Nour-Eddine Raouafi

Magnetic and Velocity Fieldsin the Solar Corona

Outline Polar Holes: Latest Results SUMER: The Polarimeter Conclusions

LOS

Open superradial expanding field lines

Source of the fast solar wind

Area of interest : polar coronal holes

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

UVCS Results

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

Interpretation of UVCS observations

10010

||T

T

Atmospheric parameters: electron density

SRrTk

SRSGpm

SRNrN

11

av

2

Be )(e )(e

1997) al.et Lamy &

1999 al.et Kohl 1999; al.et (Doyle DKL

Guhathakurta & Holzer (1994);Guhathakurta et al. (1999);

Cranmer et al. (1999) & Esser et al. (1999) :

power series

DKL

O VI : Total Intensities

The observed intensities are reasonably reproduced by most of the density models(DKL, GH94, Cra99)

Guh99 & Ess99 give relatively low intensities at low altitudes

(Raouafi & Solanki, 2004b)

O VI : Widths & Intensity Ratios The LOS-integrated profiles are very sensitive to the density stratification details

DKL density stratification gives line widths comparable to the observed ones

The calculated intensity ratios are relatively close tothe observed ones(except for Guh99 & Ess99)

(Raouafi & Solanki, 2004a,b)

N.-E. RaouafiP. LEMAIRE

S. Sahal-Brechot

The SOlar & Heliospheric Observatory

(SOHO) mission

The Solar Ultraviolet Measurementsof Emitted Radiation

Three-axis stabilized

Capacity of rolling around z-axis

Objectives ...; Coronal heating & Sources & acceleration of the solar wind(CDS, UVCS, EIT, LASCO & SUMER)

SUMER’s Optical Design

Capability of rastering

Sensitivity to the polarization

Observations Date: SoHO roll of March 19, 1996

Target: An area in the polarcoronal hole at ~1.3 R

Goal:Observe this areaangles with respectto the polar axis

Wavelength range: 1022 – 1042 Å

H I Ly- 1025 ÅO VI 1031.92 Å & 1037.61 Å

Results

Variation of the intensityratio of the O VI doublet

with the angle of observation

Signature of thepolarization of theO VI 1031.92 Å

Results

p = 9 ± 2 %

= 9 ± 6°

r = 2.88 ± 0.05

(Raouafi et al. 2002a)

First determination of the

polarization parameters

of a UV line in the corona

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. 2002a,b)

Interpretation of the observations

ConclusionSUMERSUMER showed us the way to infer thecoronal magnetic field & the solar windvelocity vectors through the Hanle effect

and the Doppler redistribution.