Lukas Papritz

Last Name

Papritz

First Name

Lukas

ORCID

0000-0002-2047-9544

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03854 - Wernli, Johann Heinrich / Wernli, Johann Heinrich

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Publications 1 - 10 of 32

Characteristics and dynamics of extreme winters in the Barents Sea in a changing climate
Hartmuth, Katharina; Wernli, Heini; Papritz, Lukas (2025)
Weather and Climate Dynamics
The Barents Sea is experiencing large declines in sea ice and increasing surface temperatures while at the same time it is a key region of weather variability in the Arctic. In this study, we identify extreme winter seasons in the Barents Sea, based on a multivariate method, as winters with large seasonal anomalies in one or several surface parameters encompassing surface temperature, precipitation, surface heat fluxes, and surface net radiation. The analyses are based on large-ensemble climate model data for historical (S2000) and end-of-century (S2100) projections following an RCP8.5 emission scenario. In the phase space of the considered seasonal-mean surface weather parameters, we find distinct clusters of extreme winters that are characterized by similar combinations of anomalies in these parameters. In particular, during extreme winters in S2000 simulations, anomalies in surface air temperature during extreme seasons tend to be spatially extended with their maximum amplitude over sea ice. This maximum shifts towards the continental land masses in a warmer climate (S2100), as the formation of intense warm or cold anomalies is damped by the increasing area of open ocean. Our results reveal that large anomalies in surface parameters during extreme seasons are characterized by distinct patterns of anomalous frequencies in cyclones, anticyclones, and cold air outbreaks because these weather systems are responsible for temperature and moisture advection, the formation or suppression of precipitation, and intense surface fluxes. We further show that anomalous surface boundary conditions at the beginning of a season - that is, sea ice concentration and sea surface temperatures - facilitate the formation of persistent anomalous surface conditions or further enhance atmospherically driven anomalies due to anomalous surface heat fluxes. However, a decrease in the variability of both sea ice and sea surface temperatures in S2100 indicates a decreasing importance of anomalous surface boundary conditions for the formation of future extreme winters in the Barents Sea, while the robust link shown for surface weather systems persists in a warmer climate.
Quantifying the physical processes leading to atmospheric hot extremes at a global scale
Röthlisberger, Matthias; Papritz, Lukas (2023)
Nature Geoscience
Heat waves are among the deadliest climate hazards. Yet the relative importance of the physical processes causing their near-surface temperature anomalies (T′)—advection of air from climatologically warmer regions, adiabatic warming in subsiding air and diabatic heating—is still a matter of debate. Here we quantify the importance of these processes by evaluating the T′ budget along air-parcel backward trajectories. We frst show that the extreme near-surface T′ during the June 2021 heat wave in western North America was produced primarily by diabatic heating and, to a smaller extent, by adiabatic warming. Systematically decomposing T′ during the hottest days of each year (TX1day events) in 1979–2020 globally, we fnd strong geographical variations with a dominance of advection over mid-latitude oceans, adiabatic warming near mountain ranges and diabatic heating over tropical and subtropical land masses. In many regions, however, TX1day events arise from a combination of these processes. In the global mean, TX1day anomalies form along trajectories over roughly 60 h and 1,000 km, although with large regional variability. This study thus reveals inherently non-local and regionally distinct formation pathways of hot extremes, quantifes the crucial factors determining their magnitude and enables new quantitative ways of climate model evaluation regarding hot extremes.
Characterizing the Local and Intense Water Cycle during a Cold Air Outbreak in the Nordic Seas
Papritz, Lukas; Sodemann, Harald (2018)
Monthly Weather Review
A Lagrangian analysis of the dynamical and thermodynamic drivers of large-scale Greenland melt events during 1979–2017
Hermann, Mauro; Papritz, Lukas; Wernli, Heini (2020)
Weather and Climate Dynamics
