The occurrence of heat waves in Europe and their circulation conditions (original) (raw)
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Circulation Conditions’ Effect on the Occurrence of Heat Waves in Western and Southwestern Europe
Atmosphere, 2017
This article aims to describe the occurrence of heat waves in Western and Southwestern Europe in the period 1976-2015 and determining pressure patterns that cause a persistence of hot days. A hot day was defined as a day on which the daily maximum air temperature was higher than the 95th annual percentile; and a heat wave was recognised as a sequence of at least five days of the abovementioned category. In the discussed multiannual period, this threshold ranged from 23.5 • C in Brest to 38.9 • C in Seville. Within the analysed area, there were from 14 (Bilbao) to 54 (Montélimar) heat waves observed. The longest heat wave took place in 2003 in Nice and lasted 49 days (14 July-31 August). The occurrence of heat waves within the analysed area was related to the ridge of high pressure located over the area of the study, providing strong solar radiation flux due to cloudlessness or a small cloud cover. Positive SLP, z500 hPa and T850 anomalies occurred over the majority of the research area.
Heat waves in Central Europe and tropospheric anomalies of temperature and geopotential heights
International Journal of Climatology, 2019
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 was 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.
Atmosphere
The aim of the study is to analyze the occurrence of hot days and heat waves in Poland, their intra-annual distribution, and their long-term variability, and to present the circulation factors favoring the appearance of extensive waves in the country. Hot days were days with Tmax not lower than the threshold value defined by the 95th percentile of summer Tmax in the period 1961–1990. Atmospheric circulation was described using sea level pressure, geopotential of 700 and 500 hPa level, and horizontal and vertical wind on these levels. A statistically significant increase in the number of hot days in the entire study period and a significant acceleration in growth after 1980 were shown. In the entire analyzed period, only 11 waves were found covering at least 25% of the country area and lasting no less than a week. Among them, only one occurred before 1990, and more than half were observed in the last decade. Four circulation patterns favoring the extensive heat waves were distinguish...
Climate Dynamics, 2011
The heat wave affecting Europe during summer of 2003 is analyzed in detail with observational and reanalysis data. Surface, middle and upper troposphere analysis reveal particular circulation patterns related to an atmospheric blocking condition. In general seasonal anomalies, like this intense heat wave, are strongly related to boundary conditions. Composites and empirical orthogonal functions analysis provide evidence for an organized structure in the sea surface temperature (SST) anomaly field: high SSTs in the Mediterranean basin, the North Sea and further north toward the Arctic Circle were observed mainly in the months of June and August. The outcome of this analysis on observational data shows the SST as one of the possible factors in enhancing the heat wave in the European area.
Heatwaves in Poland–Frequency, Trends and Relationships with Atmospheric Circulation
2009
The daily minimum and maximum temperatures at seven Polish stations were used in an analysis of the occurrence of heatwaves in the years 1951-2006. Heatwaves were defi ned as days with temperatures exceeding selected thresholds (t max ≥25°C, t max ≥30°C, t min ≥18°C). The mean length of a wave of very warm days lasts from 2-4 days, the longest no fewer than 23 days. Waves comprising hot days and nights are shorter. The frequencies of very warm and hot days and hot nights increased in the analyzed period, especially its second half (1979-2006). The occurrence of heatwaves characteristically links up with high-pressure systems over Central Europe, along with associated blocking episodes.
