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Very large hail occurrence in Poland from 2007 to 2015

Pilorz W.

Contemporary Trends in Geoscience

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2015

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Vol. 4, iss. 1

45--55

EN

Very large hail is known as a presence of a hailstone greater or equal to 5 cm in diameter. This phenomenon is rare but its significant consequences, not only to agriculture but also to automobiles, households and people outdoor makes it essential thing to examine. Hail appearance is strictly connected with storms frequency and its kind. The most hail-endangered kind of storm is supercell storm. Geographical distribution of hailstorms was compared with geographical distribution of storms in Poland. Similarities were found. The area of the largest number of storms is southeastern Poland. Analyzed European Severe Weather Database (ESWD) data showed that most of very large hail reports occurred in this part of Poland. The probable reason for this situation is the longest period of lasting tropical airmasses in southeastern Poland. Spatial distribution analysis shows also more hail incidents over Upper Silesia, Lesser Poland, Subcarpathia and Świętokrzyskie regions. The information source about hail occurrence was ESWD - open database, where everyone can add report and find reports which meet given search criteria. 69 hailstorms in the period of 2007 – 2015 were examined. They caused 121 very large hail reports. It was found that there is large disproportion in number of hailstorms and hail reports between individual years. Very large hail season in Poland begins in May and ends in September with cumulation in July. Most of hail occurs between 12:00 and 17:00 UTC, but there were some cases of very large (one extremely large) hail at night and early morning hours. However very large hail is a spectacular phenomenon, its local character determines potentially high information loss rate and it is the most significant problem in hail research.

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Radarowa detekcja superkomórek burzowych w Polsce

Pilorz W.

Teledetekcja Środowiska

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2014

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T. 51

93--105

EN

“Supercell storms are capable of producing the most violent of hail, wind and tornado events (Moller et. al. 1994); thus they are the most important storm type to forecast and detect” (Moller 2001). Supercell storm is defined by “presence of a deep and persistent, rotating updraft called a mesocyclone” (Weisman and Klemp 1984). Mesocyclone presence leads to the specific vertical storm structure seen as a Bounded Weak Echo Region. Mesocyclone presence also leads to the changes in the horizontal shape of the storm, observed on the radar reflecivity in a low elevation as a hook echo. Large hail, associated with supercells, is a very important threat to detect. It can be easily recognized by the presence of the reflecivity more than 50 dBZ, above 8 km above ground level (Burgess and Lemon 1990). Nine cases of supercells in Poland between 2007 and 2013 were examined. Results show that all quoted features were present. Moreover, most of them appeared before the threat which they indicate. It means that threats associated with supercells can be predicted in a short time.

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Human-planted alder trees as a protection against debris flows (a dendrochronological study from the Moxi Basin, Southwestern China)

Malik I., Tie Y., Owczarek P., Wistuba M., Pilorz W., Woskowicz-Ślęzak B.

Geochronometria

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2013

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Vol. 40, no. 3

208--216

EN

Large debris flows have destroyed the infrastructure and caused the death of people living in the Moxi Basin (Sichuan Province, Southwestern China). Inhabitants of the Moxi Basin live on the flat surfaces of debris-flow fans, which are also attractive for farming. During the monsoon season debris flows are being formed above the fans. Debris flows can destroy the houses of any people liv-ing within the fan surfaces. In order to prevent the adverse effects of flows, people plant alder trees (Alnus nepalensis) at the mouths of debris flow gullies running above debris flow fans. Alders are able to capture the debris transported during flow events. Trees are well adapted to surviving in con-ditions of environmental stress connected with abrupt transport and deposition of sediment from de-bris flows. Numerous wounds, tilting and bending of alder trees caused by debris flows only very rarely cause the death of trees. By dating scars and dating the time of alder tilting (through the analy-sis of annual rings), we have determined the frequency of debris flows occurring at the mouth of the Daozhao valley. In 1980-2012 within the studied debris-flow fan and the Daozhao gully, 2 large de-bris flow events occurred (1996, 2005) and some smaller events were probably recorded every 2-3 years.