Title:

Solar Magnetic Fields and their Helicity.

Alexei A. Pevtsov
National Solar Observatory


Abstract:

It has been said that without magnetic field the Sun would be a
"boring" star. Indeed, the  magnetic fields are at the origin of every
solar active phenomenon. They are present on  the spatial scales of
elementary flux tubes (<0.1 Mm), the magnetic network, sunspots  (30
Mm), coronal holes (few hundred Mm), and the Sun as a whole. The field
is  generated by the solar dynamo operating at the base of the
convection zone.  At the  surface, stressed magnetic fields cause
solar flares and coronal mass ejections (CMEs),  which "cast away"
solar plasma into interplanetary space. CMEs may trigger  geomagnetic
storms in the magnetospheres of Earth and other planets. The origin of
the  magnetic fields, their evolution, and topology may be better
understood by studying the  magnetic helicity (twist,
handedness). Among other things, helicity allows inference of
properties of dynamo and the turbulent convection below the
surface. It may also be used  in understanding the magnetic
reconnection and forecasting the severity of geomagnetic
storms. Recently, the concept of helicity was applied to the
planetary, stellar, and galactic  dynamo and to the jets from the
accretion disks.

I will review the properties of the solar magnetic fields and provide
the examples of  recent applications of magnetic helicity concept in
solar and non-solar research.