Definitions for "Interplanetary Magnetic Field"
The solar wind carries with it the Sun's coronal magnetic field as the interplanetary magnetic field. A 'southward' pointing IMF (i.e. towards the south magnetic pole) can initiate and maintain geomagnetic activity. On average the IMF is zero, but values more than about 10 nT southward will typically drive magnetic storms and substorms, depending on the duration of sustained southward field. Back to the top.
The magnetic field of the Sun drawn out by the solar wind that fills interplanetary space. The direction of the IMF controls much of the activity in the magnetosphere. When the IMF points southward, the IMF can interconnect with Earth's own magnetic field. This allows solar wind energy and particles to enter the magnetosphere leading to magnetically disturbed conditions like geomagnetic storms.
The weak magnetic field filling interplanetary space, with field lines usually connected to the Sun. The IMF is kept out of the Earth's magnetosphere, but the interaction of the two plays a major role in the flow of energy from the solar wind to the Earth's environment.