3. Results

d. Changes in the Equilibrium State (Meridional Structure)

As a preparatory step in identifying what determines the runaway limit, the meridional structures of OLR and surface temperature in the equilibrium state with increasing the value of solar constant will be summarized. Figure 1 shows the meridional distribution of the zonal mean OLR and zonal mean surface temperature for experiments S1200, S1380, S1500, S1550, and S1570. The following observations can be made based on the figure.

• Meridional distribution of OLR:
  A flattening of the meridional distribution of OLR is accompanied by an increase in incident solar radiation flux, and the value of OLA reaches 400 W/m² at all latitudes.
• Meridional distribution of surface temperature:
  As in the case of OLR, a flattening is observed in the meridional distribution of surface temperature, and the meridional contrast is reduced. In experiments S1200, S1380, and S1570, the meridional contrast of surface temperatures are approximately 50 K, 45 K, and 20 K, respectively.

Based on the above results, it may be concluded that the meridional contrast in the thermal structure of the atmosphere is reduced with increases in solar constant.

Figure 1: The meridional distribution of the zonal mean OLR (W/m², green line) and zonal mean surface temperature (K, red line) in equilibrium states for experiments S1200, S1380, S1500, S1550, and S1570.

3.d. Changes in the Equilibrium State (Meridional Structure)