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Belusic D.,University of Zagreb | Guttler I.,Meteorological and Hydrological Service
Quarterly Journal of the Royal Meteorological Society

The influence of meandering flow on dispersion of pollutants is frequently under-represented in dispersion models. In terms of measurements, meandering is primarily associated with time-scales between the turbulence and the applied averaging time, which is usually 1 h. The related spatial scales thus range roughly from 102 to 104 m (referred to here as submesoscales). As the state-of-the-art mesoscale models should be capable of reproducing flow features on scales larger than the turbulence, and as the meandering-generating mechanisms are not fully understood yet, it is useful to examine if the mesoscale models can reproduce meandering. For that purpose, the WRF/Chem model at 1/3 km horizontal resolution is used to simulate a weak-wind night during the CASES99 experiment. The measurements are used for detailed model verification. The model with its typical set-up fails to reproduce the variability at submesoscales and the locus of the under-representation is traced to too-strong horizontal diffusion. Reducing or removing the model diffusion allows the appearance of the submeso variability, whose spectral properties and the resulting plume behaviour agree well with the measurements. The linear correlation between the simulations with reproduced variability and themeasurements is low, as is the case between two simulations with only slightly different set-up. The conclusion is that mesoscale models are able to reproduce the strength of variability and the effects of meandering, but only with reduced or removed horizontal diffusion. The question arises whether it is possible to obtain a linear correlation, i.e. to correctly reproduce individual modes at these scales at all. © 2010 Royal Meteorological Society. Source

Horvath K.,Meteorological and Hydrological Service | Vilibic I.,Croatian Institute Of Oceanography And Fisheries
Natural Hazards

The article aims to test the sensitivity of high-resolution mesoscale atmospheric model to fairly reproduce atmospheric processes that were present during the Boothbay Harbor meteotsunami on 28 October 2008. The simulations were performed by the Weather and Research Forecasting (WRF) model at 1-km horizontal grid spacing by varying initial conditions (ICs) and lateral boundary conditions (LBCs), nesting strategy, simulation lead time and microphysics and convective parameterizations. It seems that the simulations that used higher-resolution IC and LBC were more successful in reproduction of precipitation zone and surface pressure oscillations caused by internal gravity waves observed during the event. The results were very sensitive to the simulation lead time and to the choice of convective parameterization, while the choice of microphysics parameterization and the type of nesting strategy (one-way or two-way) was less important for reproducibility of the event. The success of the WRF model appears limited to very short-range forecasting, most advanced parameterizations, and very high-resolution grid spacing; therefore, the applicability of present atmospheric mesoscale models to future operational meteotsunami warning systems still has a lot of room for improvements. © 2014 Springer Science+Business Media Dordrecht. Source

Vucetic V.,Meteorological and Hydrological Service
Journal of Agricultural Science

Maize is one of the most important agricultural crops in Croatia, and was selected for research of the effect of climate warming on yields. The Decision Support System for the Agrotechnology Transfer model (DSSAT) is one of the most utilized cropweather models in the world, and was used in this paper for the investigation of maize growth and production in the present and future climate. The impact of present climate on maize yield was studied using DSSAT 4.0 with meteorological data from the ZagrebMaksimir station covering the period 19492004. Pedological, physiological and genetic data from a 1999 field maize experiment at the same location were added. The location is representative of the continental climate in central Croatia. The linear trends of model outputs and the non-parametric MannKendall test indicate that the beginning of silking has advanced significantly by 1 ̇ 4 days/decade since the mid-1990s, and maturity by 4 ̇ 5 days/decade. It also shows a decrease in biomass by 122 kg/ha and in maize yield by 216 kg/ha in 10 years. Estimates of the sensitivity of maize growth and yield in future climates were made by changing the initial weather and CO2 conditions of the DSSAT 4.0 model according to the different climatic scenarios for Croatia at the end of the 21st century. Changed climate suggests increases in global solar radiation, minimal temperature and maximal temperature (×1 ̇ 07, 2 and 4 °C, respectively), but a decrease in the amount of precipitation (×0 ̇ 92), compared with weather data from the period 19492004. The reduction of maize yield was caused by the increase in minimal and maximal temperature and the decrease in precipitation amount, related to the present climate, is 6, 12 and 3%, respectively. A doubling of CO2 concentration stimulates leaf assimilation, but maize yield is only 1% higher, while global solar radiation growth by 7% increases evapotranspiration by 3%. Simultaneous application of all these climate changes suggested that the maize growth period would shorten by c. 1 month and maize yield would decrease by 9%, with the main reason for maize yield reduction in Croatia being due to extremely warm conditions in the future climate. © 2010 Cambridge University Press. Source

