  The turbulence statistics of the intermittent region in a supersonic
turbulent boundary layer are studied by direct numerical simulation. Recently,
Kwon et al. (2016) have shown that this intermittent behavior, consisting of
the coexistence of turbulent and non-turbulent flows separated by an interface,
could result in perils when the traditional Reynolds decomposition is used to
analyze data. Here, we extend the study of turbulent/non-turbulent interfaces
to the supersonic regime and report turbulence statistics conditioned to the
interface. We show that the mathematical artefact of the traditional
Reynolds/Favre decomposition contaminates the Reynolds stresses and thermal
statistics. Our conditional statistics provide direct evidence that turbulent
flow possesses positive Reynolds shear stress everywhere, whereas non-turbulent
flow carries zero Reynolds shear stress. The thermal statistics of turbulent
and non-turbulent flows exhibit opposite trends in the intermittent region, and
the difference can be traced back to the variation of total temperature
resulting from the Prandtl number.
