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Monitoring the temperature within the vineyard during the season is important for controling the maturation and planing various production activities in the vineyard. The study displays a description of the spatial variability of the temperature within the vineyard, since it has a strong effect on grape ripening and quality of the grapes. The goal of this study was to collect detailed temperature measurements at the two locations within the vineyard and to estimate temperature sensitivity at the vineyard scale. The results show that there is a great temperature variability within the vineyard and thus the need for system of zonal vineyard management. Rather than being managed uniformly, individual block can be split into zones in which management can be applied differentely.

In Croatia is observed the increasing trend in mean annual air temperature and the large variability in the measured extreme precipitation from prominent drought to severe flooding. Climatological studies based on regional climate models show the intensification of the extreme values of temperature and precipitation over Europe in the future climate. These changes in temperature and precipitation have a great impact on viticulture, considering that of all living organisms, plants react first to the change of surface temperature. Due to climate change, changes in temperature will affect: (i) differently all developmental stages of vines in certain wine-growing areas in Croatia (i.e. their phenological characteristics) and (ii) differently on different varieties. At the same time, the temperature increase changes convective activity (storms) and thus the occurrence of hail that are estimated as the second biggest cause of material damage in Croatia. The trend of increasing average duration of hailfall was also observed on the basis of measurements obtained in the low land of Croatia. Due to mentioned, the VITCLIC project (VITiculture and CLImate Change in Croatia) has several goals. Based on meteorological and climatological datasets and wine and grapevine archive data, the current situation and a monitoring system of key phenological phases of the vine due to climate change will be analyzed and established. Furthermore, the aim is to link the ripening and quality of grapes with agro-climatic indices and determine the relationship between hail parameters and the degree of damages in grapevines. The purpose is also to enable: (i) detailed agronomic and economic evaluation for preserving Croatian autochthonous grapevine varieties, (ii) determination of climate changes through agro-climatic indices in different future periods and (iii) an estimation of the increase or decrease in certain weather types which favor convective developments (and hail).

In Croatia is observed the increasing trend in mean annual air temperature and the large variability in the measured extreme precipitation from prominent drought to severe flooding. Climatological studies based on regional climate models show the intensification of the extreme values of temperature and precipitation over Europe in the future climate. These changes in temperature and precipitation have a great impact on viticulture, considering that of all living organisms, plants react first to the change of surface temperature. Due to climate change, changes in temperature will affect: (i) differently all developmental stages of vines in certain wine-growing areas in Croatia (i.e. their phenological characteristics) and (ii) differently on different varieties. At the same time, the temperature increase changes convective activity (storms) and thus the occurrence of hail that are estimated as the second biggest cause of material damage in Croatia. The trend of increasing average duration of hailfall was also observed on the basis of measurements obtained in the low land of Croatia. Due to mentioned, this project has several goals. Based on meteorological and climatological datasets and wine and grapevine archive data, the current situation and a monitoring system of key phenological phases of the vine due to climate change will be analyzed and established. Furthermore, the aim is to link the ripening and quality of grapes with agro-climatic indices and determine the relationship between hail parameters and the degree of damages in grapevines. The purpose is also to enable: (i) detailed agronomic and economic evaluation for preserving Croatian autochthonous grapevine varieties, (ii) determination of climate changes through agro-climatic indices in different future periods and (iii) an estimation of the increase or decrease in certain weather types which favor co nvective developments (and hail).

Mjerenje i registracija pojave zrna tuče na tlu zbog vremenskih i prostornih varijacija te kratkog trajanja vrlo je složeno. Potreba za točnijim podacima i objektivnim mjerenjem potaknula je znanstvenu zajednicu da konstruira i koristi jednostavni mjerni instrument – tučomjer. Postavljanjem mjernih instrumenta – tučomjera na generatorske/lansirne postaje obrane od tuče u kontinentalnom dijelu Hrvatske, kao i poligona u 2002. godini na području Zagorja započelo je mjerenje točnih fizičkih parametara tuče u Hrvatskoj. U ovom radu prikazane su izmjerene fizičke karakteristike tuče na području poligona u razdoblju 2002. – 2015. godine. Dobiveni rezultati pokazuju da su najveći parametri zrna tuče zabilježeni u lipnju. Nađen je negativni trend udjela zrna najmanjeg promjera (5.0–7.5 mm) i porast zrna većeg promjera (7.6–15.0 mm), što ukazuje na moguće povećanje intenziteta grmljavinskih oluja na tom području. Analiza spektra zrna tuče pokazala je da dvoparametarska gama funkcija daje najbolju prilagodbu raspodjele zrna tuče na tlu. Ovi rezultati mogu se koristiti u procjenama eventualnih šteta na temelju izračuna odnosa kinetičke energije ili broja zrna tuče i intenziteta oštećenja na poljoprivrednim kulturama u određenim fenofazama razvoja. Tako se primjerice za osiguravajuća društva mogu izraditi detaljnije karte rizika pojave tuče za pojedina područja u svrhu kvalitetnije i objektivnije procjene štete od tuče

