To check the validity of the numerical simulation, a comparison of its outputs with the observed background solar velocity spectrum can be performed. Fast Fourier Transforms have been applied to the two simulated series and their power density spectrum calculated. The results are presented in Fig. 5 (click here). No significative differences are seen between the two spectra. Only at very low frequencies (below 1 Hz), where the effects of the active regions are significative, some differencies can be seen.
Figure 5: Power spectral density of the calculated GOLF velocity measurements for high (1991 simulated series) and low (1986) solar activity. It is also shown the best fit to the earth-based observed estimation (Pallé et al. 1995)
In both series we have superposed the curve corresponding to the best fitting to the background solar velocity noise spectrum (B.S.V.N.S.) from earth-based observations (Pallé et al. 1995). The power of the simulated series is nearly an order of magnitude lower than the observed one in the region above Hz. This difference can be explained mainly due to the earth atmospheric noise, which has not been simulated, and the presence of power due to the window function of the one station observations. However, these effects will not contribute to the observations made in space. Effectively, measurements made by the GOLF experiment in the space (Gabriel et al. 1997) confirm our predictions at low frequencies.