Zvjezdana Bencetić Klaić

Atmospheric origin of the devastating coupled air‐sea event in the east Adriatic

Enhanced sea level oscillations with devastating effects occurred on 26/27 June 2003 in the east Adriatic. The phenomenon was recognized as a resonantly coupled air-sea interaction, where the sea wave is forced by the propagating atmospheric pressure disturbance. This study examines the dynamics and predictability of the atmospheric component of the coupled system. First, the initiation, amplification and maintenance of the system are examined. The source of the perturbation is traced back to the Alpine region, where the potentially unstable air in the westerly current lifts over the Alps resulting in convection and wave development. The wave and convective activity apparently couple in a wave-CISK manner and propagate southeastward down the eastern Adriatic coast. Due to the potentially unstable air above the Adriatic, the system additionally amplifies along its track. The dissipation of the system occurs after the landfall. Second, the performance of the numerical model at the resolution that is similar to operational NWP model resolution is examined. This severe event is highly susceptible to the details of the model configuration, presumably due to the sensitivity in coupling of the wave and MCS. Thus although the model is able to reproduce and forecast this kind of event at a fairly coarse resolution, the details of the spatial structure, as well as the time of onset, are questionable. In this case, the greatest sensitivity is primarily in the treatment of moist and convective processes.

Estimation of bora wind gusts using a limited area model

A performance of the wind gust estimate (WGE) method on the bora wind has been examined. Numerical simulations of several bora episodes have been performed using a non-hydrostatic mesoscale model MEMO6. The model captured well the onset and cessation of the bora while the agreement between simulated and observed wind speeds differed from episode to episode. In cases with accurately simulated wind speeds, the WGE results were very good, thus indicating that the method could be used in forecasting bora gusts. The performance of the WGE method for the examined bora cases also suggested a possibility of further simplification of the method for the bora applications. Inspection of the bora flow and its thermodynamical structure revealed that after the bora onset the shear instabilities completely overwhelm the buoyant forces. This means that the parcels with the maximum wind speed in the boundary layer will always be able to reach the surface and result in wind gusts. Therefore, it is enough to have only a vertical profile of the wind speed. Although completely derived from the physical considerations, this represents a very simple way of determining bora wind gusts and can thus be easily implemented in the operational bora wind forecasting models.

Mesoscale dynamics, structure and predictability of a severe Adriatic bora case

The dynamics, structure and temporal evolution of a severe Adriatic bora, which occurred during 14 and 15 November 2004 was inspected. Numerical simulation of the investigated episode was performed by the mesoscale model MM5. The model was validated against the radiosonde data and the wind data from one automatic meteorological station and three ultrasonic anemometers. Two anemometers where located in the region extremely favorable for the bora occurrence (Senj and Vratnik Pass), while the third one was placed in the mainland (Zagreb-Horvatovac). The model reproduced well the onset and the strength of the investigated bora, as well as the establishment of bora-induced potential vorticity (PV) banners. On the other hand, surface turbulent kinetic energy (TKE) was poorly predicted. Inspection of gap wind characteristics indicated the absence of strong dissipation in the flow through a mountain pass, which gives rise to a horizontally elongated jet. Appearance of wave breaking in the lee of a mountain peak leads to the creation of a mountain wake. Shear lines between individual jets and wakes created in this way are then responsible for the generation of PV banners. Also, the ability of the model to predict hourly wind gusts was validated using a recently developed method.

Croatian scientific publications in top journals according to the Science Citation Index for the 1980-2000 Period

A top journal is defined as a journal which is within the first 10% of journals ranked by impact factor in the SCI list, within a particular scientific subfield, for the year considered. Journals which were for 11 or more years within the first 10% were considered top journals during the whole period even though they were not within the first 10%, in some of the years covered by this study.In the period from 1980 to 2000, the Croatian scientists affiliated with research institutions within the Republic of Croatia, published a total of 13,021 papers in journals covered by the Science Citation Index (SCI). Out of these papers, only 2,720 were published in top journals. This amounts to 20.9% of the total, and this is below the world average of 29.5% for the same scientific subfields. Out of the above 2,720 publications, 1,250 (46.0%) were published in international collaboration, and 335 (12.3%) papers were Meeting Abstracts. The Croatian scientists were most productive in the main scientific fields: Physics (875 papers; 32.2%), Medicine (786 papers; 28.9%), and Chemistry (580 papers; 21.3%). All others fields, taken together, comprised 17.6% of the total scientific output. Of the 786 medical papers, 290 were Meeting Abstracts, or 36.9% of the total output in the field of Medicine, and medical Meeting Abstracts represent 86.6% of the total number of abstracts (335). Articles (2,060) represent 75.7% of the total Croatian scientific output in top journals.

