  Scalings of the streamwise velocity energy spectra in turbulent boundary
layers were considered in Part 1. A spectral decomposition analysis provided a
means to separate out attached and non-attached eddy contributions and was used
to generate three spectral sub-components, one of which is a close
representation of the spectral signature induced by self-similar, wall-attached
turbulence. Since sub-components of the streamwise turbulence intensity
$\overline{u^2}$ follow from an integration of the velocity energy spectra, we
here focus on the scaling of the former. Wall-normal profiles and Reynolds
number trends of the three individual, additive sub-components of the
streamwise turbulence intensity are examined. This allows for revisiting the
scaling of the turbulence intensity in more depth, in comparison to evaluating
the total streamwise turbulence intensity. Based on universal trends across all
Reynolds numbers considered, some evidence is given for a Townsend--Perry
constant of $A_1 = 0.98$, which would describe the wall-normal logarithmic
decay of the turbulence intensity per Townsend's attached-eddy hypothesis. It
is also demonstrated how this constant can be consistent with the
Reynolds-number increase of the streamwise turbulence intensity in the
near-wall region.
