The research objectives were to describe heat waves (HWs) in Central Europe and define the synoptic situations that cause their occurrence. In this article, a hot day was defined as a day when the maximum temperature was above the 95th annual percentile and an HW was considered a sequence of at least five hot days. In the analysed multi‐year period and study area, 11 HWs were observed in the north and 51 HWs were observed in the south. The occurrence of HWs was mainly connected with positive anomalies of sea level pressure and with the 500 hPa level, which shows the presence of high‐pressure systems. HWs were also accompanied by positive T850 and precipitable water (PW) anomalies.

The basic characteristics of snow cover occurrence in eastern Europe are described. For each month from October to May the range of ‘active’ snow-cover areas in Europe was determined. The boundary criterion for ‘active’ regions was adopted as snow-cover probability of between 10 and 90%. The correlation coefficients between the snow-cover characteristics (number of days with snow cover and its monthly mean depth) and other climatic variables (temperature and precipitation) were calculated. A strong positive correlation between the annual number of days with snow cover and the annual number of days with mean temperature <0 °C was discovered for most parts of the study area. A negative correlation between the monthly number of days with snow cover and monthly mean temperature was found and its spatial distribution was analysed. A positive correlation between snow depth and precipitation appeared significant only in some areas. The influence of atmospheric circulation, expressed by North Atlantic oscillation (NAO) index values, on snow cover in the particular months was analysed. The correlation between the number of days with snow cover and the NAO index is large and statistically significant only in central Europe and it becomes insignificant to the east of 30° λ E. High values are noted only in the winter months. In autumn and spring, when the range of the ‘active’ areas moves to the east and the NAO becomes weak, the correlation is very small. Copyright © 2004 Royal Meteorological Society

The FAO-56 Penman-Monteith (PMF56) model is accepted as the standard method for estimating reference crop (grass) evapotranspiration. However, poor data availability limits the use of this method in many regions. This study aimed to overcome this limitation (1) by evaluating the goodness-of-fit of selected simple evapotranspiration methods in relation to the PMF56 model and (2) by adjusting four of these models and developing a multiple regression equation for conditions in Poland using the PMF56 model as a reference. Using daily meteorological data, four simple models were calibrated by the generalised reduced gradient (GRG) method; moreover, a multiple regression equation was developed on the basis of Cochrane-Orcutt estimation because the error term of the ordinary least squares model was autocorrelated. When radiation data were lacking and sunshine duration data were available, the PMF56 method with a calibrated Ångström-based estimation of solar radiation was the most accurate method (relative error, RE = 0.096, for Sulejów). When neither radiation nor sunshine duration data were included in the dataset, the calibrated Penman method performed best (RE = 0.254). Moreover, when only temperature or pan evaporation data were available, the calibrated Hargreaves method provided the most accurate results (RE = 0.275). Much poorer results were obtained using the calibrated pan coefficient method (RE = 0.435). Ultimately, we developed a multiple regression method in this study that exhibited good performance (RE = 0.170). Taking into account the data limitations, the methods calibrated in this study are recommended for estimating evapotranspiration in Central Europe. This approach would substantially decrease the errors produced by the recommended non-calibrated equations.

Occurrence of heat and cold waves in Poland in the years 1966–2015 (1966/1967–2015/2016) was described, and their circulation conditions were determined in this study. A heat wave is defined as a period of at least 3 days with Tmax > 30.0 °C and a cold wave as a period of at least 3 days with Tmax <− 10.0 °C. Heat waves occurred most often in central and southern Poland and cold waves in north-eastern Poland. The occurrence of both heat and cold waves is related to high pressure systems. Anticyclonic blocking patterns both in winter and summer inhibit the zonal flow of air masses and intensify the meridional flow. Positive sea level pressure anomalies occurred over the study area, in the case of heat waves up to 3 hPa and in the case of cold waves up to 11 hPa. Perpendicular profiles showing geopotential height and air temperature anomalies in the troposphere were identified for the selected cases of extreme temperature episodes. Centres of geopotential height positive/negative anomalies were detected at the level of 300–250 hPa geopotential height, right over the area of the positive/negative surface temperature extremes.

The aim of the article was to provide a detailed analysis of pressure conditions, employing the anomalies of geopotential heights, during the occurrence of heat waves in Central Europe, but also in the days preceding and following their occurrence. The study uses data from 1966 to 2015 from the Institute of Meteorology and Water Management—National Research Institute, Deutscher Wetterdienst and the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR). A heat wave was defined as a sequence of at least 3 days with a maximum daily air temperature of >30°C. The study showed an increase in the number of hot days, which was statistically significant in the majority of the area. In the analysed years, an increasing number of heat waves were recorded, and this occurrence was associated with high pressure systems. Anticyclonic blocking in the summer inhibits the zonal flow of air masses and intensifies meridional flow, which in Central Europe in the summer means the presence of polar continental and tropical air masses. During heat waves, there were positive anomalies of isobaric surface heights over the study area with a maximum in the upper troposphere. On average, anomalies at the 300 hPa pressure level began to form over the Atlantic Ocean. Determining atmospheric preconditions of persisting blocking events in summer resulting in heat waves may be helpful in predicting thereof.

A 2-year study (2010–2011) of fluorides in atmospheric precipitation in the open area and in throughfall in Wielkopolski National Park (west-central Poland) showed their high concentrations, reaching a maximum value of 2 mg/l under the tree crowns. These high values indicate substantial deposition of up to 52 mg/m²/year. In 2011, over 51 % of open area precipitation was characterized by fluoride concentration higher than 0.10 mg/l, and in throughfall such concentrations were found in more than 86 % of events. In 2010, a strong connection was evident between fluoride and acid-forming ions, and in 2011, a correlation between phosphate and nitrite ions was seen. Analysis of available data on F⁻ concentrations in the air did not show an unequivocal effect on F⁻ concentrations in precipitation. To find reasons for and source areas of high fluoride pollution, the cases of extreme fluoride concentration in rainwater were related to atmospheric circulation and weather patterns. Weather conditions on days of extreme pollution were determined by movement of weather fronts over western Poland, or by small cyclonic centers with meteorological fronts. Macroscale air advection over the sampling site originated in the western quadrant (NW, W, and SW), particularly in the middle layers of the troposphere (2,500–5,000 m a.s.l.). Such directions indicate western Poland and Germany as possible sources of the pollution. At the same time in the lower troposphere, air inflow was frequently from the north, showing short distance transport from local emitters, and from the agglomeration of Poznań.