*Mei Zhang National Astronomical Observatory, Chinese Academy of SciencesSolar cycle variation of kinetic helicityCollaborators:Junwei Zhao (Stanford, USA)Mark Miesch (HAO/NCAR, USA)

Plan of the TalkMotivation: Solar-cycle variation of current helicity2. Solar-cycle variation of kinetic helicity1) In dynamo model2) By helioseismology

Magnetic fields are observed to emerge into each hemisphere with a preferred helicity sign:Positive in southern hemisphere;Negative in northern hemisphere.

Hemispheric helicity sign rule(Image credit: A. Pevtsov)(e.g. Seehafer 1990, Pevtsov et al. 1995, Bao & Zhang 1998)No argument on the existence of this hemispheric helicity sign rule.

Theory:

Longcope et al. (1998): YES: solar-cycle independent--- Helicity is produced in the process of magnetic flux tubes rising through the solar convection zone and being buffeted by turbulence with a non-vanishing kinetic helicity (-effect)

Choudhuri et al. (2004): NO: solar-cycle dependent--- Poloridal flux getting warped around a toroidal flux tube rising through the convection zone to give rise to the helicity--- Deviations from the usual sign rule at the beginning of a solar cycleHowever, there is an argument on Is this rule preserved for the whole solar cycle?

Observation:

Bao et al. (2000): NO (of hc) for the ascending phase of cycle 23 (Huairou data)Pevtsov et al. (2001): Yes for the first four years of cycle 23(Mees data)Hagino & Sakurai (2005): Yes for maximums; NO for minimums(Mitaka data, 1983-2000)Pevtsov et al. (2008): No agreement on the wrong-sign years(19 years data of different instruments)

Is this rule preserved for the whole solar cycle?

End of cycle 23: do not followBeginning of cycle 24: follow(Hao & Zhang 2011, ApJ, 733, L27 and Juan Haos talk tomorrow for more development)Hemispheric helicity sign rule by SP/HinodeHint: Choudhuri et al. (2004) may be right in its physical picture but wrong in phase prediction.Despite with the accurate measurement by SP/Hinode, the scatter is still very large.Hint: The scatter is an inherent property, not induced by measurement error. Consistent with Longcope et al. (1998).

Solar cycle variation in a convective dynamo model2aHow to understand this hemispheric helicity sign rule and its solar cycle variation?

Hemispheric helicity sign rule shows up clearly in magnetic helicity density map.Current helicity does show cycle variation, with opposite-sign patches presenting. BA Convective Babcock-Leighton Dynamo Model (Miesch & Brown 2012)hmhc(More analysis in progress)(r=0.96, 28Mm)

In the modelNo solar-cycle variation on kinetic helicity(Only vertical component, to compare with observation)

Solar cycle variation of kinetic helicitySubsurface velocity field obtained through time-distance helioseismology using HMI/SDO data

Hk with error bars

Each line: one-month averaged No solar-cycle variation of kinematic helicity(r= 0 - 1 Mm)

in Model: Miesch et al. (2006) (produce solar-like differential rotation)in HMI data, time distance method Consistency in model and observation: tendency + magnitude (r = 0 - 1 Mm)(r = 21 Mm)

meridional flow with error bars

Solar-cycle variation of meridional flow? Yes, as reported before in Zhao & Kosovichev (2004).Means that previous non-detection on Hk is not by noise.

SummaryHemispheric helicity sign rule is observed on the photosphere and shows solar cycle variation.Dynamo models (at least one of them) produce magnetic field consistent with the observed rule.Magnetic helicity better preserved than current helicity.Both the dynamo model and helioseismology observation show no solar-cycle variation of kinetic helicity.These give constrains on the mechanism of helicity production as well as dynamo models.

Thank you for your attentionHuairou Solar Observing Station, NAOC

We calculate two helicity parameters:1. average local twist2. normalized average current helicity

With two vector B representatives:1. flux density map (B1)2. true field strength (B2)sunspots

Hemispheric rule in global magnetic fieldLeft: MDI; (September 1996) Right: KPVT(Wang & Zhang 2010, ApJ, 720, 632)The same hemispheric helicity sign rule exists, extending to 60 degrees high in latitudes, and is preserved through the whole solar-cycle. (Following the approach in Petvsov & Latushko 2000)

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