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We developed a vortex identification algorithm for realistic atmospheric simulations. The algorithm enabled us to obtain a climatology of vortex shedding from Madeira Island for a 10-year simulation period. This first objective climatological analysis of vortex streets shows consistency with observed atmospheric conditions. The analysis shows a pronounced annual cycle with an increasing vortex shedding rate from April to August and a sudden decrease in September.

Arctic sea ice loss might impact the atmospheric circulation outside the Arctic and therefore extremes over mid-latitudes. Here, we analyze model experiments to initially assess the influence of sea ice loss on occurrence frequencies of large-scale circulation patterns. Some of these detected circulation changes can be linked to changes in occurrences of European temperature extremes. Compared to future global temperature increases the sea ice-related impacts are however of secondary relevance.

The Atlantic equatorial mode (AEM) of variability is responsible for 31 % of the year-to-year rainfall variability over the Guinea Coast. We use the current climate models to explore the present-day and future links between the AEM and the extreme rainfall indices over the Guinea Coast. Under future global warming, the total variability of the extreme rainfall indices increases over the Guinea Coast. However, the future impact of the AEM on the extreme events over the Guinea Coast is reduced.

The relationship between the time-average state of the atmosphere and aspects of atmospheric circulation drives general understanding of the atmospheric circulation. Here, we present new techniques to calculate local properties of the time-average atmosphere, and relate those properties to aspects of extratropical circulation with important implication for weather. This relationship should help connect changes to the atmosphere, such as under global warming, to changes in midlatitude weather.

We study the atmospheric moisture transport into East China for past, present and future climate. To this end, we use different climate and weather prediction model data with a moisture source identification method. We find that the moisture sources are relatively similar for different climates when comparing the same climate models, while differences between models are partly larger than between different climates, which has important implications for interpreting the hydroclimate from models.

As stated in the IPCC, southern Africa is one of the two land regions that are projected to suffer from the strongest precipitation reductions in the future. Simulated drying in this region is linked to the adjacent oceans and prevailing winds as warm and moist air masses are transported towards the continent. Precipitation trends in past and future climate can be partly attributed to the strength of the Agulhas Current System, the current along the east and south coast of Southern Africa.

In recent decades, cold fronts have rained less often in southeast Australia, which contributes to decreasing cool season rainfall. The largest changes in front dynamics are found to the north of the area where rain changes. Wet fronts have strong westerly winds that reach much further north than dry fronts do, and these fronts are becoming less common, linked to weakening subtropical winds and changes in the southern hemisphere circulation.

This study examines quasi-periodic variability in the tropical Pacific on interannual timescales and related physics using a recently developed timeseries analysis tool. We find that wind stress in the West-Pacific and recharge-discharge of ocean heat content are likely related to each other on ~2–4.5-year timescales (but not on other) and dominate variability in sea surface temperatures on those timescales. Further implications for climate models and long-term prediction are also discussed.

This is the first study to analyze the impact of realistic historical deforestation in West Africa using a model that does not rely on parameterization of convection. Unlike previous studies, we find rainfall increases from 18:00 to 6:00 with changes driven by changes in mesoscale circulations, in line with observations in the region. This shows the potential for future studies using similar models to examine the impact of realistic deforestation in West Africa on multi-annual time scales.

Heavy rainfall in tropical regions interacts with mid-latitude circulation patterns and this interaction can explain weather patterns in the Northern Hemisphere during summer. . In this analysis we detect these tropical – extratropical interaction pattern both in observational datasets and data obtained by atmospheric models and assess how well can atmospheric model reproduce the observed patterns. We find a good agreement although these relationships are too weak in model data.

Future European temperature extremes associated with heatwaves will be even more amplified compared to the mean increase of summer temperatures. Following the airstreams associated with heatwaves backwards in time shows, that this amplification is probably linked to a feedback between boundary-layer air and dryer soils. Moreover, in some regions stronger descent contributes to a further amplification of 2 m temperatures.

Easterly winds encircle Antarctica, moving sea ice and helping drive ocean currents which shield ice shelves from warmer waters. Our most complete picture of how these winds behave comes from reanalysis datasets. In this paper we use satellite data, surface measurements and weather balloons to test how realistic recent reanalysis estimates are. The winds are generally accurate, especially in the most recent of the datasets, but important short-term variations are often misrepresented.

Blocking describes a flow configuration in midlatitudes where stationary high-pressure systems block the propagation of weather systems. This study presents a unified framework to capture blocking dynamics from three different perspectives and quantifies the importance of different processes in the formation of a major blocking in 2016. In future work, this framework will enable a holistic view on the dynamics and the role of moist processes in different life cycle stages of the blocking.

