Tier 2 Seasonal Amplitude Change

2 figures · 1990–2014 → 2040–2049

Synthesis

Future projections reveal a dichotomy in seasonal temperature changes, characterized by winter-dominant warming over polar oceans due to sea-ice loss and summer-dominant warming over mid-latitude continents driven by surface drying.
Under SSP3-7.0 (2040-2049), the seasonal temperature amplitude undergoes a distinct latitudinal bifurcation driven by contrasting thermodynamic mechanisms. In the high northern latitudes (>60°N), the seasonal cycle is significantly damped, with zonal mean reductions in amplitude reaching -4 K in IFS-FESOM and -3 K in IFS-NEMO. This negative signal ($ΔT_{JJA} - ΔT_{DJF} < 0$) is spatially coincident with sea-ice retreat in the Arctic Ocean and North Atlantic, confirming that enhanced ocean-to-atmosphere heat fluxes in winter are accelerating warming rates in DJF relative to JJA. A similar winter-amplification mechanism appears in the Southern Ocean, where positive values indicate stronger warming during the austral winter (JJA). Conversely, Northern Hemisphere mid-latitudes (35°N–55°N) exhibit an amplification of the seasonal cycle, characterized by zonal mean increases of +0.6 K to +1.0 K. Spatially, this signal is dominated by land masses—specifically the Mediterranean, Middle East, and Central Asia—where amplitude changes exceed +2 K. This pattern indicates that summer warming is outpacing winter warming, likely driven by soil moisture-temperature feedbacks where surface drying limits evaporative cooling. A notable divergence exists over North America, where IFS-FESOM simulates a coherent, large-scale amplification of summer temperatures that is largely fragmented or absent in IFS-NEMO, suggesting model-specific sensitivities in land-atmosphere coupling or circulation changes.

Related diagnostics

sea_ice_concentration soil_moisture_content

Seasonal Amplitude Change

Seasonal Amplitude Change
Variables avg_2t
Models ifs-fesom, ifs-nemo
Units K
Baseline 1990-2014
Future 2040-2049
Method Amplitude = T_JJA − T_DJF; ΔAmplitude = amp_future − amp_hist.

Summary medium

The figure displays the projected change in seasonal temperature amplitude ($ΔT_{JJA} - ΔT_{DJF}$) for the period 2040-2049 relative to 1990-2014 under SSP3-7.0, contrasting the IFS-FESOM and IFS-NEMO models. The results highlight a physical dichotomy between high-latitude oceans, where winter warming dominates, and mid-latitude continents, where summer warming dominates.

Key Findings

  • A strong negative signal (blue, < -2 K) over the Arctic Ocean and North Atlantic indicates that winter (DJF) warming significantly exceeds summer (JJA) warming, consistent with Arctic Amplification.
  • A prominent positive signal (red, > 2 K) covers the Mediterranean, Middle East, and Central Asia, indicating that summer warming rates are accelerating faster than winter rates.
  • IFS-FESOM projects a robust amplification of the seasonal cycle (summer warming dominant) over North America, whereas IFS-NEMO shows a weaker, more heterogeneous response in this region.
  • In the Southern Ocean, bands of positive values (red) indicate stronger warming in JJA (austral winter) relative to DJF (austral summer), mirroring the winter-amplification mechanism seen in the Arctic.

Spatial Patterns

A distinct land-sea and latitudinal contrast is visible. High northern latitudes (Arctic/North Atlantic/Scandinavia) exhibit strong negative values (winter warming dominance). Conversely, mid-latitude semi-arid and continental regions (Mediterranean, Central Asia, Western US) show strong positive values (summer warming dominance). The Southern Hemisphere oceans display zonal banding with a tendency toward austral winter (JJA) amplification.

Model Agreement

Both models agree on the large-scale thermodynamic responses: 'blue' Arctic patterns (sea-ice loss signature) and 'red' Mediterranean patterns (drying feedback). However, they disagree significantly over North America, where IFS-FESOM simulates a large, coherent region of seasonal amplification that is largely absent or fragmented in IFS-NEMO.

Physical Interpretation

The negative values in the Arctic and North Atlantic are driven by the loss of sea ice, which enhances ocean-to-atmosphere heat flux primarily in winter (DJF), leading to winter-dominant warming. The positive values over mid-latitude land masses (e.g., Southern Europe, North America in FESOM) are likely driven by soil moisture-temperature feedbacks; future drying limits evaporative cooling in summer, causing temperatures to rise disproportionately compared to winter.

Caveats

  • The analysis relies on only two models, limiting the assessment of internal variability versus structural model uncertainty.
  • The discrepancy over North America suggests sensitivity to land-surface parameterizations or atmospheric circulation changes specific to each model configuration.

Zonal Seasonal Amplitude Change

Zonal Seasonal Amplitude Change
Variables avg_2t
Models ifs-fesom, ifs-nemo
Units K
Baseline 1990-2014
Future 2040-2049
Method 5° latitude bins; amplitude = T_JJA − T_DJF.

Summary high

The figure illustrates the zonal mean change in seasonal temperature amplitude (defined as T_JJA - T_DJF) between the baseline (1990-2014) and future (2040-2049) periods under SSP3-7.0 for IFS-FESOM and IFS-NEMO models.

Key Findings

  • A drastic reduction in seasonal amplitude occurs in the Arctic (>60°N), reaching -4 K in IFS-FESOM and -3 K in IFS-NEMO.
  • Northern Hemisphere mid-latitudes (35°N–55°N) exhibit an increase in seasonal amplitude, peaking at +1.0 K for IFS-FESOM and +0.6 K for IFS-NEMO.
  • Southern Hemisphere high latitudes (~65°S) show a positive change (~+1.0 K), which, given the inverted seasons, also indicates a reduction in seasonal temperature range (winter warming exceeding summer warming).

Spatial Patterns

The profile is dominated by polar amplification signals at both ends (reduced seasonality due to winter warming) and a distinct asymmetry in the mid-latitudes, where the Northern Hemisphere shows increased seasonality (positive peak) while the Southern Hemisphere oceans show weak negative changes.

Model Agreement

The models show high qualitative agreement on the latitudinal structure of changes. However, there is significant quantitative disagreement in the Northern Hemisphere: IFS-FESOM predicts substantially larger magnitudes of change than IFS-NEMO in both the Arctic (stronger amplitude reduction) and mid-latitudes (stronger amplitude increase).

Physical Interpretation

In the Arctic and Antarctic sea-ice zones, the loss of sea ice allows the ocean to release heat in winter, causing winter temperatures to rise much faster than summer temperatures (Winter Amplification), thereby shrinking the seasonal amplitude. In Northern Hemisphere mid-latitudes, the increase in amplitude is likely driven by land-surface feedbacks, such as soil moisture drying, which exacerbates summer warming relative to winter warming.

Caveats

  • The metric (T_JJA - T_DJF) requires careful interpretation in the Southern Hemisphere, where positive changes imply winter warming dominating summer warming.
  • Zonal averaging obscures the strong contrast between land and ocean responses, particularly in the Northern mid-latitudes where the signal is likely land-dominated.