dynamics of the magnetized wake and the acceleration of the slow solar wind ¹università di pisa f....
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Dynamics of the Magnetized Wake andthe Acceleration of the Slow solar Wind
¹Università di Pisa
F. Rappazzo¹, M. Velli², G. Einaudi¹, R. B. Dahlburg³
²Università di Firenze
³Laboratory for Computational Physics & Fluid Dynamics, NRL, Washington, DC
Acceleration of the slow solar wind above helmet streamers
The solar wind has two distinct components: the fast wind originates in the polar coronal holes, and the slow wind originates from the region above helmet streamers.
Observations of plasmoids detaching above helmet streamers by the LASCO coronagraph onboard SOHO
The formation and outward movement of a coronal density enhancement on 1996 May 24, as seen in running differenceimages obtained with the C2 (left) and C3 (right) coronagraphs.
From Sheeley N.R. Jr. et al., Astrophys. J., 484, 472, 1997
We model the region above the cusp of a helmet streamer as a current sheet embedded in a broader wake flow
In our simulations we use compressible, dissipative MHD equations
xAxB y tanh0 xhAxB z sec0
xhxu y sec10
1 21
MT
Equilibrium fields
1sc
uM5.1
u
cA A5
B
V
a
a
Both Kelvin-Helmoltz and tearinginstabilities have varicose modes, that have the same spatial parity.
Expanding Box Model
Melon seed force
Time evolution of magnetic islands
Density enhancement of magnetic islands
Fast wind
Fast wind
Neutral line
Mass density lowers because of radial expansion.
The melon seed force results in the initial rapid acceleration,while fluid instability shapes the global acceleration.
• Resistive instability allows the development of a
Kelvin-Helmoltz instability in the nonlinear regime.
Conclusions
• Moving plasmoids accelerating outward are observed.
• The fast wind accelerates and modulates the slow wind.