Stabilization of an injected conducting layer for artificially enhancing drag on orbital debris

The evolution of a magnetized conducting medium suspended in magnetic and gravitational fields is examined. In this paper some effects of the influence of velocity fields on the linear stability properties of such layers are investigated. A fully compressible, three-dimensional analysis of the layer is described. The relevant equations are derived and then solved by the MagnetoHydroDynamic SPEctral Compressible Linear Stability (MHDSPECLS) algorithm, a Chebyshev collocation code. The code allows for the computation of magnetic and thermal effects. A complete stabilization of the system is found above a critical velocity of approximately 2500 m/s.     

Compressible Aspects of Slow Solar Wind Formation

Recently we have shown how the slow solar wind can be formed within a coronal helmet streamer. The solar wind is modeled by a "wake-neutral" sheet, whose subsequent linear and nonlinear evolution provides clues to the development of the wind. In this paper we describe the first results of our extension of this model to the compressible regime. In particular, we show that traveling density enhancements are formed, similar to those observed by LASCO. The compressible equations are solved by an extension to MHD of the SPECLS algorithm. This revised version was published online in June 2006 with corrections to the Cover Date.     

Magnetic fluxtube reconnection

We present the results of 3D numerical simulations of initially discrete magnetic fluxtubes interacting via magnetic reconnection. The initial topology consists of two orthogonal fluxtubes. Each fluxtube has a uniform twist, force-free magnetic field specified by the Gold-Hoyle model. The fluxtubes are then forced together by an initial flow configuration consisting of two superimposed stagnation point flows. We observe three distinct types of interaction, which depend on the twist and on the Lundquist numbers, between the fluxtubes. For low twist the fluxtubes experience an elastic collision. For a higher twist complete reconnection is observed. If the Lundquist numbers are raised fluxtube tunneling occurs.     

Turbulent transition in solar surges

It has been suggested that a surge can be modelled as a jet travelling in a sheared magnetic field, and that the transition to turbulence of this MHD tearing jet can explain several key observed features. In this paper we present our preliminary results of the transition to turbulencevia secondary instabilities of the MHD tearing jet. Our results confirm that turbulent transition can decelerate the surge, with decay times which compare well with surge data. Furthermore, we find that the turbulent MHD tearing jet forms magnetic field-aligned velocity filaments similar to those often observed in the surge flow field.     

Reconnection in adjoining coronal helmet streamers

Complex magnetic and plasma structures observed in the coronal streamer belt (Crooker et al., 1993; Woo 1994) might arise from the instabilities and evolution of multiple current sheets formed by adjoining coronal helmet streamers. Previously we examined the static triple current sheet (TCS), and found that three linearly unstable modes exist, two of which are potentially observable by the LASCO instrument onboard SOHO (Dahlburg and Karpen 1995). Here we investigate the variations created in this model by the inclusion of wake flows, which have been observed in coronal streamers (see Figure 1). Our principal finding is that the structure of the modes is changed significantly by the Alfvénic and sub-Alfvénic wake flow, while their growth rates are not.