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Condensation trails (contrails) from aircraft exhausts and contrail cirrus clouds play a significant role in the atmosphere's radiation balance and the climate. The aim of this study is to analyse the physical properties of contrails with the use of satellite data and determine the atmospheric conditions favoring their formation and persistence. The contrails are detected on satellite images provided by the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) radiometer onboard the Meteosat Second Generation (MSG) satellites, using a modified version of the contrail detection algorithm by Mannstein et al. Int J Remote Sens 20(8):1641–1660. (1999) for the year 2016. The study area covers central and western Europe. Five contrail detection hotspots are located, with contrail density depending on time of day and season. The length of the detected contrails ranges between 225 and 292.5 km and the mean width between 5.1 and 8.1 km. The spatial contrail cover reaches up to 0.085% of the scene, with larger values being detected between 8 and 10 UTC and during winter. Results of the comparison with the ERA-5 reanalysis database show that contrail formation and persistence is favored in ice saturated areas (RHI≈100%), when the air temperature is between 204 and 232 Κ (− 69.2 to − 41.2 °C) and the specific humidity between 0.025 and 0.0625 g/kg. The favorable wind direction and speed lie between W and SW (240–300°) and 10 and 30 m/s, respectively. [ABSTRACT FROM AUTHOR]

The current warming of climate has led to an enhancement of the extreme temperature risks threatening various systems. Following that, we analysed the progress of the main type of the temperature-extreme weather events—heatwaves (HWs). We focused on the area of the Western Carpathians (Central Europe), since the Carpathian Mountains are widely recognised as an important biodiversity hot-spot particularly for mountain species in Europe. The HWs were identified for a range of elevations from low to high altitudes including a high mountain station. We used the percentile threshold-based calculation of HW, which in comparison to those using absolute thresholds allows for revealing the possible threats of climate warming extremes at the range of altitudes. We observed the HWs based on the maximum (HWMAX) and average (HWAVG) daily air temperatures in June–August during the period of 30 years (1989–2018) and we characterised them by the strength, frequency, and duration of the longest HW event. The Mann-Kendal trend test of these heatwave characteristics was significantly positive (p < 0.05) at most of stations throughout the region of Western Carpathians. At the high mountain station, particularly the maximum temperature exceedance increased, indicated by significant positive trends of HWMAX in strength (p = 0.02), frequency (p = 0.01), and duration of the longest event (p = 0.02). The majority of the strongest HWs occurring across Europe over the last three decades hit the area of Western Carpathians. More importantly, the area experienced the regional HWs, severity of which was comparable to those of exceptionally strong HWs, although these regional HWs were less important from the large-scale aspect. The greatest intensification of HWs is evident particularly in the last decade, although the longest HWMAX event from 1994 was not exceeded. Our results show potentially enhanced HW-induced stress to organisms as a consequence of the coincidence of HWMAX and HWAVG of the comparable strength during the last decade. [ABSTRACT FROM AUTHOR]

Remarkable climate anomalies occurred in Europe in recent years, but the reasons are not entirely disclosed. This entails further exploring the physical mechanism of anomalous climate variability over Europe on the basis of previous studies. Using NCEP-NCAR reanalysis and CMAP precipitation datasets, we investigated the relationship between the thermal condition of the Tibetan Plateau (TP) and precipitation over Europe during summer and related mechanisms behind through observational analyses and simulation experiments. The results show that the summer TP surface air temperature (SAT) is significantly correlated with the simultaneous precipitation over the region from eastern Ukraine to the North Caucasus (EUNC; 43°–51° N, 34°–46° E) during the period 1979–2017. The effect of anomalous TP heating plays, to some extent, an active role in linking the summer TP SAT with EUNC precipitation. The variability of the TP SAT is a result of the anomalous TP heating, but it can reflect the variability in temperature of a thick tropospheric air column over the TP well. Corresponding to higher (lower) TP SAT, the higher (lower) temperature anomaly appears over the TP and extends westwards through the transport of anomalous temperature fluxes from the TP to the EUNC regions in the upper troposphere, resulting in the expansion (withdrawal) of the South Asian high (SAH) and associated less (more) precipitation over the EUNC region. Numerical simulations basically reproduce the above-mentioned physical process, which confirms that, through stimulating the variability of upper-tropospheric temperatures over the TP and a larger area to its west and associated upstream large-scale atmospheric circulation, the summer TP's thermal condition can modulate and expand the impact of the SAH to the EUNC region and therefore affect the concurrent precipitation in situ. This study implies an importance of the thermal anomaly of the TP to the variability of EUNC precipitation during summer. [ABSTRACT FROM AUTHOR]

Nearly every study dealing with temperature extremes underscores the lack of a universal and broadly used method of identifying such events. The most popular are relative methods, which are based on the empirical distribution of temperature at each location (i.e., percentiles). The aim of this study was to evaluate the effects of the various percentile-based methods of defining hot days on the analysis of their frequency of occurrence, trends, and geographic patterns in summer in Europe. The basis for the research consists of daily maximum (TX) and minimum (TN) values of air temperature for 1961–2017 for Europe obtained from the E-OBS database. A hot day occurs when air temperature exceeds the 90th percentile–based threshold. These thresholds are determined using the following: (I) various temperature metrics (TX and TN), (II) various baseline periods (1961–1990, 1971–2000, 1981–2010), and (III) different timeframes within the year that the percentile is calculated for (summer season, separate summer months, and each calendar day). Our results indicate that the use of different variants of the percentile-based definition leads to differences in the geographic patterns of frequencies of and trends in summer hot days in Europe. The differences are especially substantial within the results obtained using various temperature metrics and baseline periods, and they are relatively small when different timeframes within the year that the percentile is calculated for are considered. On the example of the case study, we also show how the use of different research approaches may affect the intensity and spatial extent of an extreme temperature event. [ABSTRACT FROM AUTHOR]

