Comparison of time averages of dlnΩ/dlnr versus target latitude using 15 years of MDI data (upper panel) and five years of HMI data (lower panel). In both panels, black and blue lines show results obtained from splittings from 360-day time series of all and common modes (see, Sect. 4.1), respectively. The red and green lines show the results obtained from 72-day time series of all and common modes, respectively. The dotted lines mark the constant values of −0.9 and −1 at all latitudes. The error bars are 1σ.