Tier 1 Seasonal Decomposition

4 figures · 1990–2014 → 2040–2049

Synthesis

High-resolution projections exhibit pronounced seasonal seasonality, contrasting winter-dominant Arctic amplification with intense summer continental warming, accompanied by a dynamic reorganization of tropical rainfall belts and monsoon intensification.
The high-resolution IFS-FESOM and IFS-NEMO simulations (SSP3-7.0, 2040–2049 vs. 1990–2014) reveal a strongly seasonal climate response characterized by distinct thermodynamic and dynamic fingerprints. Temperature anomalies display robust Arctic amplification peaking in boreal winter (DJF) and autumn (SON), with warming exceeding 4 K in the Arctic Ocean driven by ice-albedo feedbacks, whereas boreal summer (JJA) warming is most intense over mid-latitude continents, particularly the Mediterranean and Central North America (>2.5 K). A persistent North Atlantic Warming Hole south of Greenland is visible across all seasons and models, consistent with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), while the Southern Ocean shows model-dependent cooling signals likely linked to deep ocean heat uptake and sea-ice dynamics. Precipitation patterns indicate a sharpening of the hydrological cycle and significant circulation shifts, resolving fine-scale features such as orographic rainfall over the Andes and Himalayas. Tropical rainfall exhibits pronounced meridional dipoles (anomalies ±1.5 × 10⁻⁵ kg/m²/s), signaling a northward migration and narrowing of the ITCZ, alongside a robust intensification of the West African and South Asian monsoons in JJA. Conversely, substantial drying is projected for the Amazon basin, Maritime Continent, and the Mediterranean, driven by enhanced evaporative demand and the poleward expansion of subtropical dry zones. While the high resolution captures sharp convective gradients, the short 10-year averaging window suggests that internal decadal variability (e.g., ENSO phases) modulates these regional patterns.

Related diagnostics

AMOC_strength_time_series sea_ice_concentration_seasonal monsoon_precipitation_indices

Seasonal 2m Temperature Change — IFS-FESOM

Seasonal 2m Temperature Change — IFS-FESOM
Variables avg_2t
Models ifs-fesom
Units K
Baseline 1990-2014
Future 2040-2049
Method Per-season future mean minus historical mean.

Summary high

The figure illustrates seasonal 2m temperature anomalies for the IFS-FESOM model (2040–2049 vs. 1990–2014), revealing a global warming trend dominated by strong Arctic amplification in boreal winter and intense continental warming in boreal summer.

Key Findings

  • Arctic amplification is pronounced, with warming exceeding the saturation scale (>4 K) in the Arctic Ocean and high-latitude Eurasia/North America during DJF and SON.
  • A North Atlantic Warming Hole (NAWH) is clearly visible south of Greenland, showing cooling or suppressed warming (down to -2 K), particularly in DJF and MAM.
  • In boreal summer (JJA), warming shifts from the Arctic to mid-latitude land masses, with intense heating (>3 K) over the Mediterranean, Central Asia, and North America.
  • The Southern Ocean exhibits a notable cooling signal (blue patch) in the Weddell Sea sector, most prominent during SON and JJA.

Spatial Patterns

There is a strong land-sea contrast where continents warm 1–3 K more than adjacent oceans. The Northern Hemisphere warms significantly faster than the Southern Hemisphere. Topographic features like the Andes and Himalayas sharpen regional temperature gradients. The warming pattern shifts seasonally: poleward in winter (DJF/SON) and over continents in summer (JJA).

Model Agreement

The general patterns (Arctic Amplification, NAWH, land-sea contrast) are consistent with the broader CMIP6 ensemble and likely agree with IFS-NEMO and ICON. However, the specific location and intensity of the Weddell Sea cooling in SON are often sensitive to ocean model formulation (unstructured FESOM vs. structured NEMO) and sea-ice coupling specifics.

Physical Interpretation

Arctic warming in DJF/SON is driven by the ice-albedo feedback and increased heat flux from the newly exposed ocean to the atmosphere. The NAWH is physically consistent with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC). Intense JJA continental warming is likely amplified by soil moisture-temperature feedbacks (drying soils reducing evaporative cooling). The Southern Ocean cooling suggests deep ocean heat uptake and delayed sea-ice retreat specific to regional ocean dynamics.