Long-term analysis of heat waves in Ukraine
International Journal of Climatology, 2013
In the past few decades, severe heat waves were representative of the weather conditions in various parts of the world. They had distinctly negative impacts on humans, plants, animals and different economic sectors. Particularly in cities, where most humans are living, their well-being, efficiency and health were affected, which even caused a relatively high mortality rate. This is why a large interest still exists to analyse heat waves in the past by use of statistical methods. As an investigation on heat waves is not available for the territory of Ukraine up to now, a retrospective analysis was conducted. Its main aims were (1) to determine the frequency of heat wave episodes for this country and (2) to analyse their spatiotemporal distribution, duration and intensity. On the basis of 13 selected stations of the meteorological network of the Ukrainian Hydrometeorological Centre, daily values of maximum air temperature (T a,max) in the summer months June to August were used to determine heat wave episodes according to the definition recommended by the IPCC. For all stations, complete and reliable T a,max time series were available for the period 1951-2011. With respect to some stations, the T a,max time series already started some years earlier, e.g. in 1936 for five stations and even in 1911 for four stations. However, the T a,max time series of almost all stations had gaps in the summer months before 1951, particularly in the 1940s of the 20th century. As they could not be filled in a satisfying way, this limitation was considered in the data analysis. The results indicate that most of the heat wave episodes occurred at stations located in Eastern Ukraine. In contrast to other decades, the number of heat wave episodes was highest for almost all stations in the decade 2001-2010. The fewest heat wave episodes were determined for the two decades 1961 to 1980. The longest heat wave duration varied between 7 d in Henichesk (southern seashore) and 24 d in Lugansk (Eastern Ukraine). For many stations, the longest heat wave duration occurred in the first two decades of August 2010, i.e. in the period of the extremely severe heat wave in Western Russia. The intensity of heat waves was analysed by use of the cumulative T a,max excess. The results show that heat waves of the longest duration mostly represented the strongest heat waves. The 24-d heat wave 2010 in Lugansk was the strongest in the investigation period quantified by a cumulative T a,max excess of 128 • C.
Strong heat and cold waves in Poland in relation with the large-scale atmospheric circulation
Theoretical and Applied Climatology
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 northeastern 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.
Heat waves in Poland in the period 1951-2015: trends, patterns and driving factors
Meteorology Hydrology and Water Management
Heat waves were analysed on the basis of maximum daily temperature from 24 meteorological stations in Poland. Heat waves are defined as the longest continuous period during which Tmax (daily maximum air temperature) is equal to or higher than 30°C in at least three days, the mean Tmax during the whole heat wave is equal or higher than 30°C and Tmax does not drop below 25°C during the whole period of heat wave duration. Heat waves occur in Poland from April to September with their maximums in July and August. Four-day-long heat waves are most frequent but the longest one lasted 31 days. The most persistent heat waves were in 1994 and 2015. An increasing trend in heat wave frequency and intensity is observed in Poland, however the increase is statistically significant at only about 60% of analysed stations. Four synoptic patterns favouring heat waves have been distinguished. A strong high over the Azores accompanies all of them, as well as slightly higher than normal pressure over Central Europethis causes calm and sunny weather over Poland. Strong blocking appears over the North Atlantic during heat wave events, proofing that the development of strong heat waves in Poland is related to large scale circulation and that they are not of local origin. The analysis of the impact of soil moisture in months leading up to the development of heat waves should be the next step in analysis.
Large-Scale Mechanisms Responsible for Heat Waves Occurrence in Romania
Romanian Journal of Physics
The heat waves, severe weather events, are generally associated with high pressure synoptic systems and tropical air mass advection. The study of the main causes and effects of these particular situations and their subsequent impacts focuses on the analysis of connections between heat waves and large-scale circulation. Daily maximum temperatures from 105 meteorological stations were used to identify the heat waves. The heat waves are identified by using thresholds imposed to the maximum temperature and to the duration of heat waves. After identification, heat waves were associated to circulation types established with GWT and WLK Catalogues developed within the COST733 Action. The most prolonged heat wave episode (18 days) was registered in 1994 at the Oradea synoptic station. The results reveal the persistence over the southeastern Europe of high pressure synoptic systems, having a northeastern circulation component at sea level and a northwestern or southwestern circulation compon...
Influence of circulation types on temperature extremes in Europe
Theoretical and Applied Climatology, 2010
The aim of this study is to determine the influence of atmospheric circulation on the recently observed changes in the number of warm days and cold days in Europe. The temperature series for stations in the European Climate Assessment and Dataset project and the Grosswetterlagen (GWL) were used here. The temperature series were first adjusted for global warming before determining the indices for cold and warm extremes.