Boundary layer structure and stability classification validated with CO2 concentrations over the Northern Spanish Plateau
Pérez, I. A.
Sánchez, M. L.
García, M. Á.
A description of the lower boundary layer is vital to enhance our
understanding of dispersion processes. In this paper, Radio Acoustic
Sounding System sodar measurements obtained over three years were used to
calculate the Brunt-Väisälä frequency and the Monin-Obukhov
length. The Brunt-Väisälä frequency enabled investigation of the
structure of this layer. At night, several layers were noticeable and the
maximum was observed at the first level, 40 m, whereas during the day, it
was present at about 320 m. The Monin-Obukhov length was calculated with the
four first levels measured, 40–100 m, by an original iterative method and
used to establish four stability classes: drainage, extremely stable, stable
and unstable. Wind speed and temperature median profiles linked to these
classes were also presented. Wind speeds were the lowest, but temperatures
were the highest and inversions were intense at night in drainage
situations. However, unstable situations were linked to high wind speeds and
superadiabatic temperature profiles. Detrended CO<sub>2</sub> concentrations were
used to determine the goodness of the classification proposed evidencing
values which under drainage at night in spring were nearly 28 ppm higher
than those corresponding to unstable situations. Finally, atmosphere
structure was presented for the proposed stability classes and related with
wind speed profiles. Under extremely stable situations, low level jets were
coupled to the surface, with median wind speeds below 8 m s<sup>−1</sup> and cores
occasionally at 120 m. However, jets were uncoupled in stable situations,
wind speed medians were higher than 11 m s<sup>−1</sup> and their core heights
were around 200 m.