SOLAR IRRADIANCE VARIABILITY OF RELEVANCE

FOR CLIMATE STUDIES

N.A. Krivova

CGD, NCAR

SUN - CLIMATE

CGD, NCAR

SOLAR TOTAL IRRADIANCE:WHAT IS KNOWN?

PMOD TSI

0.1%

CGD, NCAR

BUT... (1)

CGD, NCAR

Long-term time series needed!!!

BUT... (1)

BUT... (2)

3 different composites!!!

CGD, NCAR

BUT... (3)Different trends in Mg II and TSI composites since 1999!!!

Froehlich, priv. comm.

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

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%

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

BUT... SCIAMACHY: March-May 2004

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)

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)

1996 2000

FACULAE AGAINST SUNSPOTS

Data: MDI

1996 2000

FACULAE AGAINST SUNSPOTS

~-0.8Wm-2

1996 2000

FACULAE AGAINST SUNSPOTS

~-0.8Wm-2

~1.7Wm-2

Wenzler 2005

1996 2000

FACULAE AGAINST SUNSPOTS

~-0.8Wm-2

~1.7Wm-2

Wenzler 2005

0.1%

Fröhlich 2004

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

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

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)

SATIRE: cycle 23 (MDI-based)

Krivova et al. 2003

Data: VIRGO TSI

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

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

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

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)

Krivova et al. 2003

MODELS OF SOLAR IRRADIANCE:

Spectral irradiance

Data: VIRGO channels (862, 500 & 402 nm)

Data: SUSIM

SATIRE

MODELS OF SOLAR IRRADIANCE:

Spectral irradiance

Krivova & Solanki 2004

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

MODELS OF SOLAR IRRADIANCE:UV irradiance

Krivova et al. 2006

Krivova et al. 2006

All SATIRE reconstructions can be extended down to 115 nm

MODELS OF SOLAR IRRADIANCE:UV irradiance

Krivova et al. 2006

MODELS OF SOLAR IRRADIANCE:UV irradiance

MODELS OF SOLAR IRRADIANCE:

Krivova, Solanki & Floyd 2006

Solar cycle variation at 250-400 nm

MODELS OF SOLAR IRRADIANCE:

Spectral irradiance

Krivova et al. 2006

500 nm50 nm 100 nm

≈60%

≈8%

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

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

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

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

MODEL OF THE SUN'S MAGNETIC FLUX:

Total flux

Balmaceda et al. 2006

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

MODEL OF SOLAR IRRADIANCE:Long-term

Balmaceda et al. 2006

MODEL OF SOLAR IRRADIANCE:Long-term

Balmaceda et al. 2006

~1W/m2

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)

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

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