Kinetic and Magnetic Helicities of Solar Active Regions Ram Ajor Maurya, Ashok Ambastha And Vema...
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Transcript of Kinetic and Magnetic Helicities of Solar Active Regions Ram Ajor Maurya, Ashok Ambastha And Vema...
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
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
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?
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).
Kinetic helicity of
sub-photospheric flow
Magnetic helicity of
photospheric magnetic fields
Introduction
What is Helicity ?
Helicity of a vector field is a measure of linkage and twistedness of the field lines.
V
dVWXH
Kinetic Helicity ?dVuH
Vk
dVABHVm
Magnetic Helicity ?
Hemispheric Trend of Helicity Parameters:
Reference Helicity Parameter
North
(-ve)
%(no.)
South
(+ve)
%(no.)
Total Date
Hale (1926) HV 64(16) 50(13) 51 1901-1944
Richardson (1941) HV 71 66 141 1901-1944
Seehafer (1990) hc 91(11) 75(3) 16 SC21-22
Martin, et al. (1994) FC 100(26) 72(34) 47 SC22
Pevtsov, et al. (1995) αbest 76(25) 69(25) 69 1991-1995
Abramenko, et al. (1996) hc 79(15) 86(18) 40 1988-1994
Bao and Zhang (1998) hc 84(169) 79(177) 422 1988-1997
Longocope, et al. (1998) αbest 62(58) 66(73) 203 1991-1995
Bao, et al. (2000) αav 59(152) 65(26) 87 SC23
Pevtsov, et al. (2003) FC 80(558) 86(633) 2310 2000-2001
Lim and Chae (2009) FC 95(19) 100(18) 45 1996-2001
Hk ?
Some background
HV - Hα sunspot vorticity, hc – current helicity, FC - Hα filament chirality, αav, αbest force free parameter
Kinetic Helicity .. Some background
Komm et. al. 2007: Kinetic helicity on average is negative (positive) in northern (southern) hemisphere
Zhao and Kosovichev (2004): sub-surface kinetic helicity have a prepondence opposite to the current helicity.
Komm et al. (2004): strong signal in kinetic helicity at the location of the active region during the epoch when flares occur.
Kinetic helicity and Flares
(Maurya, Ambastha and Tripathy, 2009, Astrophys. J., 706, L235)
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.
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).
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)
Observational Data and Active Regions
Total : 91 North: 32 South: 59
GONG: Jul 2001- Aug 2007 MSFC: Jul 2001- Oct 2004 Hinode: Nov 2006 – Aug 2007
Local Helioseismology: Ring Diagram Analysis
Full disctime series
y
x
Tracked and filtered time series
Data Cube 3DFFT Ring-Fitting
Inversion
30
20
),,(k
b
UkUk
AkkP
yyxxyx
iii dzKzuU )(
Horizontal: ux, uy
Vertical: uz
(cont. eqn., Komm, et al. 2004)
∆ω = kx Ux + ky Uy
(Hill, 1988)
Measurement of Helicity
dVuHVk
dVABHVm
y
u
x
uu
Nh xy
zavzk
1)(
y
B
x
B
BNxy
z
zav
11
Vertical and helical fluctuations are an integral part of any turbulent fluid
Average flow in the Active Region NOAA 10486
3D Flow Structure Beneath the NOAA 10486
Kinetic Helicity in the Active Region NOAA 10486
Velocity and Magnetic Fields in NOAA 10486
Evolution of Kinetic and Magnetic Helicities in NOAA 10930
Latitudinal Distribution of Magnetic Helicity
Hemispheric Trend:Hemispheric Trend:
North: North: αzav< 0 (66%)< 0 (66%)
SouthSouth: αzav> 0 (63%)> 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
Latitudinal Distribution of Vertical Kinetic Helicity
Hemispheric Trend:Hemispheric Trend:
North: (North: (hk1z))av< 0 (47%)< 0 (47%)
SouthSouth: ((hk1z))av > 0 (53%)> 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: (North: (hk2z))av< 0 (69%)< 0 (69%)
SouthSouth: ((hk2z))av > 0 (56%)> 0 (56%)
Max. PDF: -4.37×10-8 (3.44×10-9) ms-2 Average ((ω2
z))av : -6.99×10-8 (1.69×10-8) ms-2
Relation Between Kinetic and Magnetic Helicities
Par. Corr. Coeff.
(hk1z)av -0.07
(hk2z)av +0.23
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.
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.
photospheric magnetic helicity has not a cause and effect relation with the sub-photospheric kinetic helicity in the depth range 0-12 Mm.
Latitudinal Distribution of Current Helicity
Hemispheric Trend:Hemispheric Trend:
North: (North: (hcz))av< 0 (56%)< 0 (56%)
SouthSouth: ((hcz))av > 0 (47%)> 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
Latitudinal Distribution of Vertical Vorticity
Hemispheric Trend:Hemispheric Trend:
North: (North: (ω1z))av< 0 (56%)< 0 (56%)
SouthSouth: ((ω1z))av > 0 (51%)> 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: (North: (ω2z))av< 0 (41%)< 0 (41%)
SouthSouth: ((ω2z))av > 0 (39%)> 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
Relation Between Kinetic and Current Helicities
Par. Corr. Coeff.
(ωz1)av -0.10
(ωz1)av +0.04
(hk1z)av -0.05
(hk2z)av +0.26
Current Helicity ? dVJBHVc
dVJBHVc
y
B
x
BB
Nh xy
zavzc
1)(