Spatiotemporal Correlations and Turbulent Photospheric Flows fromSOHO/MDI Velocity Data

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Abstract
Time series of high-resolution and full-disk velocity images obtained with the Michelson Doppler Imager (MDI) instrument on board SOHO have been used to calculate the spacetime spectrum of photospheric velocity flow. The effects of different methods for filtering acoustic oscillations have been carefully studied. It is found that the spectra show contributions both from organized structures that have their origin in the convection zone and from the turbulent flow. By considering time series of different duration and cadence in solar regions with different line-of-sight projections, it is possible to distinguish the contributions of the spectra from the two different kinds of flows. The spectra associated with the turbulent velocity fields obey power laws characterized by two scaling parameters whose values can be used to describe the type of diffusion. The first parameter is the spectral exponent of the spatial correlation function and the second is a scaling parameter of the time correlation function. Inclusion of the time parameter is an essential difference between the present work and other solar studies. Within the confidence limits of the data, the values of the two parameters indicate that the turbulent part of the flow in the scale range 16-120 Mm produces superdiffusive transport.

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