Tier 2 Zonal Mean Profiles
Synthesis
Related diagnostics
Zonal Mean 2m Temperature Change
| Variables | avg_2t |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | K |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | 5° latitude bins on HealPix cells; equal-area mean per band. |
Summary high
This diagnostic compares the zonal mean 2-meter temperature change (2040–2049 vs. 1990–2014) under the SSP3-7.0 scenario for two coupled models: IFS-FESOM and IFS-NEMO. While both models exhibit similar latitudinal structures including polar amplification, IFS-FESOM projects systematically higher warming globally, with the discrepancy maximizing in the Arctic.
Key Findings
- IFS-FESOM exhibits a consistently higher climate sensitivity than IFS-NEMO, with a global baseline offset of approximately +0.2 K in the tropics increasing to >1.0 K in the Arctic.
- Strong Arctic Amplification is present in both models; however, IFS-FESOM peaks at ~3.7 K around 80°N, whereas IFS-NEMO reaches only ~2.5 K.
- A local warming minimum is observed in the Southern Ocean (~55°S–60°S) in both models, with values dropping to ~0.7 K for IFS-FESOM and ~0.6 K for IFS-NEMO.
- Antarctic warming is substantial but asymmetrical to the Arctic, with IFS-FESOM showing ~1.8 K warming at the South Pole compared to ~1.2 K for IFS-NEMO.
Spatial Patterns
The warming profile is characterized by a flat tropical response (20°S to 20°N), a gradual increase through the Northern Hemisphere mid-latitudes (20°N to 60°N) leading into a sharp Arctic spike, and a distinct dip in the Southern Ocean followed by moderate Antarctic warming. A secondary plateau or local enhancement is visible in the Northern mid-latitudes around 40°N–50°N.
Model Agreement
The models show excellent structural agreement, with peaks and troughs occurring at identical latitudes, suggesting the atmospheric dynamical response (likely controlled by the common IFS component) is robust. The significant disagreement lies in the magnitude, particularly at high latitudes, implying that the ocean/sea-ice components (FESOM vs. NEMO) respond differently to the same forcing.
Physical Interpretation
The intense warming north of 60°N is driven by the sea-ice albedo feedback; the larger magnitude in IFS-FESOM suggests it simulates greater sea-ice loss or has lower effective sea-ice thermal inertia than IFS-NEMO. The warming minimum at ~60°S is a classic signature of efficient ocean heat uptake and vertical mixing in the Southern Ocean, which delays surface warming. The systematic tropical offset suggests differences in global climate feedback strength or global ocean heat uptake efficiency between the unstructured (FESOM) and structured (NEMO) ocean grids.
Caveats
- The analysis relies on a 10-year future average (2040-2049), which may still contain internal decadal variability masking the forced signal.
- Without sea-ice extent diagnostics, it is difficult to confirm if the Arctic discrepancy is solely due to albedo feedback or atmospheric heat transport.
Zonal Mean Total Column Water Vapour Change
| Variables | avg_tcwv |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | kg/m2 |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | 5° latitude bins on HealPix cells; equal-area mean per band. |
Summary high
The figure illustrates the zonal mean change in Total Column Water Vapour (TCWV) between the SSP3-7.0 scenario (2040–2049) and historical baseline (1990–2014) for two IFS-based coupled models, showing a robust global increase in atmospheric moisture dominated by tropical moistening.
Key Findings
- Both models exhibit a marked peak in TCWV increase in the deep tropics (0°–10°N), with IFS-FESOM reaching ~4.1 kg/m² and IFS-NEMO reaching ~3.8 kg/m².
- IFS-FESOM consistently predicts a larger increase in water vapour than IFS-NEMO across all latitudes, with the discrepancy maximizing at approximately 0.5–0.7 kg/m² in the tropics and subtropics.
- There is a notable hemispheric asymmetry; absolute TCWV increases are larger in the Northern Hemisphere mid-latitudes (e.g., ~2.3 kg/m² at 40°N in IFS-FESOM) compared to the Southern Hemisphere (e.g., ~1.4 kg/m² at 40°S).
