Magnetohydrostatic equilibria, in which the Lorentz force, the plasma pressure force and the gravitational force balance out to zero, are widely adopted as the zeroth order states of many astrophysical plasma structures. A magnetic flux-current surface is a surface, in which both magnetic field lines and current lines lie. We for the first time derive the necessary and sufficient condition for existence of magnetic flux-current surfaces in magnetohydrostatic equilibria. It is also shown that the existence of flux-current surfaces is a necessary (but not sufficient) condition for the ratio of gravity-aligned components of current density and magnetic field to be constant along each field line. However, its necessary and sufficient condition is found to be very restrictive. This finding gives a significant constraint in modeling solar coronal magnetic fields as force-free fields using photospheric magnetic field observations.

ABSTRACT
1. INTRODUCTION
2. MAGNETIC FLUX-CURRENT SURFACES OF MHS EQUILIBRIA
3. CONSTANTS IN FLUX-CURRENT SURFACESAND ALONG FIELD LINES
    3.1 Constants in Magnetic Flux-current Surfaces
    3.2 Generalization and Re-examination of the Formulation by Low (1991)
    3.3 Imposition of Special Constraints
4. DISCUSSION AND SUMMARY
REFERENCES

• G. S. CHOE(School of Space Research, Kyung Hee University, Department of Astronomy and Space Science, Kyung Hee University) Corresponding Author
• MINHWAN JANG(Department of Astronomy and Space Science, Kyung Hee University, School of Space Research, Kyung Hee University)