Volumetric and surface current densities in the global heliosphere: implications for magnetic energy storage and release

ABSTRACT Electric currents and magnetic energy storage are fundamental to plasma dynamics, magnetic reconnection, and particle acceleration in the heliosphere. However, their global distribution and quantitative budget remain poorly constrained. We present a systematic analysis of large-scale electric current density and magnetic energy storage throughout the global heliosphere. We employ a three-dimensional magnetohydrodynamic model to calculate volumetric current densities in the supersonic solar wind, heliosheath, and outer shock layer, and surface current densities at the heliospheric current sheet, termination shock, heliopause, and bow shock. We use potential field analysis to separate magnetic energy into potential and free components, quantifying the current-associated magnetic energy in each region and its deviation from a potential configuration. Surface current densities at major discontinuities (termination shock and heliopause) reach strengths comparable to the compressed heliospheric current sheet, with the heliopause current exhibiting a threefold variation with solar magnetic polarity. The heliosheath emerges as the dominant magnetic energy reservoir: magnetic energy constitutes 10–19 per cent of total energy, with approximately 80 per cent in free (non-potential) form. In contrast, the supersonic wind remains kinetically dominated (>93 per cent kinetic energy and <0.5 per cent magnetic), and despite nearly all magnetic energy being in free form ($\sim 90$ per cent), the total magnetic energy budget is insufficient for significant energy conversion processes. The outer shock layer, though magnetically significant (34 per cent magnetic energy), maintains a predominantly potential field configuration with only $\sim$6 per cent free energy. These results establish the quantitative energy budget available for interpreting Voyager observations and assessing the energetic conditions relevant to particle acceleration mechanisms throughout the outer heliosphere.