Climatological studies of downslope windstorms (DWs) in the Scandinavian mountains (Scandes) are rare. Here we use 20-year long simulations with the kilometre-scale regional climate model HCLIM38-AROME to study DWs in the Scandes in present and future climate, their connection to large-scale atmospheric circulation, and their cooling and warming effect. A DW is identified in a model grid point using a two-step conceptual model based on terrain features, and dynamic and thermodynamic variables. We find that DWs occur most frequently in winter, which is therefore the focal season for the analyses. Normally, DWs are predominantly either warming (foehn type) or cooling (bora type), but our results indicate that this distinction does not hold for the DWs in the Scandes. Even though there is a slight overall tendency towards warming, almost all locations with DWs can experience both cooling and warming. The future simulations using two parent global climate models (GCMs) show an overall decrease in the total number of DW occurrences between 7% and 17% toward the end of the century, with a decrease in the northern and central parts of the Scandes and an increase in the southeastern part. These changes can be attributed to two factors: the frequency change of certain circulation types and internal changes within the circulation types. Despite the agreement in the sign of future changes for both GCM forcings, the difference in the contribution of the two factors indicates that different mechanisms are responsible for the total future change in the DW occurrence. The complexity of DWs in the Scandes and their future change indicates that kilometre-scale or finer climate models are required for a proper depiction of DWs and that a larger ensemble of simulations with different GCM forcing is required for evaluation of different mechanisms of the future change.
Numerical weather prediction and climate models require continuous adaptation to take advantage of advances in high-performance computing hardware. This paper presents the port of the ICON model to GPUs using OpenACC compiler directives for numerical weather prediction applications. In the context of an end-to-end operational forecast application, we adopted a full-port strategy: the entire workflow, from physical parameterizations to data assimilation, was analyzed and ported to GPUs as needed. Performance tuning and mixed-precision optimization yield a 5.5× speed-up compared to the CPU baseline in a socket-to-socket comparison. The ported ICON model meets strict requirements for time-to-solution and meteorological quality, in order for MeteoSwiss to be the first national weather service to run ICON operationally on GPUs with its ICON-CH1-EPS and ICON-CH2-EPS ensemble forecasting systems. We discuss key performance strategies, operational challenges, and the broader implications of transitioning community models to GPU-based platforms.
The Climate Change Adaptation Digital Twin (Climate DT), developed as part of the European Commission's Destination Earth (DestinE) initiative, sets up an operational system for producing multi-decadal, multi-model global climate projections and translating climate data into climate impact information to support adaptation efforts. This system delivers data with local granularity at spatial resolutions of 5–10 km and hourly outputs, leading to globally consistent information at scales that matter for decision-making. It also enables the testing of what-if scenarios such as high-resolution storylines, which are physically consistent global simulations of extreme events under different climate conditions and provide contextual insights to support concrete adaptation decisions. They support the generation of more equitable (understood as accessible and relevant across regions) climate information. The Climate DT is built on cutting-edge infrastructure, expert collaboration, and digital innovation. It is designed to support on-demand responses to policy questions, with quantified uncertainty. It will foster interactivity by allowing users to influence simulation design, model output portfolios, and application integration through co-design. AI-based tools, including emulators and chatbots, are being developed in parallel to enhance climate information access. Sector-specific applications are embedded in the system to synchronously translate climate data into tailored climate-impact indicators, with examples provided for energy, water, and forest management. The applications have been co-designed with informed users. A unified, cross-platform workflow defines the orchestration of all components, which is handled by a single workflow manager and relies on containerised components, facilitating automation, portability, maintainability, and traceability. Data management is unified using standard grids (HEALPix), ensuring consistency and easing data usability under a strict governance policy. Streaming enables real-time data use by the data consumers and unlocks access to the unprecedented data wealth produced by the high-resolution simulations. Monitoring tools provide real-time quality control of data and model outputs and enable continuous assessment of the realism of the climate simulations during Climate DT operation. The compute-intensive system is powered by world-class supercomputing capabilities through a strategic partnership with the European High Performance Computing Joint Undertaking (EuroHPC). Despite high computational demands, the Climate DT sets a new benchmark for delivering equitable, credible, and actionable climate information. It complements existing initiatives like CMIP, CORDEX, and national and European climate services, and aligns with global climate science goals to support climate adaptation.
