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

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Monday, December 3, 2018

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.

Graph depicting extended solar cycles
Illustrating the appearance of the ESC in the contemporary era, extending the analysis of McIntosh et al (2014) to the present. Panel A shows the latitudinal variation of EUV bright points and their associated magnetic scale marker "g-nodes" as observed respectively by SoHO and SDO. Fitting the bright point and g-node bands in latitude-time distribution allows us to track the activity bands of solar cycle 22 (green), 23 (red), 24 (blue) and 25 (purple). Note that cycle 22 terminates in 1997, cycle 23 terminates in 2011, and that we anticipate cycle 24 to end in late 2019 or early 2020. Panel B shows something called a "band-o-gram," a schematic motivated by the data, to illustrate the magnetic polarities and potential interaction of the magnetic systems present.

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.

Publication Name: Frontiers In Space Science

First HAO Author's Name: Scott McIntosh