ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-1577-2010 27-day variation in cloud amount in the Western Pacific warm pool region and relationship to the solar cycle Takahashi Y. 1 Okazaki Y. 2 Sato M. 1 Miyahara H. 3 Sakanoi K. 4 Hong P. K. 5 Hoshino N. 2 Department of Cosmosciences, Hokkaido University, Hokkaido, Japan Department of Geophysics, Tohoku University, Tohoku, Japan Instuitute for Cosmic Ray Research, The University of Tokyo, Tokyo, Japan Department of Natural Sciences, Komazawa University, Komazawa, Japan Department of Complexity Science and Engineering, The University of Tokyo, Tokyo, Japan 15 02 2010 10 4 1577 1584 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/1577/2010/acp-10-1577-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/1577/2010/acp-10-1577-2010.pdf

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.

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