Abstract The Beobachtung von Ozean und Wolken–Das Trans ITCZ Experiment (BOWTIE) field campaign investigated how convective storm dynamics interact with the ocean surface to shape the structure of the Atlantic intertropical convergence zone (ITCZ). Conducted aboard the German Research Vessel (R/V) Meteor during August and September 2024, the campaign targeted the full meridional extent of the ITCZ while transiting the tropical Atlantic from east to west. The research was driven by evidence suggesting that storm-scale dynamics is pivotal for shaping the broader structure of the ITCZ and its connection to global circulation patterns and energy transport. BOWTIE featured high-resolution atmospheric and oceanic profiling, with a particular focus on the coupled boundary layers. Observations included cloud and humidity profiles, winds, precipitation, sea surface temperature, and upper-ocean physical and biogeochemical properties. A suite of advanced instruments provided vertically resolved cross sections of convective environments and surrounding conditions. BOWTIE was part of the larger international Organized Convection and EarthCARE Studies over the Tropical Atlantic (ORCESTRA) initiative, which coordinated eight campaigns across the Atlantic. During the voyage, the R/V Meteor served as a platform for two additional ORCESTRA campaigns: Soundings and Turbulent eddy measurements in the ITCZ with a Network of Quadcopters (STRINQS), which deployed unmanned aerial vehicles for profiling near-storm environments, and Process Investigation of Clouds and Convective Organization over the Atlantic Ocean (PICCOLO), which brought Colorado State University’s Sea-Pol scanning dual-polarization C-band radar onboard. This article provides an overview of BOWTIE’s scientific goals, campaign design, and observing strategy and presents selected early results from the extensive dataset. The combination of in situ, airborne, and radar measurements offers new insight into how ocean–atmosphere interactions at convective scales shape the ITCZ’s broader structure and behavior. Significance Statement The intertropical convergence zone (ITCZ) plays a central role in shaping tropical rainfall and global circulation, yet the processes governing its structure and variability remain incompletely understood. The Beobachtung von Ozean und Wolken–Das Trans ITCZ Experiment (BOWTIE) field campaign provides a coupled observational view of the Atlantic ITCZ by combining ship-based atmospheric and oceanic measurements with scanning and profiling radar, autonomous platforms, and coordinated aircraft and satellite observations. By sampling the full meridional extent of the ITCZ over 40 days and nights, BOWTIE reveals how convective organization, boundary layer dynamics, and upper-ocean variability interact across spatial and temporal scales. These observations advance understanding of the physical processes that regulate tropical rain belts and their day-to-day variability.
A new Earth system reanalysis framework is being introduced consisting of the intermediate complexity coupled CESAM model together with its adjoint. The results presented are a first pilot demonstration of an Earth system reanalysis that shows the potential of such an approach to (a) improving model biases through parameter estimation and (b) accomplishing a fully coupled reanalysis over long time windows. Variational data assimilation applied to nonlinear chaotic atmospheric models is limited by predictability, and therefore restricted to short assimilation windows. Applications with ocean models, however, require much longer assimilation windows to propagate sparse data information through time and space efficiently. To overcome this contradiction we employ the adjoint method together with synchronization to atmospheric data. The first application presented requires nearly complete information on the atmospheric state for synchronization, for which it relies on European Centre for Medium-Range Weather Forecasts Reanalysis v5 data, and a simple nudging technique to achieve synchronization. We demonstrate that, over 39 years, efficient assimilation of in-situ and satellite ocean data and atmospheric reanalysis data is possible by adjusting the surface fluxes and internal model parameters. Given the coarse resolution of the model of , overturning and meridional transports of heat and fresh water are less realistic than previous higher resolution ocean syntheses based on the adjoint method. However, unsynchronized model runs with adjusted parameters show an improved climate and circulation consistent with the reanalysis, suggesting low initialization shocks if the reanalysis is used for initializing decadal predictions.