Croatia and Greece are two countries in south-eastern Europe which are often affected by hailstorms , but are also attempting to reduce the corresponding risk by applying hail suppression programs. •Continental part of Croatia - flat area (26, 800 km2 ), covered with ≈ 590 hail suppression stations (CRO) ; •Hailpad polygon 30 x 20 km was installed in this area between three mountains (POL) ; •Northern Greece project area: 2670 km2 (GRE) ; •The data collected during the period 2010 – 2013 are used for comparison •Mean diameter of all hail stones, mean diameter of maximum hail stones (d), number of hailstones (n), mass (m) and kinetic energy (K.E.) are analysed. •K.E. distributions are compared on the basis of the Torro scale.

In the European Union, less-favoured area (LFA) for agriculture is an area with natural handicaps (lack of water, unfavourable climate, short crop season and tendencies of depopulation), or that is mountainous or hilly, as defined by its altitude and slope. LFAs benefit from area and headage compensatory allowances, and from a number of payments for structural adjustment, so it is a National governments obligation and interest to designate their respective LFAs. Croatia, as a new member of the European Union, prepared detailed analysis of orographic features, climatic conditions, soil characteristics and specific handicaps that induce negative affects to agricultural and rural development. Bio-physical climatic constraints and specific handicaps are analysed and presented here in details. Length of growing season defined by low air temperature and heat stress defined by high air temperature have been selected climatic parameters affecting the agriculture. The specific constraints in Croatia included strong wind and fire danger on the coast and hail inland. This work was initiated and lead by the Ministry of Agriculture while the analysis presented here was conducted in Meteorological and Hydrological Service of Croatia.

Settled in the mid latitudes of the Northern Hemisphere, Croatia is exposed to the frequent occurrence of severe thunderstorms, especially in the continental part. Therefore, occurrence of hail with a high possibility of doing heavy damage in agricultural production is very frequent. In the 1960s, aiming to protect agricultural production from hail, a hail suppression system was introduced in that area. In this study, we use observed hail and damage data collected in the 1981 – 2012 period along with the hailpad data from 2002 - 2012 period collected on hail suppression stations in the warm parts of the year (from the beginning of May to the end of September). For the spatial analysis of the observed hail and damage data, protected area is divided into 9 km x 9 km quadrants in a way that in every quadrant there is at least one hail suppression station. For each quadrant, a “hail threatening index” (HTI) as an empirical function of average number of days with hail, number of cases with hail damage (scale from 5 to 100 %) and cases with severe damage (scale from 50 to 100 %) in agriculture is calculated. The purpose of this index is to indicate locations or areas that are most frequently exposed to the crops damage caused by hail. In addition, EOF (empirical orthogonal function) analysis is performed on the kinetic energy data measured by the network of hailpads, in order to determine areas /quadrants with greater average kinetic energy in the period 2002- 2012, and hopefully confirm findings revealed by HTI. Results of this study, therefore, reveal the areas that would require additional measures of hail protection (passive or active) and/or use of the agricultural plants more resistant to hail.

Previous research showed that in most cases intensification of the storms’ updraft is followed by an increase in total flash rate. Rapidly growing flash rate increases the potential for severe weather, but doesn’t imply the development of severe weather phenomena itself. During severe thunderstorms CG lightning production seems to be decreasing, while significant increase in the number of IC flashes is registered. In the hailstorms, regions with a reduced number of lightning strokes can be detected. These regions are usually short lived and related to the wet hail growth which is not conducive to hydrometeor charging. In this work lightning characteristics are studied for ~ 40 cases of hail-producing thunderstorms occurring over Croatia in summer months (May to August), from 2008 to 2012. Lightning distribution, registered by LINET Lightning Detection Network, was compared to hail occurrences, based on data collected from a hail-pad polygon located in NW Croatia. The polygon, consisting of 150 hailpads, covers the area of app. 600 km2 with approximate distance between hailpads of up to 2 km. The results will show spatial and temporal characteristics of lightning distribution and polarity as well as portion of cloud to ground (CG) and intra cloud (IC) lightning before, during and after the time of hail occurrence. Additionally, all studied hailstorms were checked for the appearance of the overshooting tops (OT) using a method based on SEVIRI brightness temperature differences and verified in high-resolution visible (HRV) images, where available. For cases with apparent OT, detailed analysis of lightning properties and physical properties of hailstones on the ground (number, diameter and kinetic energy) is made. In order to find possible typical differences, these parameters are compared with the same parameters in cases where OT was not apparent.

