3. A numerical model simulation
It is interesting to compare these observations with the results of numerical model simulations of the solar background spectrum. The comparison has been made on the basis of results inferred from a direct and simple numerical simulation of the three scales of convective cells observed: granulation, mesogranulation and supergranulation. The model (see Andersen et al. 1994; Andersen 1991a, b) calculates the time evolution of the visible solar hemisphere with a pixel size of 8*8 . The effect of rotation is only taken into account for the supergranular signal and active regions are not included. Since the solar intensity structures are smaller than the pixel size, the high resolution observations are binned into the pixel dimension. This produces some uncertainty in the model, especially for granulation, where the accurate size distribution at its lower limit is difficult to determine. The input parameters have been chosen from high resolution observations of granulation, meso- and supergranulation: lifetimes of 500, 8000 and 72000 seconds and the r.m.s. contrast at full resolution is 11%, 3% and 2%, respectively. The power spectra of the output of such realizations by the numerical simulation is also plotted in Fig. 2.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998