.. _storylines: Storyline Simulations ##################### IFS-FESOM is the model used for the Climate DT storyline simulations. For the full experiment protocol, nudging methodology, available simulations, and Generation 2 improvements, see :ref:`storyline_simulations`. For evaluation of the storyline simulations, see :ref:`evaluation_storylines`. .. .. _storylines: .. Storylines Simulation .. ##################### .. IFS-FESOM storyline simulations replay specific observed weather events under three .. climate states — a cooler counterfactual past (~1950), the present-day climate, and .. a future +2K world — using a spectral nudging approach that constrains the .. large-scale circulation while allowing km-scale dynamics to evolve freely. .. For the full experiment protocol, nudging methodology, available simulations, and .. Generation 2 improvements, see :ref:`storyline_simulations`. .. For evaluation of the storyline simulations, see :ref:`evaluation_storylines`. .. .. list-table:: .. :header-rows: 1 .. :widths: 12 15 22 20 12 19 .. * - 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**: A more realistic thermodynamical sea ice coupling scheme is being tested, though it introduces a notable cold bias in the Arctic that requires further evaluation. .. - **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**: Different to the IFS-FESOM projections (non-nudged runs), we still keep using fractional sea ice coupling as in the GEN1 runs in order to avoid the cold bias in the Arctic that requires further evaluation. .. .. .. .. note:: .. .. Evaluation content for the IFS-FESOM storyline simulations has moved to .. .. :ref:`evaluation_ifs_fesom`. .. .. .. Annual biases of the storyline simulations (:numref:`ifs-fesom_story_annual_biases`) provide an overview of the mean-state performance of the nudged km-scale model. Since the large-scale circulation is constrained by nudging, remaining biases reflect model physics and parameterization errors rather than large-scale dynamical drift. The 2m temperature (panel a) shows a pronounced cold bias over the Arctic (exceeding -4 °C) and a warm bias around Antarctica, both likely related to sea ice representation issues. Most mid-latitude continental and oceanic regions remain within ±1 °C. Sea surface temperature biases (panel b) are generally small, with localized warm biases in the tropical Pacific and Indian Ocean and cold biases in the Southern Ocean. Total precipitation (panel c) reveals the largest biases in the tropics, with a dipole pattern suggesting a slight displacement of the Intertropical Convergence Zone (ITCZ) and excessive precipitation over the Maritime Continent. The 500 hPa geopotential height (panel d) shows a predominantly negative bias across the extratropics, with a positive anomaly near Antarctica consistent with the warm surface bias there. .. .. .. figure:: ../../../../evaluation/ifs_fesom_storylines_eval/figures/annual_biases.png .. .. :name: ifs-fesom_story_annual_biases .. .. Annual biases of the IFS-FESOM storyline simulations. .. .. Temporal Correlation .. .. ^^^^^^^^^^^^^^^^^^^^ .. .. Temporal correlation between ERA5 reanalysis and storyline simulations (:numref:`ifs-fesom_story_temporal_corr`) measures the skill of the nudged model in replaying observed weather events. Higher temporal correlations indicate that the model faithfully reproduces the timing and sequencing of synoptic-scale weather patterns, a prerequisite for meaningful event attribution. The 500 hPa geopotential height shows uniformly high correlations (>0.9) across all latitudes, as expected since this is the field constrained by nudging. For 2m temperature, correlations are high (>0.8) over most extratropical land areas, where surface temperature variability is strongly controlled by the large-scale circulation, but drop notably in the tropics and over tropical oceans where local processes such as convection and air–sea interaction play a larger role. Precipitation correlations show a similar latitude dependence, with reasonable skill in the extratropics and weaker correlations in the tropics, where precipitation is more strongly influenced by local convective processes. .. .. .. figure:: ../../../../evaluation/ifs_fesom_storylines_eval/figures/temporal_correlation.png .. .. :name: ifs-fesom_story_temporal_corr .. .. Temporal correlation between daily ERA5 reanalysis data and the IFS-FESOM storyline simulations under present-day conditions, calculated after removing the seasonal cycle, for (a) 2m temperature, (b) precipitation, and (c) 500 hPa geopotential height. .. .. Case Studies .. .. ^^^^^^^^^^^^ .. .. The storyline framework is demonstrated through two high-impact European extreme events: Storm Boris (September 2024) and the Paris heatwave (July 2019). For both cases further details can be found in `John et al. (in review) `__. .. .. **Storm Boris (September 2024)** .. .. Maps of 5-day accumulated precipitation for Storm Boris (:numref:`ifs-fesom_story_boris`) compare the km-scale IFS-FESOM ensemble against a coarser AWI-CM1 nudged run and reference datasets (ERA5, MSWEP). The historical present-day IFS-FESOM ensemble accurately reproduces the spatial structure and magnitude of the observed extreme precipitation, demonstrating the added value of km-scale resolution over coarser models. The three-scenario comparison — counterfactual past, present-day, and future +2K — reveals how the thermodynamic response to warming amplifies precipitation in this event. .. .. .. figure:: ../../../../evaluation/ifs_fesom_storylines_eval/figures/Precip_Boris_story.png .. .. :name: ifs-fesom_story_boris .. .. 5-day accumulated precipitation (mm) for Storm Boris (12--16 September 2024). Top row: (a) AWI-CM1 coarse-resolution nudged run, (b) ERA5 reanalysis, (c) MSWEP observations. Bottom row: ensemble mean from nudged km-scale IFS-FESOM storyline experiments for (d) counterfactual past climate, (e) historical present-day climate, (f) future +2K climate. . .. .. **Paris Heatwave (25 July 2019)** .. .. Maximum 2m-temperature during the peak of the 25 July 2019 European heatwave (:numref:`ifs-fesom_story_heatwave`) shows that the historical IFS-FESOM ensemble faithfully captures the spatial gradients and peak magnitudes of the observed event compared to ERA5 and E-OBS. The km-scale resolution resolves fine-scale temperature contrasts — including urban heat island signatures and orographic effects — that are smoothed out in the coarser AWI-CM1 run and ERA5. Under the +2K future scenario, the area exceeding 40 °C expands substantially, extending from France and Iberia into Germany and the Benelux region, while the counterfactual past scenario shows peak temperatures remaining below 35 °C over much of France. This progression across the three climate states quantifies the contribution of warming to the regional intensification of the heatwave. .. .. .. figure:: ../../../../evaluation/ifs_fesom_storylines_eval/figures/HW_2019_Paris_story.png .. .. :name: ifs-fesom_story_heatwave .. Maximum 2m-temperature (°C) during the peak of the 25 July 2019 European heatwave. Top row: (a) AWI-CM1 coarse-resolution nudged run, (b) ERA5 reanalysis, (c) E-OBS observations. Bottom row: ensemble mean from nudged km-scale IFS-FESOM storyline experiments for (d) counterfactual past climate, (e) historical present-day climate, (f) future +2K climate.