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Introduction
Skills and Expertise
Publications
Publications (40)
The July 2021 flood in central Europe was one of the five costliest natural disasters in Europe in the last half century with estimated total damage of EUR 32 billion. This study investigates the complex interactions between meteorological, hydrological, and hydro-morphological processes and mechanisms that led to the exceptional flood. Furthermore...
The accurate prediction of extreme weather events is an important and challenging task, and has typically relied on numerical simulations of the atmosphere. Here, we combine insights from numerical forecasts with recent developments in dynamical systems theory, which describe atmospheric states in terms of their persistence (θ−1) and local dimensio...
Physical processes on the synoptic scale are important modulators of the large-scale extratropical circulation. In particular, rapidly ascending airstreams in extratropical cyclones, so-called warm conveyor belts (WCBs), modulate the upper-tropospheric Rossby wave pattern and are sources and magnifiers of forecast uncertainty. Thus, from a process-...
Warm conveyor belts (WCBs) affect the atmospheric dynamics in midlatitudes and are highly relevant for total and extreme precipitation in many parts of the extratropics. Thus, these airstreams and their effect on midlatitude weather should be well represented in numerical weather prediction (NWP) and climate models. This study applies newly develop...
The subseasonal variability of the extratropical large-scale atmospheric flow is characterized
by recurrent or quasi-stationary circulation anomalies, termed weather regimes. Despite the usefulness
of these regimes in numerous meteorological and socioeconomic applications, there is an ongoing
debate as to whether they represent physical modes of th...
Warm conveyor belts (WCBs) associated with extratropical cyclones transport air from the lower troposphere into the tropopause region and contribute to upper-level ridge building and the formation of blocking anticyclones. Recent studies indicate that this constitutes an important source and magnifier of forecast uncertainty and errors in numerical...
The subseasonal variability of the extratropical large-scale atmospheric flow is characterized by recurrent or quasi-stationary circulation anomalies, termed weather regimes. Despite the usefulness of these regimes in numerous meteorological and socioeconomic applications, there is an ongoing debate as to whether they represent physical modes of th...
Warm conveyor belts (WCBs) affect the atmospheric dynamics in midlatitudes and are highly relevant for total and extreme precipitation in many parts of the extratropics. Thus, these air streams and their effect on midlatitude weather should be well represented in numerical weather prediction (NWP) and climate models. This study applies newly develo...
Physical processes on the synoptic scale are important modulators of the large-scale extratropical circulation. In particular, rapidly ascending air streams in extratropical cyclones, so-called warm conveyor belts (WCBs), modulate the upper-tropospheric Rossby wave pattern and are sources and magnifiers of forecast uncertainty. Thus, from a process...
Weather regime forecasts are a prominent use case of sub‐seasonal prediction in the midlatitudes. A systematic evaluation and understanding of year‐round sub‐seasonal regime forecast performance is yet still missing. Here we evaluate the representation of and forecast skill for seven year‐round Atlantic‐European weather regimes in sub‐seasonal refo...
The physical and dynamical processes associated with warm conveyor belts (WCBs) importantly affect midlatitude dynamics and are sources of forecast uncertainty. Moreover, WCBs modulate the large-scale extratropical circulation and can communicate and amplify forecast errors. Therefore, it is desirable to assess the representation ofWCBs in numerica...
Skillful forecasts of extreme weather events have a major
socioeconomic relevance. Here, we compare two complementary approaches to
diagnose the predictability of extreme weather: recent developments in
dynamical systems theory and numerical ensemble weather forecasts. The
former allows us to define atmospheric configurations in terms of their
pers...
Over 3 weeks in May and June 2018, an exceptionally large number of thunderstorms hit vast parts of western and central Europe, causing precipitation accumulations of up to 80 mm within 1 h and several flash floods.
This study examines the conditions and processes that made this particular thunderstorm episode exceptional, with a particular focus o...
Skillful forecasts of extreme weather events have a major socio-economic relevance. Here, we compare two complementary approaches to diagnose the predictability of extreme weather: recent developments in dynamical systems theory and numerical ensemble weather forecasts. The former allows us to define atmospheric configurations in terms of their per...
In both 2003 and 2018 a heatwave in Scandinavia in July was followed by a heatwave in Central Europe in August. Whereas the transition occurred abruptly in 2003, it was gradual in 2018 with a 12‐day period of concurrent heatwaves in both regions. This study contrasts these two events in the context of a heatwave climatology to elucidate the dynamic...
The El Niño phase of the El Niño Southern Oscillation (ENSO) is typically associated with below‐average cool‐season rainfall in southeastern Australia (SEA). However, there is also large case‐to‐case variability on monthly time scales. Despite recent progress in understanding the links between remote climate drivers and this variability, the underl...
Fog is a defining characteristic of the climate of the Namib Desert, and its water and nutrient input are important for local ecosystems. In part due
to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential
synoptic-scale controls have not been investigated. In th...