SAŽETAK Tuča je česta pojava u toplom dijelu godine i u mnogim područjima na svijetu nanosi veliku štetu u poljoprivredi, a u urbanim sredinama na pokretnoj i nepokretnoj imovini. Mjerenje i registracija pojave zrna tuče na tlu zbog vremenskih i prostornih varijacija te kratkog trajanja vrlo je složeno. Potreba za točnijim podacima i objektivnom registracijom, tj. za dobivanjem preciznih podataka o fizičkim svojstvima i kinetičkoj energije tuče potaknula je znanstvenu zajednicu da konstruira i koristi jednostavni mjerni instrument – tučomjer. U radu je prikazan način mjerenja fizičkih parametara zrna tuče pomoću tučomjera, dok je kinetička energija udara zrna tuče izračunata prema metodi Mezeixa i Dorasa (1981). Prikazan je način baždarenja materijala ploče tučomjera, kao i njegovo postavljanje na prostoru kontinentalne Hrvatske. Dodatno je prikazan odnos kinetičke energije i iznosa oštećenja na raznim biljnim kulturama, kao i detaljna analiza tri slučaja tuče na području posebnog poligona. U kontinentalnom dijelu Hrvatske postavljanje tučomjera na sve glavne meteorološke postaje i postaje sustava obrane od tuče počelo je tijekom sezone 2001. godine. Gusta mreža tučomjera – poligon, postavljena je početkom 2002. godine na području Hrvatskog zagorja. U razdoblju od 2002. do 2009. godine na svim postajama kontinentalnog dijela Hrvatske i poligona skupljeno je 2 276 ploča tučomjera koje su zabilježile tuču. Ovaj broj podataka s tučomjera predstavlja oko 70 % svih registriranih slučajeva tuče na postajama u kontinentalnom dijelu Hrvatske u promatranom periodu. Rezultati analize ploča tučomjera pokazuju da se broj zrna tuče, koji je pao na površinu od 1 m2 kretao od 16 do 15 104 zrna sa srednjim promjerom od 8.1 mm i najvećim zabilježenim promjerom od 35.4 mm. Godišnja distribucija promjera zrna tuče pokazuje negativni trend pojave zrna manjeg promjera i pozitivni trend pojave zrna većeg promjera na području kontinentalne Hrvatske. Izmjerene vrijednosti kinetičke energije imale su vrijednosti između 0.1 i 1 359.6 J m-2. Srednja kinetička energija za cjelokupno područje kontinentalne Hrvatske u periodu od svibnja do rujna promatranog razdoblja iznosi 36 J m-2. Mjesec lipanj, uz najveću čestinu pojave tuče, ima i najveće srednje vrijednosti kinetičke energije od 45.7 J m-2. Analiza iznosa kinetičke energije i stupnja oštećenja raznih biljnih kultura pokazuje da je u intervalu od 0.1 do 25 J m-2 zabilježena neznatna ili nikakva šteta na biljkama. Oko 70 % slučajeva tuče u tom intervalu zabilježeno je u razdoblju od 2002. do 2009. godine na području kontinentalne Hrvatske. Rezultati pokazuju da iste vrijednosti kinetičke energije na raznim biljnim kulturama i fenofazama ne daju isti stupanj oštećenja. Rezultati prostorne analize pokazuju da dio zapadnog i središnji dio Hrvatske imaju najveću čestinu slučajeva tuče većeg i velikog intenziteta, a najveći broj tih slučajeva je na području u blizini planina Ivančice, Medvednice, Bilogore i Kalnika. Dobiveni rezultati mogu se koristiti u daljnjim istraživanjima grmljavinskih oluja, klimatoloških i evaluacijskih studija, a mogu se primijeniti i u provedbi mjera zaštite cjelokupne imovine aktivnim ili pasivnim metodama. Ključne riječi: zrna tuče, tučomjer, kinetička energija (K.E.), poligon, orografija.

Located at the mid latitudes of the Northern Hemisphere, Croatia is exposed to the frequent occurrence of severe thunderstorms and hail, especially in its continental part. This area (26 000 km2) is because of terrain and climatologically conditions very suitable for agricultural production (grain maize, grape and orchards). In order to receive precise and objective hailstone data, hailpads were installed during the season 2001 on each main meteorological and hail suppression station in the continental part of Croatia. The most important data received from hailpads are number and size of hailstones and the kinetic energy, as indicators of the intensity of the hailfall which is directly connected with the grade of damage on different agriculture plants. In this paper will be shown relation between hail parameters (number of hailstones and kinetic energy) and amount of damage on different agricultural plants. The analysis also reveals that the same amount of kinetic energy or equal number of hailstones damages specific plant in different phenophasae with various intensity.

