Stable boundary layer vertical scales in the Arctic: observations and analyses at Ny-Alesund, Svalbard

Abstract

An extensive set of measurements (May？August 2012 and June？November 2013) taken at the Amundsen-Nobile Climate Change Tower located at Ny-Alesund, Svalbard, allowed investigation of some features of the vertical structure of the atmospheric stable boundary layer (SBL) at high latitudes. The main sensors are three sonic anemometers and four low-frequency thermo-hygrometers and anemometers. The momentum flux τ, the sensible heat flux Q and the turbulent kinetic energy K data at different levels demonstrated the occurrence of both the traditional and upside-down SBL cases, according to the classification proposed in the literature. Based on a linear approximation of the profiles, the vertical scales were found to be different for the different second-order moments. In the traditional case, the scales hτ , hQ and hK, defined as levels for which fluxes became zero, can be considered to approximate the boundary-layer depth. While the distributions of hτ and hQ were found to be similar, having the ratio hQ/hτ equally distributed around unity although with a positive skewness, those of hτ and hK look quite different, having the ratio hK/hτ >1 in about 90% of the cases and with a median value >2. In the upside-down case, the scales sτ, sQ and sK, defined as the height at which the value of the considered quantity doubles that at the surface, give a measure of the vertical variations of the moments. Comparing the distributions of these three scales, similar results to those for the traditional case were found, although with slightly different statistics. The values of the ratio between scales affect the vertical profile of the local Obukhov length in both the traditional and upside-down SBL cases.