Spatial Patterns
The profile follows a classic bell-shaped distribution driven by background temperature, with maxima near the thermal equator (shifted slightly north to ~5°N, indicative of the ITCZ) and minima in the polar regions (<0.5 kg/m² at 90°S/N). The gradient is steeper in the mid-latitudes (30°–60°) than in the deep tropics.
Model Agreement
The models show high structural agreement regarding the latitudinal profile shape and peak location, indicating similar atmospheric dynamics in the IFS core. However, they disagree on amplitude: the systematic positive offset in IFS-FESOM suggests a higher climate sensitivity or stronger ocean surface warming in the FESOM coupling compared to the NEMO configuration.
Physical Interpretation
The observed pattern is governed by the Clausius-Clapeyron relation, where the water vapour holding capacity of air increases exponentially with temperature (~7%/K). Consequently, the warmest regions (tropics) experience the largest absolute mass increase in precipitable water for a given warming increment. The hemispheric asymmetry likely results from the stronger projected warming over Northern Hemisphere land masses compared to the ocean-dominated Southern Hemisphere.
Caveats
- The figure shows absolute change (kg/m²); relative changes (%) would likely highlight polar amplification signals not visible here due to low baseline temperatures.
- Without a corresponding surface temperature change figure, it is unclear if the IFS-FESOM offset is due to a warmer baseline state or a stronger transient warming response.
Zonal Mean Total Precipitation Rate Change
| Variables | avg_tprate |
|---|---|
| Models | ifs-fesom, ifs-nemo |
| Units | kg/m2/s |
| Baseline | 1990-2014 |
| Future | 2040-2049 |
| Method | 5° latitude bins on HealPix cells; equal-area mean per band. |
Summary medium
The figure illustrates the zonal mean change in total precipitation rate (SSP3-7.0 2040s vs. Historical) for two IFS-coupled high-resolution models, revealing robust high-latitude wetting and SH mid-latitude drying but significant structural disagreement in the tropics.
Key Findings
- Both IFS-FESOM and IFS-NEMO show consistent precipitation increases in high latitudes (>60° N/S), with IFS-FESOM projecting a stronger Arctic wetting signal (>2.5 × 10⁻⁶ kg/m²/s) than IFS-NEMO.
- A coherent drying band is observed in the Southern Hemisphere mid-latitudes (~35°S–45°S) across both models, with reductions reaching approximately -0.7 × 10⁻⁶ kg/m²/s.
- The models diverge sharply in the tropics: IFS-NEMO exhibits a high-amplitude dipole (strong drying at ~8°S, intense wetting at ~3°N), whereas IFS-FESOM shows a much more muted, generally positive response.
- IFS-FESOM predicts distinct wetting in the Northern Hemisphere subtropics (20°N–30°N), while IFS-NEMO shows near-neutral to slight drying conditions in this band.
Spatial Patterns
The profiles follow a general thermodynamic 'wet-gets-wetter' pattern at high latitudes and a dynamic drying pattern in the SH mid-latitudes. The tropical pattern suggests a northward shift or intensification of the ITCZ, particularly pronounced in the IFS-NEMO simulation.
Model Agreement
Agreement is high in the extratropics regarding the sign and latitudinal placement of changes (SH drying, polar wetting). Agreement is poor in the tropics (10°S–10°N) and NH subtropics, likely due to differences in how the ocean components (FESOM vs. NEMO) resolve equatorial dynamics and SST gradients.
Physical Interpretation
High-latitude increases are driven by Clausius-Clapeyron scaling (increased atmospheric water vapor capacity). The SH mid-latitude drying and high-latitude wetting dipole indicates a poleward shift of the storm tracks and expansion of the Hadley cell. The tropical disagreement suggests sensitivity of the ITCZ position and strength to the underlying ocean model formulation (unstructured grid FESOM vs. structured NEMO) and resultant air-sea coupling.
Caveats
- Zonal averaging masks significant regional zonal asymmetries, such as contrasts between monsoon regions and oceanic dry zones.
- The short analysis period (10 years) may allow internal decadal variability (e.g., ENSO phases) to influence the tropical mean state, particularly for the noisy ITCZ signal.