Caveats

  • The color scale saturates at ±4 K, masking the maximum magnitude of warming in the Arctic, which likely exceeds this range significantly.
  • The 10-year averaging window (2040–2049) is relatively short, meaning internal decadal variability could still partially superimpose onto the forced climate change signal.

Seasonal 2m Temperature Change — IFS-NEMO

Seasonal 2m Temperature Change — IFS-NEMO
Variables avg_2t
Models ifs-nemo
Units K
Baseline 1990-2014
Future 2040-2049
Method Per-season future mean minus historical mean.

Summary high

The figure illustrates the seasonal evolution of near-surface temperature change ($T_{2m}$) for IFS-NEMO (SSP3-7.0, 2040s vs 1990-2014), revealing a distinct seasonality in polar amplification and continental warming patterns.

Key Findings

  • Arctic Amplification is strongly seasonal, with warming exceeding the saturation scale (>3 K) in DJF and SON, but remaining dampened in JJA due to the energy buffer of melting sea ice.
  • A persistent 'warming hole' (regional cooling) is observed in the subpolar North Atlantic south of Greenland, visible across all seasons.
  • Northern Hemisphere summer (JJA) features intense warming hotspots (>2.5 K) over the Mediterranean, North Africa, and western/central North America.

Spatial Patterns

In DJF and SON, the warming signal is polar-centric, dominating the Arctic Ocean and high-latitude landmasses (Siberia, Canada). In JJA, the pattern shifts to mid-latitude land masses, exhibiting a strong land-sea contrast where continents warm significantly faster than adjacent oceans. The Southern Ocean displays zonal bands of strong warming (likely associated with sea-ice retreat) interspersed with moderate warming.

Model Agreement

The captured North Atlantic warming hole is a robust feature consistent with CMIP6 ensembles, indicating IFS-NEMO resolves the associated ocean circulation slowdown (AMOC). The intensity of the Mediterranean summer warming aligns with high-resolution projections of land-surface drying feedbacks.

Physical Interpretation

The DJF/SON Arctic maximum is driven by the sea-ice albedo feedback and increased ocean-to-atmosphere heat fluxes during the refreezing period. The North Atlantic cooling signal results from a weakening Atlantic Meridional Overturning Circulation (AMOC) reducing northward heat transport. The JJA continental hotspots are likely amplified by soil moisture depletion, which suppresses evaporative cooling and increases sensible heat flux.

Caveats

  • The averaging period for the future slice is only 10 years (2040-2049), meaning internal decadal variability (e.g., ENSO, PDO) may contaminate the forced climate change signal.
  • The color bar saturates at ±3 K, obscuring the peak magnitude of warming in the Arctic and continental hotspots which likely exceeds this range.

Seasonal Total Precipitation Rate Change — IFS-FESOM

Seasonal Total Precipitation Rate Change — IFS-FESOM
Variables avg_tprate
Models ifs-fesom
Units kg/m2/s
Baseline 1990-2014
Future 2040-2049
Method Per-season future mean minus historical mean.

Summary medium

This figure illustrates the seasonal change in total precipitation rate projected by the IFS-FESOM model (2040–2049 vs 1990–2014) under SSP3-7.0, characterized by a 'wet-get-wetter' amplification of the hydrological cycle and significant meridional shifts in tropical rainfall bands.

Key Findings

  • A pronounced northward shift of the Intertropical Convergence Zone (ITCZ) is evident, particularly in the Atlantic and Pacific basins during JJA, creating a distinct dipole of wetting (north) and drying (equator/south).
  • The West African Monsoon exhibits a robust intensification and northward extension in JJA, marked by increased precipitation over the Sahel and drying over the Gulf of Guinea.
  • Substantial drying is observed over the Amazon basin, peaking in the dry season (JJA/SON), which suggests an exacerbation of seasonal drought stress.
  • Northern Hemisphere storm tracks (North Atlantic and North Pacific) show consistent wetting, particularly in boreal winter (DJF), consistent with thermodynamic expectations.