In this study, we systematically investigate the dynamical and thermodynamic processes that lead to 77 large-scale melt events affecting high-elevation regions of the Greenland Ice Sheet (GrIS) in June–August (JJA) 1979–2017. For that purpose, we compute 8 d kinematic backward trajectories from the lowermost ∼500 m above the GrIS during these events. The key synoptic feature accompanying the melt events is an upper-tropospheric ridge southeast of the GrIS associated with a surface high-pressure system. This circulation pattern is favorable to induce rapid poleward transport (up to 40∘ latitude) of warm (∼15 K warmer than climatological air masses arriving on the GrIS) and moist air masses from the lower troposphere to the western GrIS and subsequently to distribute them in the anticyclonic flow over north and east Greenland. During transport to the GrIS, the melt event air masses cool by ∼15 K due to ascent and radiation, which keeps them just above the critical threshold to induce melting. The thermodynamic analyses reveal that the final warm anomaly of the air masses is primarily owed to anomalous horizontal transport from a climatologically warm region of origin. However, before being transported to the GrIS, i.e., in their region of origin, these air masses were not anomalously warm. Latent heating from condensation of water vapor, occurring as the airstreams are forced to ascend orographically or dynamically, is of secondary importance. These characteristics were particularly pronounced during the most extensive melt event in early July 2012, where, importantly, the warm anomaly was not preserved from anomalously warm source regions such as North America experiencing a record heat wave. The mechanisms identified here are in contrast to melt events in the low-elevation high Arctic and to midlatitude heat waves, where adiabatic warming by large-scale subsidence is essential. Considering the impact of moisture on the surface energy balance, we find that radiative effects are closely linked to the air mass trajectories and enhance melt over the entire GrIS accumulation zone due to (i) enhanced downward longwave radiation related to poleward moisture transport and a shift in the cloud phase from ice to liquid primarily west of the ice divide and (ii) increased shortwave radiation in clear-sky regions east of the ice divide. Given the ongoing increase in the frequency and the melt extent of large-scale melt events, the understanding of upper-tropospheric ridges over the North Atlantic, i.e., also Greenland blocking, and its representation in climate models is crucial in determining future GrIS accumulation zone melt and thus global sea level rise.
Extreme Surface Energy Budget Anomalies in the High Arctic in Winter
Murto, Sonja; Papritz, Lukas; Messori, Gabriele; et al. (2023)
Journal of Climate
In recent decades, the Arctic has warmed faster than the global mean, especially during winter. This has been attributed to various causes, with recent studies highlighting the importance of enhanced downward infrared radiation associated with anomalous inflow of warm, moist air from lower latitudes. Here, we study wintertime surface energy budget (SEB) anomalies over Arctic sea ice on synoptic time scales, using ERA5 (1979–2020). We introduce a new algorithm to identify areas with extreme, positive daily mean SEB anomalies and connect them to form spatiotemporal life cycle events. Most of these events are associated with large-scale inflow from the Atlantic and Pacific Oceans, driven by poleward deflection of the storm track and blocks over northern Eurasia and Alaska. Events originate near the ice edge, where they have roughly equal contributions of net longwave radiation and turbulent fluxes to the positive SEB anomaly. As the events move farther into the Arctic, SEB anomalies decrease due to weakening sensible and latent heat-flux anomalies, while the surface temperature anomaly increases toward the peak of the events along with the downward longwave radiation anomaly. Due to these temporal and spatial differences, the largest SEB anomalies are not always related to strongest surface warming. Thus, studying temperature anomalies alone might not be sufficient to determine sea ice changes. This study highlights the importance of turbulent fluxes in driving SEB anomalies and downward longwave radiation in determining local surface warming. Therefore, both processes need to be accurately represented in climate models.
Identification, characteristics and dynamics of Arctic extreme seasons
Hartmuth, Katharina; Boettcher, Maxi; Wernli, Heini; et al. (2022)
Weather and Climate Dynamics
