Influence of Selected Mountain Barrier for the Distribution of Precipitation in the Polish Carpathians

Krawędzie gór i wyżyn stanowią istotne bariery dla przepływu mas powietrza wędrujących znad oceanów. Przy znacznej wysokości i szerokości pasm górskich mogą one stanowić zaporę trudną do przebycia albo być strefą podwyższonych opadów, zwłaszcza dla wędrujących cyklonów. Nawet niewysokie progi stanowią barierę, która objawia się w postaci prądów konwekcyjnych. Autorzy omawiają przykłady z różnych części polskich Karpat. Zwarte krawędzie Beskidu Śląskiego, Małego i Żywieckiego do 1 km wysokości wystawione są na opady ośrodków niżowych z kierunków W-NW. Ku wschodowi krawędź rozbita jest na mniejsze grupy górskie Beskidu Wyspowego, co ułatwia wnikanie opadów w głąb gór wysokich. Niekiedy chmura burzowa wędruje wzdłuż wysokiego progu (np. krawędzi Zachodnich Bieszczadów), ale i próg Pogórza wysoki tylko do 200 m sprzyja lokalnym opadom konwekcyjnym.The edges of mountains and uplands constitute significant barriers to the flow of air masses travelling from the oceans. The barriers are particularly difficult to be overcome when the height and width of mountain ranges are large, such settings can be create zones of increased rainfall, especially for roaming cyclones. Even low mountain edges form barriers which induce convectional currents. The authors discuss examples from various parts of the Polish Carpathians. The compact edges of the Silesian, Mały and Żywiecki Beskids up to 1 km high are exposed to precipitation of low-pressure systems from the W-NW directions. To the east, the edge is split into smaller mountain groups of the Beskid Wyspowy, which facilitates the penetration of high rainfall into the mountain interior. Sometimes storm clouds travel along a high edge of the mountains, e.g. along the edge of the Western Bieszczady. The edge of the foothills, only up to 200 m high, favours local convection rainfall

The role of orographic barriers in the origin of extreme rainfalls as exemplified by the front of high Eastern Himalaya and the low northern slope of Carpathians

The paper discusses the role of orographic barriers in generating torrential precipitation in mountainous regions in different climatic zones, the Eastern Himalayas (tropical zone with well-developed monsoon activity) and the northern slope of the Carpathians (temperate zone with transitional climate). Attention has been paid to the different altitudes and courses of the orographic ridges as well as their location relative to the prevailing directions of influx of moist air masses. The cases analysed included torrential rains with monsoon circulation from the S–SW direction at the 2–3 km high edge of the Himalayas, with special consideration to the distance from the margin of the mountains and the exposure of the slopes. They generate frequent flood waves, landslides, debris flows and upbuilding of the alluvial cones in the foreland of the mountain barriers. The impact of the orographic barrier is significantly less marked in the Polish Carpathians. In the western part, the compact edge of the Western Beskids with an altitude of 0.5–1 km and the WSW–NEE course, exposed to moist air masses inflowing from the northern sector, is fragmented eastward into smaller mountain groups, which facilitates the penetration of moist masses of air with occurrence of prolonged precipitation into the mountains. At times, the storm cloud moves along the mountain edge (the margin of the Western Bieszczady Mts.). The marginal scarp of the Foothills has a northern exposure and a height of 150–200 m, and promotes frequent convective precipitation causing local flash floods in small streams. The cases of downpours and high discharges selected for the analysis were those for which there was available a dense network of measuring stations. An insufficient number of stations in constructing precipitation maps based on interpolation would lead to distorting the spatial image. If this were the case, then the role of slope exposure, which has an essential impact on the distribution of precipitation in mountainous regions, would be completely neglected

Climate change in Poland in the past centuries and its relationship to European climate: Evidence from reconstructions and coupled climate models

We investigate the winter temperature and precipitation evolution over Poland over the last half millennium in comparison with the European average in reconstructions/instrumental data and in the ECHO-G and HadCM3 models and discuss the physical processes behind those variations. Results indicate very good agreement between European land and Polish winter temperatures in reconstructions and in the models. Colder winter conditions were found within the ‘Little Ice Age’ and temperatures at the turn of the twenty first century are very likely the warmest in the context of the past. The strong agreement between Polish winter temperature and European mean conditions is of major interest since some of the longest European proxy information stem from Poland and therefore can improve European temperature reconstructions significantly. Precipitation results indicate that reconstructions over Poland agree well with those of the rest of Europe, though the agreement is poorer between the reconstruction and the models. The role of the large-scale atmospheric circulation dynamics/forcing connected with the observed Polish winter temperature/precipitation changes is investigated in the reconstructions and in the model world. The most important atmospheric circulation pattern for winter temperature variability is the North Atlantic Oscillation (NAO). The Scandinavian (SCAND) and to a lesser degree also the NAO and East Atlantic/Western Russia (EA/WRUS) are of relevance for winter precipitation variations in Poland. Canonical Correlation Analysis (CCA) results show that the leading circulation modes responsible for dry/wet and warm/cold Polish winter conditions are in good agreement in the reconstructions and models. These results suggest that the models are able to reproduce the links in instrumental and proxy data and also that the large- to regional-scale relationships are robust during the last centuries. The stability of the large- to regional-scale links is relevant for downscaling approaches and also for palaeoclimate reconstructions