27-day variation in cloud amount in the Western Pacific warm pool region and relationship to the solar cycle

Abstract. Although linkages between solar activity and the earth's climate have been suggested and the 11-year cycle in solar activity evident in sunspot numbers is the most examined example of periodicity in previous studies, no quantitative evidence indicating a relationship for tropospheric phenomena has been found for a short period. Based on FFT analysis for OLR (Outgoing Longwave Radiation) compared with the F10.7 index, we clearly demonstrate a 27-day variation in the cloud amount in the region of the Western Pacific warm pool, which is only seen in the maximum years of 11-year solar activity. The average spectrum in such years also shows an enhancement in the range of the MJO (Madden-Julian Oscillation) period. Although there exist some explanations for possible mechanisms, the exact cause is unknown. Therefore, the proposed connection between 27-day cloud variation and solar cycle in the WPWP region is still a hypothesis and various kinds of varification based on other meteorological and solar parameters are strongly required.