The Arctic atmosphere is strongly affected by anthropogenic warming leading to long-term trends in surface temperature and sea ice extent. In addition, it exhibits strong variability on timescales from days to seasons. While recent research elucidated processes leading to short-term extreme conditions in the Arctic, this study investigates unusual atmospheric conditions on the seasonal timescale. Based on a principal component analysis in the phase space spanned by the seasonal-mean values of surface temperature, precipitation and the atmospheric components of the surface energy balance, individual seasons are objectively identified that deviate strongly from a running-mean climatology and that we define as extreme seasons. Given the strongly varying surface conditions in the Arctic, this analysis is done separately in Arctic sub-regions that are climatologically characterized by either sea ice, open ocean or mixed conditions. Using ERA5 reanalyses for the years 1979–2018, our approach identifies two to three extreme seasons for each of winter, spring, summer and autumn, with strongly differing characteristics and affecting different Arctic sub-regions. Two extreme winters affecting the Kara and Barents seas are selected for a detailed investigation of their substructure, the role of synoptic-scale weather systems, and potential preconditioning by anomalous sea ice extent and/or sea surface temperature at the beginning of the season. Winter 2011/12 started with average sea ice coverage and was characterized by constantly above-average temperatures during the season related mainly to frequent warm air advection by quasi-stationary cyclones in the Nordic Seas. In contrast, winter 2016/17 started with reduced sea ice and enhanced sea surface temperatures in the Kara and Barents seas, which, together with increased frequencies of cold air outbreaks and cyclones, led to large upward surface heat flux anomalies and strongly increased precipitation during this extreme season. In summary, this study shows that extreme seasonal conditions in the Arctic are spatially heterogeneous, related to different near-surface parameters and caused by different synoptic-scale weather systems, potentially in combination with surface preconditioning due to anomalous ocean and sea ice conditions at the beginning of the season. The framework developed in this study and the insight gained from analyzing the ERA5 period will be beneficial for addressing the effects of global warming on Arctic extreme seasons.
Synoptic perspective on the conversion and maintenance of local available potential energy in extratropical cyclones
Federer, Marc; Papritz, Lukas; Sprenger, Michael; et al. (2025)
Weather and Climate Dynamics
Extratropical cyclones are the predominant weather system in the midlatitudes. They intensify through baroclinic instability, a process in which available potential energy (APE) is converted into kinetic energy (KE). While the planetary-scale conversion of APE to KE is well understood as a mechanism for maintaining the general atmospheric circulation against dissipation, the synoptic-scale perspective on this conversion is less explored. In this study, we analyze the three-dimensional distribution of APE and the physical processes that consume APE for an illustrative case study and a climatology of 285 intense North Atlantic extratropical cyclones in the winters of 1979-2021 using the ERA5 reanalysis. We utilize a recently introduced local APE framework that allows for APE to be quantified at the level of individual air parcels. The geographical APE distribution is shown to be controlled by the large-scale upper-level circulation. Cyclones draw energy from the upper-tropospheric polar APE reservoir along with the development of the associated upper-level trough. This upper-level APE is converted into KE by air descending along the trough's western flank and acts as the incipient cyclone's primary source of KE. Conversely, KE is converted back into APE during the ascent ahead of the trough, reflecting the deceleration of air parcels as they exit the cyclone region. The diabatic dissipation of APE due to surface sensible heat fluxes along the Gulf Stream front is small compared to the adiabatic conversion of APE to KE, since most of the APE is concentrated and consumed in the middle to upper troposphere and cannot be exposed to surface diabatic forcing. In conclusion, by employing a local APE framework, this study provides a detailed investigation of the synoptic dynamics linking extratropical cyclones and planetary-scale energetics.
On the Thermodynamic Preconditioning of Arctic Air Masses and the Role of Tropopause Polar Vortices for Cold Air Outbreaks From Fram Strait
Papritz, Lukas; Rouges, Emmanuel; Aemisegger, Franziska; et al. (2019)
Journal of Geophysical Research: Atmospheres
Understanding the vertical temperature structure of recent record-shattering heatwaves
Hotz, Belinda; Papritz, Lukas; Röthlisberger, Matthias (2024)
