Storyline Simulations¶
The storyline simulations use global coupled climate experiments, produced with IFS-FESOM, to investigate how weather events that occurred between 2017 and 2025 — such as heatwaves, storms, and floods — would unfold under different climate conditions.
The approach replays the same large-scale weather pattern through three scenarios: a cooler past (1950 conditions), the historical present-day climate, and a future warmer climate (+2K). By nudging the large-scale atmospheric circulation toward the ERA5 reanalysis, the simulations maintain the observed synoptic evolution while allowing the km-scale model to freely generate mesoscale dynamics, convection, and air-sea interaction. This makes it possible to assess changes in the intensity and spatial structure of extreme events that are due to the thermodynamic differences between these climate states. The method is described in detail by John et al. (2026).
The IFS-FESOM simulations are performed with a horizontal grid resolution of approximately 10 km for the atmosphere and 5 km (NG5 mesh) for the ocean and sea-ice. For each climate condition (past, present, future), the storyline simulations are run as a five-member ensemble to sample internal variability. All data are on the MN5 data bridge.
Nudging methodology¶
The nudging methodology follows a spectral nudging (Newtonian relaxation) approach, where only vorticity and divergence are constrained toward ERA5 reanalysis data using a T60 triangular truncation (retaining wavenumbers up to 60). Nudging is applied between 100 and 700 hPa, with a sigmoid transition to non-nudged levels, allowing the planetary boundary layer and air–sea–ice coupling to evolve freely. An e-folding time of 1 hour ensures effective constraint of the large-scale circulation while preserving the model’s km-scale dynamics and physics at smaller spatiotemporal scales. For further details and sensitivity experiments, see John et al. (2026).
Available simulations¶
Model |
Simulation |
Spatial Resolution |
Time |
Realization |
Experiment ID |
|---|---|---|---|---|---|
IFS-FESOM |
present climate |
10km atmosphere, 5km ocean/sea-ice |
01/01/2017–31/12/2025 |
1,2,3,4,5 |
climatedt-gen2-ifs-fesom-10km-story-nudging-hist-r1
climatedt-gen2-ifs-fesom-10km-story-nudging-hist-r2
climatedt-gen2-ifs-fesom-10km-story-nudging-hist-r3
climatedt-gen2-ifs-fesom-10km-story-nudging-hist-r4
climatedt-gen2-ifs-fesom-10km-story-nudging-hist-r5
|
IFS-FESOM |
past climate |
10km atmosphere, 5km ocean/sea-ice |
01/01/2017–31/12/2025 |
1,2,3,4,5 |
climatedt-gen2-ifs-fesom-10km-story-nudging-cont-r1
climatedt-gen2-ifs-fesom-10km-story-nudging-cont-r2
climatedt-gen2-ifs-fesom-10km-story-nudging-cont-r3
climatedt-gen2-ifs-fesom-10km-story-nudging-cont-r4
climatedt-gen2-ifs-fesom-10km-story-nudging-cont-r5
|
IFS-FESOM |
future climate (+2K) |
10km atmosphere, 5km ocean/sea-ice |
01/01/2017–31/12/2025 |
1,2,3,4,5 |
climatedt-gen2-ifs-fesom-10km-story-nudging-Tplus2K-r1
climatedt-gen2-ifs-fesom-10km-story-nudging-Tplus2K-r2
climatedt-gen2-ifs-fesom-10km-story-nudging-Tplus2K-r3
climatedt-gen2-ifs-fesom-10km-story-nudging-Tplus2K-r4
climatedt-gen2-ifs-fesom-10km-story-nudging-Tplus2K-r5
|
Generation 2 Improvements¶
The storyline experiments in Climate DT generation 1 were highly successful, resulting in multiple publications and ongoing applications. For generation 2, key improvements were made to ensure greater consistency and physical realism:
Initialization: Generation 2 simulations are initialized from coupled spin-up states provided by the EERIE project, ensuring that differences between scenarios stem from their respective climate conditions rather than from inconsistencies in the initialization procedure.
Forcing scenario: The forcing was transitioned from SSP3-7.0 to SSP2-4.5 to remain aligned with the EERIE simulations.
Ocean model updates: The generation 2 setup employs an updated version of FESOM with improvements in the computation of residual heat and thermodynamics relevant to buffer heat storage capacity, as well as an interactive runoff mapper that incorporates runoff computed by the IFS model as freshwater input for the FESOM ocean model.
Sea ice coupling: The storyline simulations use fractional sea ice coupling, consistent with the Generation 1 configuration, rather than the thermodynamical coupling used in the Generation 2 multi-decadal runs.
For evaluation of the storyline simulations, see Storyline Evaluation.