Magnetic and Velocity Fields in the Solar Corona

Magnetic and Velocity Fields in the Solar Corona Nour-Eddine Raouafi Outline ü Polar Holes: Latest Results ü SUMER: The Polarimeter ü Conclusions

Area of interest : polar coronal holes LOS FOpen superradial expanding field lines FSource of the fast solar wind

UVCS Results Very broad line profiles emitted by heavy ions (O VI, Mg X) in the polar coronal holes

Interpretation of UVCS observations Wave-particle energy exchange at cyclotron frequencies of the solar wind species High anisotropies in the velocity distributions of the scattering atoms Impact on the mechanisms of acceleration & heating of the coronal plasma

Atmospheric parameters: electron density DKL Guhathakurta & Holzer (1994); Guhathakurta et al. (1999); Cranmer et al. (1999) & Esser et al. (1999) : power series

O VI : Total Intensities The observed intensities are reasonably reproduced by most of the density models (DKL, GH 94, Cra 99) Guh 99 & Ess 99 give relatively low intensities at low altitudes (Raouafi & Solanki, 2004 b)

O VI : Widths & Intensity Ratios Ø The LOS-integrated profiles are very sensitive to the density stratification details ØDKL density stratification gives line widths comparable to the observed ones ØThe calculated intensity ratios are relatively close to the observed ones (except for Guh 99 & Ess 99) (Raouafi & Solanki, 2004 a, b)

N. -E. Raouafi P. LEMAIRE S. Sahal-Brechot

The SOlar & Heliospheric Observatory (SOHO) mission Three-axis stabilized Capacity of rolling around z-axis Objectives. . . ; Coronal heating & Sources & acceleration of the solar wind (CDS, UVCS, EIT, LASCO & SUMER) The Solar Ultraviolet Measurements of Emitted Radiation

SUMER’s Optical Design Sensitivity to the polarization Capability of rastering

Observations Ø Date: So. HO roll of March 19, 1996 Ø Target: An area in the polar coronal hole at ~1. 3 R Ø Goal: Observe this area angles with respect to the polar axis

Wavelength range: 1022 – 1042 Å H I Ly-b 1025 Å O VI 1031. 92 Å & 1037. 61 Å

Results Variation of the intensity ratio of the O VI doublet with the angle of observation Signature of the polarization of the O VI 1031. 92 Å

Results First determination of the polarization parameters of a UV line in the corona p=9± 2% = 9 ± 6° r = 2. 88 ± 0. 05 (Raouafi et al. 2002 a)

Interpretation of the observations Polarization measurements & Quantum theory of matter-radiation interaction (Raouafi 2002) Constraints on the Coronal magnetic field: Hanle effect (< 3 Gauss) Solar wind velocity vector: Doppler redistribution (40 – 70 km s-1) (Raouafi et al. 2002 a, b)

Conclusion SUMER showed us the way to infer the coronal magnetic field & the solar wind velocity vectors through the Hanle effect and the Doppler redistribution.