The aim of the research was to identify connections between the occurrence of heat load across Poland and large-scale factors, which will allow statistical models to be derived that are useful to describe bioclimatic conditions in Poland in the summer. Atmospheric circulation over the North Atlantic Ocean and Europe and near-surface air temperature over the central part of Europe were considered. The monthly frequency of the occurrence of combined "moderate, strong, very strong and extreme heat stress" based on the assessment scale of the Universal Thermal Climate Index (UTCI) in the summer months accounted for 6% to more than 30% of all cases. The statistical downscaling procedure of canonical correlation analysis (CCA) with respect to the period 1971–2000 was applied to extract the main modes of large-scale factors and their local responses. The greatest explained variance of local field response to atmospheric circulation as well as to near-surface air temperature is above 70%. Warm air flow from the east and from the southeast has the strongest influence on the increase in frequency of the occurrence of heat stress on human beings in Poland. The spatial differentiation of the air temperature anomaly over central Europe is an important determinant of the occurrence of heat stress in Poland. The validation of constructed models encompassed the periods 1951–1970 and 2001–2010. The best reliability of results was reached for the reconstructed series in July. The results are less useful in June and August and in the coastal region. [ABSTRACT FROM AUTHOR]

The paper focuses on exceptionally hot summers (EHS) as a manifestation of contemporary climate warming. The study identifies EHS occurrences in Central and Eastern Europe and describes the characteristic features of the region's thermal conditions. Average air temperatures in June, July and August were considered, as well as the number of days with maximum temperatures exceeding 25, 30 and 35 °C, and with a minimum temperature greater than >20 °C, as recorded at 59 weather stations in 1951-2010. Extremely hot summers are defined as having an average temperature equal to or greater than the long-term average plus 2 SD. A calendar of EHSs was compiled and their spatial extent identified. The region experienced 12 EHSs, which occurred in a given year at 5 % or more stations (1972, 1981, 1988, 1992, 1997, 1998, 1999, 2002, 2003, 2006, 2007 and 2010). The EHS frequency of occurrence was found to be clearly on an increase. Indeed, only one EHS occurred during the first 30 years, but these occurred five times during the last 10 years of the study period. Their geographical extent varied both in terms of location and size. EHSs were observed at 57 out of the total of 59 weather stations in the study (the exceptions were Pecora and Cluj). The average air temperature of EHSs tended to exceed the relevant long-term average by 2-4 °C. The summer of 2010 was among the hottest (temperature anomaly 5.5-6 °C) and spatially largest. [ABSTRACT FROM AUTHOR]

The study examines two methods for classification of daily pressure-pattern sequences (extended PCA and extended cluster analysis) and evaluates whether sequence classification is more suitable to describe surface air-temperature conditions in Europe. For this purpose, sequences of daily sea-level pressure fields are classified for each month of the year using a wide range of class numbers (2–40) and sequence lengths from 1 to 6 days. In each case, the classification is used to reconstruct temperature variability in 5°×5° grid-boxes throughout Europe for the period 1850–2003 in order to compare the circulation type based reconstruction to monthly observations for skill estimation. Results show that extended PCA leads to more dynamic pattern sequences for subordinated classes, but also that it is limited in skill, because classes of very low frequencies are generated. In contrast, extended cluster analysis offers higher skill levels for temperature downscaling. However, both methods can benefit from using sequences instead of single days for classification, especially for continental regions. [ABSTRACT FROM AUTHOR]

Anomalies of mean air temperature of 12 consecutive months were detected recently at a number of spatial scales: from local via national and continental, to hemispheric. At all these spatial scales, pre-2007 records were exceeded by considerable margins. The recent rise in the mean temperature of 12 consecutive months at several scales has remained largely unnoticed, because the 12-month means are seldom analyzed. Broad attention is typically focused on monthly, seasonal and annual temperatures. Analysis of shifted 12-month periods helps spot peculiar 12-month episodes with remarkable temperature anomalies that do not coincide with a calendar year. Introducing 12-month running mean temperatures into the global warming debate can prove useful. [ABSTRACT FROM AUTHOR]

Using temperature and pressure records from Czech meteorological stations and NCEP/NCAR reanalysis series, we tested for the presence of detectable nonlinearity in univariate and multivariate climatic time series. The method of surrogate data was utilized for nonlinearity detection – results of nonlinear prediction for the original series were compared to the results for series whose nonlinear structure was randomized. The prediction was done by means of local linear models in the reconstructed phase space. None or very weak nonlinearity was found in the single (univariate) series, and pressure series generally exhibited stronger nonlinearity than series of temperature (daily mean, minimum or maximum). Distinct nonlinearity was found in all tested multivariate systems, especially when both temperatures and pressures were used simultaneously to form the phase space. Nonlinearity tests were carried out for 30-year and 10-year-long datasets and nonlinear behavior was generally more apparent in the longer versions. In addition, the tested systems showed more substantial nonlinearity when the success of short-range prediction was used as the discriminating statistic; with an increase of the prediction time, detectable nonlinearity became weaker and it disappeared completely for long-term prediction. [ABSTRACT FROM AUTHOR]