Dynamics of Magnetic Flux Elements in the Solar Photosphere

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Abstract

The interaction of magnetic elds and convection is investigated in the context of the coronal heating problem. We study the motions of photospheric magnetic elements using a time series of high-resolution G-band and continuum ltergrams obtained at the Swedish Vacuum Solar Telescope at La Palma. The G-band images show bright points arranged in linear structures ("" ligree ) located in the lanes between neighboring granule cells. We measure the motions of these bright points using an object tracking technique, and we determine the autocorrelation function describing the temporal variation of the bright point velocity. The correlation time of the velocity is about 100 s. To understand the processes that determine the spatial distribution of the bright points, we perform simulations of horizontal motions of magnetic ux elements in response to solar granulation ows. Models of the granulation ow are derived from the observed granulation intensity images using a simple two-dimensional model that includes both inertia and horizontal temperature gradients ; the magnetic ux elements are assumed to be passively advected by this granulation ow. The results suggest that this passive advection model is in reasonable agreement with the observations, indicating that on a timescale of 1 hr the ux tubes are not strongly a ected by their anchoring at large depth. Finally, we use potential-eld modeling to extrapolate the magnetic and velocity elds to larger height. We nd that the velocity in the chromosphere can be locally enhanced at the separatrix surfaces between neighboring ux tubes. The predicted velocities are several km s~1, signicantly larger than those of the photospheric ux tubes. The implications of these results for coronal heating are discussed.

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