Energy amplification of a weak magnetic field initially perpendicular (solid contours, and ﹩\,{\mathrm{log}}_{10}{({B}_{\perp }/{\tilde{B}}_{\perp })}^{2}﹩ cube-helix (Green 2011) colormap) or parallel (dashed contours) to the subsonic ﹩\gamma =5/3﹩ flow at a normalized distance ﹩\delta =(r-1)﹩ in front of a sphere of Mach number ﹩\tilde{M}﹩. Close to the sphere, the field is predominantly perpendicular, and approximately given (dotted–dashed contours) by Equation (23).