Measuring magnetic helicity in the Sun from ground and space: message for dynamo theory.
Dr. Kirill Kuzanyan (IZMIRAN, Russian Academy of Sciences)
Thursday 24th September, 2015 14:00-15:00 Maths 203
We report results of a series of statistical studies on the current
helicity and twist of magnetic fields in solar active regions observed
with several ground based telescopes and recently with the
Spectro-Polarimeter (SP) of Hinode Solar Optical Telescope.
Current helicity as an observable measure of breaking of mirror
anti-symmetry in solar magnetoconvectionhas been studied since 1990s
when systematic correlation between the electric current and the
magnetic field were noted. The most important property is the
so-called hemispheric sign rule, namely the helicity is mainly
negative/positive in the northern/southern hemispheres of the Sun. The
previous studies have also identified some specific situations when
this rule is reversed.
We analysed a 20 year long series of ground based observations
extended with the new data obtained by SOT SP from 2006 to 2014. We
computed average values of current helicity and twist of magnetic
fields by exploring various ranges of weak, medium, and strong
magnetic fields as well as by combining statistically significant data
numbers in terms of latitude, time, and regions. We also performed
artificial reduction of SOT resolution in order to mimic the
ground-based data which have been obtained for much longer period.
Generally, the hemispheric sign rule has been reconfirmed. At certain
phases of the solar cycle we also found different patterns of
inversion of the hemispheric rule visible in either weak or strong
fields, alternately. We established that strong and weak magnetic
fields often show opposite trends regarding this rule. General
regularities of helicity distribution are formulated for future
insight to development of solar dynamo models.