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Kinetic and Magnetic Helicities of Solar Active Regions

Kinetic and Magnetic Helicities of Solar Active Regions. Ram Ajor Maurya, Ashok Ambastha And Vema Reddy. Udaipur Solar Observatory Physical Research Laboratory, India. Outline. Objectives Introduction and background The Data and Sample of Active Regions

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Kinetic and Magnetic Helicities of Solar Active Regions

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  1. Kinetic and Magnetic Helicities of Solar Active Regions Ram Ajor Maurya, Ashok Ambastha And Vema Reddy Udaipur Solar Observatory Physical Research Laboratory, India

  2. Outline • Objectives • Introduction and background • The Data and Sample of Active Regions • Measurement of Helicities – Kinetic and Magnetic • Results Evolution of Helicity in NOAA 10930 : 8-15 Dec 2006 Hemispheric Distribution Association of Kinetic and Magnetic Helicities Variations in Helicities and transient activities • Summary and Conclusions

  3. Objective • Evolution of Kinetic and Magnetic Helicities in ARs • Variation in Helicities During Energetic Transients • Latitudinal distribution of Kinetic and Magnetic Helicities • Association of Kinetic and Magnetic Helicities?

  4. Introduction • Active regions: 3D magnetic structure extending from sub-photosphere to coronal heights • magnetic helicity observed at the photosphere is due to shear at larger depths and strong turbulence in the convection zone (Pevtsov, et al. 1994). • The kinetic helicity of turbulent flows twists the rising flux tube (Longcope et al. 1998). • The other possibility of twist in the rising tube is dynamo action (Choudhuri 2003) . • flux tube created at the base of the convection zone, rises toward the photosphere where turbulent flows braid and intertwine (Priest and Forbes 2002). Magnetic helicity of photospheric magnetic fields Kinetic helicity of sub-photospheric flow

  5. What is Helicity ? Helicity of a vector field is a measure of linkage and twistedness of the field lines. Kinetic Helicity ? Magnetic Helicity ?

  6. Some background Hemispheric Trend of Helicity Parameters: Hk? HV - Hα sunspot vorticity, hc – current helicity, FC - Hα filament chirality, αav, αbest force free parameter

  7. Kinetic Helicity .. Some background • Zhao and Kosovichev (2004): sub-surface kinetic helicity have a prepondence opposite to the current helicity. • Komm et. al. 2007: Kinetic helicity on average is negative (positive) in northern (southern) hemisphere Kinetic helicity and Flares • Komm et al. (2004): strong signal in kinetic helicity at the location of the active region during the epoch when flares occur.

  8. Solar oscillations could be excited by the mechanical impulse of large flare (Wolf 1972). • Flare related effects on p-modes: Chaplin et al. (2000), Ambastha et al.(2003), Howe et al. (2004). GOES-12 flux for 1.0 - 0.8Å (solid line) and 0.5 - 0.4Å (dotted line). The horizontal lines with labels Ri, i = 1, . . . 5, represent time span taken for the five data sets. (Maurya, Ambastha and Tripathy, 2009, Astrophys. J., 706, L235)

  9. presence of three sheared layers in the depth range 0 to 10 Mm of 44 ARs • two extrema in meridional velocity profiles of these ARs were found to be located at the depths of 1.92±0.15 and 4.69±0.30 Mm. • ARs having two extrema possessed as large as twice the mean magnetic field (MI) and mean GOES X-ray flux. • presence of steep gradients in meridional velocity at depths ranging from 1.5 to 5 Mm • hemispheric trend of gradient: negative (positive) signs in the northern (southern) hemisphere. • ARs of larger MI possessed steeper gradient in meridional velocity profiles. • flaring activity of ARs are associated with depth of the first extremum of vertical vorticity. (Maurya and Ambastha, 2010, Astrophys. J., 714, L196)

  10. Observational Data and Active Regions Total : 91North: 32 South: 59 • GONG: Jul 2001- Aug 2007 • MSFC: Jul 2001- Oct 2004 • Hinode: Nov 2006 – Aug 2007

  11. y x Local Helioseismology: Ring Diagram Analysis Data Cube 3DFFT Ring-Fitting Full disc time series Inversion Horizontal: ux, uy (cont. eqn., Komm, et al. 2004) ∆ω = kx Ux + ky Uy Tracked and filtered time series Vertical: uz (Hill, 1988)

  12. Measurement of Helicity • Vertical and helical fluctuations are an integral part of any turbulent fluid

  13. Average flow in the Active Region NOAA 10486

  14. 3D Flow Structure Beneath the NOAA 10486

  15. Kinetic Helicity in the Active Region NOAA 10486

  16. Velocity and Magnetic Fields in NOAA 10486

  17. Evolution of Kinetic and Magnetic Helicities in NOAA 10930

  18. Latitudinal Distribution of Magnetic Helicity Hemispheric Trend: North: αzav< 0 (66%) South: αzav> 0 (63%) Max. PDF: -9.37×10-9(+1.72×10-9) m-1 Average αzav:-1.39×10-9(+3.05×10-9) m-1

  19. Latitudinal Distribution of Vertical Kinetic Helicity Hemispheric Trend: North: (hk1z)av< 0 (47%) South: (hk1z)av > 0 (53%) Max. PDF: +2.50×10-8(-4.48×10-9) ms-2 Average (hk1z)av:1.88×10-9(-7.62×10-9) ms-2 North: (hk2z)av< 0 (69%) South: (hk2z)av > 0 (56%) Max. PDF: -4.37×10-8(3.44×10-9) ms-2 Average (ω2z)av : -6.99×10-8(1.69×10-8) ms-2

  20. Relation Between Kinetic and Magnetic Helicities

  21. Summary and Conclusions • Magnetic helicity parameter αzav shows significant hemispheric trend - in agreement with earlier reports. • The average vertical vorticity for the depth range 2.5-12 Mm shows an opposite hemispheric trend while there is no hemispheric trend for the depth range 0.0-2.5 Mm. • There is no clear hemispheric preponderance for the average vertical kinetic helicity for the depth range 0.0-2.5 Mm while strong hemispheric trend is discernible for the depth range 2.5-12 Mm. • We do not find any clear association between the twists of surface magnetic fields and sub-surface flows. • photospheric magnetic helicity has not a cause and effect relation with the sub-photospheric kinetic helicity in the depth range 0-12 Mm. • Absolute mean magnetic field of ARs shows a mild correlation with the twist of magnetic fields while no association with the twist of sub-surface flows. • The GOES XHR flux also shows a mild correlation with vertical vorticity averaged over depths 2.5-12 Mm.

  22. Latitudinal Distribution of Current Helicity Hemispheric Trend: North: (hcz)av< 0 (56%) South: (hcz)av > 0 (47%) Max. PDF: 0.00×10-9( 0.00×10-9) m-1 Average (hcz)av:-1.93×10-9(+0.00×10-9) m-1

  23. Latitudinal Distribution of Vertical Vorticity Hemispheric Trend: North: (ω1z)av< 0 (56%) South: (ω1z)av > 0 (51%) Max. PDF: -1.12×10-7(+8.62×10-9) s-1 Average (ω1z)av :-2.56×10-9(+3.83×10-8) s-1 North: (ω2z)av< 0 (41%) South: (ω2z)av > 0 (39%) Max. PDF: +3.50×10-7(-1.17×10-7) s-1 Average (ω2z)av : +9.89×10-9(-9.99×10-8) s-1

  24. Relation Between Kinetic and Current Helicities

  25. Current Helicity ?

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