Continental part of Croatia is exposed to the thunderstorms with severe rain and hail, especially in the summer months. This area is very important in terms of agriculture. Hence, in order to document hail events in details, a hailpad polygon 30×20 km in size was installed in the north-western part of this area (Zagorje) before the hail fall season in 2002. The polygon is settled between three mountains (Fig. 1): Ivančica on the north, Medvednica on the south and Kalnik on the northeast. A dense network with 150 hail pads with linear spacing of 2 km (1 hail pad per 4 km2) was obtained. Hail parameters that are obtained from hailpads can be used in climatologically and dynamical studies of hail. In this study, we use the data gathered in the hailpad polygon within the period 2002 – 2010. We analyzed the intensity (kinetic energy, K.E.) of hail, the maximum hailstone diameter and the hail fall duration, but only the results for K.E. are shown here. The goal is to investigate what are the factors that have influence on spatial and temporal distributions of these parameters in the polygon. There are some indications that orography could have significant influence (Počakal et al. 2009). Our approach is to implement the empirical orthogonal functions (EOF) method to the data from the hailpad polygon in the above mentioned 9-years period and to inspect this hypothesis.

Croatia is because of his location in the mid latitudes of the Northern Hemisphere, especially in the summer months exposed to the frequent occurrence of severe thunderstorms, especially in the continental part where modest climate, orography and rich soil enable intensive agricultural production. Hail is frequent with a high possibility of doing heavy damage in agriculture and other mobile and immobile property. Measuring of hail parameters on the ground is because of spatial and temporal variability, as well as short duration very complex. For receiving objective and exact hail data on the ground, several measuring instruments were developed. Very good results in practical measuring of hail stones where received from a simple and cheap measuring device, a hailpad. The most important data received from hailpads are number and size of hailstones and the kinetic energy, as indicators of the intensity of the hailfall which is directly connected with the grade of damage on different agriculture plants. In order to receive precise and objective hailstone data, hailpads were installed during the season 2001 on each main meteorological and hail suppression station in continental part of Croatia. On that way, a dense network with a 730 hailpads was obtained. Received results can be used for evaluation and climatology studies, also for the design and construction of passive protection devices (anti-hail nets). By nets design, the most important parameters are maximum kinetic energy, mass and number of stones per square meter, as there spatial distribution. In this paper will be shown the maximum hailstone parameters together with the construction and characteristics of protecting nets types which are used for protection of important agricultural plants in Croatia. In addition will be shown different armature types where the nets are placed in horizontal, vertical and at different angle. Depending of frequency and intensity of hail it is considering the economic validity of placing the protective nets in different areas.

Settled in the mid latitudes of the Northern Hemisphere, Croatia is exposed to the frequent occurrence of severe thunderstorms and hail, especially in the continental part between Sava, Drava and Mura rivers (Panonian basin). On the basis of hail data collected in continental part of Croatia (26 800 km2) in period 1981-2006, it is found that in this area of Croatia which is protected from hail, two different areas can be identified: western (hilly) part with the greatest number of days with hail, and eastern (generally flat) part which has mostly minimum days with hail. Through spatial distribution of hailfall duration, it is shown that majority of quadrants with longer average duration of hailfall is in front of the mountain, and concerning the analysis of Cb cells movement, it is also found that the areas with greater diameter of hail can be found in front of the mountain.

Hail is a frequent phenomenon in a warm part of a year and causes in many areas around the world great damage in agriculture, also to mobile and immobile property in cities. Areas with greater frequency of hail occurrence are mostly in the mid latitudes in the northern and southern Hemisphere. Croatia is also settled in this area ; especially his continental part is exposed to the frequent occurrence of thunderstorms. On the basis of hail and radar data sets collected in period 1981-2008 (meteorological, hail suppression stations and hailpads) in this paper are shown physical, spatial and temporal parameters of hail in continental part of Croatia Results show influence of the orography on this parameters and increasing trend of the mean hail fall duration calculated from 27 seasons (May-September) indicates a possible influence of climate changes to the hail fall.

