Boundary layer structure and stability classification validated with CO2 concentrations over the Northern Spanish Plateau

摘要

A description of the lower boundary layer is vital to enhance ourunderstanding of dispersion processes. In this paper, Radio AcousticSounding System sodar measurements obtained over three years were used tocalculate the Brunt-Väisälä frequency and the Monin-Obukhovlength. The Brunt-Väisälä frequency enabled investigation of thestructure of this layer. At night, several layers were noticeable and themaximum was observed at the first level, 40 m, whereas during the day, itwas present at about 320 m. The Monin-Obukhov length was calculated with thefour first levels measured, 40–100 m, by an original iterative method andused to establish four stability classes: drainage, extremely stable, stableand unstable. Wind speed and temperature median profiles linked to theseclasses were also presented. Wind speeds were the lowest, but temperatureswere the highest and inversions were intense at night in drainagesituations. However, unstable situations were linked to high wind speeds andsuperadiabatic temperature profiles. Detrended CO concentrations wereused to determine the goodness of the classification proposed evidencingvalues which under drainage at night in spring were nearly 28 ppm higherthan those corresponding to unstable situations. Finally, atmospherestructure was presented for the proposed stability classes and related withwind speed profiles. Under extremely stable situations, low level jets werecoupled to the surface, with median wind speeds below 8 m s and coresoccasionally at 120 m. However, jets were uncoupled in stable situations,wind speed medians were higher than 11 m s and their core heightswere around 200 m.