A Study of Oscillations in Solar Active Regionslibrary/Maurya_R_A_2010_abst.pdf · A Study of...

A Study of Oscillations in SolarActive Regions

A THESIS

submitted for the award of Ph.D. degree of

MOHANLAL SUKHADIA UNIVERSITY

in the

Faculty of Science

by

Ram Ajor Maurya

Under the Supervision of

Dr. Ashok Ambastha

Professor

UDAIPUR SOLAR OBSERVATORY

PHYSICAL RESEARCH LABORATORY, UDAIPUR

DEPARTMENT OF PHYSICS

FACULTY OF SCIENCE

MOHANLAL SUKHADIA UNIVERSITY

UDAIPUR

2010

DECLARATION

I hereby declare that the work incorporated in the present thesis entitled “A

Study of Oscillations in Solar Active Regions” is my own work and is

original. This work (in part or in full) has not been submitted to any University

for the award of a Degree or a Diploma.

Date:Ram Ajor Maurya

(Author)Udaipur Solar Observatory

Physical Research LaboratoryDewali, Badi Road

Udaipur 313 001India.

CERTIFICATE

I feel great pleasure in certifying that the thesis entitled “A Study of Os-

cillations in Solar Active Regions” embodies a record of the results of in-

vestigation carried out by Mr. Ram Ajor Maurya under my guidance. I am

satisfied with the analysis of data, interpretation of results and conclusions drawn.

He has completed the residential requirement as per the rules.

I recommend the submission of thesis.

Date:

Countersigned byHead of the Department

Prof. Ashok Ambastha(Thesis Supervisor)

Udaipur Solar ObservatoryPhysical Research Laboratory

Dewali, Badi RoadUdaipur 313 001

India.

To my parents

Contents

List of Figures v

List of Tables viii

Acknowledgments ix

Abstract xi

1 Introduction 11.1 The Discovery of Solar Oscillations . . . . . . . . . . . . . . . . . . 21.2 Global Helioseismology . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 Modes of Solar Oscillation . . . . . . . . . . . . . . . . . . . 51.2.2 Results of Global Helioseismology . . . . . . . . . . . . . . . 71.2.3 Limitations of Global Helioseismology . . . . . . . . . . . . . 8

1.3 Local Helioseismology . . . . . . . . . . . . . . . . . . . . . . . . . 81.3.1 Ring Diagram Analysis . . . . . . . . . . . . . . . . . . . . . 91.3.2 Time-Distance Analysis . . . . . . . . . . . . . . . . . . . . 91.3.3 Helioseismic Holography . . . . . . . . . . . . . . . . . . . . 91.3.4 Results of Local Helioseismology . . . . . . . . . . . . . . . . 10

1.4 Motivations and Organization of the Thesis . . . . . . . . . . . . . 11

2 The Observational Data and Methods of Analysis 152.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.2 The Observational Data . . . . . . . . . . . . . . . . . . . . . . . . 16

2.2.1 Data for Helioseismic Studies . . . . . . . . . . . . . . . . . 162.2.2 Data for the Study of Solar Transients . . . . . . . . . . . . 22

2.3 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . 27

3 Flare Ribbon Separation and Energy Release 293.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.2 Basic Formalism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.3 Feature Development using Mathematical Morphology . . . . . . . 35

3.3.1 Feature Extraction . . . . . . . . . . . . . . . . . . . . . . . 363.3.2 Hole Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

i

Contents

3.4 Determination of Flare Ribbon Separation . . . . . . . . . . . . . . 403.4.1 Energy Release during the X17/4B Flare . . . . . . . . . . . 43


4 Flare Associated Variations in Magnetic and Velocity Fields ofActive Region NOAA 10486 494.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494.2 The Super Active Region NOAA 10486 and its Flares . . . . . . . . 524.3 The Observational Data and Analysis . . . . . . . . . . . . . . . . . 544.4 The X17/4B Flare of 28 October 2003 . . . . . . . . . . . . . . . . 55

4.4.1 Evolution of Magnetic and Doppler Velocity Fields . . . . . 564.4.2 Magnetic Polarity Reversal during the X17/4B Flare . . . . 594.4.3 Motion of the Magnetic/Doppler Transients and Flare Kernels 614.4.4 Association of MFs with HXR Sources and White-Light

