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Helicity of the solar magnetic field

Published online by Cambridge University Press:  26 August 2011

Sanjiv Kumar Tiwari
Sanjiv Kumar Tiwari*
Affiliation:
Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur - 313 001, India email: [email protected]
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Abstract

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Helicity measures complexity in the field. Magnetic helicity is given by a volume integral over the scalar product of magnetic field B and its vector potential A. A direct computation of magnetic helicity in the solar atmosphere is not possible due to unavailability of the observations at different heights and also due to non-uniqueness of A. The force-free parameter α has been used as a proxy of magnetic helicity for a long time. We have clarified the physical meaning of α and its relationship with the magnetic helicity. We have studied the effect of polarimetric noise on estimation of various magnetic parameters. Fine structures of sunspots in terms of vertical current (Jz) and α have been examined. We have introduced the concept of signed shear angle (SSA) for sunspots and established its importance for non force-free fields. We find that there is no net current in sunspots even in presence of a significant twist, showing consistency with their fibril-bundle nature. The finding of existence of a lower limit of SASSA for a given class of X-ray flare will be very useful for space weather forecasting. A good correlation is found between the sign of helicity in the sunspots and the chirality of the associated chromospheric and coronal features. We find that a large number of sunspots observed in the declining phase of solar cycle 23 do not follow the hemispheric helicity rule whereas most of the sunspots observed in the beginning of new solar cycle 24 do follow. This indicates a long term behaviour of the hemispheric helicity patterns in the Sun. The above sums up my PhD thesis.

Keywords

Sun: atmosphereSun: magnetic fieldsSun: sunspots
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S273: The Physics of Sun and Star Spots , August 2010 , pp. 21 - 27
Copyright
Copyright © International Astronomical Union 2011

References

Baty, H. 2000, A&A, 360, 345Google Scholar
Berger, M. A. & Field, G. B. 1984, Journal of Fluid Mechanics, 147, 133CrossRefGoogle Scholar
Elsasser, W. M. 1956, Rev. Mod. Phys., 28, 135CrossRefGoogle Scholar
Fan, Y. & Gibson, S. E. 2004, ApJ, 609, 1123CrossRefGoogle Scholar
Gosain, S., Tiwari, S. K., & Venkatakrishnan, P. 2010, ApJ, 720, 1281CrossRefGoogle Scholar
Hagino, M. & Sakurai, T. 2004, PASJ, 56, 831CrossRefGoogle Scholar
Ichimoto, K., et al. 2008, Solar Phys., 249, 233CrossRefGoogle Scholar
Jing, J., Tan, C., Yuan, Y., Wang, B., Wiegelmann, T., Xu, Y., & Wang, H. 2010, ApJ, 713, 440CrossRefGoogle Scholar
Lagg, A., Woch, J., Krupp, N., & Solanki, S. K. 2004, A&A, 414, 1109Google Scholar
Low, B. C. 1982, Solar Phys., 77, 43CrossRefGoogle Scholar
Martin, S. F. 1998, in Astronomical Society of the Pacific Conference Series, Vol. 150, IAU Colloq. 167: New Perspectives on Solar Prominences, ed. Webb, D. F., Schmieder, B., & Rust, D. M., 419Google Scholar
Moffatt, H. K. 1978, Magnetic field generation in electrically conducting fluids, ed. Moffatt, H. K.Google Scholar
Parker, E. N. 1979, Cosmical magnetic fields: Their origin and their activity (Oxford, Clarendon Press; New York, Oxford University Press, 1979)Google Scholar
Parker, E. N. 1996, ApJ, 471, 485CrossRefGoogle Scholar
Su, J. T., Sakurai, T., Suematsu, Y., Hagino, M., & Liu, Y. 2009, Astrophys. J. Lett., 697, L103CrossRefGoogle Scholar
Taylor, J. B. 1974, Physical Review Letters, 33, 1139CrossRefGoogle Scholar
Tiwari, S. K. 2009, Ph.D. thesis, Udaipur Solar Observatory/Physical Research Laboratory, Mohanlal Sukhadia University, UdaipurGoogle Scholar
Tiwari, S. K. 2010, Helicity of the Solar Magnetic Field: An application to predicting the severity of solar flares (Lambert Academic Publishing, 2010, ISBN: 978-3-8383-9771-9)Google Scholar
Tiwari, S. K., Joshi, J., Gosain, S., & Venkatakrishnan, P. 2008, in Turbulence, Dynamos, Accretion Disks, Pulsars and Collective Plasma Processes, ed. Hasan, S. S., Gangadhara, R. T., & Krishan, V., Astrophysics and Space Science Proceedings, 329Google Scholar
Tiwari, S. K., Venkatakrishnan, P., & Gosain, S. 2010a, ApJ, 721, 622CrossRefGoogle Scholar
Tiwari, S. K., Venkatakrishnan, P., Gosain, S., & Joshi, J. 2009a, ApJ, 700, 199CrossRefGoogle Scholar
Tiwari, S. K., Venkatakrishnan, P., & Sankarasubramanian, K. 2009b, Astrophys. J. Lett., 702, L133CrossRefGoogle Scholar
Tiwari, S. K., Venkatakrishnan, P., & Sankarasubramanian, K. 2010b, in Magnetic Coupling between the Interior and Atmosphere of the Sun, ed. by Hasan, S. S. and Rutten, R. J.; Astrophysics and Space Science Proceedings. Published by Springer Berlin Heidelberg; ISBN 978-3-642-02858-8 (Print) 978-3-642-02859-5 (Online), pp. 443-447Google Scholar
Venkatakrishnan, P. & Tiwari, S. K. 2009, Astrophys. J. Lett., 706, L114CrossRefGoogle Scholar
Venkatakrishnan, P. & Tiwari, S. K. 2010, A&A, 516, L5Google Scholar
Wang, H. 1992, Solar Phys., 140, 85CrossRefGoogle Scholar
Woltjer, L. 1958, ApJ, 128, 384CrossRefGoogle Scholar