FIVE-YEAR RESULTS AND STATISTICAL ANALYSIS OF HAIL PARAMETERS FOR TWO DIFFERENT SEEDED AREAS IN WESTERN PART OF CROATIA MEASURED WITH HAILPADS
Damir Pocakal 1 and Janez Stalec2
1Meteorological and Hydrological Service of Croatia, 10000 Zagreb Gric 3, Croatia, 2Department of Mathematics University of Zagreb,10000 Zagreb Horvatovac bb, Crotia April 27, 2007
The protected area today is 25,177 km2 and has about 530 hail suppression stations which are managed with eight radar centres.(image at right of current forecast of Croatia, from Meteorological and Hydrological Service of Croatia)
During 2001 hailpads were installed on all stations and [a]hailpad polygon[was] established in 2002.
[A]Polygon with dimensions [of] 30 x 20 km [was] located in the middle of the western part of [the] protected area, where [a] 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. (map highlighting associated countries, originally from mapZones.com)
Because of forbiddance of launching rockets across the state borders, Cb-s (cloud bases) that [are] 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.
PRESENTATION OF RESEARCH
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 (complexity of thunderstorms, spatial and temporal variability of hail, climatic changes and air pollution, etc.).
(right image: example of hailpad, from Llansadwrn Weather)
The data collected on the hailpad polygon were compared with data from the border area, where damage causing hail is very frequent.
The purpose of this paper is to analyse and compare hailstone parameters measured with hailpads.
RESULTS AND CONCLUSIONS
Radar data analysis (1981-2006) shows that more than 66% of Cb (cloud base) 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 [a] significant difference between the hail data from border and data from [the] polygon area, and [the] 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 [could] also [mean] that the reduction of hail parameters in the polygon area could be a positive result of seeding.