1. VI. Forecasting Solar EUV/UV Radiation – EUV spectral synthesis
Margit Haberreiter
Juan Fontenla
LASP, University of Colorado
Boulder, USA

2. Motivation
EUV/UV influences the neutral density in the thermosphere/ionosphere
Influence on satallite drag
Aim: forecast the EUV radiation based on physical principles over a solar rotation
Focus: physics-based EUV spectral synthesis

3. EUV spectrum Contribution from Input to our model: chromophere
transition region
corona
Input to our model:
temperature and density structures of each of these regimes for various regions on the solar disk

4. Atmosphere structures – chromosphere
Upper chromosphere
Lower chromosphere
Quiet Sun
Quiet Netw.
Active Netw.
Plage
Faculae
Semi-empirical NLTE structures reproduce radiance observations at 1-2‘‘(Fontenla et al 2008, in prep.) The models describes the distribution of heated areas on solar disk

5. Coronal models

6. SRPM Multi level atoms Chromosphere and transition region: Corona
373 ions, from neutral H to Ni with ioncharge 25
~14’000 atomic levels
~170’000 spectral lines
Chromosphere and transition region:
for ioncharge up to 2:
full NLTE (Fontenla et al., 1999; 2006; 2007)
plus optically thin transition region lines
Corona
ioncharge >2: optically thin, i.e. collisions and spontaneous emission

7. Extension of Corona

8. Spherical Symmetry
Spherical symmetrie: Calculation of intensities at and beyond the limb
In total:
2 x area of solar disk
Plane parallel:
Only disk rays
are calculated

9. Fe IX 17.1 nm - disk integrated Plane parallel vs. spherical

10. EVE rocket flight
Calibration flight on April 10, 2008 at “Solar minimum“ conditions (EVE rocket team at LASP: Tom Woods, Frank Evapier, Phil Chamberlin, Rahel Hock, a.o., Chamberlin et al., in preparation)

11. EUV irradiance spectra

12. EUV irradiance spectra
0.75 Quiet Sun (B) (Quiet Network) Active Network (F)
Lyman continuum matches well with EVE rocket spectrum from April 10, 2008

13. EUV irradiance spectra at instrument resolution

14. Shorter than 50 nm coronal/upper TR lines form a pseudo continuum

15. EUV Irradiance QS nm

16. EUV radiance spectra of quiet Sun
0.75 Quiet Sun (B) (Quiet Network) Active Network (F)
Good agreement with average QS (SUMER Atlas, Curdt et al.)

17. Masks of active regions
Solar minimum: April 10, 2008
Solar maximum: September 22, 2001

18. EUV spectrum Active Sun

19. Conclusions The vast number of spectral lines have to be included
Due to the extension of the corona spherical symmetry is essential for coronal lines
SRPM EUV spectra agree well with EVE rocket irradiance spectrum and SUMER radiance spectra

20. Future plans Validation against more EUV observations
include coronal holes and active region loops in the calculation of the spectrum
Produce daily EUV/UV spectra
changing distribution of coronal features, e.g. coronal holes, active region loops
Apply the forcasting scheme as shown before