HAILPAD DATA ANALYSIS FOR CONTINENTAL PART OF CROATIA Damir Pocakal 1Meteorological and Hydrological Service of Croatia, 10000 Zagreb, Gric 3, Croatia, dhmz-rc@vz.htnet.hr (Dated: 11 September 2009) I. INTRODUCTION Mainly in the summer months, Croatia is exposed to the thunderstorms with severe rain and hail, especially in its continental part. In the 1960s, aiming to protect and reduce heavy damage in agriculture and other mobile and immobile properties, a hail suppression system was introduced to this area. This mostly flat area (26, 800 km2) is part of Panonian basin with some greater mountains in his western part and is covered with about 590 hail suppression stations which are managed with 8 radar centres. Several authors (Fraile et al. 2003 ; Dessens et al. 2009 ; Siutas et al. 2009) accent importance of hail measuring with hailpads for climatology and evaluation studies in different countries. In order to receive precise and objective hailstone parameters, hailpads were installed during the season 2001 on each main meteorological and hail suppression station in continental part of Croatia. The total number of hailpads today is 730 (stations and polygon). II. PRESENTATION OF RESEARCH During the hail season (01.May-30.September) in time period from 1981 to 2008, around 12500 reports of hail are collected. These reports contain exact information about the location, date and time of hailfall. Unfortunately there are not physical parameters of hail in these reports. They contain only a short description or size comparison with other objects (corn, pea, walnut, golf ball, etc.). Spatial analysis of mean number of days with hail, based on this reports (Pocakal et al. 2009) shows that the area with maximum hail days (Zagorje) is in the western continental part of Croatia near the Slovenian border. The hailpad polygon (POL), 30 x 20 km in size was established in this area before the hailfall season in 2002. Hailpads were installed between the existing hailpads on hail suppression stations. On that way, a dense network with 150 hailpads with linear spacing of 2 km (1 hailpad /4km2) was obtained. This paper presents analysis of all hailpad data collected in period from 2002 to 2008, for the whole protected area, different sub regions and especially for hailpad polygon. III. RESULTS AND CONCLUSIONS Analysis was made on the bases of all 2049 hail cases recorded on hailpads (this number represents about 70% of all observed and reported hail cases on hail suppression stations) in the continental part of Croatia. Average values per square meter, for max. diameter, number of stones, mass and kinetic energy are calculated: (dmax.= 13.2 mm ; n = 1197 ; m = 492.0 g and K.E.= 36.5 J). For polygon these parameters are: (dmax.= 16.2 mm ; n = 935 ; m = 397.4 g and K.E.= 29.1 J). Annual average values for continental part of Croatia and polygon are shown in Tab.1. For easier comparison with similar analysis in other countries, Torro scale (Webb et all. 2001 ; Sioutas et all. 2009) is used for kinetic energy distribution. This distribution shows that 65.3 % of all recorded hail cases in continental part of Croatia have kinetic energy less than 20 Joule /m2. Only three hail cases with intensity scale H5 and maximum hail stone size between 31.3-35.4 mm, are recorded in time period 2002-2008. Spatial analysis shows that the locations of these three cases were in eastern flat part of continental part of Croatia. Relative frequency distribution of kinetic energy (point hail fall) for Croatia and polygon are shown in Fig. 1. Average / Year 2002 2003 2004 2005 2006 2007 2008 number of stones/ m2 1197 1089 1220 1363 900 990 1172 max. diam. (mm) 11.8 14.1 12.3 12.4 12.7 13.6 14.4 mass (g/m2) 555.4 470.3 472.6 483.1 317.7 459.7 643.5 K.E. (J/m2) 30.3 35.9 37.6 33.1 22.1 32.2 53.9 TABLE 1: Average annual values for hail parameters in continental part of Croatia. FIG.1: Hail kinetic energy (J/m2) distribution for Croatia and polygon based on the Torro scale (2002-2008). Relative frequency distribution of hailstone size, shows that the first four size classes (interval 2.5 mm) from 5.0 mm till 15.0 mm, contain more than 95 % of all hailstones. Annually distribution for these four size classes show decreasing trend of smaller stones (5.0 – 7.5 mm) and increasing trend for greater hailstones (10.1 – 15.0 mm). This trend is larger for the polygon (Fig. 2), than for the whole protected area in Croatia Results show that the western parts have the highest frequency of hail fall with intensity between H0 – H4 of Torro scale. Increase of damaged hailpads per hail day on polygon from 2.1 in 2002 to 7.8 in 2008, together with the greater number of larger stones indicate a possible increase of hailstorm intensity in continental part of Croatia. FIG. 2: Distribution and trend of different hailstone sizes (mm) on polygon (2002-2008). IV. REFERENCES Dessens J. Berthet C. and Sanchez J.L., 2009: Seeding optimization for hail prevention with ground generators. Jour.of Wea. Mod., 41 119-126. Fraile R., Berthet C., Dessens J. and Sanchez J.L., 2003: Return periods of severe hailfals computed from hailpad data. Atmos. Res., 67-68 189-202. Pocakal D., Vecenaj Z., and Stalec J., 2009: Hail Characteristics of Different Regions in Continental Part of Croatia. Atmos. Res., 93 516-525. Sioutas M., Meaden T. and Webb J.D.C., 2009: Hail Frequency, Distribution and Intensity in Northern Greece. Atmos. Res., 93 526-533. Webb J.D.C., Elsom D.M., and Reynolds D.J., 2001:Climatology of severe hailstorms in Great Britain.. Atmos. Res., 56 293-310.

