Derivation of the Solar Plage Index using the

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
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)
Hα (Balmer line of hydrogen n=3→n=2)
is used for diagnostics
Corona ... >1 million K
source of EUV and X-rays
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 longterm UV radiation by
using Hα images?
What is the source of the
solar UV variation?
Plage
Plage
Filament
Filament
Low-latitude or polar
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
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
raw
calibrated
pseudo-flat
(shown ±10%)
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)
Result
Plage index (full-sun) monthly averaged
0.024
25%
0.018
sunspot number
Latitude Variation
lat. 0°~30°
(Active region belt)
0.021
0.019
(−10%)
lat. 30°~60°
0.03
0.02
(−33%)
lat.
>60°(Polar)
0.05
0.03
(−40%)
Plage index in the two
solar minimum
1996 (minimum)
2001 (maximum)
2008 (minimum)
In low latitude (0~30°), plage index is
1996 > 2008 (−10%)
In polar region (>60°), plage index is
1996 >> 2008 (−40%)
25%
Compare with polar
field observation
Wilcox Solar Observatory
1995
2010
no reduction
−15%
Total Electron Current
Geomagnetic solar
at Ionosphere
quiet daily variation (Sq)
[nT]
Comparison with other
parameters
−15%
−30%
Courtesy to A. Shinbori
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

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