Abstract. Cyclones, which develop over the western Mediterranean and move northeastward are a major source of extreme weather and known to be responsible for heavy precipitation over the northern side of the Alpine range and Central Europe. As the relevant processes triggering these so-called Vb events and their impact on extreme precipitation are not yet fully understood, this study focuses on gaining insight into the dynamics of past events. For this, a cyclone detection and tracking tool is applied to the ERA-Interim reanalysis to identify prominent Vb situations. Precipitation in the ERA-Interim and the E-OBS data sets is used to evaluate case-to-case precipitation amounts and to assess consistency between the two data sets. Both data sets exhibit high variability in precipitation amounts among different Vb events. While only 23 % of all Vb events are associated with extreme precipitation, around 15 % of all extreme precipitation days (99 percentile) over the northern Alpine region and Central Europe are induced by Vb events, although Vb cyclones are rare events (2.3 per year). To obtain a better understanding of the variability within Vb events, the analysis of the 10 heaviest and lowest precipitation Vb events reveals noticeable differences in the state of the atmosphere. These differences are most pronounced in the geopotential height and potential vorticity field, indicating a much stronger cyclone for heavy precipitation events. The related differences in wind direction are responsible for the moisture transport around the Alps and the orographical lifting along the northern slopes of the Alps. These effects are the main reasons for a disastrous outcome of Vb events, and consequently are absent in the Vb events associated with low precipitation. Hence, our results point out that heavy precipitation related to Vb events is mainly related to large-scale dynamics rather than to thermodynamic processes.

Despite frequent complications and recurring signs of lower urinary tract disease, 32.2 per cent of the cats had a disease-free long-term outcome (mean four years, median 3.9 years), and 88.6 per cent of clients interviewed thought that their cats had a good quality of life after surgery.

Abstract. Extratropical cyclones of type Vb, which develop over the western Mediterranean and move northeastward, are major natural hazards that are responsible for heavy precipitation over central Europe. To gain further understanding in the governing processes of these Vb cyclones, the study explores the role of soil moisture and sea surface temperature (SST) and their contribution to the atmospheric moisture content. Thereby, recent Vb events identified in the ERA-Interim reanalysis are dynamically downscaled with the Weather Research and Forecasting (WRF) model. Results indicate that a mean high-impact summer Vb event is mostly sensitive to an increase in the Mediterranean SSTs and rather insensitive to Atlantic SSTs and soil moisture changes. Hence, an increase of +5 K in Mediterranean SSTs leads to an average increase of 24 % in precipitation over central Europe. This increase in precipitation is mainly induced by larger mean upward moisture flux over the Mediterranean with increasing Mediterranean SSTs. This further invokes an increase in latent energy release, which leads to an increase in atmospheric instability, i.e. in convective available potential energy. Both the increased availability of atmospheric moisture and the increased instability of the atmosphere, which is able to remove extra moisture from the atmosphere due to convective processes, are responsible for the strong increase in precipitation over the entire region influenced by Vb events. Precipitation patterns further indicate that a strong increase in precipitation is found at the eastern coast of the Adriatic Sea for increased Mediterranean SSTs. This premature loss in atmospheric moisture leads to a significant decrease in atmospheric moisture transport to central Europe and the northeastern flanks of the Alpine mountain chain. This leads to a reduction in precipitation in this high-impact region of the Vb event for an increase in Mediterranean SSTs of +5 K. Furthermore, the intensity of the Vb cyclones, measured as a gradient in the 850 hPa geopotential height field around the cyclone centre, indicates that an upper bound for intensity might be reached for the most intense Vb event.

A climatology of the marine atmospheric boundary layer (MABL) and the lower free troposphere over the Southern Ocean (SO) is constructed using 2,186 high-resolution atmospheric soundings from four recent campaigns conducted in the period of 2016-2018. Relationships between the synoptic meteorology and MABL thermodynamic structure are examined using a k-means cluster analysis, complemented by front and cyclone composite analyses. Seven distinct clusters are identified, five of which are consistent with an established climatology over the SO storm track. Two new clusters (C1 and C2) are introduced over the high-latitude SO. C1 is commonly located poleward of the ocean polar front near mesocyclones, while C2 is located along the Antarctic coastline. A multilayer cloud structure is frequently present in clusters in the vicinity of fronts and cyclones, while a single-layer coverage is more common in a suppressed environment, particularly at lower latitudes. A cloud-free, multilevel inversion is frequently observed in cluster C2, possibly linked to the descending, dry, katabatic winds off the Antarctic coast. A strong, primary inversion is typically present in clusters at lower latitudes with high mean sea level pressure. Across the SO storm track and higher latitudes (cluster C1), a multilevel inversion structure is also commonly observed. A preliminary analysis of two case studies suggests that upper level advection and detrainment of convection associated with mesocyclones are potential drivers of the multilayer cloud coverage over the high-latitude SO rather than the decoupling mechanisms common in the subtropics.

