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

An extensive set of measurements (May-August 2012 and June-November 2013) taken at the Amundsen-Nobile Climate Change Tower located at Ny-Ålesund, Svalbard, allowed to investigate some features of the vertical structure of the atmospheric stable boundary layer (SBL) at high latitudes. The main sensors are 3 sonic anemometers and 4 low frequency thermo-hygrometers and anemometers. The momentum flux ?, the sensible heat flux Q and the turbulent kinetic energy K data at different levels evidenced 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 h? , hQ and hK, defined as levels for which fluxes became zero, can be considered to approximate the boundary layer depth. While the distributions of h? and hQ were found to be similar, being the ratio hQ/h? equally distributed around 1 even if with a positive skewness, those of h? and hK look quite different, being the ratio hK/h? > 1 in about 90% of the cases and with a median value > 2. In the upside-down case, the scales s? , 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 pertaining to the traditional case were found, even 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.