Resonant excitation of the quasi-decadal oscillation by the 11-year signal in the Sun's irradiance



[1] The quasidecadal oscillation (QDO) of 9- to 13-year period in the Earth's climate system has been found governed by a delayed action oscillator (DAO) mechanism in the tropical Pacific Ocean similar to that governing the El Niño–Southern Oscillation (ENSO) of 3- to 5-year period. It also fluctuated in phase with the ∼11-year-period signal in the Sun's total irradiance throughout the twentieth century. In earlier attempts to explain this association, a conceptual ocean-atmosphere coupled model of the DAO mechanism in the tropical Pacific Basin was driven by 11-year-period solar forcing, producing a QDO that was in damped resonance with the solar forcing. In the present study, we likewise force a fully coupled ocean-atmosphere general circulation model (i.e., Fast Ocean-Atmosphere Model (FOAM)) of Jacob et al. (2001), adding an 11-year-period cosine signal of amplitude ∼2.0 W m−2 to the solar constant in the model. In the presence of this 11-year-period solar forcing the FOAM simulates both the ENSO and the QDO, while in its absence the FOAM simulates only the ENSO. We find the model QDO governed by a tropical DAO mechanism with patterns and evolution similar to those observed. We find its warm phase lagging peak solar forcing by ∼1–3 years, as observed and consistent with damped-resonant excitation of the tropical DAO of the QDO by the 11-year-period solar forcing in the earlier conceptual model.