1. 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)

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

3. 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

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

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

6. 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.

7. Derivation of Plage Index

8. 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

9. limb darkening removed
Data calibration
No flat observation before ⇒ 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

10. 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)

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

12. 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%)

13. 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
> (−10%)
25%
1996 >> (−40%)

14. Compare with polar field observation
Wilcox Solar Observatory
1995
2010

15. 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%

16. 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 than in minimum around 2008 ➡ good correlation with geomagnetic indices
The source of variation of the plage index may lie in polar region