http://arxiv.org/abs/1710.02114
We present in this work the development of a solar data assimilation method based on an axisymmetric mean field dynamo model and magnetic surface data, our mid-term goal is to predict the solar quasi cyclic activity. Here we focus on the ability of our algorithm to constrain the deep meridional circulation of the Sun based on solar magnetic observations. To that end, we develop a variational data assimilation technique. Within a given assimilation window, the assimilation procedure minimizes the differences between data and the forecast from the model, by finding an optimal meridional circulation in the convection zone, and an optimal initial magnetic field, via a quasi-Newton algorithm. We demonstrate the capability of the technique to estimate the meridional flow by a closed-loop experiment involving 40 years of synthetic, solar-like data. By assimilating the synthetic magnetic proxies annually, we are able to reconstruct a (stochastic) time-varying meridional circulation which is also slightly equatorially asymmetric. We show that the method is robust in estimating a flow whose level of fluctuation can reach 30% about the average, and that the horizon of predictive capability of the method is of the order of 1 cycle length.
C. Hung, A. Brun, A. Fournier, et. al.
Fri, 6 Oct 17
9/51
Comments: Accepted for publication in ApJ. 23 figures, 20 pages. 1 Institut de Physique du Globe de Paris, 75005 Paris, France, 2 AIM/SAp CEA-Saclay, 91191 Gif-Sur-Yvette, France, 3 Institut de Recherche en Astrophysique et Plan\'{e}tologie, 31028 Toulouse, France, 4 Laboratoire de m\'{e}t\'{e}orologie dynamique, Ecole Normale Sup\'{e}rieure, Paris, France
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