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Belusic D.,University of Zagreb | Guttler I.,Meteorological and Hydrological Service
Quarterly Journal of the Royal Meteorological Society | Year: 2010

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.

Pandzic K.,Meteorological and Hydrological Service | Likso T.,Meteorological and Hydrological Service
International Journal of Climatology | Year: 2010

Homogeneity of the mean annual air temperature values at 2 m above ground for 22 stations in Croatia, in the period 1961-2000, is considered. The standard normal homogeneity test (SNHT) has been applied for this purpose, detecting both abrupt and gradual linear trend homogeneity breaks. For a group of lower-rank weather stations (poorer data quality), the results indicating inhomogeneity are sometimes difficult to explain. It has been shown that homogeneity breaks in multiannual averages are not higher than 0.5°C, which could influence the natural trend analysis as well as some other statistical structures such as climatological normals, correlation functions or smoothed time series. Because of this, homogenization has usually to be adapted to the newest situation. On the other hand, the first principal component amplitude, describing more than 90% of the considered air temperature field variance, indicates that the spatial average of the mean annual temperature for the whole territory of Croatia is not dependent on inhomogeneities present in a particular time series. This result is in accordance with those previously obtained for Sweden and Switzerland as well as with some similar results obtained for larger continental and global scales. ['However, Easterling and Peterson (1995a, b) found that on very large spatial scales (half a continent to global), positive and negative homogeneity adjustments in individual station's maximum and minimum temperature time series largely balance out so when averaged into a single time series, the adjusted and unadjusted trend were similar.'-cited by Peterson et al. (1998)]. © 2009 Royal Meteorological Society.

Horvath K.,Meteorological and Hydrological Service | Vilibic I.,Croatian Institute Of Oceanography And Fisheries
Natural Hazards | Year: 2014

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.

Sepic J.,Croatian Institute Of Oceanography And Fisheries | Vilibic I.,Croatian Institute Of Oceanography And Fisheries | Strelec Mahovi N.,Meteorological and Hydrological Service
Journal of Geophysical Research: Oceans | Year: 2012

A total of 16 events of tsunami-like sea level oscillations are documented in the northern Adriatic between 1955 and 2010. These oscillations, recorded at the long-term operating Rovinj tide gauge, are characterized by wave heights of up to 60 cm, periods of 20 to 150 min, and duration of 1 to 48 h. The sea level oscillations are found to be coincident with pronounced atmospheric pressure disturbances characterized by a 2-4 hPa air pressure change over 10 min. Convective activity is recognized as the most likely source of atmospheric pressure disturbances. Analysis of propagation speed and direction of the atmospheric pressure disturbances indicates that the sea level oscillations were generated and enhanced via the Proudman resonance over a wide and shallow northern Adriatic shelf. Typical conditions under which pronounced air pressure disturbances occur include an air pressure surface minimum centered over the northern Adriatic, a temperature front at a height of approximately 850 hPa, and a strong southwesterly jet stream with wind speeds reaching 20-30 m/s at a height of approximately 500 hPa over the northern Adriatic. Based on these parameters, a possibility for forecasting tsunami-like sea level oscillations from synoptic conditions is discussed. It appears that under favorable synoptic conditions sea level oscillations are more likely to occur than to not. However, no reliable conclusion on strength of an event can be reached from synoptic conditions only. Copyright 2012 by the American Geophysical Union.

Mikus P.,Meteorological and Hydrological Service | Telisman Prtenjak M.,University of Zagreb | Strelec Mahovic N.,Meteorological and Hydrological Service
Atmospheric Research | Year: 2012

In this study, deep convective activity, identified by lightning measurements and associated favorable synoptic conditions, is analyzed. The focus was on the warm part of the year (April to October) during the period 2006-2009 over six sub-regions in Croatia. A convectively active day is defined as a day with at least ten lightning strikes over the target sub-region. The obtained dataset is used to determine the climatology of the frequency and regional distribution of convective days and their inter-month variability. The analysis shows that 56% of all examined days, i.e., every second day during the warm part of the year, are days with convective activity. The most convectively active sub-region is the North Adriatic, with 62.4% of all days in the analyzed sample. The areas eastward of 16°E exhibit a peak in convective activity in June, contrary to the more western sub-regions, which show a maximum later in the summer, from July to August. The average temporal characteristics, such as typical duration, onset and cessation of convection, are also estimated. In all sub-regions, the convective activity begins in the early afternoon and ends mostly in the evening. Nocturnal convection occurs more frequently along the Adriatic coast.In the second part of this study, the dominant large-scale weather types and upper-level flow regimes, corresponding to the convectively active days, were determined using surface and upper-levels pressure fields. The lightning flashes are frequently detected in the non-gradient pressure field (23%); in the center (18%), in the leading (15%) and in the rear (12%) parts of the cyclone; and in the front part of a trough (11%). The southwesterly upper-level flow represents the most common flow regime (38%) in the days with convective activity. Slightly less is the northeasterly flow, which occurs with a frequency of approximately 23%, and the northwesterly flow, with a frequency of 18% of all selected days. © 2011 Elsevier B.V.

