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Front. Astron. Space Sci. | doi: 10.3389/fspas.2018.00038

The Extended Solar Cycle: Muddying the Waters of Solar/Stellar Dynamo Modeling Or Providing Crucial Observational Constraints?

 Abhishek K. Srivastava1*,  Scott W. McIntosh2, N. Arge3,  Dipankar Banerjee4,  Edward Cliver5,  Mausumi Dikpati2,  Bhola N. Dwivedi1,  Madhulika Guhathakurta6, B Karak1,  Robert J. Leamon3, P. Martens7, Shibu K. Matthew8,  Andres Munoz-Jaramillo9, D. Nandi10,  Aimee Norton11, L. Upton2, S. Chatterjee4,  Rakesh Mazumder4, Yamini Rao1 and Rahul Yadav8
  • 1Indian Institute of Technology (BHU), India
  • 2High Altitude Observatory (UCAR), United States
  • 3Goddard Space Flight Center, United States
  • 4Indian Institute of Astrophysics, India
  • 5National Solar Observatory, United States
  • 6National Aeronautics and Space Administration (NASA), United States
  • 7Georgia State University, United States
  • 8Udaipur Solar Observatory, India
  • 9Southwest Research Institute Boulder, United States
  • 10Indian Institute of Science Education and Research Kolkata, India
  • 11Stanford University, United States

In 1844 Schwabe discovered that the number of sunspots increased and decreased over a period of about 11 years, that variation became known as the sunspot cycle. Almost eighty years later, Hale described the nature of the Sun's magnetic field, identifying that it takes about 22 years for the Sun's magnetic polarity to cycle. It was also identified that the latitudinal distribution of sunspots resembles the wings of a butterfly \-- showing migration of sunspots in each hemisphere that abruptly start at mid-latitudes (about $\pm$35$^{o}$) towards the Sun's equator over the next 11 years. These sunspot patterns were shown to be asymmetric across the equator. In intervening years, it was deduced that the Sun (and sun-like stars) possess magnetic activity cycles that are assumed to be the physical manifestation of a dynamo process that results from complex circulatory transport processes in the star's interior. Understanding the Sun's magnetism, its origin and its variation, has become a fundamental scientific objective \-- the distribution of magnetism, and its interaction with convective processes, drives various plasma processes in the outer atmosphere that generate particulate, radiative, eruptive phenomena and shape the heliosphere. In the past few decades, a range of diagnostic techniques have been employed to systematically study finer scale magnetized objects, and associated phenomena. The patterns discerned became known as the ``Extended Solar Cycle'' (ESC). The patterns of the ESC appeared to extend the wings of the activity butterfly back in time, nearly a decade before the formation of the sunspot pattern, and to much higher solar latitudes. In this short review, we describe their observational patterns of the ESC and discuss possible connections to the solar dynamo as we depart on a multi-national collaboration to investigate the origins of solar magnetism through a blend of archived and contemporary data analysis with the goal of improving solar dynamo understanding and modeling.

Keywords: Sun – magnetic, Sun, Photosphere, solar cycle, solar dynamo

Received: 19 Jul 2018; Accepted: 12 Oct 2018.

Edited by:

Valery M. Nakariakov, University of Warwick, United Kingdom

Reviewed by:

Sergei Zharkov, University of Hull, United Kingdom
Ilpo Virtanen, University of Oulu, Finland  

Copyright: © 2018 Srivastava, McIntosh, Arge, Banerjee, Cliver, Dikpati, Dwivedi, Guhathakurta, Karak, Leamon, Martens, Matthew, Munoz-Jaramillo, Nandi, Norton, Upton, Chatterjee, Mazumder, Rao and Yadav. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Abhishek K. Srivastava, Indian Institute of Technology (BHU), Varanasi, India, asrivastava.app@iitbhu.ac.in