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SOLAR IRRADIANCE VARIABILITY OF RELEVANCE
FOR CLIMATE STUDIES
N.A. Krivova
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CGD, NCAR
SUN - CLIMATE
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CGD, NCAR
SOLAR TOTAL IRRADIANCE:WHAT IS KNOWN?
PMOD TSI
0.1%
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CGD, NCAR
BUT... (1)
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CGD, NCAR
Long-term time series needed!!!
BUT... (1)
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BUT... (2)
3 different composites!!!
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CGD, NCAR
BUT... (3)Different trends in Mg II and TSI composites since 1999!!!
Froehlich, priv. comm.
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SOLAR SPECTRAL IRRADIANCE:WHAT IS KNOWN?
SME (Solar Mesosphere Explorer): 1981-1989, 10-20% uncertainty in the UV
SOLSTICE & SUSIM on UARS: 1991-1.8.2005, daily, 120-400nm with ~1 nm resolution
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BUT...
SME (Solar Mesosphere Explore)SME (Solar Mesosphere Explore):: 1981-1989, 10-20% uncertainty in the UV
SOLSTICE & SUSIM on UARSSOLSTICE & SUSIM on UARS:: 1991-1.8.2005, daily, 120-400nm with ~1 nm resolution
200-209 nm 270-274 nmSOLSTICE
SUSIM
difference
1=2-3%
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SOLAR SPECTRAL IRRADIANCE:WHAT IS KNOWN?
SME (Solar Mesosphere Explorer): 1981-1989, 10-20% uncertainty in the UV
SOLSTICE & SUSIM on UARS: 1991-1.8.2005, daily, 120-400nm with ~1 nm resolution
SORCE andSCIAMACHY: since 2003, broadrange from UV to IR
SORCE: 310-1599 nm Dec 31, 2005
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BUT... SCIAMACHY: March-May 2004
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MODELS OF SOLAR IRRADIANCE
Changes in quiet photosphere:
r-mode oscillations, thermal shadowing, changes in the convection properties etc. (Wolff & Hickey 1987; Parker 1987, 1995; Kuhn et al. 1999)
Changes in surface structure:
darkening due to sunspots and brightening due to faculae and the network:
Stot(t)=Ss(t)+Sf(t)
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MODELS OF SOLAR IRRADIANCE
Changes in surface structure:
darkening due to sunspots and brightening due to faculae and the network:
Stot(t)=Ss(t)+Sf(t)
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1996 2000
FACULAE AGAINST SUNSPOTS
Data: MDI
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1996 2000
FACULAE AGAINST SUNSPOTS
~-0.8Wm-2
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1996 2000
FACULAE AGAINST SUNSPOTS
~-0.8Wm-2
~1.7Wm-2
Wenzler 2005
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1996 2000
FACULAE AGAINST SUNSPOTS
~-0.8Wm-2
~1.7Wm-2
Wenzler 2005
0.1%
Fröhlich 2004
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MODELS OF SOLAR IRRADIANCE
Changes in surface structure:
Regressions of sets of proxies:
Stot(t)=Sq+sSs(t)+fSf(t)
e.g., Foukal & Lean 1986, 1988; Chapman et al. 1994, 1996; Lean et al. 1998; Fligge et al. 1998; Preminger et al. 2002; Jain & Hasan 2004
Maps of a given proxy + semi-empirical model atmospheres:
Stot(t)=q(t)Sq+s(t)Ss+f(t)Sf
Fontenla et al. 1999, 2004; Unruh et al. 1999; Fligge et al. 2000; Krivova et al. 2003; Ermolli et al. 2003; Wenzler et al. 2004, 2005
quiet Sunsunspotsfaculae
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MODELS OF SOLAR IRRADIANCE:
SATIRE (Spectral And Total Irradiance
REconstructions)Basic assumption: all solar irradiance changes on time scales longer than a day are due to solar surface magnetism
Input: magnetic field distribution (observations <e.g., MDI or KP> or model); spectra of photospheric components (model atmospheres)
Output: solar total and spectral irradiance vs. time
Free parameters: 1
Unruh et al. 1999; Fligge et al. 2000; Krivova et al. 2003;Wenzler et al. 2004, 2005
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SATIRE: 4-component model
Iq() - quiet Sun intensity
T=5777K (Kurucz 1991)I
s() - sunspot int.; separate
umbra/penumbra (cool Kurucz models)
s( t ) - filling factor of
sunspots (MDI or KP continuum)I
f() - facular intensity
(modified P-model; Fontenla et al. 1993; Unruh et al. 1999)
f(t) - filling factor of
faculae (MDI or KP magnetograms)
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SATIRE: cycle 23 (MDI-based)
Krivova et al. 2003
Data: VIRGO TSI
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SATIRE:cycles 21-23 (KP-based)
Ground-based: variable seeing
2 different instruments: cross-calibration NASA/NSO 512-channel Diode Array Magnetograph (Feb. 1974 - Apr. 1992); NASA/NSO spectromagnetograph (Nov. 1992 - Sep. 2003)
Poorer quality of earlier data: identification of umbrae/ penumbrae
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Wenzler et al. 2006
Data: PMOD TSI composite
SATIRE:cycles 21-23 (KP-based)
The dominant part of the solar irradiance variations are due to
the surface magnetic field
Rc=0.91
Reconstruction of TSI back to 1974
