Discoveries

Predictive flux-transport dynamo developments

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	(a) The observed sunspot area (smoothed by Gaussian running average over 13 rotations) plotted as a function of time. (b) The simulated toroidal magnetic flux in the overshoot tachocline within mid-latitudes for a meridional flow that is assumed to be steady (solid red area and curve), and for the time-varying meridional flow incorporated since 1996 (dashed red curve). After a few early cycles during which magnetic fields are first transported from the surface to the tachocline at the bottom of the convection zone, the model is able to reproduce the relative peaks of subsequent observed cycles.
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	The pop, middle and bottom frames on the right represent observational synoptic maps of Kitt Peak magnetic field data for Carrington rotations 1921, 1927 and 1936; the three theoretical synoptic maps on the left are derived from the superposition of three unstable global MHD modes for a band of toroidal magnetic field of strength 20 kilogauss at times equivalent to 0, 6, and 15 Carrington rotations. The yellow arrows in the frames on the right denote new cycle spots, while the spot inside the dotted circle in the top frame is an old cycle spot. The white arrows in the frames on the left show the longitudes at which the spots erupted at the surface; the only spot that does not fall in a bulge produced by the unstable modes (red areas) is circled in the lower right frame.

Over the past 50 years, many attempts to predict important properties of the next solar been made, including its amplitude, duration, and aspects of the patterns of solar activity that are produced, such as so-called `active longitudes.' These efforts have met with, at best, modest and uncertain success. There is strong motivation to achieve reliable predictions, both to gain deeper understanding of solar magnetism, and to forecast with skill the impacts of solar activity on the Earth. Communications, power transmission, and many other industries and activities are sensitive to the level and type of solar activity. Progress in solar cycle and magnetic activity simulations and predictions supports two strategic priorities of NCAR and ESSL: (i) working towards a comprehensive understanding of the Sun and the sources and manifestations of solar activity, and (ii) working towards a comprehensive understanding of solar influences on the Earth system.

This ongoing project involves the development and exploitation of both axisymmetric and nonaxisymmetric, physics-based, predictive models of solar cycle properties. The models are intialized with and constrained by observations of both solar flow fields (the differetial rotation and meridional circulation) and solar magnetic fields (sunspot areas and `butterfly' diagrams, and synoptic magnetograms). Work on the project began in about 2000 when HAO/NCAR scientist Dr. Mausumi Dikpati concluded that the use of such models to make solar cycle predictions was feasible. Actual predictions of solar cycle timing, including the influence of meridional circulation variations in the Sun, were made in FY2004, and the first predictions of solar cycle amplitudes and the evolution of active longitudes were made in FY2006.

In project plans for FY2005, it was decided that the first predictions of both the solar cycle amplitude and the evolution of active longitudes would be completed and announced in FY2006; this goal was achieved, with the publication of results for cycle amplitudes in 2006 (GRL, 33, L05102 and ApJ, 649, 498) and active longitudes in 2005 (ApJ, 635, L193). With respect to the cycle amplitudes, the relative peaks of the past 8 solar cycles were successfully simulated, and it was forecast that the peak of the upcoming solar cycle would be 30 - 50% higher than the current cycle 23. This would make cycle 24 on of the strongest cycles on record, the strongest since the dawn of the `space age' in the 1960s. With respect to active longitudes, it was shown that a simple forward propagation of unstable global MHD modes in the solar tachocline can track the evolving positions of solar active regions and active longitudes for at least a year during the rising phase of the current solar cycle. The solar cycle 24 prediction is being used by both U.S. and EU cycle 24 prediction panels to advise NASA, ESA, and industry on what to expect for solar activity and terrestrial response levels over the next decade. The results of the project were publicized in a joint NASA/NSF/UCAR telecon in March 2006, attended by approximately 35 members of the print and broadcast media. At least 200 news-websites subsequently featured articles on the results.

During FY2007 and FY2008, efforts will be directed toward accomplishing the following tasks as part of this project: (i) simulating and predicting solar activity peaks separately for the North and South hemispheres of the Sun; (ii) testing predictive skill of the flux-transport dynamo model for various treatments of the properties of past solar cycles and for variations in the meridional circulation; (iii) determining the skill of predictions for solar cycles more than one cycle ahead; (iv) developing and exploiting nonlinear hydrodynamic and magnetohydrodynamic models of the solar tachocline for the purpose of building and testing a prediction system for active longitudes; and (v) continuing developmental work on a nonaxisymmetric flux transport dynamo model, to simulate and predict solar cycles and active longitudes together. It is expected that several new findings will be reported in publications, and multiple forecasts for future cycles will be announced. These results are expected to be used by NASA for mission planning, and by solar activity-sensitive industries. Forecasts of future solar cycles will have impacts on both government and industry, as well as on the development of climate modeling scenarios for the 21st century. This project has been supported by the NSF as well as by NASA Living with a Star funds.