@article{21657, abstract = {We compare three global kilometer-scale models (ICON, IFS and NICAM) to clarify the advantages and challenges of high-resolution global weather and climate modeling, using different approaches to represent convection, from fully parameterized to fully explicit. Our analysis focuses on tropical precipitation characteristics spanning a wide range of spatio-temporal scales—including the diurnal cycle, extreme precipitation, convective organization, and the Madden-Julian Oscillation (MJO)—along with interactions between convection and the thermodynamic environment. All three models commonly show weaker convective organization with smaller precipitation cells than observed, though the strength of the bias varies by model. This diversity is introduced by differences in the representation of (a) convective initiation affected by the convective sensitivity to moisture and (b) tropospheric moistening associated with deep convection. Models with stronger thermodynamic-convection coupling increase environmental moisture near convection, thereby enhancing convective organization. This has important upscale effects on the MJO; while IFS and NICAM capture its eastward propagation well, ICON has difficulty reproducing it. The amplitudes and phases of precipitation diurnal cycles over land show much greater disagreement among the models than over ocean, influenced by how convection is initiated. Biases in rain evaporation and cold pool formation hinder the propagation of mesoscale convection, leading to errors such as the misrepresentation of nocturnal convection moving off the coast of Sumatra in IFS and ICON. These results highlight the importance of thermodynamic-convection coupling in realistically simulating tropical convection across scales. To improve this coupling, kilometer-scale models require better representation of the interaction between resolved convection and three-dimensional turbulent mixing.}, author = {Takasuka, Daisuke and Becker, Tobias and Bao, Jiawei}, issn = {1942-2466}, journal = {Journal of Advances in Modeling Earth Systems}, number = {3}, publisher = {Wiley}, title = {{Precipitation characteristics and thermodynamic-convection coupling in global kilometer-scale simulations}}, doi = {10.1029/2025MS005343}, volume = {18}, year = {2026}, } @article{21233, abstract = {Potential self-perpetuating dieback of the Amazon rain forest has been a topic of concern. The concern is that initial deforestation could critically impair the forest’s water recycling capacities, further harming the remaining forest through reduced annual precipitation. Many studies have focused on annual mean precipitation changes, due to its widespread perception as a central control on the Amazon rain forest’s stability. However, the impact of deforestation goes beyond changes in the annual mean precipitation. Yet, global coarse-resolution climate models are not well suited to investigate changes in short-duration and localized events due to their coarse resolution. Here, we circumvent these issues by analyzing a full-deforestation scenario simulated by a global storm-resolving model. We focus on changes in the tail of the hourly distribution of precipitation, temperature, and wind. Hourly precipitation becomes more extreme in the absence of the forest than in an intact forest, with an increased occurrence of both no rain and intense rainfall. These changes are driven by enhanced moisture convergence that strengthens vertical velocity. On average, the near-surface temperature rises significantly by about 3.84 °C, and the daily minimum temperature after deforestation becomes similar to the daily maximum temperature before deforestation. Except for wet-bulb temperature, human heat stress indicators shift to more severe levels, with implications for health and a significant reduction in work productivity. Finally, the mean 10 m wind speed intensifies by a factor of four, with the 99th percentile wind speed doubling. To summarize, our findings, while based on an idealized case, provide a stark warning of the effects of continuing deforestation of the Amazon.