We studied how mid-latitude cyclones are likely to change in the future. We used a state-of-the-art numerical model and performed a control and a warm experiment. The total number of cyclones did not change with warming and neither did the average strength, but there were more stronger and more weaker storms in the warm experiment. Precipitation associated with the most extreme mid-latitude cyclones increased by up to 50 % and occurred in a more poleward location in the warmer experiment.

The 2013–2014 winter sea surface temperature (SST) was anomalously cool in the mid-North Atlantic region. We investigate the processes by which cyclones can lead to SST cooling and their contribution towards the 2013–2014 SST anomaly. We find that cyclones induce a cold wake, which extends along the cyclones' cold front. Cyclones account for over 40 % of the observed cooling in the mid-North Atlantic. Thus, cyclones play a major role in determining the extreme 2013–2014 winter SST cooling.

In this study we quantify how much the coldest, middle and hottest third of all days during extremely hot summers contribute to their respective seasonal mean anomaly. This extreme-summer substructure varies substantially across the Northern Hemisphere and is directly related to the local physical drivers of extreme summers. Furthermore, comparing re-analysis (i.e. measurement-based) and climate model extreme-summer substructures reveals a remarkable level of agreement.

Sting jets (SJs) can lead to strong surface winds by descending into the frontal-fracture region of intense extratropical cyclones. In this study we look at idealised simulations of SJ-containing cyclones produced using an improved initial state and a wide set of sensitivity experiments. The results clarify the role of dry instabilities in SJ dynamics and evolution, supporting a recent conceptual model. The simulations also highlight the robustness of SJ occurrence in these intense cyclones.

Sudden stratospheric warmings (SSWs) are extreme events that influence surface weather up to 2 months after onset. We remove wave–wave interactions (WWIs) in vertical sections of a general circulation model to investigate the role of WWIs in SSW formation. We show that the effects of WWIs depend strongly on the pressure levels where they occur and the zonal structure of the wave forcing in the troposphere. Our results highlight the importance of upper-level processes in stratospheric dynamics.

This paper investigates the waveguidability of midlatitude jets, i.e., their ability to duct Rossby waves in the zonal direction. Waveguidability is quantified in the framework of an idealized numerical model and compared with the predictions from two complementary theoretical concepts. It is found that the concept of ray tracing, which has been used extensively in the past, does not provide a satisfactory explanation for the numerical results. Further analysis uncovers the underlying reasons.

Warm conveyor belts (WCBs) are important, mainly stratiform cloud forming airstreams in extratropical cyclones that can include embedded convection. This WCB case study systematically compares the characteristics of convective vs. slantwise ascent of the WCB. We find that embedded convection leads to regions of significantly stronger precipitation. Moreover, it strongly modifies the potential vorticity distribution in the lower and upper troposphere, where its also influences the waveguide.

We perform 50-year-long time-slice experiments using the Met Office HadGEM3 global climate model in order to decompose the Brewer–Dobson circulation (BDC) response to an abrupt quadrupling of CO₂ in three distinct components, (a) the rapid adjustment, associated with CO₂ radiative effects; (b) a global uniform sea surface temperature warming; and (c) sea surface temperature patterns. This demonstrates a potential for fast and slow timescales of the response of the BDC to greenhouse gas forcing.

In this paper, we take a second look at the development of an intense storm that made landfall in Norway a few hours into the new year of 1992, focussing on the effect of the Scandinavian mountains on the storm. We find that the cyclone core evolves largely unaffected, although both the warm and the cold fronts decay rapidly while passing over the mountains. This result suggests that the fronts of a cyclone can become detached from their cyclone core as part of the cyclone’s occlusion process.

We analyse the formation of upper-tropospheric anticyclones connected to European surface heat waves. Tracing air masses backwards from these anticyclones, we found that trajectories are diabatically heated in two branches, either by North Atlantic cyclones or by convection closer to the heat wave anticyclone. The first branch primarily affects the onset of the anticyclone, while the second branch is more relevant for the maintenance. Our results are relevant for heat wave predictions.

The mesoscale convective system (MCS) that affected Germany at Pentecost 2014 was one of the most severe for decades. However, the predictability of this system was very low. By moving the model domain by just one grid point changed whether the MCS was successfully simulated or not. The decisive factor seems to be small differences in the initial track of the convection: cooler air near the coast inhibited development there, but tracks slightly more inland found more favorable conditions.

Atmospheric predictability over Europe on subseasonal to seasonal timescales remains limited. However, the remote impact from the El Niño–Southern Oscillation (ENSO) can help to improve predictability. Research has suggested that the ENSO impact in the North Atlantic region is affected by nonlinearities. Here, we isolate the nonlinearities in the tropospheric pathway through the North Pacific, finding that a strong El Niño leads to a stronger and distinct impact compared to a strong La Niña.

Tropical storms are key for harnessing midlatitude weather prediction skill 2–8 weeks into the future. Recently, stratospheric activity was shown to impact tropical storminess and thus may also be important for midlatitude prediction skill on these timescales. This work analyzes two forecast systems to assess whether they capture this additional skill. We find there is enhanced prediction out through week 4 when both the tropical and stratospheric phenomena are active.

Arctic sea ice loss has been linked to changes in mid-latitude weather and climate. However, the literature offers differing views on the strength, robustness, and even existence of these linkages. We use a statistical tool (Causal Effect Networks) to show that one proposed pathway linking Barents–Kara ice and mid-latitude circulation is intermittent in observations and likely only active under certain conditions. This result may help explain apparent inconsistencies across previous studies.

In blocking situations the westerly atmospheric flow in the midlatitudes is blocked by near-stationary high-pressure systems. Blocking can be associated with extremes such as cold spells and heat waves. Climate models are known to underestimate blocking occurrence. Here, we assess the latest generation of models and find improvements in simulated blocking, partly due to increases in model resolution. These new models are therefore more suitable for studying climate extremes related to blocking.