The Quiet Sun TSI During 2009
by
G.A. Chapman, A.M. Cookson
and D.G. Preminger
San Fernando Observatory
Department of Physics and Astronomy
CSU, Northridge 91330
1
Abstract
The extended solar minimum of 2008-2009 provides a period of time of few sunspots and
very low solar activity including faculae and
network. Comparing facular indices with the
SORCE TIM/TSI we are able to determine
the quiet sun (QS) irradiance with less interference from solar activity. We find a multiple
regression analysis gives an R2 of 0.60 and a
QS TSI of 1360.62±0.04W/m2 . The complete
regression equation is given by Eq. 1.
T IM = 1360.62±0.042+(205±43.3)10−5 DEF
+ (74±6.4)10−6 ΣN K (1)
2
Abstract (continued)
Images are from the SFO Cartesian Full Disk
Telescope no. 2 (CFDT2) which has 2.5” x
2.5” pixels. The time period is from 6 May
2009 through 30 November 2009 giving 98
days of data. The index, DEF, is the sunspot
deficit. It is the sum over all sunspot pixels. The coefficient for the sunspot deficit is
5 times its error. The facular signal is represented by ΣN K . It is the sum over all pixels on
a K-line contrast image. Its coefficient is 11
times its error. The subscript NK represents
the narrow K-line filter (BP=0.3 nm). Both
indices are in parts per million of the quiet sun.
We will compare the QS TSI determined during this interval with the QS TSI during more
active times.
This research was partially supported by NSF
Grant ATM-0848518.
3
Space-based radiometry measures the Total Solar Irradiance, without hindrance from the earth’s
atmosphere. Most radiometers are not able to
image the sun and thus are unable to determine the sources of variability. Ground-based
photometry, on the other hand, can image the
sun but can only obtain relative changes in
brightness. Properly calibrated images can be
a useful complement to space-based measurements of TSI. For example, Ground-based photometry can bridge periods when a spacecraft
anomaly occurs (Lee et al. 1995, Chapman et
al. 1996)∗ . However, an important, simplifying assumption is that the irradiance from the
non-magnetic sun is contant over time. The
unusually low level of solar magnetism during
the past minimum provides a chance to examine more carefully the quiet sun.
∗ See
poster by Cookson et al.
4
Photometry at the San Fernando Observatory
produces images on a daily basis using two
telescopes, CFDT1 and CFDT2. Images are
calibrated (Walton et al. 1998) and analyzed
to produce photometric indices representing
sunspots and faculae and network. For sunspots
the photometric deficit is calculated pixel by
pixel for all sunspots. A sunspot pixel is one
with a contrast equal to or less than -8.5%.
The photometric deficit is defined as
DEF =
X
ci(µ) × Φ(µi ),
(2)
i
where ci(µ) is the contrast of pixel i and Φ(µi )
is the observed quiet sun limb darkening at
pixel i.
For faculae and the network, an index is calculated from K-line images. It is defined as
5
ΣK =
X
c(µ) × Φ(µ),
(3)
all
where the sum is over all pixels on a contrast
image. This index will measure the contribution of faint, bright pixels.
summer 2009
TIM vs. DEF2, Sigma_NK
1361.1
calc.
TIM/TSI (W/m^2)
1361.05
obs.
1361
1360.95
1360.9
1360.85
1360.8
1360.75
06-May-2009
06-Jul-2009
Date
26-Aug-2009
03-Nov-2009
This figure shows the fit of CFDT2 data from
SFO with the latest SORCE/TIM (version 10)
for the time period 6 May 2009 through 30
November 2009, a period of very low solar
activity. The calculated points are given by
Eq. 1. The observed points are from TIM.
During the middle period, there appears to
be approximately 0.25 to 0.3 W/m2 of excess
emission from the faculae and network based
on the quiet sun irradiance of 1360.6 W/m2 in
Eq. 1.
6
1362
TIM@21h vs. SFO CFDT2(pfifa,d2r)
1361.5
1361
W/m^2
1360.5
1360
1359.5
1359
1358.5
1358
1357.5
1357
jun-01-03 sep-09-03 dec-18-03 mar-27-04 jul-05-04 oct-13-04
date
TIM
def2+pfifa2
Shown is the fit to TIM/TSI during a very active time in 2003. The regression (R2 = 0.9547,
N = 345) of TIM to CFDT2 data is given by
T IM = 1360.76±0.11 + (1358±40)10−6 DEF
+(1631 ±19)10−6 P F IF A.(4)
7
The index PFIFA is defined in Chapman et al.
(1996). (The TIM data are from an earlier
version.)
References
Chapman, G.A., Cookson, A.M. and Dobias,
J.J. 1996, J.G.R. 101, 13541.
Lee, R.B.III, Wilson, R.S., Thomas, S., and
Gibson, M.A. 1995, J.G.R. 100, 1667.
Walton, S.R., Chapman, G.A., Cookson, A.M.,
Dobias, J.J. and Premiinger, D.G.. 1998, Solar Phys. 179, 31.
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