Spatial Patterns

Tropical regions display sharp zonal banding of anomalies exceeding ±1.5e-5 kg/m²/s. The Maritime Continent shows a predominant drying signal (DJF/SON). Southern Europe and the Mediterranean exhibit drying in JJA. High latitudes show widespread, moderate wetting.

Model Agreement

The broad patterns (Mediterranean drying, high-latitude wetting) align well with the CMIP6 ensemble consensus. However, the sharp resolution of the ITCZ rainbands and the specific structure of the West African Monsoon dipole are features more clearly resolved in this high-resolution simulation compared to standard-resolution coupled models.

Physical Interpretation

The patterns are driven primarily by the Clausius-Clapeyron response (increasing moisture availability intensifying convergence zones) and dynamical shifts. The northward migration of the ITCZ suggests an inter-hemispheric energy asymmetry (warmer Northern Hemisphere). The drying in subtropics and the Amazon reflects enhanced evaporative demand and potential distinct circulation shifts (e.g., Hadley cell expansion).

Caveats

  • The analysis uses a short 10-year future period (2040–2049), making the precipitation signals susceptible to internal decadal variability (e.g., ENSO phases) rather than purely forced trends.
  • The precipitation response in the 'grey zone' of convection (~5 km resolution) may rely on parameterizations that behave differently from coarser CMIP models.

Seasonal Total Precipitation Rate Change — IFS-NEMO

Seasonal Total Precipitation Rate Change — IFS-NEMO
Variables avg_tprate
Models ifs-nemo
Units kg/m2/s
Baseline 1990-2014
Future 2040-2049
Method Per-season future mean minus historical mean.

Summary medium

The IFS-NEMO model projects distinct seasonal precipitation shifts for the 2040–2049 period under SSP3-7.0, characterized by intensified tropical convective bands, enhanced Northern Hemisphere monsoons, and robust subtropical drying.

Key Findings

  • A pronounced meridional dipole emerges in the Tropical Pacific and Atlantic ITCZ regions across all seasons, particularly in DJF and MAM, indicating a narrowing or equatorward shift of precipitation belts with anomalies reaching ±1.5 × 10⁻⁵ kg/m²/s.
  • The West African (Sahel) and South Asian monsoons exhibit significant intensification (wetting) in JJA, consistent with enhanced moisture convergence in a warming climate.
  • The Maritime Continent and Indonesian Archipelago show a strong drying trend, most prominent in SON and DJF, suggesting a zonal shift in the Walker Circulation.
  • Southern Europe and the Mediterranean basin display consistent drying, particularly in JJA and DJF, reflecting the poleward expansion of subtropical dry zones.

Spatial Patterns

The high resolution (~5 km) resolves fine-scale orographic precipitation features, visible in the Andes and Himalayas. The tropics are dominated by sharp, zonal bands of alternating wetting and drying, while high latitudes (North Atlantic, Southern Ocean) show broad, dynamically driven wetting trends.

Model Agreement

While only IFS-NEMO is analyzed here, the large-scale patterns (Mediterranean drying, high-latitude wetting, monsoon enhancement) are qualitatively consistent with the broader CMIP6 HighResMIP ensemble; however, the sharpness of the ITCZ bands and the magnitude of the Sahel wetting are likely model-specific features enhanced by the high resolution.

Physical Interpretation

The patterns reflect a combination of thermodynamic 'wet-gets-wetter' amplification (driven by the Clausius-Clapeyron relation) and dynamic circulation changes. The Mediterranean drying is mechanically linked to the poleward expansion of the Hadley Cell, while the tropical dipoles suggest a reorganization of the ITCZ and potential modulation by internal variability modes (e.g., ENSO-like patterns).

Caveats

  • The future averaging period (2040–2049) is only 10 years, meaning decadal internal variability (such as ENSO phases) likely conflates with the forced climate change signal, particularly in the Tropical Pacific.
  • This analysis relies on a single model realization (IFS-NEMO), and structural biases in convection parameterization may overly sharpen tropical rainfall gradients.