The Sun's Magnetic Field and How it Gets Twisted
Montana State University
The Sun, like most astronomical bodies including the Earth, generates its
own magnetic field. Over the past 50 years astronomers have concluded
that the primary source the Sun's field is a dynamo layer just below its
outer convective envelope (about 200,000 km beneath the visible surface).
The field generated there becomes buoyant and floats to the solar surface
in long strands, called flux tubes, which we observe as sunspots. Theoretical
models of this emergence process have succeeded in explaining many observed
properties of sunspots.
Evidence has accumulated during the past decade that the solar field emerges
with a preferred helical handedness depending on its latitude: left-handed
in the North and right-handed in the South. This sense of twist, present
at the solar surface, propagates into the over-lying corona and through the
solar wind to the Earth and beyond. The handedness must ultimately
originate in the Coriolis effect at some point in the generation or emergence
processes. I will show that the handedness is most likely imparted
by the interaction of the rising field with turbulent eddies which the Coriolis
effect have endowed with a slight tendency for helical handedness.
The majority of Northern eddies deflect the axes of the rising tubes into
right-handed helices causing their internal field to twist in the opposite