Wyniki wyszukiwania - BazTech

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Symulacja pola przepływu powietrza nad aglomeracją miejską na przykładzie Krakowa

Kamiński K., Petera J., Tomczak E.

Inżynieria i Aparatura Chemiczna

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2006

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Nr 5s

52-54

2

Obiektywna metoda klasyfikacji pól wektorowych na przykładzie górnotroposferycznych prądów strumieniowych

Degirmendzić J.

Przegląd Geofizyczny

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2005

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Z. 1-2

59-72

EN

In the paper there is presented the method designed for vector fields classification. It is based on the algorithm proposed by Lund (1963). The replacement of Pearson correlation coefficient with vector correlation coefficient defined by Crosby (1993) is the essential change that makes this technique suitable for treatment of vector fields. The correlation threshold, set a priori in scalar analyses, is calculated objectively, with the help of PVCR index introduced by Huth (1996). PVCR index expresses the proportion of average similarity between objects classified into different categories to objects grouped in the same classes. PVCR is computed for selected range of threshold values and minimum value indicates the ,,best" correlation threshold. The classification was carried out for wind fields at the 250 hPa surface over Europe for winter season during 1958-2003 period. 20 classes of jet stream patterns were distinguished, which constitute 60.7% of the sample. Basic statistics, i.e. average and maximum frequency and duration time, were calculated for the first six key jet types. The main features of upper circulation field as well as temperature and pressure distribution in the lower troposphere associated with the jet types were also described.

3

Fale termiczne nad Polską w zimie w zależności od pola wiatru w Europie

Degirmendzić J.

Przegląd Geofizyczny

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2004

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Z. 1-2

11-23

EN

The main goal of this paper is to analyze transformation of wind field over Europe associated with change of intensity of thermal wave in Poland during winter. Thermally anomalous periods were distinguished on the basis of daily mean temperature record at 52.5°N, 20°E grid point. Wind field was defined by meridional and zonal wind components. Both, temperature and wind data were retrieved from NCEP/NCAR Reanalysis. The analysis was performed for the period of 1950-2001 and 850 hPa isobaric level. Cold/heat waves were categorized into three thermal classes - extreme, moderate and weak. In order to analyze wind field the following parameters were employed: relative vorticity, wind speed and directional steadiness of wind vector. Additionally, the structure of streamlines was analyzed. Temperature rise in Poland is forced by the development of dipole-like structure, clearly seen on the map of anomalies of relative vorticity. Positive anomalies are situated over Norwegian See, eastern Atlantic and Scandinavia, while negative vorticity advection is observed in southern Europe. Simultaneously with dipole development the increase of wind speed in middle Europe is also noted - supposedly it constitutes significant feature of wind field responsible for temperature increase in Poland in winter. In case of extreme heat waves the source region of warm advection is shifted southwards. Streamline pattern indicates more parallel flow over the Atlantic to the Iberian Peninsula and change of wind direction over Poland, from westerly to south-westerly. Intensive transport of heat over the northern Europe reduces temperature contrast at the Mediterranean front, which consequently decelerates western flow and lowers directional steadiness of wind vector down to 50% over the southern part of continent. Field of vorticity anomalies corresponding to the cold waves occurrence over Poland posseses dipole-like structure, however its polarization is reversed. Anticyclonic vorticity advection occurs in northern Europe and northern Atlantic while southern Europe experiences increase of cyclonic vorticity. Cooling in central Europe is associated with transformation of circulation field into blocking type - simultaneously the source region of cold advection shifts northwards over the Scandinavia (around 70°N). Enhanced thermal contrasts over southern Europe together with air masses inflow from the north, i.e. possessing surplus of cyclonic vorticity, strengthen the Mediterranean front.