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SATIRE:cycles 21-23 (KP-based)
Wenzler et al. 2006
Data: PMOD, ACRIM and IRMB TSI composites
Rc=0.84
Rc=0.91
Rc=0.87
PMOD
ACRIM
IRMB
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SATIRE:cycles 21-23 (KP-based)
Wenzler et al. 2005
Data:Data: PMOD, ACRIM and PMOD, ACRIM and IRMB TSI compositesIRMB TSI composites
Rc=0.84
Rc=0.91
Rc=0.87
PMOD
ACRIM
IRMB
No minimum-to-minimum trend is seen (similarly to PMOD composite)
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Krivova et al. 2003
MODELS OF SOLAR IRRADIANCE:
Spectral irradiance
Data: VIRGO channels (862, 500 & 402 nm)
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Data: SUSIM
SATIRE
MODELS OF SOLAR IRRADIANCE:
Spectral irradiance
Krivova & Solanki 2004
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SATIRESATIRE
SUSIM SUSIM
MODELS OF SOLAR IRRADIANCE:UV irradiance
Krivova et al. 2006
SATIRESUSIM
Regressions
F()/F(220 -240)
vs. F(220 -240)
for every
SUSIM: daily,1991- 2002 Rc=0.97
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MODELS OF SOLAR IRRADIANCE:UV irradiance
Krivova et al. 2006
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Krivova et al. 2006
All SATIRE reconstructions can be extended down to 115 nm
MODELS OF SOLAR IRRADIANCE:UV irradiance
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Krivova et al. 2006
MODELS OF SOLAR IRRADIANCE:UV irradiance
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MODELS OF SOLAR IRRADIANCE:
Krivova, Solanki & Floyd 2006
Solar cycle variation at 250-400 nm
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MODELS OF SOLAR IRRADIANCE:
Spectral irradiance
Krivova et al. 2006
500 nm50 nm 100 nm
≈60%
≈8%
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Krivova et al. 2006
500 nm50 nm 100 nm
≈60%
≈8%
More attention should be paid to the Sun's varying UV radiation
MODELS OF SOLAR IRRADIANCE:
Spectral irradiance
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MODELS OF SOLAR IRRADIANCE:
Cyclic componentProxies: Zurich Sunspot Number, Rz
(1700 ff.)Group Sunspot Number, Rg
(1610 ff.)Sunspot areas, As (1874 ff.)Facular areas, Af (1874 ff.)Ca II plage areas, Ap
(1915 ff.)
Foukal & Lean 1990,Hoyt & Schatten 1993,Lean et al. 1995,Solanki & Fligge 1998, 1999,Lockwood & Stamper 1999,Fligge & Solanki 2000,Foster & Lockwood 2003
Solanki & Fligge 1999
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SUN'S MAGNETIC FLUX:Secular change
Cyclic flux emergence in (large) active regions and (small) ephemeral regions
Take sunspot number (R) as a `proxy´
Extended cycle for ephemeral regions
ER start earlier
More extended, overlapping cycles
Open flux decays slowly
More extended cyclestime
active regionsephemeral regions
open flux
Solanki et al. 2002
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MODEL OF THE SUN'S MAGNETIC FLUX:
Open flux
10Be Open solar flux
Interplanetary field
Solanki et al. 2000
Lockwood et al. 1999
Beer et al. 1990
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MODEL OF THE SUN'S MAGNETIC FLUX:
Total flux
Balmaceda et al. 2006
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take reconstructed magnetic fluxes: act(t),
eph(t), open (t)
use sunspot number Rz (or sunspot area) to separate sunspot and facular contributions to act
eph +open describes the evolution of the network
use the conversion scheme from the short-term rec. (Krivova et al. 2003) to convert magnetic flux into irradiance
MODELS OF SOLAR IRRADIANCE:
Long-term total flux
ephemeral regions active regions
open flux Solanki et al. 2002
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MODEL OF SOLAR IRRADIANCE:Long-term
Balmaceda et al. 2006
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MODEL OF SOLAR IRRADIANCE:Long-term
Balmaceda et al. 2006
~1W/m2
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MODELS OF SOLAR IRRADIANCE:
SummaryContemporary models:
explain >≈90% of the observed TSI variations in cycles 23 and 22 and >≈80% of the observed variations in cycle 21;
show no bias between the 3 cycles;
do not show any significant minimum-to-minimum change;
reproduce measured variations of the solar spectral irradiance down to 115 nm;
emphasise the importance of the irradiance variations in the UV and stress the need for higher accuracy measurements between 300 and 400 nm;
point to a secular trend of about 1W/m2 (lower than previous estimates)
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MODELS OF SOLAR IRRADIANCE:... and outlook
removal of the remaining free parameter;
tests for spectral irradiance using new data from SORCE
and SCIAMACHY and improvement of models on their
basis;
reconstruction of solar UV irradiance back to 1974 and
the end of the Maunder minimum;
reconstruction of solar irradiance on longer (millenia)
time scales
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SATIRE:SATIRE:filling factorsfilling factors
Zakharov (priv. comm)
u= 0 or 1
p= 0 or 10≤f≤
1
q=1- u-p-
f
For each pixel:
I(t)=u(t)Iu()+p(t)Ip()+f(t)If()+q(t)Iq()
and sum up over all pixels