Shunya Koseki

This study evaluates nextGEMS Earth system models (ESMs) with storm-resolving spatial scales. Taking advantage of the fine-scale resolution of nextGEMS ESMs, we compare their simulations of Southeast Asian climate and weather systems–strongly influenced by complex sea-land contrasts–to observations and to several CMIP6-class ESMs with coarser horizontal resolution. The nextGEMS ESMs realistically reproduce the sharp structure and seasonal development of the South China Sea cold sea surface temperature (SST) during the winter monsoon season, while most of the selected CMIP6 ESMs fail to simulate these cold SST characteristics. The nextGEMS ESMs also represent the climatological precipitation pattern well. On shorter time scales, they capture the characteristics of monsoon cold surges and Borneo vortices well. Furthermore, dry spells in Southeast Asia are assessed. In particular, nextGEMS ESMs can simulate the increase in winter dry days around the equator during intense El Niño events. Because Southeast Asia is one of the regions most vulnerable to climate change in terms of wet and dry spells, we highlight the potential benefits of kilometer-scale ESMs for producing climate predictions and assessing climate projections in marginal sea areas.

Mesoscale Convective Systems (MCSs) account for most of the rainfall over the Sahel and contribute substantially to extreme precipitation events (EPEs) that cause flooding in West Africa. However, the low density of ground-based observation networks limits the accurate monitoring and characterization of these events. Regional climate models, such as the Weather Research and Forecasting (WRF) model, help to compensate for this observational gap but still exhibit significant biases in simulating extreme precipitation.This study aims to reduce these biases by integrating the WRF model into a Supermodelling framework based on the dynamic combination of multiple model configurations, designed to exploit their complementary strengths.Two supermodels, SUPPERT-WRFA and SUPPERT-WRFB, are developed from three distinct WRF configurations that mainly differ in their convection schemes. SUPPERT-WRFA is trained using satellite-based IMERG precipitation, while SUPPERT-WRFB relies on atmospheric dynamical variables (U, V, and T) from ERA5. In both cases, the training strategy is based on a metric combining spatial correlation and root-mean-square error.The performance of the supermodels is evaluated for the simulation of EPEs in West Africa through a case study of an extreme precipitation event that occurred on 5 September 2020 in Senegal. The results show a significant improvement in the representation of extreme precipitation compared to individual WRF configurations, highlighting the strong potential of Supermodelling to improve extreme event prediction in regions with sparse observational coverage.

Global warming is expected to substantially weaken the Atlantic Meridional Overturning Circulation (AMOC). However, climate models disagree greatly on the magnitude of AMOC weakening. This adds uncertainties in climate change projections, across the globe, through influencing poleward ocean and atmospheric energy transports. Here, we show through multi-model analysis of future climate change projections that AMOC weakening during this century will strongly influence precipitation and its extremes over Brazil. Such weakening dominates over the direct global warming impacts, causing drying in the Amazon, while completely mitigating them in northeast Brazil. We trace this to a tropical Atlantic warming, consistent with weakened heat transport along the southern branch of the South Equatorial Current. This induces a cross-equatorial sea surface temperature gradient and changes in latent heat flux, shifting the intertropical convergence zone southward. Our findings highlight the need to reduce uncertainties in the AMOC response to global warming and its oceanic mediated influences on Brazilian climate.

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.

The Next Generation of Earth Modeling Systems (nextGEMS) project aimed to produce multi-decadal climate simulations, for the first time, with resolved kilometer-scale (km-scale) processes in the ocean, land, and atmosphere. In only three 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 one 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 participants in hackathons 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 of 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 timeframe, 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.

The Next Generation of Earth Modeling Systems (nextGEMS) project aimed to produce multi-decadal climate simulations, for the first time, with resolved kilometer-scale (km-scale) processes in the ocean, land, and atmosphere. In only three 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 one 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 participants in hackathons 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 of 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 timeframe, 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.

