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Jericevic A.,Croatian Meteorological and Hydrological Service | Koracin D.,Desert Research Institute | Jiang J.,Desert Research Institute | Chow J.,Desert Research Institute | And 3 more authors.
NATO Science for Peace and Security Series C: Environmental Security | Year: 2013

Physical and chemical characteristics within the two distinct meteorological regimes, i.e., convective and stable atmospheric conditions in a complex highly urbanized terrain of the California South Coast Air Basin (CSCAB; the Los Angeles area) were investigated. The Community Multi-scale Air Quality (CMAQ) model was used with a horizontal resolution of 5 km × 5 km to produce the 3D fields of pollutant concentrations. Input meteorological fields were obtained by the MM5 numerical weather prediction model while the input emissions were provided by the Californian Environmental Protection Agency. Modeled meteorological surface parameters and their vertical profiles as well as modeled planetary boundary layer heights (PBL) were compared to the corresponding measurements. The CMAQ simulations of ozone concentrations were compared against the relatively large number of measurements from the CSCAB area. The main goal of the research was to identify the governing atmospheric processes and sources in the coastal area that contributed to the high levels of pollution and to investigate the air quality model's capabilities to simulate the air quality in the complex topography. © Springer Science+Business Media Dordrecht 2014. Source

Trosic T.,Croatian Meteorological and Hydrological Service
Boundary-Layer Meteorology | Year: 2010

The severe bora case that lasted from 13 to 15 November 2004 has been selected for the analysis of the bora of Pag's ribs, which occurs in the northern part of the eastern Adriatic coast over the Pag island area (Croatia). According to the measurements from automatic stations, the MM5 numerical model is successful in the 10-min mean wind speed prediction at 10-m height. The vertical analysis of the wind speed and potential temperature also gave satisfactory results. At the commencement of the bora the modelled wind had a magnitude of 20ms-1 at 10-m height in the Pag island area, which sharply attenuated in the cross direction and to the open sea. In this way the model has proved successful in predicting the characteristics of the bora of Pag's ribs. Potential vorticity (PV) at 600m has lower values within PV banners than during the developed bora. The consequence is a strong jet emanating from the nearest gap. The vertical cross-sections through the centre of the gap point out a permanent hydraulic-like flow. At the time of the bora of Pag's ribs the highest modelled turbulent kinetic energy is found in the jump-like region above the inversion and within the boundary layer along the lower boundary, ranging from 6-8m2 s-2. It is concluded that the dissipation in the hydraulic jumps and the wave breaking regions are the reasons for PV generation. © Springer Science+Business Media B.V. 2009. Source

Tudor M.,Croatian Meteorological and Hydrological Service
Meteorology and Atmospheric Physics | Year: 2010

Fog and low stratus forecasting experiments have been carried out with the numerical weather prediction model ALADIN on a case of long lasting fog. The model has been used with different radiation, cloud diagnosing and horizontal diffusion schemes, different representation of orography, increased vertical resolution and with or without prognostic condensates and turbulent kinetic energy (TKE). Some of the numerical set-ups are able to reproduce the fog (low stratus) field as seen in the satellite images as well as the measured 2m temperature and relative humidity diurnal cycles. The results show that cloud diagnosing schemes and overlap assumptions play a more important role than a more sophisticated radiation scheme, or introduction of prognostic cloud water, ice, rain, snow or TKE. More realistic orography representation and a more physical horizontal diffusion scheme significantly improve the modelled low stratus and 2m temperature in the areas with variable orography. © 2010 Springer-Verlag. Source

Tudor M.,Croatian Meteorological and Hydrological Service | Termonia P.,Royal Meteorological Institute of Belgium
Monthly Weather Review | Year: 2010

Limited-area models (LAMs) use higher resolutions and more advanced parameterizations of physical processes than global numerical weather prediction models, but suffer from one additional source of error-the lateral boundary condition (LBC). The large-scale model passes the information on its fields to the LAM only over the narrow coupling zone at discrete times separated by a coupling interval of several hours. The LBC temporal resolution can be lower than the time necessary for a particular meteorological feature to cross the boundary. A LAM user who depends on LBC data acquired from an independent prior analysis or parent model run can find that usual schemes for temporal interpolation of large-scale data provide LBC data of inadequate quality. The problem of a quickly moving depression that is not recognized by the operationally used gridpoint coupling scheme is examined using a simple one-dimensional model. A spectral method for nesting a LAM in a larger-scale model is implemented and tested. Results for a traditional flow-relaxation scheme combined with temporal interpolation in spectral space are also presented. © 2010 American Meteorological Society. Source

Belusic D.,Monash University | Hrastinski M.,Croatian Meteorological and Hydrological Service | Vezcenaj Z.,University of Zagreb | Grisogono B.,University of Zagreb
Journal of Applied Meteorology and Climatology | Year: 2013

Winds through the Vratnik Pass, a mountain gap in the Dinaric Alps, Croatia, are polarized along the gap axis that extends in the northeast-southwest direction. Although stronger northeasterly wind at the Vratnik Pass is frequently related to the Adriatic bora wind, especially at the downstream town of Senj, there are many cases in which the wind at Senj is directionally decoupled from the wind at the Vratnik Pass. Acluster analysis reveals that this decoupling is sometimes related to lower wind speeds or a shallow southeasterly sirocco wind along the Adriatic, but in many cases the bora blows over a wider region, while only Senj has a different wind direction. Several mechanisms can be responsible for the latter phenomenon, including the formation of a lee wave rotor. A numerical model simulation corroborates the decoupling caused by a rotor for a single case. The prevalence of northeasterly winds at the Vratnik Pass during southeasterly sirocco episodes is another result that challenges the current understanding. It is shown that, at least in one of these episodes, this phenomenon is related to a secondary mesoscale low pressure center in the eastern lee of the Apennines that forms as a subsystem of a broader Genoa cyclone. Less frequent southwesterly winds through the gap are predominantly related to the thermal sea breeze and anabatic circulations that are sometimes superimposed on the geostrophic wind. © 2013 American Meteorological Society. Source

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