Settled in the mid latitudes of the Northern Hemisphere, Croatia is exposed to the frequent occurrence of severe thunderstorms, especially in the continental part between Sava, Drava and Mura rivers. In the 1960s, aiming to protect agricultural production and reduce damage from hail, a hail suppression system was introduced in that area. The mountain relief starts in the neighbouring Slovenia and extend in the western part of Croatia. Middle part is low land and in the eastern part are some greater mountains. A radar monitoring of the Cb movement shows that Cb in the short distance from the front of the mountain stagnate, begins to grow and the intensity of hailfal increase (Curic, 2001 ; Pocakal, 1999). This paper investigates orographyc influence on Cb clouds movement and connected with it, spatial distribution and other hail characteristics in different regions of continental part of Croatia. During hail season, in the period 1981-2006, about 11000 reports of hail were collected from main meteorological and hail suppression stations. Radar data collected for the same period show that more than 66 % come from western directions (W, NW and SW), with average speed. For better comparison of data, the whole area is divided into quadrants (9 x 9 km), in such a way that in every quadrant there is at least one station (Pocakal 2003). During the 2001 year a hail pad were installed on all stations in this area, and in 2002 hail pad polygon is installed in the middle of western hilly part. Hail pad data collected in period 2001-2006 are also used in this analysis. Spatial analysis of mean number of days with hail shows three different areas. Western (hilly) part is area with the greatest number of days with hail, specially are visible areas (Zagorje) with average more than two days per season. Middle flat area has mostly minimum days with hail, and the values ranges from 0, 1 to 0, 9 days (Fig.1). Eastern part is combination of these two above mentioned parts. Areas with low mountains have greater number of days with hail then parts that are completely flat (Pocakal, 2006). For all quadrants is calculated average duration of hail fall, using data from all stations. Analysis of spatial distribution (Fig.2) shows mostly longer average duration of hail fall in front of the mountain. The analysis shows influence of orography, especially in the western part with some greater mountains, and this influence is seen primary in a greater number of days with hail and a longer duration (5-7 min.) of hail in front of the mountain.

In the continental part of Croatia operational hail suppression has been conducted for more than 30 years. The protected area today is 25, 177 km2 and has about 530 hail suppression stations which are managed with eight radar centres. During 2001 hailpads were installed on all stations and hailpad polygon is established in 2002. Polygon with dimensions 30 x 20 km was located in the middle of the western part of protected area, where hail suppression system could act without limitations. The larger part of this western area is located close to the state border (Slovenia, Hungary and Bosnia and Herzegovina) and near unprotected part of Croatia. Because of forbiddance of launching rockets across the state borders, Cb-s that is spreading from west towards Croatia, enter the hail protected border area not seeded. After crossing the borders, stations begin with seeding, but because of a short time interval, the seeding nuclei were not completely active in clouds over the border area (Fukuta, 1980, Peti. 1991). The polygon is located in the middle of western part, where the Cb clouds are optimally seeded regarding The modification of weather phenomena to prevent or reduce the occurrence of hail on the ground is connected with the problem of assessing the modification results among all other influences among all other influences (complexity of thunderstorms, spatial and temporal variability of hail, climatic changes and air pollution, etc.). With the installation of hailpads in the protected area, exact data from hail characteristics were obtained. The data collected on the hailpad polygon were compared with data from the border area, were damage causing hail is very frequent. The purpose of this paper is to analyse and compare hailstone parameters measured with hailpads in two differently seeded areas. Four parameters are used in the statistical analysis – the average diameter of hailstones, number of classes (2, 5-mm interval), hailstone mass and kinetic energy. Radar data analysis (1981-2006) shows that more than 66 % of Cb cells come from western directions (W, NW and SW), at the velocity between 25 and 75 km/h. Results of linear discriminant analysis show that there is significant difference between the hail data from border and data from polygon area, and t-test shows significant reduction of average values of all parameters (except for average diameter) regarding the border area. These results may explain the increased number with hail and heavy damage in the border area and also that the reduction of hail parameters in the polygon area could be a positive result of seeding.