This study investigated how the extreme rainfall event over eastern Northeast Brazil (ENEB), occurring at the end of May 2022, was induced dynamically using observational and reanalysis data. On a monthly time scale, a wet‐spell condition was found over the ENEB region in May 2022, indicated by enhanced onshore‐ward moisture flux and a widely spreading positive precipitation anomaly. At a shorter time scale, the ENEB region experienced continually intense rainy days from May 21st to 28th peaking on May 28th. Focusing on the most intense rainfall event on May 28th, a shallow vortex disturbance of a tropical easterly wave can be responsible for this intense event. This easterly wave is initiated over the south tropical Atlantic adjacent to the ENEB region, and we suggest that a strong zonal wind shear zone associated with a synoptic‐scale high‐pressure system generates the vortex as barotropic instability. Even though the vortex center did not make a landfall over the ENEB region, a part of the vortex band is elongated along the coastal line of the ENEB region and the vorticity and moisture flux convergence intensify drastically over the coastal ENEB region. Reinforced fluid deformation along the coastal line indicates the extension and intensification of the vortex band. The coastal enhancement of vorticity, convergence, and deformation can be interactive, and the sea‐land contrast may cause the enhancements due to surface condition change. This study provides a new dynamical insight into the intense precipitation over the ENEB region.

The Next Generation of Earth Modeling Systems (nextGEMS) project aimed to produce multi-decadal climate simulations, for the first time, with resolved kilometer-scale (km-scale) processes in the ocean, land, and atmosphere. In only three 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 one 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 participants in hackathons 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 of 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 timeframe, 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.

The variability and predictability of the Tropical Atlantic primary productivity remains little explored on interannual-to-decadal time scales. Here, we present the results of two studies, in which find a decadal scale variability in phytoplankton abundance that can be predicted three years ahead. The predictions are made with NorCPM, which is a fully coupled climate prediction model with ocean biogeochemistry that assimilates temperature and salinity to reconstruct past variability. From these reconstructions, predictions are initialized that are run freely ten years ahead. We find that the predictability is a result of nutrient pulses that are advected with the southern branch of the South Equatorial Current from the most southern part of the Atlantic, and that then get caught in the Equatorial undercurrent before they reach the surface in the Tropical Atlantic Ocean. A more detailed analysis is being done in order to pinpoint the underlying mechanisms in a forced ocean model, where we find a link to the Pan-Atlantic decadal oscillation.

Both the tropical Pacific and Atlantic upwelling systems are modulated by their respective Ninos (ENSO and Atlantic Nino), which significantly affect the regional and global climate variability. Coincidentally, two of largest ocean carbon outgassing systems are also located in these domains. As a result, the interannual variability of ocean CO2 fluxes in these regions have predominant imprint on the globally integrated variations (Landschutzer et al., 2016). In contrast to the effect of anomalously cold surface temperature, the upwelling of deep-water rich in dissolved inorganic carbon is understood to be the main driver for the mean CO2 outgassing. In the tropical Pacific, El Nino (La Nina) leads to a suppressed (stronger) upwelling condition and an anomalously weaker (stronger) carbon outgassing. On the other hand, the Atlantic Nino and Nina exert considerable variability in the surface freshwater and temperature, which leads to spatially heterogeneous responses in the contemporary CO2 fluxes. In both systems, we discover a critical role of subsurface alkalinity in regulating the observed variability, primarily through altering the surface buffering capacity (Koseki et al., 2023). We show that bias in CMIP6 Earth system models in simulating the mean contemporary alkalinity state in the tropical Pacific leads to contrasting future impacts (Vaittinada Ayar et al., 2022) and could have ramifications on the climate carbon cycle feedback. ReferencesKoseki, S., J. Tjiputra, F. Fransner, L. R. Crespo, and N. S. Keenlyside (2023), Disentangling the impact of Atlantic Nino on sea-air CO2 fluxes, Nature Communications, 14, 3649, https://doi.org/10.1038/s41467-023-38718-9.Landschützer, P., N. Gruber, and D. C. E. Bakker (2016), Decadal variations and trends of the global ocean carbon sink, Global Bio- geochem. Cycles, 30, 1396–1417, http://doi.org/10.1002/2015GB005359.Vaittinada Ayar, P., L. Bopp, J. R. Christian, T. Ilyina, J. P. Krasting, R. Séférian, H. Tsujino, M. Watanabe, A. Yool, and J. Tjiputra (2022), Contrasting projections of the ENSO-driven CO2 flux variability in the equatorial Pacific under high-warming scenario, Earth Syst. Dynam., 13, 1097–1118, https://doi.org/10.5194/esd-13-1097-2022.