The Sun's Magnetic Field and How it Gets Twisted

Dana Longcope
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 sense.