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Paper: Dynamics of Magnetic Elements in the Photosphere and the Formation of Spicules
Volume: 183, High Resolution Solar Physics: Theory, Observations, and Techniques
Page: 30
Authors: van Ballegooijen, A. A.; Nisenson, P.
Abstract: We consider the proper motions of photospheric magnetic elements, and the effects of these motions on flows at larger heights. We summarize the results from recent analyses of high resolution G-band data obtained at the Swedish Vacuum Solar Telescope (SVST) on La Palma. The G-band images show small bright features which are known to correspond to kilogauss magnetic fields. We measure the motions of these bright points and find that the autocorrelation time of the bright point velocity is about 100 s. From the observed continuum intensity images, we derive a model of the granulation flow velocity as function of time and position on the Sun. We use this flow model to simulate the horizontal motions of photospheric magnetic elements, assuming that the elements are passively advected by the granulation flow. We find that this passive advection model is in reasonable agreement with the observed spatial distribution of the G-band bright points. Finally, we use potential-field modeling to extrapolate the magnetic and velocity fields from the photosphere, where the flux tubes are well separated, to a height of 1500 km in the chromosphere, where the flux tubes fill the available volume due to the spreading out of the field lines. We find that strong shear flows occur near separatrix surfaces where neighboring flux tubes slide past each other in the chromosphere. We propose that spicules are formed in these separatrix layers.
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