Post-tropical cyclones (PTCs) can bring severe weather to Europe. By tracking and identifying PTCs in 5 global climate models, we investigate how the frequency and intensity of PTCs may change across Europe by 2100. We find no robust change in the frequency or intensity of Europe-impacting PTCs in the future. This study indicates that large uncertainties surround future Europe-impacting PTCs, and provides a framework for evaluating PTCs in future generations of climate models.

This paper investigates large scale atmospheric variability in polar regions, specifically the balance between large scale turbulence and Rossby wave activity. The polar regions are relatively more dominated by turbulence than lower latitudes, but Rossby waves are found to play a role and can even be triggered from high latitudes under certain conditions. Features such as cyclone lifetimes, high-latitude blocks and annular modes are discussed from this perspective.

Accurately predicting the response of the mid-latitude jet stream to climate change is very important, but climate models show a variety of possible scenarios. Previous work has identified a relationship between climatological jet latitude and future jet shift in the southern hemispheric winter. However, we show that the jet latitude is not a well-defined metric in in austral winter, due to zonal asymmetries in the mid-latitude jet. The usefulness of the relationship is therefore questionable.

Sudden stratospheric warming events can severely affect the subsequent weather at the surface. We use a large ensemble of climate model hindcasts to investigate features of the climate that make strong impacts more likely, through negative NAO conditions. This allows a more robust assessment than using observations alone. Air pressure over the Arctic prior to an SSW, and the zonal mean zonal wind in the lower stratosphere, have the strongest relationship with the subsequent NAO response.

We investigate the dynamical origin of the lower-atmospheric PV (linked to the intensity of cyclones) in Mediterranean cyclones. Therefore, we quantify the contribution of the cyclone and the environment by tracing PV backward in time and space and linking it to the track of the cyclone. We find that the the lower-tropospheric PV is produced shortly prior the cyclone's stage of highest intensity. Further, we investiage the driving processes. We use a global dataset and a process resolving one.

Warm conveyor belts (WCBs) are the main cloud and precipitation producing airstreams in extratropical cyclones. The latent heat release that occurs during cloud formation often contributes to the intensification of the associated cyclone. Based on CESM-LE coupled climate simulations, here we show that WCBs and the associated latent heating will become stronger in a future climate and be even more important for explosive cyclone intensification than in the present-day climate.

Warm conveyor belts (WCBs) are strongly ascending, cloud and precipitation forming airstreams in extratropical cyclones. In this study we assess their representation in a climate simulation and their changes under global warming. They become moister, more intense and reach higher altitudes in a future climate, implying that they potentially have an increased impact on the mid-latitude flow.

Sudden stratospheric warmings are extreme weather events where the winter polar stratosphere warms by about 25 K. An improved representation of small-scale gravity waves in sub-seasonal prediction models can reduce forecast errors since their impact on the large-scale circulation is predictable multiple weeks ahead. After a sudden stratospheric warming, vertically propagating gravity waves break at a lower altitude than usual which strengthens the long-lasting positive temperature anomalies.

This study revises and extends a previously presented 3-D objective front detection method and demonstrates its benefits to analyse weather dynamics in numerical simulation data. Based on two case studies of extratropical cyclones, we demonstrate the evaluation of conceptual models from dynamic meteorology, illustrate the benefits of our interactive analysis approach by comparing fronts in data with different model resolutions, and study the impact of convection on fronts.

This work has identified characteristic spatial and temporal scales for non-Gaussian outbreaks in forecasts, specifically, bimodality. Methodology is introduced which allows one to connect meteorological phenomena to bimodal outbreaks. Large-scale circulation interacting with local processes is uncovered as a frequent ingredient to such outbreaks. These insights not only provide a deeper understanding of the dynamical processes involved, but also have drastic implications for forecast skill.

We use a statistical model to generate precipitation forecasts at lead times of 2–6 weeks over southwest Asia, needed to support humanitarian food distribution. Model signal-to-noise ratio is used to identify a smaller subset of forecasts with particularly high skill, so-called 'subseasonal forecasts of opportunity' (SFOs). Precipitation SFOs over southwest Asia are often related to slowly evolving tropical phenomena, namely the El Niño-Southern Oscillation and Madden-Julian Oscillation.

Forecasting extratropical cyclones are challenging due to many physical factors influencing their behavior. One factor that is understudied is the impact of heating and cooling in the atmosphere by the interaction between clouds and radiation. In this study, we show that cloud radiative heating (CRH) increases the intensity of the cyclone and affects its predictability. We find that CRH affects the cyclone mostly via increasing latent heat release and subsequently the cyclone's circulation.