}, author = {Yoon, Arim and Hohenegger, Cathy and Bao, Jiawei and Brunner, Lukas}, issn = {2190-4987}, journal = {Earth System Dynamics}, number = {1}, pages = {167--179}, publisher = {Copernicus Publications}, title = {{Extreme events in the Amazon after deforestation}}, doi = {10.5194/esd-17-167-2026}, volume = {17}, year = {2026}, } @article{19662, abstract = {We investigate the effect of changes in the Coriolis force caused by changes in the rotation rate on the top-of-atmosphere (TOA) radiant energy budget of an aquaplanet general circulation model with prescribed sea surface temperatures. We analyse the effective radiative forcing caused by changes from Earth-like rotation to values between 1/32 and 8 times the Earth's rotation rate. The forcing differs by about 60 W m−2 between the fastest and slowest rotation cases, with a monotonically increasing positive forcing for faster-than-Earth-like rotations and a non-monotonically increasing negative forcing for slower rotations. The largest contributions to the forcing are due to changes in, in this order, the shortwave cloud radiative effect (SWCRE) and the clear-sky outgoing longwave radiation (OLR). From the fastest to the slowest rotation, the Hadley cell expands and the troposphere becomes drier, increasing the OLR. This contributes to negative forcing at slower-than-Earth-like rotations and to positive forcing at faster-than-Earth-like rotations. The SWCRE is influenced by changes in the low-level cloudiness within the Hadley cell and the baroclinic regime. With the expansion of the Hadley cell, the area of enhanced tropospheric stability increases, resulting in more low-level clouds, a higher SWCRE, and increased negative forcing. The non-monotonicity results from an intermediate decrease in the SWCRE caused by the disappearance of baroclinic eddies as the Hadley cell reaches global extension. At rotations faster than Earth-like, the decrease in the SWCRE, mainly due to the weakening of baroclinic eddies and storm systems, leads to an increase in positive forcing. In summary, changes in the SWCRE, driven by different circulation responses at slower-than-Earth-like and faster-than-Earth-like rotations, strongly influence the TOA radiant energy budget. These effects, along with a substantial contribution from the clear-sky OLR, could impact the habitability of Earth-like rotating planets.}, author = {Gnanaraj, Abisha Mary and Bao, Jiawei and Schmidt, Hauke}, issn = {2698-4016}, journal = {Weather and Climate Dynamics}, number = {2}, pages = {489--503}, publisher = {Copernicus Publications}, title = {{The impact of the rotation rate on an aquaplanet's radiant energy budget: Insights from experiments varying the Coriolis parameter}}, doi = {10.5194/wcd-6-489-2025}, volume = {6}, year = {2025}, } @article{20685, abstract = {The Next Generation of Earth Modeling Systems (nextGEMS) project aimed to produce multidecadal climate simulations, for the first time, with resolved kilometer-scale (km-scale) processes in the ocean, land, and atmosphere. In only 3 years, nextGEMS achieved this milestone with the two km-scale Earth system models, ICOsahedral Non-hydrostatic model (ICON) and Integrated Forecasting System coupled to the Finite-volumE Sea ice-Ocean Model (IFS-FESOM). nextGEMS was based on three cornerstones: (1) developing km-scale Earth system models with small errors in the energy and water balance, (2) performing km-scale climate simulations with a throughput greater than 1 simulated year per day, and (3) facilitating new workflows for an efficient analysis of the large simulations with common data structures and output variables. These cornerstones shaped the timeline of nextGEMS, divided into four cycles. Each cycle marked the release of a new configuration of ICON and IFS-FESOM, which were evaluated at hackathons. The hackathon participants included experts from climate science, software engineering, and high-performance computing as well as users from the energy and agricultural sectors. The continuous efforts over the four cycles allowed us to produce 30-year simulations with ICON and IFS-FESOM, spanning the period 2020–2049 under the SSP3-7.0 scenario. The throughput was about 500 simulated days per day on the Levante supercomputer of the German Climate Computing Center (DKRZ). The simulations employed a horizontal grid of about 5 km resolution in the ocean and 10 km resolution in the atmosphere and land. Aside from this technical achievement, the simulations allowed us to gain new insights into the realism of ICON and IFS-FESOM. Beyond its time frame, nextGEMS builds the foundation of the Climate Change Adaptation Digital Twin developed in the Destination Earth initiative and paves the way for future European research on climate change.