Estimation of the splitting frequencies. Main panel: L = 364 ACFs corresponding to the available solar one-day subseries observed in 1996 with the blue SPM channel (gray lines) and their mean ACF (black). The mean ACF allows the automatic derivation of the upper and lower frequencies surrounding the acoustic mode regime {f_h, f_c }. Inset panel: logarithm representation of the associated PSD estimates computed using Eq. (1). The PSD allows us to localize the flicker frequency {f_g }. The lower frequency {f_ℓ} is set by the window length of the SG filter applied to each one-day subseries to remove the long-term variability. In both panels,the splitting frequencies are indicated by the dotted vertical red lines. The blue dotted line represents the slope of the PSD (see Eq. (2)) measured in the frequency region associated with the granulation regime ν ∈ [f_g, f_c]. From high to low frequency, the distinct regions are denoted by letters A to D.