Settled in the mid latitudes (460) of the Northern Hemisphere (European hail belt), Croatia is exposed to the frequent occurrence of severe thunderstorms, especially in the continental part, between the Drava and Sava rivers. Hail is also frequent with a high possibility of doing heavy damage in agricultural production and on mobile and immobile properties. On the basis of 25 years (1981-2005) observed hail and damage data are collected from main meteorological and hail suppression stations, spatial distribution maps are made to show the most frequent areas with hail and damage. Result of analysis shows areas with maximum days with hail that is in western (hilly) part of the continental Croatia. The flat middle and eastern parts has the minimum days with hail in the season (01.5. - 30.09.) Areas near orographyc obstacles are connected with higher frequencies of hail and heavy damage. Data analysis shows two especially exposed areas in continental part of Croatia, the whole western part, and area around Požega valley. These maps can be used as a basis for planning different prevention’ s methods (insurance, mechanical protection, etc.).

In the continental part of Croatia operational hail suppression has been conducted more then 30 years. The protected area is between Sava, Drava and Mura rivers and is part of Panonian basin. In the neighbouring Slovenia, very close to the western border of protected area, are mountains such as Pohorje, Haloze that are eastern ends of Alps, and also mountains in Croatia - Ivančica, Ravna Gora, Strahinčica, Plešivica, Medvednica and Kalnik, all with top heights of about 400 to 1100 m above mean sea level. The mountains in the eastern part of protected area, Psunj, Krndija, Papuk and Dilj are connected with above mentioned in the western part through relative lower mountain – Bilogora. The analysis shows influence of orography, especially in the western part with some greater mountains. This influence is seen in a greater number of days with hail and small hail in a hilly terrain and in a shorter average duration of a hailfall in the lee side of the mountains.

In the continental part of Croatia operational hail suppression has been conducted for more than 30 years. The current protected area is 24, 100 km2 in size and has 528 hail suppression stations that are managed with 8 weather radar centres. During 2001, hailpads were installed on all hail suppression stations, and a hailpad polygon was established in 2002. The polygon measuring 30 x 20 km (with 150 hailpads) was located in the middle of the western part of the hail-protected area, where the hail suppression system could work without limitations. The larger part of this western area is located close to the state border (with Slovenia, Hungary and Bosnia and Herzegovina), and also near the hail-unprotected part of Croatia. Because of the ban on launching rockets across the state borders, hailbearing Cb clouds that are spreading from the west towards Croatia, enter the hail protected border area not seeded. After crossing the borders, hail suppression stations begin with seeding, but because of a short time interval, the seeding nuclei are not completely effective in clouds in the border area. In this paper data collected from hailpad polygon are statistically compared with the data collected from hailpads in this border area in the period 2001 to 2003. Four parameters are used in the analysis – the average diameter of hailstone, the number of classes, hailstone mass and kinetic energy. The results of the linear discriminant analysis show that there is a significant difference between the data from the border area and the data from the polygon area. The t-test shows a significant decrease of average values of all parameters regarding the border area.

Sažetak: Umjetno djelovanje na vremenske procese radi sprečavanja i smanjivanja pojave tuče na tlu, povezano je s problemom ocjene rezultata djelovanja (složenost oluja, prostorna i vremenska varijabilnost tuče, klimatske promjene, onečišćenje zraka). U pojedinim zemljama provode se ili su se provodili znanstveno-istraživački eksperimenti radi procjene učinkovitosti sustava obrane od tuče. Prema objavljenim rezultatima svjetskih eksperimenata i analiza parametara vezanih za pojavu tuče i djelovanje sustava obrane u većini zemalja, pokazuje se da postoji signifikantni pozitivni učinak djelovanja tog sustava. Razlike u tim rezultatima odnose se na stupanj uspješnosti, koji se kreće od 19.7% pa čak do 80%, ovisno o tehnologiji, metodi i analiziranim parametrima. Postavljanjem poligona tučomjera na zapadnom dijelu branjenog područja Hrvatske u 2002. započelo je provođenje znanstveno-istraživačkog eksperimenta koji bi u sljedećim godinama mogao dati odgovor na stupanj uspješnosti sustava obrane od tuče kod nas.

This paper presents hail characteristics for two separate periods in the western part of protected area, which is settled along border between Croatia and Slovenia. The purpose of this work is to establish if hail characteristics on that border area have changed, taking into account above mentioned reasons. This results of this paper can be used for hail suppression improvement. It can be said that in second period is increased average diameter, especially in range from 15-30 mm. Also, there there is an increasing number of areas in which we have larger ratio of hail with heavy damage on the ground, compared with first period.

