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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.

We test whether any association between solar activity and meteorological conditions in the north Atlantic – European sector could be detected. We find associations consistent with those found by previous studies, with a slightly better statistical significance, and with less methodological biases which have impaired previous studies. Our study should help strengthen the recognition of meteorological impacts of solar activity.

The stratosphere contains under a fifth of the atmosphere's mass but through its variability has a significant influence at ground level. Features of the variability are high-latitude sudden stratospheric warmings and a tropical quasi-biennial oscillation. Much of the variability is dynamical due to waves from the troposphere interacting with the mean flow. Dynamical stratospheric variability, its representation and predictability in models and coupling to the troposphere are reviewed.

While the Arctic is warming rapidly, some counterintuitive regional impacts have emerged, including the pronounced cooling over the Eurasian subcontinent that has been linked to retreating Arctic sea ice. However, there is strong disagreement among the scientific community around the strength and even existence of this link, as well as the possible causes of Eurasian cooling. Here we provide a review of the state of understanding and a perspective that helps reconcile apparent disagreements.

More than half of India’s summer monsoon rainfall arises from low-pressure systems: storms originating over the Bay of Bengal. In observation-based data, we examine how the generation and pathway of these storms are changed by the “Boreal summer intraseasonal oscillation” – the chief means of large-scale control on the monsoon at time scales of a few weeks. Our study offers new insights for useful prediction of these storms, important for both water resources planning and disaster early warning.

Mid-latitude weather is dominated by the formation and decay of large cyclonic and anticyclonic eddies, mostly formed during the growth and breaking of baroclinic waves. One way to study these phenomena is via idealised numerical life-cycle simulations, which are typically characterised by cyclonic or anticyclonic wave breaking, depending on the details of the system. We show that all systems exhibit predominantly anticyclonic character if a range of wave modes is allowed to grow simultaneously.

Understanding the location and intensity of hazardous weather across the Arctic is important for assessing risks to infrastructure, shipping, and coastal communities. This study describes the typical lifetime and structure of intense winter and summer Arctic cyclones. Results show the composite development and structure of intense Arctic summer cyclones is different to intense winter Arctic and North Atlantic Ocean extra-tropical cyclones, and to conceptual models.

Assessing annual time series of local Rossby wave packet amplitude, phase, and phase speed on reanalysis data reveals that trends outweigh interannual variability in several regions and seasons. While no covariance emerges between amplitude and phase speed at decadal scales, the frequency of DJF large-amplitude quasi-stationary waves increases in several areas during 1999–2019. These outcomes prompt further investigations on the causes and implications of local variations in RWP properties.

Mesoscale high-wind features within extratropical cyclones can cause immense damage. Here, we present RAMEFI, a novel approach to objectively identify the wind features based on a probabilistic random forest. RAMEFI enables a wide range of applications such as probabilistic predictions for the occurrence or a multi-decadal climatology of these features, which will be the focus of Part II of the study, with the goal of improving wind and specifically wind gust forecasts in the long run.