Question: What is the spiral called that is caused by the rotation of the Sun?
About the article "Aurora", section "Frequency of occurrence".

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The pioneer of studies of the rotation of the Galaxy and the formation of the spiral arms was Bertil Lindblad in 1925.
He realized that the idea of stars arranged permanently in a spiral shape was untenable.
Since the angular speed of rotation of the galactic disk varies with distance from the centre of the galaxy (via a standard solar system type of gravitational model), a radial arm (like a spoke) would quickly become curved as the galaxy rotates.
The arm would, after a few galactic rotations, become increasingly curved and wind around the galaxy ever tighter.
This is called the "winding problem".
Measurements in the late 1960s showed that the orbital velocity of stars in spiral galaxies with respect to their distance from the galactic center is indeed higher than expected from Newtonian dynamics but still cannot explain the stability of the spiral structure.
Since the 1960s, there have been two leading hypotheses or models for the spiral structures of galaxies:  Star formation caused by density waves in the galactic disk of the galaxy.
The SSPSF model – star formation caused by shock waves in the interstellar medium.
These different hypotheses do not have to be mutually exclusive, as they may explain different types of spiral arms. 
Ballerina's skirt shape.
As the Sun rotates, its magnetic field twists into a Parker spiral,The spiral nature of the heliospheric magnetic field had been 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.
Further dynamics have suggested that "The Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward".
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 uniform rate, 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.
Unlike the jet from a sprinkler, the solar wind is tied to the magnetic field by MHD effects, so that magnetic field lines are tied to the material in the jet and take on an arithmetic spiral shape.
The cause of the 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.
The Parker spiral shape of the solar wind changes the shape of the Sun's magnetic field in the outer solar system: beyond about 10-20 astronomical units from the Sun, the magnetic field is nearly toroidal (pointed around the equator of the Sun) rather than poloidal (pointed from the North to the South pole, as in a bar magnet) or radial (pointed outward or inward, as might be expected from the flow of the solar wind if the Sun were not rotating).
The spiral shape also greatly amplifies the strength of the solar magnetic field in the outer solar system.
The Parker spiral may be responsible for the differential solar rotation, in which the Sun's poles rotate more slowly (about a 35-day rotation period) than the equator (about a 27-day rotation period).
The solar wind is guided by the Sun's magnetic field and hence largely emanates from the polar regions of the Sun; the induced spiral shape of the field causes a drag torque on the poles due to the magnetic tension force.
During solar maximum the entire magnetic field of the sun flips, thus alternating the polarity of the field every solar cycle.
The cause of the ballerina spiral shape has sometimes been called the "garden sprinkler effect" or "garden hose effect", and likened to holding a lawn sprinkler, and moving it in your hand vertically up and down, while your body rotates.
The stream of water represents the Solar Wind, and moves radially outwards at all times. 
In geometry, the spiral of Theodorus (also called "square root spiral", "Einstein spiral" or "Pythagorean spiral") is a spiral composed of contiguous right triangles.
It was first constructed by Theodorus of Cyrene. 
[[File:Heliospheric-current-sheet.gif|thumb|right|The heliospheric current sheet extends to the outer reaches of the Solar System, and results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium.
]]The Sun is a magnetically active star.
It supports a strong, changing magnetic field that varies year-to-year and reverses direction about every eleven years around solar maximum.
The Sun's magnetic field leads to many effects that are collectively called solar activity, including sunspots on the surface of the Sun, solar flares, and variations in solar wind that carry material through the Solar System.
The effects of solar activity on Earth include auroras at moderate to high latitudes and the disruption of radio communications and electric power.
Solar activity is thought to have played a large role in the formation and evolution of the Solar System.
Solar activity changes the structure of Earth's outer atmosphere.
All matter in the Sun is in the form of gas and at high temperatures, plasma.
This makes it possible for the Sun to rotate faster at its equator (about 25 days) than it does at higher latitudes (about 35 days near its poles).
The differential rotation of the Sun's latitudes causes its magnetic field lines to become twisted together over time, producing magnetic field loops to erupt from the Sun's surface and trigger the formation of the Sun's dramatic sunspots and solar prominences (see magnetic reconnection).
This twisting action creates the solar dynamo and an 11-year solar cycle of magnetic activity as the Sun's magnetic field reverses itself about every 11 years.
The solar magnetic field extends well beyond the Sun itself.
The magnetized solar wind plasma carries the Sun's magnetic field into space forming what is called the interplanetary magnetic field.
Since the plasma can only move along the magnetic field lines, the interplanetary magnetic field is initially stretched radially away from the Sun.
Because the fields above and below the solar equator have different polarities pointing towards and away from the Sun, there exists a thin current layer in the solar equatorial plane, which is called the heliospheric current sheet.
At great distances, the rotation of the Sun twists the magnetic field and the current sheet into the Archimedean spiral like structure called the Parker spiral.
The interplanetary magnetic field is much stronger than the dipole component of the solar magnetic field.
The Sun's dipole magnetic field of 50–400 μT (at the photosphere) reduces with the cube of the distance to about 0.1 nT at the distance of the Earth.
However, according to spacecraft observations the interplanetary field at the Earth's location is around 5 nT, about a hundred times greater.
The difference is due to magnetic fields generated by electrical currents in the plasma surrounding the Sun. 
The Carrington rotation of the Sun is a system for comparing locations on the Sun over a period of time, allowing the following of sunspot groups or reappearance of eruptions at a later time.
Because the Solar rotation is variable with latitude, depth and time, any such system is necessarily arbitrary and only makes comparison meaningful over moderate periods of time.
Differential rotation is when different latitudes rotate at different rates and applies to all fluid bodies including all stars and the surface of gas giant planets.
Solar rotation is arbitrarily taken to be 27.2753 days for the purpose of Carrington rotations.
Each rotation of the Sun under this scheme is given a unique number called the Carrington Rotation Number, starting from November 9, 1853.
(The Bartels Rotation Number is a similar numbering scheme that uses a period of exactly 27 days and starts from February 8, 1832.
)The heliographic longitude of a solar feature conventionally refers to its angular distance relative to the central meridian, i.e.
that which the Sun-Earth line defines.
The "Carrington longitude" of the same feature refers it to an arbitrary fixed reference point of an imagined rigid rotation, as defined originally by Carrington.
Richard Christopher Carrington determined the solar rotation rate from low latitude sunspots in the 1850s and arrived at 25.38 days for the sidereal rotation period.
Sidereal rotation is measured relative to the stars, but because the Earth is orbiting the Sun, we see this period as 27.2753 days.
It is possible to construct a diagram with the longitude of sunspots horizontally and time vertically.
The longitude is measured by the time of crossing the central meridian and based on the Carrington rotations.
In each rotation, plotted under the preceding ones, most sunspots or other phenomena will reappear directly below the same phenomenon on the previous rotation.
There may be slight drifts left or right over longer periods of time.
The Bartels "musical diagram" or the Condegram spiral plot are other techniques for expressing the approximate 27 day periodicity of various phenomena originating at the solar surface.