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): , 10-20% uncertainty in the UV SOLSTICE & SUSIM on UARS: , daily, nm with ~1 nm resolution

BUT... SME (Solar Mesosphere Explore): SME (Solar Mesosphere Explore): , 10-20% uncertainty in the UV SOLSTICE & SUSIM on UARS: SOLSTICE & SUSIM on UARS: , daily, nm with ~1 nm resolution nm nm SOLSTICE SUSIM difference 1  =2-3%

SOLAR SPECTRAL IRRADIANCE: WHAT IS KNOWN? SME (Solar Mesosphere Explorer): , 10-20% uncertainty in the UV SOLSTICE & SUSIM on UARS: , daily, nm with ~1 nm resolution SORCE and SCIAMACHY: since 2003, broad range from UV to IR SORCE: 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:  S tot (t)=  S s (t)+  S f (t)

MODELS OF SOLAR IRRADIANCE Changes in surface structure: darkening due to sunspots and brightening due to faculae and the network:  S tot (t)=  S s (t)+  S f (t)

FACULAE AGAINST SUNSPOTS Data: MDI

FACULAE AGAINST SUNSPOTS ~-0.8Wm -2

FACULAE AGAINST SUNSPOTS ~-0.8Wm -2 ~1.7Wm -2 Wenzler 2005

FACULAE AGAINST SUNSPOTS ~-0.8Wm -2 ~1.7Wm -2 Wenzler % Fröhlich 2004

MODELS OF SOLAR IRRADIANCE Changes in surface structure:  Regressions of sets of proxies: S tot (t)=S q +  s S s (t)+  f S f (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: S tot (t)=  q (t)S q +  s (t)S s +  f (t)S f 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 Sun sunspots faculae

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 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 I q (  ) - 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 Data: VIRGO TSI

SATIRE: cycles (KP-based) Ground-based: variable seeing 2 different instruments: cross-calibration NASA/NSO 512-channel Diode Array Magnetograph (Feb Apr. 1992); NASA/NSO spectromagnetograph (Nov Sep. 2003) Poorer quality of earlier data: identification of umbrae/ penumbrae

Wenzler et al Data: PMOD TSI composite SATIRE: cycles (KP-based) The dominant part of the solar irradiance variations are due to the surface magnetic field R c =0.91 Reconstruction of TSI back to 1974

SATIRE: cycles (KP-based) Wenzler et al Data: PMOD, ACRIM and IRMB TSI composites R c =0.84 R c =0.91 R c =0.87 PMOD ACRIM IRMB

SATIRE: cycles (KP-based) Wenzler et al Data: PMOD, ACRIM and IRMB TSI composites R c =0.84 R c =0.91 R c =0.87 PMOD ACRIM IRMB No minimum-to-minimum trend is seen (similarly to PMOD composite)

Krivova et al 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

SATIRE SUSIM MODELS OF SOLAR IRRADIANCE: UV irradiance Krivova et al SATIRE SUSIM Regressions F(  )/F( ) vs. F( ) for every SUSIM: daily, R c =0.97

MODELS OF SOLAR IRRADIANCE: UV irradiance Krivova et al. 2006

All SATIRE reconstructions can be extended down to 115 nm MODELS OF SOLAR IRRADIANCE: UV irradiance

Krivova et al MODELS OF SOLAR IRRADIANCE: UV irradiance

MODELS OF SOLAR IRRADIANCE: Krivova, Solanki & Floyd 2006 Solar cycle variation at nm

MODELS OF SOLAR IRRADIANCE: Spectral irradiance Krivova et al nm 50 nm 100 nm ≈60% ≈8%

Krivova et al nm 50 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 component Proxies: Zurich Sunspot Number, R z (1700 ff.) Group Sunspot Number, R g (1610 ff.) Sunspot areas, A s (1874 ff.) Facular areas, A f (1874 ff.) Ca II plage areas, A p (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 S olanki & 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 cycles time active regionsephemeral regions open flux Solanki et al. 2002

MODEL OF THE SUN'S MAGNETIC FLUX: Open flux 10 Be Open solar flux Interplanetary field Solanki et al Lockwood et al 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 R z (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 ~1W/m 2

MODELS OF SOLAR IRRADIANCE: Summary Contemporary 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/m 2 (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: filling factors Zakharov (priv. comm)  u = 0 or 1  p = 0 or 1 0≤  f ≤1   q =1-  u -  p -  f For each pixel: I(  t)=  u (t)I u (  )+  p (t)I p (  )+  f (t)I f (  )+  q (t)I q (  ) and sum up over all pixels