Volume 486, Number 2, August I 2008
|Page(s)||569 - 575|
|Published online||06 May 2008|
Chromospheric magnetic reconnection: two-fluid simulations of coalescing current loops
Institute for Materials Research, University of Salford, Greater Manchester, M5 4WT, UK e-mail: p.d.Smith@pgr.salford.ac.uk
2 Laboratory for Plasma Astrophysics, Faculty of Engineering, University of Toyama, 3190, Gofuku, Toyama, 930-8555, Japan
Accepted: 16 April 2008
Aims. We investigate magnetic reconnection rates during the coalescence of two current loops in the solar chromosphere, by altering the neutral-hydrogen to proton density ratio, ionisation/recombination coefficients, collision frequency, and relative helicity of the loops.
Methods. We used a newly developed two-fluid (ion-neutral) numerical code to perform 2.5D simulations of coalescing chromospheric current loops. Developed from the Artificial Wind scheme, the numerical code includes the effects of ion-neutral collisions, ionisation/recombination, thermal/resistive diffusivity, and collisional/resistive heating.
Results. It was found that the rates of magnetic reconnection strongly depend on the neutral-hydrogen to proton density ratio: increasing the density ratio a thousandfold decreased the rate of magnetic reconnection twentyfold. This result implies that magnetic reconnection proceeds significantly faster in the upper chromosphere, where the density of ions (protons) and neutral-hydrogen is comparable, than in the lower chromosphere, where the density of neutral-hydrogen is over a thousand times the ion density. This result also implies that jets associated with fast magnetic reconnection tends to occur in the upper chromosphere / lower corona. The inclusion of ionisation/recombination, an important physical effect in the chromosphere, increases the total reconnected magnetic flux, but does not alter the rate of magnetic reconnection. Reductions in the ion-neutral collision frequency result in small increases to the rates of magnetic reconnection. The relative helicity of the two current loops was not observed to have any significant effect on the rates of magnetic reconnection. Comparisons of two-fluid and MHD (Magnetohydrodynamic) simulations show significant differences in the measured rates of magnetic reconnection, particularly for the higher neutral density cases which represent the lower chromosphere. This demonstrates that MHD is not an appropriate model for simulating magnetic reconnection in the solar chromosphere.
Conclusions. The magnetic reconnection rates of coalescing current loops are strongly affected by the inclusion of neutral-hydrogen particles. It is therefore essential that ion-neutral collisions are included in future analytical/numerical models of chromospheric magnetic reconnection.
Key words: plasmas / methods: numerical / Sun: magnetic fields / Sun: chromosphere / Sun: photosphere
© ESO, 2008
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.