Local and urban scale modeling - Air Pollution Modeling and Its Application - page 87

3. Results

The simulations provided a vast data base for different studies, such as validation
of the model performance on measured meteorological data; sensitivity tests for
the influence of the resolution, boundary conditions and surface parametrisations
on the simulations. Example of the modeled (Case 1, Table 1) and measured
surface sensible heat flux and 10 m wind speed are shown in Figs. 1 and 2. Most
difficult is to simulate correctly the exchange processes during night time and
transition periods (morning and evening) when the atmosphere is stably stratified.
The model predicts the daytime sensible heat flux within the limits given by
measured data variability, Fig. 1 . Still, it has to be noted that the model predicts
the surface sensible heat flux (2 m), while the acoustic anemometers were
mounted at 20 and 40 m above ground.

Sofia Experiment, 28 september - 3 October 2003

600

Rams6.0 surface sensible heat flux
modelled flux - variability of measurements
modelled flux + variability of measurements
sensible heat flux measured at 40 m
sensible heat flux measured at 20 m

500

400

300

200

100

0

-100

271 272 273 274 275 276 277

Fig. 1. Sensible heat flux (modeled surface values, measured at 20 and 40 m height, standard
deviations)

Julian Day of 2003 (GMT)

The measured wind speed at 20 and 40 m above ground is considerably lower
the modeled wind speed at 10 m height and lies outside the large variability inter-
val estimated on those measurements ( Fig. 2 ). The measured wind shows complex
diurnal variation caused by the mountain-valley circulations typical for Sofia. The
measuring site is relatively close to Vitosha Mountain.