Interplanetary Magnetic Field Strength Falloff: A Flux-Conserving Bound Against Parker Solar Probe Values

How the total magnetic field strength falls with distance from the Sun is fixed, in the simplest picture, by two different power laws acting on its two components. This study computes that falloff with the radial component anchored at 3.0 nanotesla at 1 AU and declining as the inverse square, and the azimuthal component following the Parker spiral at 400 kilometres per second. The total strength is 4.40 nanotesla at 1 AU, 49.7 nanotesla at 0.25 AU and 0.65 nanotesla at 5 AU. At the Parker Solar Probe perihelion distance of 0.095 AU the flux-conserving value reaches 334.1 nanotesla, well above the roughly 100 nanotesla scale of typical perihelion fields reported from the encounters, so the pure inverse-square law acts as an upper bound rather than a description in the innermost region: the discrepancy is stated plainly as a negative result for the unmodified law, and it quantifies the super-radial expansion or flux redistribution the real corona must supply. The study is simulated and computed, not measured.