Dynamics of the Magnetized Wake and the 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 difference images 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

Equilibrium fields

Both Kelvin-Helmoltz and tearing instabilities 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 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.