Japan Geoscience Union Meeting 2014

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International Session (Oral)

Symbol P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM09_29AM2] VarSITI - Variability of the Sun and Its Terrestrial Impact

Tue. Apr 29, 2014 11:00 AM - 12:45 PM 501 (5F)

Convener:*Kazuo Shiokawa(Solar-Terrestrial Environment Laboratory, Nagoya University), Taro Sakao(Institute of Space and Astronautical Science Japan Aerospace Exploration Agency), Toshihiko Hirooka(Department of Earth and Planetary Scinences, Kyushu University), Chair:Mitsumu K. Ejiri(National Institute of Polar Research), Shin Suzuki(Solar-Terrestrial Environment Laboratory, Nagoya University)

11:00 AM - 11:15 AM

★ [PEM09-29] The effect of Solar radiation on the Climate of Yakushima

*Yasushi MURAKI1, Shoichi SHIBATA2, Takashi SHIBATA3 (1.Solar-Terrestrial Environment Laboratory, Nagoya University, 2.Department of Engeneering, Chubu University, 3.Graduate School of Environment Studies, Nagoya University)

Keywords:solar activity, solar Ultra-Violet light, cloud, daylight hours, aerosols, Passific Decadal Oscillation

Yakushima (Yaku-island) is located to the south of Kyushu in Japan and is known as one of the world natural heritages of UNESCO. There aremountains on the island with heights of about 2,000m where cedar trees have lived for more than 2000 years. We analyzed meteorological data for the island from 1938 to 2013 and found several interesting results: (1) Eleven and 20-30-year-periodicities are present in the data on daylight hours. Similar periodicities are, however, not seen in the data on temperature or water vapor pressure. (2) The 11-year-periodicty appears strongly in June, the rainy season of the island, while the 20-30-year-periodicty is seen throughout the year except in April.(3) An 11-year-periodicty can be also seen in the data for June and July at the other remote island Hachijyojima situated 300km to the south of Tokyo. Both islands are located on the Kuroshio warm current. (4) The daylight hour data for January increased systematically around 1976. This may be related to the change of the North Hemisphere Temperature (NHT) in 1976. In order to explain the observations, we examined the followinghypothesis. Ocean waves produce large numbers of tiny salty droplets which contain plankton on the sea surface. These droplets (aerosols) arewinded up and reach at the top of the mountain. They may act as cloudcondensation nuclei (CCN). It is known that the intensity of the UV light from the Sun is modulatedby solar activity. It is also possible that the growth rate of CCN is affected by the solar UV radiation in the early stage of the aerosol formation process. We speculate that this may be why solar activity is recognized in the daylight hour data. We have not accounted for the 20-30-year-periodicity in the data, but we speculate that this could be related to the Pacific Decadal Oscillation (PDO). Details will be presented at the conference.