engleski

Quasy-steady state equilibrium boundary layer height determination in urban conditions

Stable boundary layer height (H), either measured or determined from an atmospheric model, is a very important and complex parameter used in many meteorological applications. Even though the models provide numerical values of H with high resolution in space and time, they still represent a simplification of reality especially in urban areas Representation of the boundary layer structure in all its complexity and variability depends on the specific model characteristics and applied parameterisations. Therefore a continuous comparative assessment of H calculated from various data sources and with different methods is needed. The evolution of urban H is highly non-stationary, especially during the first few hours after sunset. Even later during the night an approach to quasi-steady state equilibrium height (He) can be very slow. Basically, we can distinguish two approaches for the determination of H: diagnostic and prognostic. The prognostic equation that describes the development of H toward He ought to be better than a diagnostic relationship in modelling evolution of the H under stable but also evolving conditions. According to Seibert et al., (2000), the prognostic equations have rarely been tested systematically ; only single case studies are typically reported (e.g., Hanna, 1969 ; Arya, 1981 ; Koračin and Berkowicz, 1988). In Zilitinkevich et al. (2002) diagnostic and prognostic equations for the depth of stably stratified Ekman boundary layer are validated against measurements. Moreover, H from NWP models in urban stable conditions needs to be analyzed through diagnostic and prognostic equations. Here ALADIN (Aire Limitee Adaptation Dynamique development InterNational) (Geleyn et al. 1992), a spectral hydrostatic limited area NWP model for short-range forecasts, is used. Here two different methods for determination of H: a prognostic equation of a linear relaxation type, and widely used diagnostic bulk Richardson number, RiB, method (Mahrt, 1981 ; Troen and Mahrt, 1986 ; Holtslag et al. 1990 ; Sø rensen et al. 1996 ; Jeričević and Grisogono, 2006) are employed. These methods are applied on radio sounding and NWP data in an urban area where stationary conditions are very rare. The analysis presented, based on significant data set (more than 200 hourly values) showed that the prognostic approach can be more convenient for the H determination in urban night time conditions.

urban conditions; stable boundary layer

nije evidentirano