The aim of this study was to investigate possible effects of two hypothetical scenarios of the urbanization of Zagreb's surroundings on the local winds, which are established under summertime anticyclonic conditions. For this purpose, the nonhydrostatic mesoscale meteorological model MEMO was applied to the greater Zagreb area. Three simulations were performed. One employed the current land-use distribution, while the other two corresponded to an increase of the densely urbanized area by 12.5% (test 1) and 37.5% (test 2), respectively. Apart from the hypothetically urbanized areas, where average surface wind speed reductions of 8% and 18% were obtained for test 1 and test 2, respectively, the rest of the domain was not signi®cantly affected by hypothetical urbanization. The differences between the wind vectors for the predicted current state and the hypothetical state were more pronounced and found at higher altitudes during the night compared to daytime values. For all three simulations the same diurnal variation of the depth of anabatic=katabatic wind¯ow generated on south-facing slopes of 1 km high mountain Medvednica was obtained. During the night the depth of well-developed katabatic¯ow was about 370 m, while during the day the depth of anabatic ow grew from about 550 m in the late morning up to about 1140 m in the late afternoon.

SUMMARY A summertime anticyclonic situation over the northern part of the eastern Adriatic coast is studied using a three-dimensional nonhydrostatic mesoscale model. The aim is to evaluate small-scale variability, such as mesoscale eddies, sea-breeze convergence zones (CZs) and the coastal jet-like flow in the thermally driven mesoscale circulations over very complex terrain. The results show that the model reproduces main known features of the diurnal flow with certain local specific characteristics, in addition to some new ones, previously only somewhat qualitatively known. After comparisons with measurements, further analyses are performed by sensitivity tests in which topography and synoptic input are varied.The simulations show a development of two diurnal intensive mesoscale eddies inside Kvarner Bay (∼20 km × 20 km). The night-time deeper eddies exhibit anticlockwise rotation, while the late afternoon shallow one shows the opposite rotation. Their appearance and dynamics are connected primarily to the coastline shape and topography; meanwhile, the large-scale flow in the anticyclonic weather type, as addressed here, has small influence. Moreover, a CZ develops over Istria and the island of Krk as a result of merged sea breezes. The intensity, speed, position and configuration of the sea-breeze cells are examined. The results also show that the topography is more important for the formation of the CZ over the island of Krk and for the coastal jet-like flow between the island and mainland than for the Istrian CZ.

SUMMARYThe aim of the present study is the analysis and evaluation of the influence of both the complex terrain and land-use on the formation of the sea breeze in a coastal environment. The Greater Rijeka Area, a region with complex topography and several islands, offers the opportunity to examine these relationships. According to the results, the MEMO model proved capable of simulating the mesoscale wind flow reasonably well. However, further investigation into the choice of some of the input model parameters and the parametrization employed was considered valuable as a means to improve model performance. For this reason, the influence of individual islands on the sea-breeze structure was investigated, and the model results for two different land-use databases were compared with the available measurements. The results indicated that the alteration of the model topography achieved by the removal of the islands from the Rijeka gulf had a significant impact on the simulated mesoscale circulation patterns, whereas the land surface heterogeneity had only a slight influence on the airflow.

Abstract. Stable atmospheric conditions are often connected with the occurrence of high pollution episodes especially in urban or industrial areas. In this work we investigate a severe SO 2 episode observed on 3-5 February 2002 in a coastal industrial town of Rijeka, Croatia, where very high daily mean concentrations (up to 353.5 µg m −3 ) were measured. The episode occurred under high air pressure conditions, which were accompanied with a fog and low wind speeds. Three air quality models (50-km EMEP model, 10-km EMEP4HR model and 1-km CAMx model) were used to simulate SO 2 concentrations fields and to evaluate the relative contribution of distant and local pollution sources to observed concentrations. Results suggest that the episode was caused predominately by local sources. Furthermore, using three-dimensional, higher-order turbulence closure mesoscale meteorological model (WRF), the wind regimes and thermo-dynamical structure of the lower troposphere above the greater Rijeka area (GRA) were examined in detail. Modelled atmospheric fields suggest several factors whose simultaneous acting was responsible for elevated SO 2 concentrations. Established small scale wind directions supported the transport of air from nearby industrial areas with major pollution sources towards Rijeka. This transport was associated with strong, ground-based temperature inversion and correspondingly, very low mixing layer (at most up to about 140 m). Additionally, the surface winds in Rijeka were light or almost calm thus, preventing ventilation of polluted Correspondence to: M. T. Prtenjak (telisman@irb.hr) air. Finally, a vertical circulation cell formed between the mainland and a nearby island, supported the air subsidence and the increase of static stability.