This paper proposes a new classification scheme of atmospheric cyclone tracks over Europe. The cyclones are classified into nine types, based on the geographic regions, the cyclones traverse before entering central Europe. The method is applied to ERA‐40 data for 1961–2002, considering all significant cyclones above a relative vorticity threshold. About 120 and 80 cyclone tracks per year are identified at sea level pressure and 700 hPa geopotential height, respectively. About 25% are Atlantic type cyclones, 25% emerge directly over central Europe, and another 25% originate from the lee of the Alps. The other types are less frequent (Mediterranean 12%, Polar 7%, Continental 2%, and Vb 4%). The track types show distinct characteristics in terms of cyclone intensity and cyclone life stage when entering central Europe. Cyclones of type Vb are, on average, the most intense cyclones over central Europe and even more intense than Atlantic cyclones in summer, pointing to their potential for generating extreme precipitation. The identified cyclones account for 46%–76% of long‐term precipitation in a focus region in central Europe. Precipitation differs significantly between cyclones, with Atlantic and Vb cyclones producing the highest and Continental and Polar cyclones producing the lowest long‐term precipitation totals. The contributions of cyclone types to total precipitation show distinct spatial patterns within central Europe. The new cyclone type catalog will be useful for identifying the relevance of specific track types for precipitation extremes in central Europe and analyze their temporal behavior in the context of climate change.
Precipitation patterns over Europe are largely controlled by atmospheric cyclones embedded in the general circulation of the mid‐latitudes. This study evaluates the climatologic features of precipitation for selected regions in central Europe with respect to cyclone track types for 1959–2015, focusing on large‐scale heavy precipitation.The analysis suggests that each of the cyclone track types is connected to a specific pattern of the upper level atmospheric flow, usually characterized by a major trough located over Europe. A dominant upper level cut‐off low (COL) is found over Europe for strong continental (CON) and van Bebber's type (Vb) cyclones which move from the east and southeast into central Europe. Strong Vb cyclones revealed the longest residence times, mainly due to circular propagation paths.The central European cyclone precipitation climate can largely be explained by seasonal track‐type frequency and cyclone intensity; however, additional factors are needed to explain a secondary precipitation maximum in early autumn. The occurrence of large precipitation totals for track events is strongly related to the track type and the region, with the highest value of 45% of all Vb cyclones connected to heavy precipitation in summer over the Czech Republic and eastern Austria. In western Germany, Atlantic winter cyclones are most relevant for heavy precipitation. The analysis of the top 50 precipitation events revealed an outstanding heavy precipitation period from 2006 to 2011 in the Czech Republic, but no gradual long‐term change. The findings help better understand spatio‐temporal variability of heavy precipitation in the context of floods and may be used for evaluating climate models.
Three homogenization methods (ACMANT, MASH and HOMOP) have been evaluated for their efficiency in homogenizing daily relative humidity data. A homogeneous surrogate data set based on Austrian stations was created and perturbed to simulate inhomogeneous, realistic time series ("validation data sets"). Two validation data sets ("simple" and "complex") were created. In both data sets the magnitude of the breaks depends on the time of year and the measured values. They differ in the number of missing values and especially on whether the break signal was perturbed by white noise. In the latter case, the noise also changed to take into account changes in random measurements errors and other physical factors. The evaluation showed high agreement in statistical characteristics between the real data and the surrogate data set. The homogenization methods were compared in their ability both to detect breaks and to reproduce the homogeneous surrogate data set. For the evaluation of the final data set the distribution, trends and root-mean-square error (RMSE) were analysed. The percentage of improved time series depends on the evaluation parameter considered. Less stations were improved when using the "complex" validation data set. Because of the large number of breaks and the small signal-to-noise ratio, an improvement of the data by homogenization was non-ideal for all methods used, with each having its advantages and disadvantages. The quality of the ACMANT and HOMOP methods is comparable, with ACMANT solving less stations but declaring less stations falsely as homogeneous. To get an impression of the influence on real data, ACMANT was applied to homogenize daily Austrian time series of relative humidity. While the quality of data from some stations can be improved through the homogenization, this is not the case for all time series. A final evaluation of homogenized time series should be performed to ensure their quality before further use.
<p>Several major flood events of recent years have encouraged research focused on a&#160;better understanding of climatological and hydrological causes of floods. In practice, these findings can be used in flood risk management, and in the light of ongoing climate change, also in preparing effective adaptation strategies. This study builds on the results of the Wetrax+ research project which combined a&#160;stochastic weather generator and a&#160;high-resolution fully-distributed rainfall-runoff model to produce a&#160;unique dataset of 10&#160;000 years of hourly simulations of air temperatures, precipitations and river discharges in the Upper Danube River basin. As the generated dataset accounted for the expected changes in the frequencies and persistence of the identified weather patterns, it was used to assess the possible changes in the very extreme flows in the study basin. The length of the dataset maintained that numerous flood events that were larger than the most extreme observed floods occurred in the dataset and were available for analysis. The results indicated that on average the floods should occur sooner in the year in most of the Upper Danube sub-basins. Moreover, the frequency of floods associated with weather patterns related to heavy precipitation also increased. Despite the predictions about the future, changes in weather pattern frequencies cannot be taken for granted the results of the study can be useful in identifying the sources and causes of the most extreme floods helping those responsible to focus their mitigation efforts on certain sub-basins.</p>
<p>&#8216;A picture is worth a thousand words&#8217; and &#8216;seeing is believing&#8217;. Clearly, images are considered to be incredibly powerful communication tools. The project &#8218;Images of Change&#8217;, which is funded by the Austrian Climate Research Program, wants to harness the power of visuals in climate change communication. To do so, the project focusses at developing different visual communication formats aimed at young adults, with the goal to support a better understanding of facts and invite climate friendly behavior as well as policy acceptance. In order to hit the ground running, existing (visual) climate change communication formats of different national meteorological and environmental organizations, academia, the media as well as non- governmental organizations (NGOs) were collected, analyzed and compared to best practices as reported in climate communication research. Here, we will present an overview of the key findings from psychological as well as communication research on how to successfully communicate the causes, impacts and solutions of climate change to non-scientists. Specifics on how to engage young adults as well as how to implement visuals in climate change communication in order to achieve the highest impact and increase the motivation to act in a climate friendly manner will also be highlighted. Finally, a selection of existing visual communication campaigns will be presented and discussed. Based on these formats, we will take a deeper look into how the best practice guidelines postulated by the communication science community may be implemented in our own work as climate communicators in academia as well as national weather services.</p>
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