Figure 4. Top panel, temperature profiles at hourly intervals for an MSS site at Mašun, Slovenia (see Figure 1), at depths of 20 cm (dark grey line), 50 cm (black line) and 80 cm (grey line). Upper centre panel, spectral densities (y-axis) for different cycle periods (x-axis) for cycles up to 100 days for the upper MSS site. Note the strong 24 hour period. Lower centre panel, spectral densities (y-axis) for different cycle periods (x-axis) for cycles up to 100 days for the intermediate MSS site. Note the weak 24 hour period. Lower panel, spectral densities (y-axis) for different cycle periods (x-axis) for cycles up to 100 days for the deep MSS site. Note the absence of any 24 hour period, even at low spectral densities.