Solar activity has an important impact not only on the intensity of cosmic rays but also on the environment of Earth. In the present paper, a coupled oscillator model is proposed to explain solar activity. This model can be used to naturally reduce the 89-year Gleissberg cycle. Furthermore, as an application of the coupled oscillator model, we herein attempt to apply the proposed model to El Niño-southern oscillation (ENSO). As a result, the 22-year oscillation of the Pacific Ocean is naturally explained. Finally, we search for a possible explanation for coupled oscillators in actual solar activity.