ENSO is frequency modulated. An analytical model in which the natural period of ENSO is frequency modulated by long term centennial range variation in solar activity was developed and shown to correlate well with the observed ENSO and reconstructed ENSO variation in the decadal periodicity range. A method for identifying the occurrence and the period of frequency modulation in climate variables was developed and tested. • Proposes that climate oscillatory systems like ENSO are frequency modulated by the long term variation in solar activity • Characterises the variation in long term solar activity from observed and reconstructed sunspot number records • Develops a model for the frequency modulation of the ENSO and compares the model time variation with the observed time variation in the decadal periodicity range • Establishes a method for recovering frequency modulation periods from climate variability records • Provides support for the proposal from a range of instrumental and reconstructed climate records