Flare Ribbons . . . . . . . . . . . . . . . . . . . . . . . . . . 684.5 The X10/2B Flare of 29 October 2003 . . . . . . . . . . . . . . . . 71

4.5.1 Magnetic Polarity Reversal during the X10/2B Flare . . . . 734.5.2 Motion of Magnetic/Doppler Transients and Flare Kernels . 734.5.3 The Association of HXR Sources and White-Light Flare Rib-

bons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764.6 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . 78

5 Ring-Diagram Analysis and Inversion Techniques 815.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815.2 The Observational Data . . . . . . . . . . . . . . . . . . . . . . . . 825.3 Data Reduction and Power Spectra . . . . . . . . . . . . . . . . . . 83

5.3.1 The Data Cube . . . . . . . . . . . . . . . . . . . . . . . . . 835.3.2 Remapping and Tracking . . . . . . . . . . . . . . . . . . . . 855.3.3 Interpolation and Apodization . . . . . . . . . . . . . . . . . 865.3.4 Temporal Filtering and Three-Dimensional Power Spectra . 87

5.4 Ring-Diagram Fitting . . . . . . . . . . . . . . . . . . . . . . . . . . 905.4.1 Asymmetric Peak Profile (APP) Fitting . . . . . . . . . . . 915.4.2 Dense-Pack (DP) Fitting . . . . . . . . . . . . . . . . . . . . 945.4.3 Comparison of APP and DP Fittings . . . . . . . . . . . . . 96

5.5 Sub-Photospheric Velocity Inversion . . . . . . . . . . . . . . . . . . 995.5.1 SOLA Inversion . . . . . . . . . . . . . . . . . . . . . . . . . 1025.5.2 RLS Inversion . . . . . . . . . . . . . . . . . . . . . . . . . . 1095.5.3 Comparison of SOLA and RLS Inversions . . . . . . . . . . 115


6 Energetic Transients and p-Mode Parameters 1186.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186.2 Flare Associated Changes in the p-Mode Parameters . . . . . . . . 121

ii

Contents

6.2.1 The White-Light Superflare of NOAA 10486 . . . . . . . . . 1216.2.2 The Observational Data . . . . . . . . . . . . . . . . . . . . 1226.2.3 Determination of Mode Energy . . . . . . . . . . . . . . . . 1236.2.4 Results and Discussions . . . . . . . . . . . . . . . . . . . . 124

6.3 Evolution of p-Mode Parameters in NOAA 10486 . . . . . . . . . . 1266.4 Statistics of Flares and p-Modes Energy . . . . . . . . . . . . . . . 128

6.4.1 Flare Productive ARs of Solar Cycle 23 . . . . . . . . . . . . 1296.4.2 The Observational Data and Analysis . . . . . . . . . . . . . 1296.4.3 Results and Discussions . . . . . . . . . . . . . . . . . . . . 133


7 Sub-photospheric Flows in Solar Active Regions 1387.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1387.2 The Basic Formalism . . . . . . . . . . . . . . . . . . . . . . . . . . 141

7.2.1 Gradient, Divergence and Vorticity of Horizontal Flows . . . 1417.2.2 Vertical Component of Flow . . . . . . . . . . . . . . . . . . 143

7.3 Three Dimensional Flow Distribution Beneath NOAA 10486 . . . . 1447.4 Variations in Sub-photospheric Flows with a Large Flare . . . . . . 147

7.4.1 The Observational Data and Analysis . . . . . . . . . . . . . 1477.4.2 Results and Discussions . . . . . . . . . . . . . . . . . . . . 147

7.5 Sub-photospheric Meridional Flow, Vorticity and the Lifetime ofActive Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1507.5.1 The Observational Data and Analysis . . . . . . . . . . . . . 1517.5.2 Results and Discussions . . . . . . . . . . . . . . . . . . . . 151


8 Kinetic and Magnetic Helicities of Solar Active Regions 1628.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1628.2 Measurements of Magnetic and Kinetic Helicities . . . . . . . . . . 1688.3 Evolution of Kinetic and Magnetic Helicities in NOAA 10930 . . . . 1708.4 Statistics of Helicities in Sub-photospheric Flows and Photospheric

Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1728.4.1 The Observational Data and Analysis . . . . . . . . . . . . . 1728.4.2 Twist Parameters of Photospheric Magnetic Fields . . . . . 1758.4.3 Twist Parameters of Sub-photospheric Velocity Fields . . . . 1778.4.4 Relation between Kinetic and Magnetic Helicities . . . . . . 1818.4.5 Activity Related Variation in Twist Parameters . . . . . . . 183


9 Summary, Conclusions and Future Plan 1879.1 Present Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

9.1.1 Determination of Flare Ribbon Separation . . . . . . . . . . 188

iii

Contents

9.1.2 Transient Magnetic and Doppler Features Related to theWhite-Light Flares in NOAA 10486 . . . . . . . . . . . . . . 189

9.1.3 Ring-Diagram Analysis and Inversion Techniques . . . . . . 1909.1.4 Variations in p-Mode Parameters with Changing Onset Time

of a Large Flare . . . . . . . . . . . . . . . . . . . . . . . . . 1919.1.5 Three-dimensional Flow Distribution Beneath the Active Re-

gions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1929.1.6 Topology of Sub-photospheric Flows and the Lifetime of Ac-

tive Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1939.1.7 Kinetic and Magnetic Helicities of Solar Active Regions . . . 194

9.2 Limitations of the Techniques . . . . . . . . . . . . . . . . . . . . . 1949.3 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

9.3.1 Association of Photospheric p-Mode Parameters with Ener-getic Transients . . . . . . . . . . . . . . . . . . . . . . . . . 195

9.3.2 Association of Sub-photospheric Flows with Energetic Tran-sients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

9.3.3 Sub-photospheric Fluid Topology and the Lifetime of ActiveRegions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

9.3.4 Long Term Evolution of Super Active Regions . . . . . . . . 1979.3.5 Chromospheric Oscillations . . . . . . . . . . . . . . . . . . 197

A A New Method of Trapezoidal Integration 199

Bibliography 201

List of Publications 220

iv

List of Figures

1.1 Spherical harmonic representation of the solar oscillations for differ-ent ` and m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 The `− ν diagram for mode frequencies up to 10 mHz and ` = 1000 5

2.1 Positions of four band passes in Ni i line profile used in SOHO/MDI 20

3.1 Post flare loops of the X17/4B flare of 28 October 2003 . . . . . . . 313.2 Results of MMO applied to a typical Hα filtergram obtained for the

X17/4B flare of 28 October 2003 at 11:03 UT . . . . . . . . . . . . . 373.3 Cartoon of a two ribbon flare illustrating a method to determine

flare ribbon separation . . . . . . . . . . . . . . . . . . . . . . . . . 413.4 Separation of different parts of flare ribbons from the neutral line

during the X17/4B flare of 28 October 2003 . . . . . . . . . . . . . 443.5 Flare ribbon separation and energy released during the X17/4B flare 45

4.1 Disk integrated GOES X-ray flux observed during 22 October - 6November 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

4.2 A mosaic of NOAA 10486 observed in different wavelengths duringthe peak phase of the X17/4B flare of 28 October 2003 . . . . . . . 56

4.3 Magnetogram image of the NOAA 10486 overlaid with dopplergramcontours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

4.4 Variations in the net magnetic and Doppler velocity fields of NOAA10486 during 27-28 October 2003 . . . . . . . . . . . . . . . . . . . 58

4.5 The direction of magnetic and Doppler features motion observedduring the X17/4B flare of 28 October 2003 . . . . . . . . . . . . . 59

4.6 Magnetic flux along the lines RS and PQ of NOAA 10486 measuredduring the pre- and peak phases of the X17/4B flare . . . . . . . . . 60

4.7 A mosaic of various observations obtained with time during the im-pulsive phase of the X17/4B super-flare of 28 October 2003 . . . . . 63

4.8 Separation velocities of transient features and flare ribbons duringthe X17/4B flare of 28 October 2003 . . . . . . . . . . . . . . . . . 64

4.9 Magnetic flux and the feature motion along the reference line AB . 674.10 The association of magnetic features, white-light patches and hard

X-ray flux for the event X17/4B of 28 October 2003 . . . . . . . . . 69

v

List of Figures

4.11 Mosaic of images of NOAA 10486 observed in different wavelengthsduring the peak phase of the X10/2B flare of 29 October 2003 . . . 71

4.12 The direction of magnetic and Doppler features motion observedduring the event X10/2B flare of 29 October 2003 . . . . . . . . . . 72

