The Interplanetary Magnetic Field (IMF)

• At high latitudes, Ulysses measured the IMF to have a nearly uniform polarity set by its coronal source region.

• But near the ecliptic it repeatedly switched sign as the spacecraft crossed a warped, spiral current sheet surface.

• The generally low-speed ecliptic-plane wind also shows abrupt switches to high-speed streams that originate from low-latitude coronal holes.

• The rotation of the sun brings about a collision between these high- and low-speed streams along spiral Co-rotating Interaction Regions, forming abrupt shock discontinuities in plasma conditions that are measured by spacecraft, often with a repetition c

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