Weather and Climate Dynamics
Extreme heatwaves are one of the most impactful natural hazards, posing risks to human health, infrastructure, and ecosystems. Recent theoretical and observational studies have suggested that the vertical temperature structure during heatwaves limits the magnitude of near-surface heat through convective instability. In this study, we thus examine in detail the vertical temperature structure during three recent record-shattering heatwaves, the Pacific Northwest (PNW) heatwave in 2021, the western Russian (RU) heatwave in 2010, and the western European and UK (UK) heatwave in 2022, by decomposing temperature anomalies (T 0) in the entire tropospheric column above the surface into contributions from advection, adiabatic warming and cooling, and diabatic processes. All three heatwaves exhibited bottom-heavy yet vertically deep positive T 0 extending throughout the troposphere. Importantly, though, the T 0 magnitude and the underlying physical processes varied greatly in the vertical within each heatwave, as well as across distinct heatwaves, reflecting the diverse synoptic storylines of these events. The PNW heatwave was strongly influenced by an upstream cyclone and an associated warm conveyor belt, which amplified an extreme quasi-stationary ridge and generated substantial mid-to upper-tropospheric positive T 0 through advection and diabatic heating. In some contrast, positive upper-tropospheric T 0 during the RU heatwave was caused by advection, while during the UK heatwave, it exhibited modest positive diabatic contributions from upstream latent heating only during the early phase of the respective ridge. Adiabatic warming notably contributed positively to lower-tropospheric T 0 in all three heatwaves, but only in the lowermost 200–300 hPa. Near the surface, all three processes contributed positively to T 0 in the PNW and RU heatwaves, while near-surface diabatic T 0 was negligible during the UK heatwave. Moreover, there is clear evidence of an amplification and downward propagation of adiabatic T 0 during the PNW and UK heatwaves, whereby the maximum near-surface T 0 coincided with the arrival of maximum adiabatic T 0 in the boundary layer. Additionally, the widespread ageing of near-surface T 0 over the course of these events is fully consistent with the notion of heat domes, within which air recirculates and accumulates heat. Our results for the first time document the four-dimensional functioning of anticyclone–heatwave couplets in terms of advection, adiabatic cooling or warming, and diabatic processes and suggest that a complex interplay between large-scale dynamics, moist convection, and boundary layer processes ultimately determines near-surface temperatures during heatwaves.
On the Local Available Potential Energy Perspective of Baroclinic Wave Development
Federer, Marc; Papritz, Lukas; Sprenger, Michael; et al. (2024)
Journal of the Atmospheric Sciences
Extratropical cyclones convert available potential energy (APE) to kinetic energy. However, our current understanding of APE conversion on synoptic scales is limited, as the well-established Lorenz APE framework is only applicable in a global, volume-integrated sense. Here, we employ a recently developed local APE framework to investigate APE and its tendencies in a highly idealized, dispersive baroclinic wave, which leads to the formation of a primary and a downstream cyclone. By utilizing a Lagrangian approach, we demonstrate that locally the downstream cyclone not only consumes APE but also generates it. Initially, APE is transported from both poleward and equatorward reservoirs into the baroclinic zone, where it is then consumed by the vertical displacement of air parcels associated with the developing cyclone. To a lesser extent, APE is also created within the cyclone when air parcels overshoot their reference state; i.e., air colder than its reference state is lifted and air warmer than its reference state is lowered. The volume integral of the APE tendency is dominated by slow vertical displacements of large air masses, whereas the dry intrusion (DI) and warm conveyor belt (WCB) of the cyclone are responsible for the largest local APE tendencies. Diabatic effects within the DI and WCB contribute to the generation of APE in regions where it is consumed adiabatically, thereby enhancing baroclinic conversion in situ. Our findings provide a comprehensive and mechanistic understanding of the local APE tendency on synoptic scales within an idealized setting and complement existing frameworks explaining the energetics of cyclone intensification.

Publications 1 - 10 of 32

Lukas Papritz

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