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Hailpad data analysis for continental part of Croatia (CROSBI ID 556015)

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Počakal, Damir Hailpad data analysis for continental part of Croatia // PREPRINTS - ECSS 2009, 5th European Conference on Severe Storms. Landshut, 2009. str. 99-100

Podaci o odgovornosti

Počakal, Damir

engleski

Hailpad data analysis for continental part of Croatia

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.

hailpads; kinetic energy; polygon

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Podaci o prilogu

99-100.

2009.

nije evidentirano

objavljeno

Podaci o matičnoj publikaciji

PREPRINTS - ECSS 2009, 5th European Conference on Severe Storms

Landshut:

Podaci o skupu

ECSS 2009, 5th European Conference on Severe Storms

poster

12.10.2009-16.10.2009

Landshut, Njemačka

Povezanost rada

Fizika