Vucetic V.,Meteorological and Hydrological Service
Journal of Agricultural Science | Year: 2011

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.

Gajic-Capka M.,Meteorological and Hydrological Service
Theoretical and Applied Climatology | Year: 2011

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.

Sokol Jurkovic R.,Meteorological and Hydrological Service | Pasaric Z.,University of Zagreb
International Journal of Climatology | Year: 2013

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.

Tudor M.,Meteorological and Hydrological Service
Geoscientific Model Development | Year: 2015

Three-hourly temporal resolution of lateral boundary data for limited area models (LAMs) can be too infrequent to resolve rapidly moving storms. This problem is expected to be worse with increasing horizontal resolution. In order to detect intensive disturbances in surface pressure moving rapidly through the model domain, a filtered surface pressure field (MCUF) is computed operationally in the ARPEGE global model of Météo France. The field is distributed in the coupling files along with conventional meteorological fields used for lateral boundary conditions (LBCs) for the operational forecast using limited area model ALADIN (Aire Limitée Adaptation dynamique Développement InterNational) in the Meteorological and Hydrological Service of Croatia (DHMZ). Here an analysis is performed of the MCUF field for the LACE coupling domain for the period from 23 January 2006, when it became available, until 15 November 2014. The MCUF field is a good indicator of rapidly moving pressure disturbances (RMPDs). Its spatial and temporal distribution can be associated with the usual cyclone tracks and areas known to be supporting cyclogenesis. An alternative set of coupling files from the IFS operational run in the European Centre for Medium-Range Weather Forecasts (ECMWF) is also available operationally in DHMZ with 3-hourly temporal resolution, but the MCUF field is not available. Here, several methods are tested that detect RMPDs in surface pressure a posteriori from the IFS model fields provided in the coupling files. MCUF is computed by running ALADIN on the coupling files from IFS. The error function is computed using one-time-step integration of ALADIN on the coupling files without initialization, initialized with digital filter initialization (DFI) or scale-selective DFI (SSDFI). Finally, the amplitude of changes in the mean sea level pressure is computed from the fields in the coupling files. The results are compared to the MCUF field of ARPEGE and the results of same methods applied to the coupling files from ARPEGE. Most methods give a signal for the RMPDs, but DFI reduces the storms too much to be detected. The error functions without filtering and amplitude have more noise, but the signal of a RMPD is also stronger. The methods are tested for NWP LAM ALADIN, but could be applied to other LAMs and benefit the performance of climate LAMs. © Author(s) 2015.

Mikus P.,Meteorological and Hydrological Service | Strelec Mahovic N.,Meteorological and Hydrological Service
Atmospheric Research | Year: 2013

The paper addresses two topics: the possibilities of satellite-based automatic detection of overshooting convective cloud tops and the connection between the overshootings and the occurrence of severe weather on the ground. Because the use of visible images is restricted to daytime, four detection methods based on the Meteosat Second Generation SEVIRI 10.8. μm infra-red window channel and the absorption channels of water vapor (6.2. μm), ozone (9.7. μm) and carbon dioxide (13.4. μm) in the form of brightness temperature differences were used. The theoretical background of all four methods is explained, and the detection results are compared with daytime high-resolution visible (HRV) satellite images to validate each method. Of the four tested methods, the best performance is found for the combination of brightness temperature differences 6.2-10.8 and 9.7-10.8. μm, which are correlated to overshootings in HRV images in 80% of the cases. The second part of the research is focused on determining whether the appearance of the overshooting top, a manifestation of a very strong updraft in the cloud, can be connected to an abrupt change of certain weather elements on the ground. For all overshooting tops found by the above-mentioned combined method, automatic station data within the range of 0.1° and available hail observations within 0.2° were analyzed. The results show that the overshootings are connected to precipitation in 80% and to wind gusts in 70% of the cases; in contrast, a slightly lower correlation was found for temperature and humidity changes. Hail is observed in the vicinity of the overshooting in 38% of the cases. © 2012 Elsevier B.V.

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