Derivation of Vertical Wind and Turbulence Profiles, the Mixing-Layer Height, and the Vertical Turbulent Exchange Coefficient from Sodar and Ceilometer Soundings in Urban Measurement Campaigns - Meteorological and Air Quality Models for Urban Areas - page 121

(a)
(b)
Fig. 13.1 Monthly mean wind speed over Budapest in July 2003: (a) diurnal variation and (b)
vertical profiles
proven for the first time from sodar measurements by Reitebuch et al. (2000). This
turbulence is essential for urban air quality because it mixes ozone and other air pol-
lutants downward from the residual layer (Sect. 13.2.3, Fig. 13.5) into the nocturnal
surface layer. The nocturnal increase of near-surface ozone concentrations is doc-
umented in Reitebuch et al. (2000) and Alföldy et al. (2007). This special feature
of the vertically increasing variance is an example for the interaction of the UBL,
which is coined by enhanced turbulence, with a typical nocturnal phenomenon of
the rural boundary layer, the low-level jet.
From Fig. 13.4 it is clearly visible that the variance of the vertical wind compo-
nent of air coming from built-up areas is considerably larger than in air coming from
rural areas. The diurnal variation of the variance of the vertical wind component