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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.

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.

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.

Tudor M.,Croatian Meteorological and Hydrological Service | Ivatek-Sahdan S.,Croatian Meteorological and Hydrological Service
Meteorologische Zeitschrift | Year: 2010

Two cases when the operational forecast seriously underestimated the wind speed maxima are analysed. The first one in the night between 1st and 2nd February 2007 and the second one in the evening of 3 rd February 2007. The two cases are analyzed using measured data from Split and Makarska automatic stations as well as vertical soundings from Zagreb and Zadar and ALADIN model simulations. For the purpose of this study, ALADIN 72 hour forecast was run on 2 km resolution using the complete set of physics parametrizations, hydrostatic and nonhydrostatic dynamics. Results show the potential benefit of nonhydrostatic dynamics for operational forecast does not lie in improvement of the 10 m wind forecast as much as in forecasting clear air turbulence associated with the lee waves. © Gebrüder Borntraeger, Stuttgart 2010.

Guttler I.,Croatian Meteorological and Hydrological Service | Brankovic C.,Croatian Meteorological and Hydrological Service | Srnec L.,Croatian Meteorological and Hydrological Service | Patarcic M.,Croatian Meteorological and Hydrological Service
Climatic Change | Year: 2013

The surface energy budget components from two simulations of the regional climate model RegCM4.2 over the European/North African domain during the period 1989-2005 are analysed. The simulations differ in specified boundary forcings which were obtained from ERA-Interim reanalysis and the HadGEM2-ES Earth system model. Surface radiative and turbulent fluxes are compared against ERA-Interim. Errors in surface radiative fluxes are derived with respect to the Global Energy and Water Cycle Experiment/Surface Radiation Budget satellite-based products. In both space and time, we find a high degree of realism in the RegCM surface energy budget components, but some substantial errors and differences between the two simulations are also present. The most prominent error is an overestimation of the net surface shortwave radiation flux of more than 50 W/m2 over central and southeastern Europe during summer months. This error strongly correlates with errors in the representation of total cloud cover, and less strongly with errors in surface albedo. During other seasons, the amplitude of the surface energy budget components is more in line with reference datasets. The errors may limit the usefulness of RegCM simulations in applications (e.g. high-quality simulation-driven impact studies). However, by using a simple diagnostic model for error interpretation, we suggest potential sensitivity studies aiming to reduce the underestimation of cloud cover and overestimation of shortwave radiation flux. © 2013 Springer Science+Business Media Dordrecht.

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.

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.

Tudor M.,Croatian Meteorological and Hydrological Service
Geoscientific Model Development | Year: 2013

Meteorological numerical weather prediction (NWP) models solve a system of partial differential equations in time and space. Semi-lagrangian advection schemes allow for long time steps. These longer time steps can result in instabilities occurring in the model physics. A system of differential equations in which some solution components decay more rapidly than others is stiff. In this case it is stability rather than accuracy that restricts the time step. The vertical diffusion parametrization can cause fast non-meteorological oscillations around the slowly evolving true solution (fibrillations). These are treated with an anti-fibrillation scheme, but small oscillations remain in operational weather forecasts using ARPÉGE and ALADIN models. In this paper, a simple test is designed to reveal if the formulation of particular a physical parametrization is a stiff problem or potentially numerically unstable in combination with any other part of the model. When the test is applied to a stable scheme, the solution remains stable. However, applying the test to a potentially unstable scheme yields a solution with fibrillations of substantial amplitude. The parametrizations of the NWP model ARPÉGE were tested one by one to see which one may be the source of unstable model behaviour. The test identified the set of equations in the stratiform precipitation scheme (a diagnostic Kessler-type scheme) as a stiff problem, particularly the combination of terms arising due to the evaporation of snow. © 2013 Author(s). CC Attribution 3.0 License.

Tudor M.,Croatian Meteorological and Hydrological Service
Hrvatski Meteoroloski Casopis | Year: 2011

DART (Dynamics of the Adriatic in Real-Time) is a project devoted to real time observational and modelling study of the Adriatic Sea involving a considerable number of organisations from Europe and US. Several ocean and wave models were run using different meteorological model outputs for input atmospheric conditions. Two field campaigns (research cruises) were organised, during March and August 2006. This paper presents the role of meteorology and operational meteorological models in an oceanographic research cruise. Realtime measurement and model capabilities are described in detail with brief analysis of two severe weather events.

Guttler I.,Croatian Meteorological and Hydrological Service
Hrvatski Meteoroloski Casopis | Year: 2011

Large warm bias in near-surface temperature during winter was detected over northeastern Europe in simulations with RegCM4 regional climate model when compared to observational dataset. Modifications to alleviate warm bias included reductions of the low-level cloud cover fraction and the minimum turbulent mixing in stable planetary boundary layer. When implemented, these modifications reduced warm bias up to 50% and did not degrade, or substantially impact, the variables analyzed outside the region and season considered. Validations of the planetary boundary layer and cloud features were limited due to unavailability of appropriate observational data at climatological timescales.

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