4.13 Magnetic flux along the reference lines XY and LM of NOAA 10486measured during the pre- and peak phases of the X10/2B flare . . . 72

4.14 A mosaic of various observations obtained with time during the im-pulsive phase of the flare X10/2B of 29 October 2003 . . . . . . . . 74

4.15 Separation of flare ribbons during the X10/2B flare of 29 October2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

4.16 The association of magnetic features, white-light patches and hardX-ray flux for the event X10/2B of 29 October 2003 . . . . . . . . . 77

5.1 A schematic diagram of main steps of the ring diagram analysis . . 845.2 Truncation of rings near the edges due to aliasing of higher frequen-

cies toward lower side. . . . . . . . . . . . . . . . . . . . . . . . . . 865.3 Two-dimensional p-mode power spectra at different frequencies . . . 885.4 Wave propagating in the presence/absence of a mean flow field . . . 895.5 Asymmetry parameter (S) for different radial order . . . . . . . . . 925.6 p-mode parameters obtained from the APP fitting . . . . . . . . . . 935.7 Dense-pack ring diagram maps with centers separated by 7.5◦ . . . 945.8 p-mode parameters obtained from the DP fitting . . . . . . . . . . . 955.9 A comparison of `− ν diagram obtained from APP and DP fittings 965.10 A comparison of p-mode amplitudes obtained from APP and DP

fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975.11 A comparison of p-mode width obtained from APP and DP fittings 985.12 A comparison of p-mode frequency shift obtained from APP and DP

fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995.13 A comparison of zonal velocities obtained from APP and DP fittings 1005.14 A comparison of meridional velocities obtained from APP and DP

fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.15 Velocities of photospheric flow fields obtained using a forward tech-

nique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1055.16 SOLA averaging kernels at target radius z0 = 0.98R� for different

inversion parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 1065.17 SOLA inversion trade-off diagram . . . . . . . . . . . . . . . . . . . 1075.18 SOLA averaging kernels for different depths. . . . . . . . . . . . . . 1085.19 A comparison of exact and SOLA inverted velocity profiles . . . . . 1095.20 The cubic B-splines at ten equally spaced knots. . . . . . . . . . . . 1105.21 L-curve to determine the optimum value of regularization parameter

in RLS inversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1135.22 A comparison of exact and RLS inverted velocity profiles . . . . . . 1145.23 A comparison of SOLA and RLS inverted velocity profiles . . . . . 115

vi

List of Figures

6.1 GOES X-ray flux and data cubes used for the study of flare onsettime associated changes in p-mode parameters . . . . . . . . . . . . 122

6.2 Mode inertia as a function of frequency for radial order n = 0, . . . , 5 1246.3 Relative variation in p-mode amplitude with frequency at different

radial order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256.4 Evolution in surface p-mode parameters of ARs . . . . . . . . . . . 1276.5 A map showing the positions of 74 selected ARs used in our study . 1306.6 Association of mode energy and magnetic index of ARs. . . . . . . 1346.7 Association of p-mode energy and flare index . . . . . . . . . . . . . 135

7.1 A map of solar sub-photospheric flows of 27-28 October 2003 . . . . 1457.2 Sub-photospheric flows beneath active and quiet regions . . . . . . 1467.3 Zonal and meridional flows during pre- to post- flare phases of the

event X17/4B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1487.4 Profiles of sub-photospheric flow parameters during pre- to post-

flare phases of the X17/4B . . . . . . . . . . . . . . . . . . . . . . . 1497.5 Sub-photospheric meridional velocity profiles of NOAA 10030 and

10486 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1527.6 Sub-photospheric meridional velocity profiles of nine selected ARs . 1537.7 Latitudinal distribution of the meridional velocity gradient of 74 ARs1567.8 Vertical vorticity profiles of sub-photospheric flows beneath NOAA

10030 and 10226 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1597.9 Latitudinal distribution of meridional velocity gradients of 74 ARs . 160

8.1 Evolution of vertical vorticity, kinetic helicity and magnetic helicityin NOAA 10930 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

