multifluid models of the solar wind leon ofman catholic university of america nasa gsfc, code 612.1,...
TRANSCRIPT
Multifluid models of the solar wind
Leon OfmanCatholic University of America
NASA GSFC, Code 612.1, Greenbelt, MD 20771, USA
UVCS Observations of a coronal streamer
(Strachan et al 2002)
Nonthermal motions in coronal holes (SOHO/SUMER)
(Banerjee et al 1998)
Nonthermal broadening of Si VIIIContext image
WKB Alfvén wave amplitude:V~-1/4
Three-fluid model vs. UVCS observations
pO5+
r=5Rs
r=1.8Rs
Co-latitude (deg)
r=2.33Rs
180 90135
V (
km/s
)
3f model (Ofman 2000) UVCS (Strachan et al 2002)
Slow Solar WindUVCS observations vs. 3-fluid model (Ofman 2000)
UVCS Observations
O VI
Ly
Oxygen (O VI)
Protons (Ly )
Three-fluid model equations
where Zk is the charge number; Ak is the atomic mass number of species k.
Normalized three fluid equations for V<<c, with gravity, resistivity, viscosity, and Coulomb friction, neglecting electron inertia, assuming quasi-neutrality:
k=5/3
Formation of a streamer: 3-fluid polytropic (=1.05) model with He++
R R
Formation of a streamer: 3-fluid polytropic (=1.05) model with He++
1
R [Rs]
6
R [Rs]
1
6
J2 Te
Magnetic field and flow
O5+ vs He++
O5+ He++
Heat conductive three-fluid model (e, p, He++)
“Active region” streamer model
Alfvén wave source
Alfvén wave driver is modeled by
Where ai=i-1/2, i is the ith mode, and i() is the ith random phase. The parameters are Vd=0.034 or 0.05, 1=1, N=100, N=100, <<p
Power spectrum:-1
Heating terms
• Electron heating by current dissipation:
• Proton heating by viscous dissipation:
• Empirical heating term for ions:
• Heat Conduction is included for protons and electrons along the magnetic field.
2j
Se
22
21
2
0 3
4)(
pppr
pr
p
VV
rr
V
r
VrS
krkk erSS /,0 )1(
use =10-4
use =10-4, 0~0.
Classical heat conduction is used up to 2Rs with smooth cutoff to zero for r> 2Rs
BB
BTTH kc
22/5
Alfvén wave driven fast solar wind with He++
(Ofman 2004)
Alfvén wave driven fast solar wind: 2.5D 3-fluid model: e-p-He++
R [S
olar
rad
ii]
Vp Vpr Te
1
20
1.2 1.95 1.2 1.2 1.951.95
Evolution of magnetic field Alfvénic fluctuations
|F()|2
Power spectrum at 18Rs
-2
-5/3
-Averaged radial outflow speed:3-fluid model(Ofman 2004)
p
He++O5+
p
p
p
He++
He++
H0p=0.5H0i=12Vd=0.034
H0p=0H0i=12Vd=0.05
H0p=0.5H0i=0.5Vd=0.034
H0p=0.5H0i=10Vd=0.034
Linearized multifluid equations and dispersion relation
Momentum:
Inductance:
Quasineutrality:
Dispersion Relation:
Four-fluid dispersion relation
Velocity amplitude ratios |Vi/Vp|using three fluid dispersion
He++ O6+
(Ofman, Davila, Nakariakov, and Viñas 2005, in press)
Vlasov dispersion relation for finite plasma
(Ofman, Davila, Nakariakov, and Viñas 2005, in press)
Dispersion relation from three-ion (p, He++,O6+) hybrid simulations
BVp
VHe++ VO6+
(Ofman, Davila, Nakariakov, and Viñas 2005, in press)
Velocity amplitude ratios from hybrid simulation dispersion
(Ofman, Davila, Nakariakov, and Viñas 2005, in press)
VHe++/Vp
VO6+/Vp
kCA/p~0
kCA/p=0.6
Conclusions
• Recent observations of minor ion emission lines in coronal holes provide clues for the acceleration and heating mechanism of the fast wind, and require multi-fluid and kinetic modeling in order to interpret the results.
• The slow solar wind has been modeled with 2D three-fluid code, and the basic features of streamers and acceleration profiles are recovered for protons and heavy ions.
• Wave driven wind in coronal holes was modeled with the three-fluid code in a self-consistent model, and the different proton and heavy ions flow profiles are reproduced.
• High frequency waves (in the ion-cyclotron frequency range) produce different perpendicular velocities for protons and heavy ion in the multifluid model, as well is in the hybrid simulations.