Hiroko Watanabe (Kyoto Univ.) Derivation of the Solar Plage Index using the Flare Monitoring Telescope at the Hida Observatory Hiroko Watanabe (Kyoto Univ.) Collaborators: Ayumi Asai, Satoru UeNo, Reizaburo Kitai (Kyoto Univ.), Satoshi Morita(NAOJ)

Solar irradiance 11-year solar cycle variation Impact on the earth’s and space weather

Important to estimate solar UV radiation Importance of UV Solar UV (10-400nm) is absorbed in the earth’s ionosphere Correlation with climate and geomagnetic activity Important to estimate solar UV radiation

UV radiation from the Sun Photosphere ... ~6000K source of visible light Chromosphere ... ~10,000K source of UV (100-300nm) Corona ... >1 million K source of EUV and X-rays Hα (Balmer line of hydrogen n=3→n=2) is used for diagnostics

Archive of Hα images Flare Monitoring Telescope @ Hida Observatory, Kyoto Univ. Moved to the Ica University at Peru in 2009 Since 1996 until today covers two solar minimum (1995-1996, 2007-2009) and one solar maximum (2000-2002) 1996Sep

Question to be addressed Can we derive the long- term UV radiation by using Hα images? What is the source of the solar UV variation? Plage Filament Low-latitude or polar Plage Filament This work is supported by RISH, Kyoto-U and STEL, Nagoya-U.

Derivation of Plage Index

Observation Flare Monitoring Telescope 6.4 cm aperture telescope x 5 Use Hα center image 1 min cadence 4.2 arcsec/pixel 512 x 512 average observing day per month is 20.6

limb darkening removed Data calibration No flat observation before 2009 ⇒ Make pseudo-flat by averaging 2-month’s images Remaining fringe pattern (daily variation) is reduced by additional treatment pseudo-flat (shown ±10%) raw calibrated limb darkening removed

Plage Index Plage index : defined as the percentage of the area of the solar disk covered by plages + active network Reproduction of the solar irradiance variation requires the contribution not only of active region plages but also of the enhanced network (Foukal et al. 2009) Intensity threshold method : pixels brighter than average+2σ(standard deviation) Plage brightness does not affect the plage contribution to irradiance variation (Worden et al. 1998)

Plage index (full-sun) monthly averaged Result Plage index (full-sun) monthly averaged 0.024 25% 0.018 sunspot number

Latitude Variation 0.021 0.019 (−10%) 0.03 0.02 (−33%) 0.05 (−40%) (Active region belt) lat. >60°(Polar) lat. 30°~60° 0.021 0.019 (−10%) 0.03 0.02 (−33%) 0.05 (−40%)

Plage index in the two solar minimum 2001 (maximum) 2008 (minimum) In low latitude (0~30°), plage index is In polar region (>60°), plage index is 1996 > 2008 (−10%) 25% 1996 >> 2008 (−40%)

Compare with polar field observation Wilcox Solar Observatory 1995 2010

Comparison with other parameters Courtesy to A. Shinbori Geomagnetic solar quiet daily variation (Sq) [nT] Total Electron Current at Ionosphere −15% no reduction −15% −30%

SUMMARY We attempt to use “plage index” to know the long-term variation of the solar UV radiation. The plage index is lower in minimum around 1996 than in minimum around 2008 ➡ good correlation with geomagnetic indices The source of variation of the plage index may lie in polar region