}, author = {Segura, Hans and Pedruzo-Bagazgoitia, Xabier and Weiss, Philipp and Müller, Sebastian K. and Rackow, Thomas and Lee, Junhong and Dolores-Tesillos, Edgar and Benedict, Imme and Aengenheyster, Matthias and Aguridan, Razvan and Arduini, Gabriele and Baker, Alexander J. and Bao, Jiawei and Bastin, Swantje and Baulenas, Eulàlia and Becker, Tobias and Beyer, Sebastian and Bockelmann, Hendryk and Brüggemann, Nils and Brunner, Lukas and Cheedela, Suvarchal K. and Das, Sushant and Denissen, Jasper and Dragaud, Ian and Dziekan, Piotr and Ekblom, Madeleine and Engels, Jan Frederik and Esch, Monika and Forbes, Richard and Frauen, Claudia and Freischem, Lilli and García-Maroto, Diego and Geier, Philipp and Gierz, Paul and González-Cervera, Álvaro and Grayson, Katherine and Griffith, Matthew and Gutjahr, Oliver and Haak, Helmuth and Hadade, Ioan and Haslehner, Kerstin and ul Hasson, Shabeh and Hegewald, Jan and Kluft, Lukas and Koldunov, Aleksei and Koldunov, Nikolay and Kölling, Tobias and Koseki, Shunya and Kosukhin, Sergey and Kousal, Josh and Kuma, Peter and Kumar, Arjun U. and Li, Rumeng and Maury, Nicolas and Meindl, Maximilian and Milinski, Sebastian and Mogensen, Kristian and Niraula, Bimochan and Nowak, Jakub and Praturi, Divya Sri and Proske, Ulrike and Putrasahan, Dian and Redler, René and Santuy, David and Sármány, Domokos and Schnur, Reiner and Scholz, Patrick and Sidorenko, Dmitry and Spät, Dorian and Sützl, Birgit and Takasuka, Daisuke and Tompkins, Adrian and Uribe, Alejandro and Valentini, Mirco and Veerman, Menno and Voigt, Aiko and Warnau, Sarah and Wachsmann, Fabian and Wacławczyk, Marta and Wedi, Nils and Wieners, Karl-Hermann and Wille, Jonathan and Winkler, Marius and Wu, Yuting and Ziemen, Florian and Zimmermann, Janos and Bender, Frida A.-M. and Bojovic, Dragana and Bony, Sandrine and Bordoni, Simona and Brehmer, Patrice and Dengler, Marcus and Dutra, Emanuel and Faye, Saliou and Fischer, Erich and van Heerwaarden, Chiel and Hohenegger, Cathy and Järvinen, Heikki and Jochum, Markus and Jung, Thomas and Jungclaus, Johann H. and Keenlyside, Noel S. and Klocke, Daniel and Konow, Heike and Klose, Martina and Malinowski, Szymon and Martius, Olivia and Mauritsen, Thorsten and Mellado, Juan Pedro and Mieslinger, Theresa and Mohino, Elsa and Pawłowska, Hanna and Peters-von Gehlen, Karsten and Sarré, Abdoulaye and Sobhani, Pajam and Stier, Philip and Tuppi, Lauri and Vidale, Pier Luigi and Sandu, Irina and Stevens, Bjorn}, issn = {1991-9603}, journal = {Geoscientific Model Development}, number = {20}, pages = {7735--7761}, publisher = {Copernicus Publications}, title = {{nextGEMS: Entering the era of kilometer-scale Earth system modeling}}, doi = {10.5194/gmd-18-7735-2025}, volume = {18}, year = {2025}, } @article{20795, abstract = {The tropical climate variability is characterized by various oscillations across a range of timescales. Oscillations that imprint the tropical mean state are generally attributed to slow processes, such as the seasonal cycle or interannual variability. Here, we identify a pronounced tropics-wide intraseasonal oscillation (TWISO) in satellite observations and reanalyses. This oscillation, with a period of 30 to 60 d, is evident across multiple variables and involves interactions between convection, radiation, surface fluxes, and large-scale circulation. It is primarily manifested as convective perturbations in the tropical Indo-Pacific warm pool accompanied by oscillations in the large-scale tropical overturning circulation. Here, we examine the relationship between TWISO, the Madden–Julian Oscillation (MJO), and the instability of radiative-convective equilibrium. Certain phases of TWISO coincide with specific phases of the MJO, suggesting a potential connection between the two. However, although the MJO can amplify the oscillation amplitude of TWISO, it is not essential for TWISO to occur. Finally, due to its broad manifestation across the tropics, TWISO potentially exerts widespread influence on tropical weather and climate at regional scales.