1. Modeling the Solar EUV irradiance
Margit Haberreiter
PMOD/WRC, Davos, Switzerland
IPC XI
Sept 26 – Oct 15, 2010

2. Picard

3. 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!!

4. Peculiar Minimum 23/24
Claus Froehlich, PMOD TSI composite

5. 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?
15%
decrease
Solomon et al, 2010, GRL, 37, L16103

6. SDO/AIA image

7. EUV spectrum Wavelengths Contribution from the UV: 120 – 400 nm
Chromophere
Transition region
Corona

8. 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 8

9. Masks from Precision Solar Photometric Telescope
Continuum, 607 nm (PICARD)
Disk mask on 2005/9/12 obtained from PSPT data, Mauna Loa, Hawaii
(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
Ca II 393.4, FWHM=0.27nm

10. Solar Chromosphere (Ca II) of quiet Sun
Intergranular
Cells
Model B
Quiet
Network
Model D s
Active
Network
Model F
Problem, only normalized
Shape of the contrast is a function of wavelength
Fontenla et al., 2009, ApJ

11. Faculae Plage Active network Quiet network Intergranular Cells
Fontenla et al., 2009, ApJ 707,

12. G-Band of CH molecular lines
Fontenla et al., 2009, ApJ 707,

13. Violet CN Band
Fontenla et al., 2009, ApJ 707,

14. Modeling the EUV e.g. Fe XV 284 Å

15. 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

16. 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

17. Spherical symmetry

18. 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:
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)

19. Spectrum from Corona, TR and Chromosphere

20. EUV spectrum Haberreiter, 2010, submitted to Solar Physics
EVE rocket calibration flight: Chamberlin et al., 2009, GRL

21. EUV spectrum Haberreiter, 2010, submitted to Solar Physics
EVE rocket calibration flight: Chamberlin et al., 2009, GRL

22. SOHO/EIT images Fe IX 17.1 nm He II 30.4 nm Fe XV 28.4 nm Fe XII

23. EIT passbands
Fe IX 17.1 nm
Fe XII 19.5 nm
Fe XV 28.4 nm
He II 30.4 nm

24. EIT wavelengths
SRPM
EVE

25. Variability of solar activity features
EIT 19.5 nm
10/01/2002
EIT 17.1nm
07/01/2005
EIT 30.4 nm
07/10/2006
EIT 28.4 nm
10/10/2003
coronal holes – quiet Sun – quiet coronal network –
active coronal network - hot loop – super hot loop

26. 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

27. Does the quiet Sun intensity change
Barra et al, 2009 already performed the analysis for 3 components.

28. Outlook: Shape of coronal holes influences strength of solar wind streams
Gibson et al, 2009

29. 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....

30. 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 ....

31. 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