27-day variation in cloud amount in the Western Pacific warm pool region and relationship to the solar cycle
Linkages between solar activity and the earth's climate have been suggested in previous studies. The 11-year cycle in solar activity evident in sunspot numbers is the most examined example of periodicity, and it is clearly recognized in variations in the thermal structure and dynamical motion of the stratospheric atmosphere. Also the variations in the stratosphere related to the period of apparent solar rotation have also been suggested; however, for such a short period, no quantitative evidence indicating a relationship to the tropospheric phenomena. 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 solar maximum years of the 11-year cycle. The average spectrum in solar maximum years also shows an enhancement in the range of MJO period. Long-term variations in the tropospheric phenomena, including the 11-year cycle, are generally investigated based on monthly or even yearly averaged data, but the present results may suggest an alternative possibility: short-period variations could modulate longer periodic phenomena.