8.2 A map showing the positions and areas of 91 selected ARs . . . . . 1748.3 Latitudinal distribution of magnetic and kinetic helicities of 91 ARs 1768.4 Probability density function of magnetic helicity of 91 ARs . . . . . 1778.5 Latitudinal distribution of the vertical component of vorticity and

kinetic helicity density of 91 ARs . . . . . . . . . . . . . . . . . . . 1798.6 Probability density function of the vertical component of vorticity

and kinetic helicity density of 91 ARs . . . . . . . . . . . . . . . . . 1808.7 Association of magnetic and kinetic helicities . . . . . . . . . . . . . 1828.8 Association of current and kinetic helicities . . . . . . . . . . . . . . 184

A.1 Graphic illustration of trapezoidal rule . . . . . . . . . . . . . . . . 200

vii

List of Tables

4.1 Maximum distances, velocities, and time at the maximum velocitiesof transients of the X17/4B flare of 28 October 2003. . . . . . . . . 65

4.2 Maximum distances and velocities of the flare kernels during theX10/2B flare of 29 October 2003. . . . . . . . . . . . . . . . . . . . 76

6.1 The characteristics of ARs selected for the study . . . . . . . . . . . 131

8.1 A list of references showing hemispheric trend of helicity parameters. 1668.2 Latitudinal distribution of kinetic and magnetic helicities of 91 ARs. 1818.3 Correlation table of various twist parameters of 91 ARs. . . . . . . 183

viii

Acknowledgments

It is my great pleasure to express sincere thanks to my supervisor Prof. Ashok

Ambastha for his valuable guidance and encouragement in carrying out this work.

I am grateful to him for giving me this opportunity to work with him. Thank you

sir, for your patience, your help and your care. Thank you for teaching me so

much about solar physics and for accepting to take me as your PhD. student.

I am thankful to Prof. J.N. Goswami, Director PRL, for providing the nec-

essary facilities required during this work. I would like to express my sincere grat-

itude to Prof. H.M. Antia of TIFR, Mumbai, for kindly giving me an opportunity

to work with him for a month at TIFR during the initial stages of my research and

for valuable discussions and help whenever needed. I am also thankful to Prof. P.

Venkatakrishnan for many useful discussions on various concepts of solar physics.

I would like to record my sincere thanks to Dr. Frank Hill (NSO, USA),

Dr. R. Komm (NSO, USA), Prof. M. Thomson (University of Sheffield, UK),

Prof. Sarbani Basu (Yale University, USA), and Prof. J. Christensen-Dalsgaard

(Danish AsteroSeismology Centre, Denmark) for their valuable communications

on helioseismology at various stages of my work. Dr. J. Harvey (NSO, USA) was

very kind in describing the basic principles of GONG and MDI observations and

providing their comparisons. I am thankful to Dr. Sushant Tripathy (NSO, USA)

for providing the required GONG data during my thesis work.

It is a pleasure for me to express my heartfelt thanks to all the faculty mem-

bers of USO; Dr. Nandita Srivastava, Dr. Shibu Mathew, Dr. Sanjay Gosain,

Dr. Brajesh Kumar, Dr. Bhuwan Joshi, Mr. Raja Bayanna and Dr. R. Bhat-

tacharyya for providing their help whenever required. I would like to thank my

friends Sanjeev, Vinay, Rohan, Jayant, Anand, Vema and Babulal for giving me

their good company and sharing the moments of happiness. I am very much thank-

ful to the families of Prof. Ambastha and Prof. Venkatakrishnan for their help and

encouragement during my research, and to the families of Mr. Sudhir Gupta, Dr.

Brajesh Kumar, Dr. Sanjay Gosain, Mr. Raja Bayanna, Dr. Bhuwan Joshi, Mr.

Babulal Madhukar and Mr. Manoj Bhatnagar for helping me out whenever I faced

problems.

The administrative staff of USO had been very supportive all through and I

ix

wish to express my sincere thanks to them, particularly, to Mr. Raju Koshy, Mr.

Rakesh Jaroli, Mr. Pinakin Shikari and Mr. Shankarlal Paliwal. I am thankful

to Mr. Naresh Jain for providing the USO Hα data used in this study. I thanks

to USO staff, Mr. Laxmilal Suthar, Mr. Jagdish Singh Chauhan, Mr. Dalchand

Purohit, Mr. Ramchandra Carpenter and Mukesh Bhai Saradawa for their help at

various stages of my work. I am thankful to all those members of USO and PRL

staff who have helped me directly or indirectly in this study and helped in completing

my thesis.