Purpose of Review
This review brings together recent research on the structure, characteristics, dynamics, and impacts of extratropical cyclones in the future. It draws on research using idealized models and complex climate simulations, to evaluate what is known and unknown about these future changes.
Recent Findings
There are interacting processe...
Nocturnal low-level stratus clouds (LLCs) are frequently observed in the atmospheric boundary layer (ABL) over southern West Africa (SWA) during the summer monsoon season. Considering the effect these clouds have on the surface energy and radiation budgets as well as on the diurnal cycle of the ABL, they are undoubtedly important for the regional c...
Fog is a defining characteristic of the climate of the Namib Desert and its water and nutrient input are important for local ecosystems. In part due to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential synoptic-scale controls have not been investigated. In thi...
Fog is a defining characteristic of the climate of the Namib Desert and its water and nutrient input are important for local ecosystems. In part due to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential synoptic-scale controls have not been investigated. In thi...
Nocturnal low-level stratus clouds (LLC) are frequently observed in the atmospheric boundary layer (ABL) over southern West Africa (SWA) during the summer monsoon season. Considering the effect these clouds have on the surface energy and radiation budgets as well as on the diurnal cycle of the ABL, they are undoubtedly important for the regional cl...
Plain Language Summary
Equatorward and poleward perturbations propagating eastward along the fast flowing air currents in the upper troposphere are commonly referred to as Rossby wave packets (RWPs). These packets have been linked to extreme weather events such as intense low‐pressure systems, extreme temperatures, and precipitation. Hence, an adeq...
Motivated by the record-breaking heatwaves of early 2017, the synoptic structure and evolution of summer (December–February) heatwaves in the Sydney area is investigated through composite and trajectory analyses. In the upper troposphere, the main features of the composite structure are an isolated upper-tropospheric anticyclonic potential vorticit...
The extratropical transition (ET) of tropical cyclones often has an important impact on the nature and predictability of the midlatitude flow. This review synthesizes the current understanding of the dynamical and physical processes that govern this impact and highlights the relationship of downstream development during ET to highimpact weather, wi...
In May and September 2016, two intense hybrid cyclones (HCs) developed over the Great Australian Bight damaging infrastructure and causing a state‐wide power outage in South Australia. These two cyclones motivate the compilation of the first synoptic climatology of HCs in the Australian region, including an analysis of their importance for wind and...
Hybrid cyclones (HCs) in the Australian region typically reach their peak intensity in an amplified flow comprising upper‐tropospheric ridges upstream and downstream of the cyclone and a north–south elongated trough. Nonetheless, there is considerable case‐to‐case variability. Taking a composite viewpoint, the present study investigates how such va...
The physical mechanisms by which heat waves in the Brisbane region of Australia develop are elucidated through trajectory and composite analyses. Trajectories are started close to the surface during heat waves and integrated backward. Those trajectories for which the net diabatic heating lies in the uppermost pentile are called strongly diabatic, w...
The North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) explored the impact of diabatic processes on disturbances of the jet stream and their influence on downstream high-impact weather through the deployment of four research aircraft, each with a sophisticated set of remote sensing and in situ instruments, and coordinated with a sui...
Potential vorticity (PV) cutoffs are stratospheric air masses separated from the circumpolar stratospheric reservoir on an isentropic surface. They typically form via Rossby wave breaking and can strongly influence midlatitude weather; however, the processes governing their evolution are not fully understood. A detailed analysis of two exceptionall...
Extratropical transition (ET) is the process by which a tropical cyclone, upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes, transforms into an extratropical cyclone. This process is influenced by, and influences, phenomena from the tropics to the midlatitudes and from themeso- to the planetary scale...
Although heat waves account for more premature deaths in the Australian region than any other natural disaster, an understanding of their dynamics is still incomplete. The present study identifies the dynamical mechanisms responsible for heat waves in southeastern Australia using 10-day backward trajectories computed from the ERA-Interim reanalyses...
Tropospheric forcing of planetary wavenumber 2 is examined in the prephase of the major stratospheric sudden warming event in January 2009 (MSSW 2009). Because of a huge increase in Eliassen-Palm fluxes induced mainly by wavenumber 2, easterly angular momentum is transported into the Arctic stratosphere, deposited, and then decelerates the polar ni...
Many studies have highlighted the importance of recurving tropical cyclones (TCs) in triggering Rossby waves. This study investigates the impact of western North Pacific (WNP), south Indian Ocean, and North Atlantic recurving TCs on the amplitude and frequency of synoptic-scale Rossby wave packets (RWPs) over a 30-yr period. The results indicate a...
The structure and the environment of Typhoon Sinlaku (2008) were investigated during its life cycle in The Observing System Research and Predictability Experiment (THORPEX) Pacific Asian Regional Campaign (T-PARC). On 20 September 2008, during the transformation stage of Sinlaku's extratropical transition (ET), research aircraft equipped with dual-...