Precipitation chemistry in Croatia during the period 1981–2006

The spatial, temporal changes and trends changes in precipitation chemistry in Croatia during the period 1981-2006 were analysed using data from 27 sampling sites. The origins of air masses that arrived over Croatia were evaluated by the sector analysis of two-dimensional back trajectories. The distribution per sector of the volume-weighted concentrations of the main ions (sulfate, nitrate, chloride, ammonium, calcium, magnesium, sodium, and potassium) and the pH were also inspected. The trend in the annual volume-weighted concentrations of the major ions in precipitation and pH was tested using the nonparametric Mann-Kendall test and Sens slope estimator. The sulfate and nitrate ion concentrations significantly decreased for the majority of sites. The main decline of the sulfate ion concentration occurred after 1990. Changes in the anthropogenic sulfur emission patterns over Europe in the last two decades resulted in different acidity and sulfate ion concentrations related to a particular sector compared to earlier times. In addition, precipitation chemistry in Croatia was also influenced by geographical and climatological diversity. Finally, the war and post-war activities were identified as possible anthropogenic sources of some base cations, i.e., potassium and calcium.

PM10, CO and NOx concentrations in the Tuhobic road tunnel, Croatia

Particulate matter (PM10 particle fraction) and trace gases (CO, NO and NO2) have been sampled during six weeks in the Tuhobic road tunnel, Croatia, whose length is 2140 m. Eight mini portable air samplers (Air Metrics, USA) were placed in the centre of the tunnel at a height of 1.70-m above the ground. PM10 samples were collected on Whatman quartz filters with the diameter of 47 mm, while gases were collected in Tedlar bags. Diurnal variations of pollutant concentrations for weekends and weekdays were determined based on cumulative eight- and four-hour sampling intervals, respectively. Results revealed the dependence of air pollution levels on both, the traffic density and pollution history, i.e., traffic density in times prior to the time interval concerned. The highest correlation between PM10 and trace gases concentrations was found for NO2, while among the trace gases NO and CO were the best correlated.

Meteorological simulations with use of satellite data for assessing urban heat island under summertime anticyclonic conditions

The aim of this study was to investigate the formation, evolution and evaluation of topography effects on the urban heat island over the city of Zagreb. For this purpose, the non-hydrostatic mesoscale meteorological model MEMO was used and high-resolution simulations were carried out for two summertime anticyclonic periods. Satellite data were used to improve the models performance. The simulation results were compared to available observations and it was proved that the model is capable of simulating the mesoscale wind flow reasonably well. The importance of the impact of nearby mountains on the urban heat island was also examined showing that local topography had an important role on its formation and damping.

Two simple wind speed models for practical application under stable conditions

This paper deals with the utility of Monin-Obukhov similarity theory for wind speed simulation in stable conditions over flat terrain in northern Croatia. Wind speed profiles observed through a 150-m deep layer are compared with those obtained from two simple wind speed models. For this purpose, the similarity functions for two stable classes based on Monin-Obukhov theory are locally determined. They are tested in wind speed simulations using a model based on the Monin-Obukhov theory (MO) and a model which combines the surface-layer model of Monin-Obukhov theory and the Ekman-Taylor type model (MOE). Under less stable conditions the combined model (MOE) produces better skill, whereas the model based on the Monin-Obukhov theory (MO) performed better under more stable conditions. Copyright

The Influence of Meteorological Conditions on Fine Particle (PM1.0) Levels in the Urban Atmosphere

It is well known that airborne particulate matter (PM) can damage human health and affect climate. Fine particles with an aerodynamic diameter less than 1 μm (PM1.0) are generally more harmful to humans compared to coarser particles. This study investigates the relationships between 1-min average PM1.0 mass concentrations and atmospheric conditions at the same time-scale. Concentrations were measured by the DUSTTRAKTM Aerosol Monitor, which was located in Zagreb’s residential quarter, far from major pollution sources. The monitor was placed at a height of 15.8 m above the ground. While the influences of temperature and global radiation remained unclear, it was shown that PM1.0 levels depended on horizontal and vertical wind speed, air pressure and relative humidity. Thus, climate change may at least locally modify PM pollution levels and accordingly affect human health. Finally, results suggested that a nearby road, at a distance of approximately 100 m, with weak to moderate traffic did not affect PM1.0 levels. Instead, recorded concentrations mainly originated from other urban sources that were several kilometers away.

Wind Effects on Man-Made Structures in a World with a Changing Climate

A number of epidemiologic studies reported correlations between ambient concentrations of air pollution and adverse health effects, such as respiratory and heart diseases, premature mortality, premature delivery and low birth weight. Apart from indirect effects of the wind on health, humans can experience ‘mechanical’ wind-induced injuries due to collapsing engineering structures, windborne debris, and wind-induced traffic accidents. In this study, basic features of the wind/structure interaction were briefly addressed and some effects of a changing climate on local wind characteristics were reported. Therefore, wind-tunnel simulations of the atmospheric boundary layer flow indicate the applicability of truncated vortex generators in reproducing the wind characteristics in the lower atmosphere. A loading of a vehicle exposed to cross-wind gusting gives evidence about the aerodynamics significantly different than on vehicles exposed to ‘standard’ atmospheric turbulence.