Moisture transport over the northeastern Atlantic Ocean is an important process governing precipitation distribution and variability over western Europe. To assess its long-term variability, the vertically integrated horizontal water vapor transport (IVT) from a long-term climate simulation spanning the period 850–2100 CE was used. Results show a steady increase in moisture transport toward western Europe since the late-nineteenth century that is projected to expand during the twenty-first century under the RCP8.5 scenario. The projected IVT for 2070–99 significantly exceeds the range given by interannual–interdecadal variability of the last millennium. Changes in IVT are in line with significant increases in tropospheric moisture content, driven by the concurrent rise in surface temperatures associated with the anthropogenic climate trend. On regional scales, recent and projected precipitation changes over the British Isles follow the global positive IVT trend, whereas a robust precipitation decrease over Iberia is identified in the twenty-first century, particularly during autumn. This indicates a possible extension of stable and dry summer conditions and a decoupling between moisture availability and dynamical forcing. The investigation of circulation features reveals a mean poleward shift of moisture corridors and associated atmospheric rivers. In particular, in Iberia, a significant increase in the frequency of dry weather types is observed, accompanied by a decrease in the frequency of wet types. An opposite response is observed over the British Isles. These changes imply a stronger meridional north–south dipole in terms of pressure and precipitation distributions, enhancing the transport toward central Europe rather than to Iberia.

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Abstract. Extratropical cyclones in winter and their characteristics are investigated in depth for the Atlantic European region, as they are responsible for a significant part of the rainfall and extreme wind and/or precipitation-induced hazards. The analysis is based on a seamless transient simulation with a state-of-the-art fully coupled Earth system model from 850 to 2100 CE. The Representative Concentration Pathway 8.5 (RCP8.5) scenario is used in the 21st century. During the Common Era, cyclone characteristics show pronounced variations on interannual and decadal timescales, but no external forcing imprint is found prior to 1850. Thus, variations of extratropical cyclone characteristics are mainly caused by internal variability of the coupled climate system. When anthropogenic forcing becomes dominant in the 20th century, a decrease of the cyclone occurrences mainly over the Mediterranean and a strong increase of extreme cyclone-related precipitation become detectable. The latter is due to thermodynamics as it follows the Clausius–Clapeyron relation. An important finding, though, is that the relation between temperature and extreme cyclone-related precipitation is not always controlled by the Clausius–Clapeyron relation, which suggests that dynamical processes can play an important role in generating extreme cyclone-related precipitation – for example, in the absence of anomalously warm background conditions. Thus, the importance of dynamical processes, even on decadal timescales, might explain the conundrum that proxy records suggest enhanced occurrence of precipitation extremes during rather cold periods in the past.

Abstract. Extratropical cyclones in winter and their characteristics are investigated in depth for the Atlantic European region, as they are responsible for a significant part of the rainfall and extreme wind and/or precipitation-induced hazards. Here, we use a seamless transient simulation with a state-of-the-art fully-coupled Earth System Model from 850 to 2100 CE as basis for the analysis. The RCP8.5 scenario is applied in the 21st century. During the Common Era, cyclone characteristics show pronounced variations on interannual and decadal time scales, but no external forcing imprint is found prior to 1850. Thus, variations of extratropical cyclone characteristics are mainly caused by internal variability of the coupled climate system. When anthropogenic forcing becomes dominant in the 20th century, a decrease of the cyclone occurrences mainly over the Mediterranean and a strong increase of extreme cyclone-related precipitation become detectable. The latter is due to thermodynamics as it follows the Clausius-Clapeyron relation. An important finding, though, is that the relation between temperature and extreme cyclone-related precipitation is not always controlled by the Clausius-Clapeyron relation, which suggests that dynamical processes can play an important role in generating extreme cyclone-related precipitation – for example in the absence of anomalously warm background conditions. Thus, the importance of dynamical processes, even on decadal time scales, might explain the conundrum that proxy records suggest enhanced occurrence of precipitation extremes during rather cold periods in the past.