I am deeply indebted to the GONG and SOHO/MDI teams for providing

their data, i.e., magnetograms, dopplergrams and intensitygrams. My work has

made extensive use of MLSO, TRACE, GOES, MSFC, RHESSI and Hinode data,

which I would like to acknowledge here.

Finally, words fail me in expressing the deep sense of gratitude to my parents

for their continuous encouragement to work in science and undertake the long and

arduous journey of a research scholar. I am grateful to my late grand mother for

her inspiration and to my sister for her affection. My wife Shashikala has been very

helpful and understanding throughout and provided me with delicious food when I

came back home after a long and hard day’s work. My lovely daughter Divya gave

me her delightful company to play with and to make me happy and relaxed.

My life at Udaipur included moments of happiness and sadness, comfort and

hardship, laughter and depression. However, all these moments shall be cherished

by me as beautiful lifelong memories.

Ram Ajor Maurya

x

Abstract

Solar active regions (ARs) are three-dimensional magnetic structures extend-

ing from deep sub-photosphere to coronal heights. These ARs are responsible for

producing most of the energetic transients, such as flares and Coronal Mass Ejec-

tions (CMEs), due to a complex interplay of their magnetic and velocity fields.

Therefore, accurate high spatial and temporal measurements of solar magnetic and

velocity fields are essential ingredients for the understanding of the evolution and

energetic activities of ARs. However, availability of these measurements is limited

only to the photosphere and to some extent, to the chromosphere. The energetic

charged particles released during these transients may also affect the measurements

of magnetic and Doppler velocity fields. In addition, the energetic transients are

expected to excite p-mode oscillations in ARs by imparting a mechanical impulse

associated with their thermal expansion on the photosphere.

While studying the magnetic and velocity fields in AR NOAA 10486, we de-

tected some puzzling moving transient features during the X17/4B and the X10/2B

flares of 28 and 29 October 2003, respectively. Both these flares were extremely

energetic white-light events. The transient features appeared during impulsive

phases of the flares and moved with speeds ranging from 30 to 50 km s−1. These

features were located near the previously reported compact acoustic (Donea and

Lindsey, 2005) and seismic sources (Zharkova and Zharkov, 2007). We have exam-

ined the origin of these features and their relationship with various other aspects of

the flares, viz., hard X-ray emission sources and flare kernels observed at different

layers - i) photosphere (white-light continuum), ii) chromosphere (Hα 6563A), iii)

temperature minimum region (UV 1600A), and iv) transition region (UV 284A).

We have determined the characteristic properties of local oscillation modes by

applying the ring diagram technique to 3-D power spectra of NOAA 10486. Strong

evidence of substantial increase in mode amplitude and systematic variations in

sub-surface flows are found from comparison of the pre- to the post-flare phases

of the energetic X17/4B flare of 28 October 2003. Furthermore, we have found

statistically significant association between the mode energy and flare energy from

xi

the study of several ARs of Solar Cycle 23.

Our study has revealed the prevalence of strongly twisted flows in the interior

of ARs having complex magnetic fields. Using the Doppler data obtained by the

Global Oscillation Network Group (GONG) project for a sample of 74 ARs, we

have discovered the presence of steep gradients in meridional velocity at depths

ranging from 1.5 to 5 Mm in flare productive ARs. The gradients showed an

interesting hemispheric trend of negative (positive) sign in the northern (southern)

hemispheres.

We have discovered presence of three sheared layers in the depth range of

0–10 Mm in many flare productive ARs, providing an evidence of their complex

flow structures as compared to the dormant or less productive ARs. An important

inference derived from our analysis is that the location of the deepest zero vertical

vorticity is correlated with the remaining lifetime of ARs. These new findings may

be employed as important tool for predicting the life expectancy of an AR and

space weather predictions.

Finally, we have studied the kinetic helicity in sub-photospheric flows and

magnetic helicity in photospheric magnetic fields of 91 ARs of solar cycle 23. We

have investigated the hemispheric trend in the kinetic helicity of sub-photospheric

flows averaged over depths 2.5-12 Mm. This has been examined with magnetic

helicity parameter obtained for the ARs by using photospheric vector magnetic

fields. However, any significant association between the twists of sub-photospheric

flows and photospheric magnetic fields is not found.

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