Sokol Jurkovic R.,Meteorological and Hydrological Service | Pasaric Z.,University of Zagreb
International Journal of Climatology

This study assesses the variability of the amounts of annual precipitation in global land areas (excluding Greenland and Antarctica) from 1951 to 2000. The analysis is based on 0.5° longitude/latitude gridded data. Three different data sets were analysed (University of East Anglia Climate Research Unit's (UEA CRU) TS 2.1 data set, the Global Precipitation Climatology Centre's (GPCC) Full Data Reanalysis version 5 data set, Variability Analysis of Surface Climate Observations (VASClimO) version 1.1 data set), and all led to very similar results. The results included here correspond to the VasClimO project data. Precipitation variability is examined through the anomaly of the coefficient of variation, which is shown to be a robust concept. It is defined as the departure of the actual coefficient of variation from the value that could be expected 'on average', conditioned on the total annual amount of precipitation. A brief discussion of the so-called Jackknife error is included. The analysis revealed diverse areas of larger-than-normal, smaller-than-normal and close-to-normal variability. Negative anomalies occur more often but have, on an average, lower values than do positive anomalies. Large areas of slightly negative anomalies were found inland for all continents except Australia. A zonal pattern in the distribution of the anomalies was clearly seen at subtropical latitudes, which generally showed positive anomalies. This general picture is modified by various local factors, such as cold ocean currents, monsoon activity and cyclone formation areas. Global modes of climate variability, such as the El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO), affect the variability of precipitation either directly or by modifying other relevant atmospheric and oceanic processes. Their influence is seen in many areas with higher-than-normal variability and is especially true if the high variability is accompanied by large amounts of mean annual precipitation. The authors believe that the present methodology may be useful in assessing the quality of future global data sets. It is, however, very desirable that such data sets include interpolation error estimates. © 2012 Royal Meteorological Society. Source

Gajic-Capka M.,Meteorological and Hydrological Service
Theoretical and Applied Climatology

The presence of snow along a portion of the Croatian highlands has enabled the development of winter tourism that is primarily oriented toward snow-related activities. Snow is more abundant and stays on the ground longer in the mountainous district of Gorski kotar (south eastern edge of the Alps) and on Mount Velebit (Dinaric Alps), which have elevations of up to 1,600 m and are close to the Adriatic coast than over the inland hilly region of north western Croatia where the summits are not more than approximately 1,000 m high. Basic information about the snow conditions at these locations was gathered for this study, including the annual cycle and probabilities for various snow parameters at different altitudes. As requested by the Croatian Ski Association, the relation between the air temperature and the relative humidity was investigated to determine the feasibility of artificial snowmaking. The snow parameters are highly correlated to air temperature, surface air pressure and precipitation, with certain differences occurring as a result of the altitude. Since the beginning of the second half of the twentieth century, winter warming and a significant increase in the mean air pressure (more anticyclonic situations) have been detected at all sites. Winter precipitation totals decreased at medium altitudes and increased at the summit of Mount Velebit, but these trends were not significant. The frequency of precipitation days and of snowfall decreased whereas an increasing fraction of the precipitation days at high altitudes involved solid precipitation. In contrast, a decreasing fraction of the precipitation days at medium altitudes involved solid precipitation, probably because of the different warming intensities at different altitudes. The mean daily snow depth and the duration of snow cover both slightly decreased at medium altitudes whereas the snow cover duration slightly increased at the mountainous summit of Mount Velebit. © 2010 Springer-Verlag. Source

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