Modeling the Solar EUV irradiance

Margit Haberreiter

PMOD/WRC, Davos, Switzerland

IPC XI

Sept 26 – Oct 15, 2010

Picard

Absorption of EUV in the Earth‘s atmosphere

Altitude-wavelength dependence of energy deposition from solar irradiance

units of Log10(Wm-4)

From Solomon and Qian 2005

Solar minimum conditions

EUV varies by a factor of 2 and more!!

Peculiar Minimum 23/24

Claus Froehlich, PMOD TSI composite

Is there an EUV long-term trend?

The SOHO/SEM measurements (36-34 nm)indicate a decrease in the EUV by15%

Uncertainty ~ 6%

Not explained by F10.7 or sunspot number

What is the role of coronal holes?

Solomon et al, 2010, GRL, 37, L16103 15%decrease

SDO/AIA image

EUV spectrum

• Wavelengths –UV: 120 – 400 nm

–EUV: 10 – 120 nm

• Contribution from the – Chromophere

– Transition region

– Corona

Solar Modeling (SolMod)

• Multi level atoms– 373 ions, from H to Ni with ioncharge 25– ~14’000 atomic levels– ~170’000 spectral lines – Statistical equation is solved to get the level populations

• Chromosphere and transition region – for ioncharge 2: – full NLTE (Fontenla et al., 2006; 2007; 2009)

– plus optically thin transition region lines– Spherical symmetry

• Corona– ioncharge >2 – optically thin, i.e. collisions and spontaneous emission– Line of sight integration accounts for opacity– Spherical symmetry

Masks from Precision Solar Photometric Telescope

Disk mask on 2005/9/12 obtained from PSPT data, Mauna Loa, Hawaiihttp://lasp.colorado.edu/pspt_access/

(R) Sunspot Penumbra(S) Sunspot Umbra(P) Faculae(H) Plage(F) Active network(D) Quiet network (white)

(B) Intergranular Cells

Determined by the contrast as a function of the position on the disk-Only possible with respect to a -normalized quiet Sun intensity

Continuum, 607 nm (PICARD)

Ca II 393.4, FWHM=0.27nm

Solar Chromosphere (Ca II) of quiet Sun

IntergranularCellsModel B

Quiet NetworkModel D

Fontenla et al., 2009, ApJ

ss

ActiveNetworkModel F

0.1 1 10 100 1 103

1 104

1 105

4000

6000

8000

B 1001D 1002F 1003H 1004P 1005

B 1001D 1002F 1003H 1004P 1005

Pressure (dyn cm^-2)

Tem

pera

ture

(K

)

FaculaePlageActive networkQuiet networkIntergranular Cells

Fontenla et al., 2009, ApJ 707, 482-502

G-Band of CH molecular lines

Fontenla et al., 2009, ApJ 707, 482-502

Violet CN Band

Fontenla et al., 2009, ApJ 707, 482-502

Modeling the EUVe.g. Fe XV 284 Å

Coronal models

• Coronal Models are based on temperature and densities given by

• Doschek (1997), ApJ, 476, 903

• Singh et al., 1982, J. Astrophys. 3, 249

• Cranmer et al, 2007, ApJS 171, 520

Spherical Symmetry

Allows the calculation of intensities at and beyond the limb

(e.g. Haberreiter et al. 2008)

Account for corona over 2 x area of solar disk

Adopted from Mihalas, 1978

Spherical symmetry

28.4 28.41 28.42

5 103

0.01

sphericalplane-parallel

Wavelength (nm)

Irra

dian

ce (

W m

-2 n

m-1

)

Optical depth• Fe XV 17.1 nm:

– Disk center: max = 0.06

– Limb: (r=1.02): max = 0.63 (~900,000K)

• Fe XV 19.5 nm:

– Disk center: max = 0.06

– Limb: (r=1.02): max = 0.34 (~1,100,000K)

• Fe XV 28.4 nm:

– Disk center: max = 0.39

– Limb: (r=1.02): max = 0.88 (~2,000,000K)

Spectrum from Corona, TR and Chromosphere

50 1001 10

7

1 106

1 105

1 104

1 103

0.01

0.1

1

SPRM 1SPRM 2SPRM 3SPRM 4SPRM 5

Wavelength (nm)

Irra

dian

ce (

erg

cm-2

s-1

nm

-1)

EUV spectrum

Haberreiter, 2010, submitted to Solar PhysicsEVE rocket calibration flight: Chamberlin et al., 2009, GRL

EUV spectrum

Haberreiter, 2010, submitted to Solar PhysicsEVE rocket calibration flight: Chamberlin et al., 2009, GRL

SOHO/EIT images

284 Angstroms171 Angstroms

195 Angstroms 304 Angstroms

Fe XII 1.3x105 K He II 8x104 K

He II 30.4 nm

Fe XV 28.4 nm

Fe IX 17.1 nm

Fe XII 19.5 nm

EIT passbands

Fe IX 17.1 nm

Fe XII 19.5 nm

Fe XV 28.4 nm

He II 30.4 nm

EIT wavelengthsSRPMEVE

Variability of solar activity features

EIT 17.1nm07/01/2005

EIT 19.5 nm10/01/2002

EIT 28.4 nm10/10/2003

EIT 30.4 nm07/10/2006

coronal holes – quiet Sun – quiet coronal network – active coronal network - hot loop – super hot loop

EIT image analysis

• Radial dependence for outer corona

• Thresholds based on intenstiy histogram of the EIT images

• Maximum value of histogram varies with solar cycle (in particular for 284 Ǻ)

• Does the coronal hole/quiet Sun intensity changes with solar cycle→ identification of coroanl features not trivial

Does the quiet Sun intensity change

Barra et al, 2009 already performed the analysis for 3 components.

Outlook: Shape of coronal holes influences strength of solar wind streams

Gibson et al, 2009

Conclusions• Good agreement between the synthetic spectra

and the observed EVE quiet Sun spectrum

• Our calculations indicate that opacity effects have to be taken into account for some prominent lines, i.e. the EIT lines

• Challenge for feature identification: potential change of coronal hole and quiet Sun intensity

• Spectral reconstruction over a full solar cycle still to come....

Further plans• Valicate the identification scheme of coronal

holes, active regions

• Account for temporal variability

– changing distribution of features, e.g. coronal holes, active regions

• LYRA measurements very important for validation/comparison

• 1 TB/day from SDO/AIA and SDO/EVE ....

References

• Cranmer et al, 2007, Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence, ApJS 171, 520

• Doschek (1997), Emission Mesaures and Electron Densities for the solar transition region, ApJ, 476, 903.

• Fontenla et al., 2009, Semi-empirical Models of the Solar AtmosphereIII. Set of NLTE Models for FUV/EUV Irradiance Computation, ApJ, accepted for publication

• Klimchuk (2006), On Solving the Coronal Heating Problem, Solar Physics 234, 41-77

• Singh et al., 1982, Eclipse Observations of Coronal Emission Lines, J. Astrophys. 3, 249