}, author = {Bao, Jiawei and Bony, Sandrine and Takasuka, Daisuke and Muller, Caroline J}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, number = {48}, publisher = {National Academy of Sciences}, title = {{Tropics-wide intraseasonal oscillations}}, doi = {10.1073/pnas.2511549122}, volume = {122}, year = {2025}, } @article{15047, abstract = {Tropical precipitation extremes and their changes with surface warming are investigated using global storm resolving simulations and high-resolution observations. The simulations demonstrate that the mesoscale organization of convection, a process that cannot be physically represented by conventional global climate models, is important for the variations of tropical daily accumulated precipitation extremes. In both the simulations and observations, daily precipitation extremes increase in a more organized state, in association with larger, but less frequent, storms. Repeating the simulations for a warmer climate results in a robust increase in monthly-mean daily precipitation extremes. Higher precipitation percentiles have a greater sensitivity to convective organization, which is predicted to increase with warming. Without changes in organization, the strongest daily precipitation extremes over the tropical oceans increase at a rate close to Clausius-Clapeyron (CC) scaling. Thus, in a future warmer state with increased organization, the strongest daily precipitation extremes over oceans increase at a faster rate than CC scaling.}, author = {Bao, Jiawei and Stevens, Bjorn and Kluft, Lukas and Muller, Caroline J}, issn = {2375-2548}, journal = {Science Advances}, number = {8}, publisher = {American Association for the Advancement of Science}, title = {{Intensification of daily tropical precipitation extremes from more organized convection}}, doi = {10.1126/sciadv.adj6801}, volume = {10}, year = {2024}, } @article{15097, abstract = {Global storm-resolving models (GSRMs) use strongly refined horizontal grids compared with the climate models typically used in the Coupled Model Intercomparison Project (CMIP) but employ comparable vertical grid spacings. Here, we study how changes in the vertical grid spacing and adjustments to the integration time step affect the basic climate quantities simulated by the ICON-Sapphire atmospheric GSRM. Simulations are performed over a 45 d period for five different vertical grids with between 55 and 540 vertical layers and maximum tropospheric vertical grid spacings of between 800 and 50 m, respectively. The effects of changes in the vertical grid spacing are compared with the effects of reducing the horizontal grid spacing from 5 to 2.5 km. For most of the quantities considered, halving the vertical grid spacing has a smaller effect than halving the horizontal grid spacing, but it is not negligible. Each halving of the vertical grid spacing, along with the necessary reductions in time step length, increases cloud liquid water by about 7 %, compared with an approximate 16 % decrease for halving the horizontal grid spacing. The effect is due to both the vertical grid refinement and the time step reduction. There is no tendency toward convergence in the range of grid spacings tested here. The cloud ice amount also increases with a refinement in the vertical grid, but it is hardly affected by the time step length and does show a tendency to converge. While the effect on shortwave radiation is globally dominated by the altered reflection due to the change in the cloud liquid water content, the effect on longwave radiation is more difficult to interpret because changes in the cloud ice concentration and cloud fraction are anticorrelated in some regions. The simulations show that using a maximum tropospheric vertical grid spacing larger than 400 m would increase the truncation error strongly. Computing time investments in a further vertical grid refinement can affect the truncation errors of GSRMs similarly to comparable investments in horizontal refinement, because halving the vertical grid spacing is generally cheaper than halving the horizontal grid spacing. However, convergence of boundary layer cloud properties cannot be expected, even for the smallest maximum tropospheric grid spacing of 50 m used in this study.}, author = {Schmidt, Hauke and Rast, Sebastian and Bao, Jiawei and Cassim, Amrit and Fang, Shih Wei and Jimenez-De La Cuesta, Diego and Keil, Paul and Kluft, Lukas and Kroll, Clarissa and Lang, Theresa and Niemeier, Ulrike and Schneidereit, Andrea and Williams, Andrew I.L. and Stevens, Bjorn}, issn = {1991-9603}, journal = {Geoscientific Model Development}, number = {4}, pages = {1563--1584}, publisher = {European Geosciences Union}, title = {{Effects of vertical grid spacing on the climate simulated in the ICON-Sapphire global storm-resolving model}}, doi = {10.5194/gmd-17-1563-2024}, volume = {17}, year = {2024}, }