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Concept
Heliospheric current sheet
Summary
The heliospheric current sheet, or interplanetary current sheet, is a surface separating regions of the heliosphere where the interplanetary magnetic field points toward and away from the Sun. A small electrical current with a current density of about 10−10 A/m2 flows within this surface, forming a current sheet confined to this surface. The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium. The thickness of the current sheet is about near the orbit of the Earth.
As the Sun rotates, its magnetic field twists into an Archimedean spiral, as it extends through the Solar System. This phenomenon is often called the Parker spiral, after Eugene Parker's work that predicted the structure of the interplanetary magnetic field.
The spiral nature of the heliospheric magnetic field was noted earlier by Hannes Alfvén, based on the structure of comet tails.
The influence of this spiral-shaped magnetic field on the interplanetary medium (solar wind) creates the largest structure in the Solar System, the heliospheric current sheet.
Parker's spiral magnetic field was divided in two by a current sheet, a mathematical model first developed in the early 1970s by Schatten. It warps into a wavy spiral shape that has been likened to a ballerina's skirt. The waviness of the current sheet is due to the magnetic field dipole axis' tilt angle to the solar rotation axis and variations from an ideal dipole field.
Unlike the familiar shape of the field from a bar magnet, the Sun's extended field is twisted into an arithmetic spiral by the magnetohydrodynamic influence of the solar wind. The solar wind travels outward from the Sun at a rate of 200-800km/s, but an individual jet of solar wind from a particular feature on the Sun's surface rotates with the solar rotation, making a spiral pattern in space. The cause of this ballerina spiral shape has sometimes been called the "garden sprinkler effect" or "garden hose effect", because it is likened to a lawn sprinkler with nozzle that moves up and down while it spins; the stream of water represents the solar wind.
Official source
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