This paper is dealing with geographical distribution of relative frequencies of days with hail in the northern part of Croatia (25177 km2), where hail suppression system works with rockets over 20 years. The data set was collected from the observational reports of hail suppression launching station network in time period from to 1991. The average number of launching stations during this period was about 450 and total number of reports was 5011. This data set includes hail and small hail with or without damage on the ground. The western part of protected area is mainly a hilly terrain and an eastern part is flat with some lower hills. Statistical analysis shows that in both parts the dominant directions of Cb clouds with hail on the ground are W and NW with velocity 25 km/h on average. Considering radar measured heights of the Cb clouds from these directions, they are greater then heights from other directions. The geographical analysis shows strong influence of orography, especially parts with high frequencies of days with hail per season are E or SE of the orographic barriers. The area SE from mountain Strahinčica have a maximum of 3.5 days per season. This distributions map can be useful for hail suppression system, agriculture, insurance companies and others.

This paper is dealing with analysis of operational hail suppression activities in northern Croatia. The basic idea was to estimate number of seeded artificial ice nuclei during hail suppression activities and to investigate possible connections with hailfalls. Ten cases of operational seeding of hail clouds were selected on the basis of sufficient data set collection. For the purpose of estimation of achieved artificial ice nuclei (AIN) concentrations in seeded hail clouds, a special simple method was applied. Vertical mass flow velocity was simulated for several values and in this paper only two cases are presented: for w1 = 6 m/s and for w2 = 20 m/s. Estimated achieved artificial ice nuclei concentrations in seeded clouds for w1 were within range 2*104 and 7*105 ; for w2 within range 8*103 and 2*105 AIN/m3 . In cases of small vertical velocity, artificial ice nuclei concentrations were continuously over 2*104 , but in the cases of high vertical velocity AIN concentrations were falling down to natural level. The comparison with ground observations data gives indications of the existence of connection, but due to small number of cases it was impossible to have final conclusions. The preliminary analysis indicates that usually, after the decrease of AIN concentration, in time interval of about 10 to 12 minutes, the hailfall or its intensification observed on the ground.

This paper is dealing with relative frequency distribution of hailstone diameter and duration of hailfals in Croatia. The data set was collected from the observational reports of hail suppression station network in period 1981-1990 (on average 450 stations, and 5011 reports). In this paper, the hourly relative frequency is presented. Two dimensional distribution analysis is also done to connect the characteristics of hailfals in both time and and average diameter of hailstones. The comparison of these frequency distributions shows the shift towards the smaller diameters and shorter duration of hail fallinf for the cases of performed operational seeding with meteorological reagent.

This paper gives a comparison of the hailstone diameter in the cases when hailcell seeding was interrupted by Air Traffic Control ban, with the diameter of hailstone found on the ground after the continuos seeding. The comparison is based on the hailfall data collected at the launching stations of Croatia and Slovenia during several years. The comparison results indicate that the percentage of number of launching stations which had occurrence of hailfall with average diameter of hailstones ranging from 15 to 50 mm is higher in the cases of banned seeding than in cases when hail suppression service was able to carry a continuos seeding

On the 18th of August 1991, during the early afternoon hours, a heavy hailstorm hit Northeastern Slovenia and Northwestern Croatia regions. It was caused by the penetration of cold air over the Alps. A stormy development of the tempestuous multicell cumulonimbus was accompanied by heavy showers of rain and hail and stormy wind, all of which resulted in considerable damages to field crops along the Cb trajectory passage. During the second half of the afternoon and early evening, stormy weather of a lower intensity hit other parts of Northern Croatia. This paper is an attempt of description of an extremely intensive hailstorm and its characteristics, also trying to show, in are rather simplified way, the connection between meteorological data and hail suppression activities, especially the applied seeding of meteorological reagent.

On the 31.08.1985 it was registered the highest instability ever recorded from the beginning of hail suppression activity in Croatia. The maximum intensity of hailstorms was located in the Požega valley, where is hailpad network installed on launching stations. This paper is the description of measured and calculated hail stone parameters and kinetic energy. The hail fals were recorded in several cases on that day (nearly at 3 pm, 5 pm and 20 pm), for every interval separately. The hail fall kinetic energy, reagent and radar parameters of the correspondent hailstorms are compared.

The characteristics of convective cell movements over the territory of Varaždin in the northwest part of Croatia have been determined on the basis of radar data. The analysis has been made especially for those stations where hail as well as for the other ones. Results show that more than 72 % of cells with hail on the ground come from western directions. The obtained results might be used in planing and supplying hail suppression stations.

Mjerenja veličine zrna tuče vrši se pomoću tučomjera na kojem se hvata otisak zrna tuče. U radu je prikazana metoda baždarenja koja se primjenjuje u sistemu umjetnog djelovanja na vrijeme u obrani od tuče na području Hrvatske, a u cilju određivanja zrna tuče