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Register a new userConvectively driven vortex flows in the Sun
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Authors
J. A. Bonet
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We have discovered small whirlpools in the Sun, with a size similar to the terrestrial hurricanes (<~0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral in their way to be engulfed by a downdraft. Our disk center observations show 0.009 vortexes per Mm^2, with a lifetime of the order of 5 min, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs.
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We characterize the observational properties of the convectively driven vortex flows recently discovered on the quiet Sun, using magnetograms, Dopplergrams and images obtained with the 1-m balloon-borne Sunrise telescope. By visual inspection of time series, we find some 3.1e-3 vortices/(Mm^2 min), which is a factor of 1.7 larger than previous estimates. The mean duration of the individual events turns out to be 7.9 min, with a standard deviation of 3.2 min. In addition, we find several events appearing at the same locations along the duration of the time series (31.6 min). Such recurrent vortices show up in the proper motion flow field map averaged over the time series. The typical vertical vorticities are <= 6e-3 1/sec, which corresponds to a period of rotation of some 35 min. The vortices show a preferred counterclockwise sense of rotation, which we conjecture may have to do with the preferred vorticity impinged by the solar differential rotation.
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A classical problem for the two-dimensional Euler flow for an incompressible fluid confined to a smooth domain. is that of finding regular solutions with highly concentrated vorticities around $N$ moving {em vortices}. The formal dynamic law for such objects was first derived in the 19th century by Kirkhoff and Routh. In this paper we devise a {em gluing approach} for the construction of smooth $N$-vortex solutions. We capture in high precision the core of each vortex as a scaled finite mass solution of Liouvilles equation plus small, more regular terms. Gluing methods have been a powerful tool in geometric constructions by {em desingularization}. We succeed in applying those ideas in this highly challenging setting.
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