Heliospheric current sheet · tilted dipole + quadrupole

Ballerina Skirt Explorer

The current sheet separates outward-pointing field from inward-pointing field. On the Sun it is a wavy line. The solar wind carries that line outward while the Sun turns, and the line sweeps out a wavy sheet. Tilt sets how high the waves go. Wind speed sets how far apart they are. The flat version of this model is UCLA's Neutral Sheet Model, 3-D Structure module.

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Neutral line on the source surface

Field points outward Field points inward Neutral line What the observer samples

Same axes as the left panel of UCLA's Neutral Sheet Model module. This is the pattern on the Sun before the wind carries it outward, so wind speed does not change it.

What a spacecraft at 1 AU measures

Field polarity over one 27-day apparent rotation, at the observer latitude. Each colored block is a sector.

Things to try

  1. Set q to 0. Compare α = 10° and α = 25° in the Side (x-z) view. What changes? Read "highest latitude the sheet reaches". How does it compare with α?
  2. Hold α fixed and move V from 200 to 800 km/s. What happens to the spacing between folds, and to the source-surface map?
  3. Set α to 0. What shape is the sheet? How many sectors does an observer on the equator see?
  4. Set the observer's latitude above α. What happens to the sector count, and why?
  5. Raise q slowly from 0. At what point does the sector count jump from 2 to 4? What does the neutral line look like when it does?