764 research outputs found
New dynamo pattern revealed by solar helical magnetic fields
Previously unobservable mirror asymmetry of the solar magnetic field -- a key
ingredient of the dynamo mechanism which is believed to drive the 11-year
activity cycle -- has now been measured. This was achieved through systematic
monitoring of solar active regions carried out for more than 20 years at
observatories in Mees, Huairou, and Mitaka. In this paper we report on detailed
analysis of vector magnetic field data, obtained at Huairou Solar Observing
Station in China. Electric current helicity (the product of current and
magnetic field component in the same direction) was estimated from the data and
a latitude-time plot of solar helicity during the last two solar cycles has
been produced. We find that like sunspots helicity patterns propagate
equatorwards but unlike sunspot polarity helicity in each solar hemisphere does
not change sign from cycle to cycle - confirming the theory. There are,
however, two significant time-latitudinal domains in each cycle when the sign
does briefly invert. Our findings shed new light on stellar and planetary
dynamos and has yet to be included in the theory.Comment: 4 pages, 2 figures 0 tables. MNRAS Letters, accepte
Helicity at Photospheric and Chromospheric Heights
In the solar atmosphere the twist parameter has the same sign as
magnetic helicity. It has been observed using photospheric vector magnetograms
that negative/positive helicity is dominant in the northern/southern hemisphere
of the Sun. Chromospheric features show dextral/sinistral dominance in the
northern/southern hemisphere and sigmoids observed in X-rays also have a
dominant sense of reverse-S/forward-S in the northern/southern hemisphere. It
is of interest whether individual features have one-to-one correspondence in
terms of helicity at different atmospheric heights. We use UBF \Halpha images
from the Dunn Solar Telescope (DST) and other \Halpha data from Udaipur Solar
Observatory and Big Bear Solar Observatory. Near-simultaneous vector
magnetograms from the DST are used to establish one-to-one correspondence of
helicity at photospheric and chromospheric heights. We plan to extend this
investigation with more data including coronal intensities.Comment: 5 pages, 1 figure, 1 table To appear in "Magnetic Coupling between
the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten,
Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg,
Berlin, 200
Hemispheric Helicity Trend for Solar Cycle 24
Using vector magnetograms obtained with the Spectro-polarimeter (SP) on
aboard Hinode satellite, we studied two helicity parameters (local twist and
current helicity) of 64 active regions occurred in the descending phase of
solar cycle 23 and the ascending phase of solar cycle 24. Our analysis gives
the following results. (1) The 34 active regions of the solar cycle 24 follow
the so-called hemispheric helicity rule, whereas the 30 active regions of the
solar cycle 23 do not. (2) When combining all 64 active regions as one sample,
they follow the hemispheric helicity sign rule as in most other observations.
(3) Despite with the so-far most accurate measurement of vector magnetic field
given by SP/Hinode, the rule is still weak with large scatters. (4) The data
show evidence of different helicity signs between strong and weak fields,
confirming previous result from a large sample of ground-based observations.
(5) With two example sunspots we show that the helicity parameters change sign
from the inner umbra to the outer penumbra, where the sign of penumbra agrees
with the sign of the active region as a whole. From these results, we speculate
that both the Sigma-effect (turbulent convection) and the dynamo have
contributed in the generation of helicity, whereas in both cases turbulence in
the convection zone has played a significant role.Comment: accepted by ApJ Letter
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