Blob formation and acceleration in the solar wind: role of converging flows and viscosity

TL;DR

This study uses resistive MHD simulations to explore how viscosity and converging flows influence blob formation and acceleration in the slow solar wind, revealing new mechanisms of momentum transfer and the impact of magnetic structures.

Contribution

It introduces a novel mechanism for enhanced momentum transfer via electric fields caused by tearing instability and highlights the role of magnetic cusps in flow convergence and blob acceleration.

Findings

Electric fields extend into the fast solar wind, increasing momentum transfer.

Magnetic cusps cause flow convergence, enhancing blob acceleration.

Viscosity and magnetic topology significantly influence blob dynamics.

Abstract

The effect of viscosity and of converging flows on the formation of blobs in the slow solar wind is analysed by means of resistive MHD simulations. The regions above coronal streamers where blobs are formed (Sheeley et al., 1997) are simulated using a model previously proposed by Einaudi et al. (1999). The result of our investigation is twofold. First, we demonstrate a new mechanism for enhanced momentum transfer between a forming blob and the fast solar wind surrounding it. The effect is caused by the longer range of the electric field caused by the tearing instability forming the blob. The electric field reaches into the fast solar wind and interacts with it, causing a viscous drag that is global in nature rather than local across fluid layers as it is the case in normal uncharged fluids (like water). Second, the presence of a magnetic cusp at the tip of a coronal helmet streamer causes a converging of the flows on the two sides of the streamer and a direct push of the forming island by the fast solar wind, resulting in a more efficient momentum exchange.