The effect of an interplanetary magnetic field on the solar wind

A weak interplanetary magnetic field is shown to be compressed into a boundary layer of high magnetic-field intensity several earth radii deep at the surface of the magnetosphere. Thus, if the solar wind consisted of streams of plasma interspersed with an interplanetary magnetic field, magnetic intensity beyond the magnetopause would be expected to fluctuate for several earth radii from zero to as high as the value at the boundary of the magnetosphere. The compressed field is tangential to the boundary and, in general, unrelated in direction to the field inside the boundary. Both conclusions are in agreement with satellite measurements. Particles in the solar wind travel smoothly around to the dark side of the earth where their pressure and the compressed interplanetary magnetic pressure may be expected to close the hollow the geomagnetic field creates in the solar wind.