Observations collected by the NCAR C-130 research aircraft during the Eastern Pacific Investigation of Climate Processes (EPIC) field program in 2001 have been used to examine the upper atmospheric boundary layer (ABL) and inversion layer (IL) structure over the cold tongue. Processes occurring at the top of the ABL ultimately impact surface winds and hence air-sea interactions. Previous work by McGauley et al. based on momentum budgets suggests that entrainment is relatively important over the cold tongue. The purpose of the present study is to examine how the observed turbulence at the top of the ABL is related to the mean properties of the ABL and IL. The vertical wind shear in the IL over the cold tongue ranged by a factor of four during the eight cases sampled during EPIC. This variation in vertical wind shear is less due to variations in the change in the horizontal pressure gradient with height in the upper ABL and IL (which did not vary much from case to case during EPIC) and hence must be more due to variations in the vertical distribution of the turbulent momentum fluxes. It was expected that the variability in the vertical wind shear itself would represent an important cause of case to case variability in the turbulence of the upper ABL and IL over the cold tongue. The tentative result of analysis of the flight-level data from the C-130 is that the turbulence at the interface of the ABL and IL is more closely related to the presence or absence of ABL stratus clouds than to IL vertical wind shear. The latter appears to chiefly influence the depth of the IL.