The High Altitude Observatory at the National Center for Atmospheric Research
Boulder, Colorado

The last five years have seen substantial progress in our understanding of the solar dynamo, fueled by continuing advances in observations and modeling. With the launch of NASA’s Solar Dynamics Observatory (SDO) in 2010 came an unprecedented window on the evolving magnetic topology of the Sun, highlighting its intricate 3D structure and global connectivity. The Helioseismic Magnetic Imager (HMI) instrument on SDO in particular has provided potentially transformative yet enigmatic insights into the internal dynamics of the solar convection zone that underlie the dynamo. Attempts to detect subsurface convective motions from helioseismic inversions have yielded only upper limits on the large-scale convective amplitude, challenging our understanding of global solar convection. Yet, potential signatures of giant cells have been detected in photospheric Dopplergrams. Estimates of the meridional flow from HMI and complementary instruments (SOHO/MDI and GONG) have been equally tantalizing and enigmatic. Several disparate techniques, including local and global helioseismic inversions and correlation tracking of surface features, have yielded evidence of a multi-cellular meridional flow but they differ on the detailed flow structure and amplitude. This multi-cellular meridional flow has potentially profound implications for flux-transport dynamo models that previously assumed a very different structure with a single circulation cell per hemisphere.

From a modeling perspective, the last five years have seen dramatic advances in global convective dynamo simulations. These now exhibit magnetic self-organization of chaotic turbulent fields into cyclic mean fields that bear some similarity with solar cycle observations. These convective dynamos operate very differently than Babcock-Leighton dynamo models which require flux emergence in order to operate and which are also backed by some observational support. Which of these paradigms applies to the Sun? Answers may only come by bridging the gaps between the two by understanding how convective dynamos generate emerging magnetic flux structures. Progress on this front has also been made in recent years with the spontaneous generation of rising flux structures in convective dynamo simulations and with the advent of 3D Babcock-Leighton/Flux-Transport dynamo models. Increasingly sophisticated simulations of solar surface convection suggest that flux systems can coalesce into sunspot pairs after emergence. Furthermore, the efficiency of small-scale dynamo action in these surface convection simulations suggests that turbulent fields may permeate the convection zone and dominate the magnetic energy. Meanwhile, growing research on data assimilation into solar dynamo models promises to provide a powerful new means to calibrate models, to identify model biases, to distinguish between competing models, and to potentially forecast future solar activity.

The time is ripe for a careful assessment of these new observational and modeling results and their implications for solar dynamo research. This workshop will bring together observers, modelers, and theorists to determine which recent developments are most robust, to identify the most pressing and tractable challenges, and to suggest a path forward for further research. The format will include invited talks, contributed talks, and open discussion and participation will be open to the community.