Behavior of the Refractive Index Structure Parameter in the Entraining Convective Boundary Layer

Abstract

The refractive index structure parameter CN2 has contributions from the temperature and humidity structure parameters Cr2 and CQ2 and from the joint structure parameter CTQ. We briefly review the behavior of these structure parameters in the surface layer. We show that the surface-layer similarity expressions for Cr2, CTQ and CQ2 yield, in the unstable limit, mixed-layer scaling laws which are in good agreement with data at small z/zi, where zi is the mixed-layer depth. However, we show that entrainment effects cause large departures from these laws in mid and upper regions of the convective boundary layer. Using Deardorff's idealization of the structure of the interfacial region at the top of a convective boundary layer, we use a ?mean-field closure? approach to develop scaling expressions for the structure parameters generated by the entrainment process there. The available data on CT2, CTQ and CQ2 near the convective boundary-layer top, from both steady and evolving cases, are shown to be consistent with these new scaling expressions.