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IAU Symposium 286 on Comparative Magnetic Minima
Working Group Overview
The solar activity cycle, as manifested by repeated increase and then decrease in the number of sunspots visible on the Sun, has been observed and analyzed for centuries. However, only for the past few ~11-year activity cycles have new capabilities in satellite and ground-based observations allowed us to consider how a broad range of solar, heliospheric, and geospace observables vary within and between cycles. These observations, in conjunction with theoretical and numerical modeling advances, enable an interdisciplinary, system-wide view on the origins and impacts of solar cycle variation.
Solar minimum represents the time of lowest solar activity and simplest heliospheric structure, and as such is a good place to begin putting together such a system-wide understanding. However, recent observations and analyses imply complexities in the variation within and between solar minima that have implications for analyzing and predicting space weather responses at the Earth during solar quiet intervals, and also for interpreting the Sun's past behavior as preserved in cosmogenic isotopes and historical sunspot and auroral records.
Determining the solar origins and net impacts at the Earth of solar minimum differences will require coordinated, interdisciplinary modeling efforts to bring the pieces together. Thus our mission overlaps with international programs such as CAWSES . The international observational and modeling coordinated campaigns known as the Whole Sun Month (WSM) and the Whole Heliosphere Interval (WHI) are specific examples of such efforts for solar minimum periods (1996 and 2008, respectively). The goals of these campaigns were to characterize the 3-D solar minimum heliosphere and to trace the effects of solar structures and activity through the solar wind to the Earth and other planetary systems, and beyond. A direct comparison of these two periods illustrates how very different solar minima may be.
The mission of our IAU working group is to facilitate international and interdisciplinary research that focusses on the coupled Sun-Earth system during solar minimum periods. Such research seeks to characterize the system at its most basic, "ground state", but also to understand the degree and nature of variations within and between solar minima.
We will build from the WSM and WHI legacy, with the goals of
Our focus, at least initially, will be on variations between solar minima, but it will be essential to consider how such variations arise. This will require some degree of broader consideration of the solar cycle, both in the context of how a given solar minimum may depend upon the transport of solar magnetic flux in the years preceding it, and in the even greater context of long-term solar cycle variations. Solar activity in the past few decades has been very high compared to the past millenium. What was the heliospheric state during periods of the lowest sunspot activity, e. g., the Maunder minimum of the 17th century? Is there a minimum "ground state" for solar/heliospheric behavior? How might complexities in the solar magnetic configuration have influenced the Earth's response during such intervals? Finally, as we study the cyclic interactions of the heliophysical system, we will be mindful of the insights we gain into stellar variability over multiple time scales.