tokens: ocean with a depth of 50 m everywhere; no continent is considered. Sea ice is allowed to form when the surface temperature is below the freezing point (271.35 K), and the albedos of sea ice and snow depend on the stellar spectrum. For the visible band (0.7 μ m), the snow albedo is 0.80 and the ice albedo is 0.67. For the near-infrared band (>0.7 μ m), it is 0.68 for snow and 0.30 for sea ice. Neither oceanic dynamics nor sea ice dynamics are included in the simulations. By default, the time step of the experiments is 30 minutes, except for the f05_L26, f19_L51, and f19_L74 experiments, within which the time step is 15 minutes to avoid numerical instability. Each experiment was run for tens of Earth years until the sea ice and surface temperature reach equilibrium and the global-mean net energy imbalance at the top of the atmosphere (TOA) is within 1.0 W m −2 . Averages of the last 5 or 10 Earth years were used here. 3. Results 3.1. Effect of Varying the Horizontal Resolution Table 1 summarizes the global-mean characteristics of the slow rotation experiments. Overall, varying the horizontal resolution has a small effect on the surface temperature (Figures 1 (a)–(c)). In global mean, the surface temperature in the experiment of f45_L26 is 3.7 K higher than that of f19_L26 and 3.2 K higher than that of f05_L26. In the rapid rotation experiments, the difference is also small (Figure 2 ): the surface temperature difference between f45_L26 and f05_L26 is 1.0 K in global mean. In the following analyses, we focus on the results of slow rotation experiments, because the underlying mechanisms are the same. Figure 1. Surface temperature (K) in five experiments with resolutions of f45_L26, f19_L26, f05_L26, f19_L51, and f19_L74 (see Section 2 for detailed descriptions). In all these experiments, the stellar flux is 1800 W m −2 , star temperature is 3700 K, and rotation period (=orbital period) is 38.66 Earth days. Figure 2. Surface temperature in the rapid rotation experiments with two resolutions of f45_L26 (a) and f05_L26 (b). In these two experiments, the stellar flux is 1300 W m −2 , the star temperature is 2600 K, and the rotation period (=orbital period) is 4.25 Earth days. The global-mean surface temperature is 294.7 K in (a) and 293.7 K in (b). Table 1 Global-mean Characteristics of the Simulated Climate of a Slow Rotation Aquaplanet Under Five Different Resolutions in the Model ExoCAM Note. For the definition of total relative humidity, please see the text. The clear-sky greenhouse effect is defined as the difference in upward thermal infrared flux between the surface and the top of the model. For planetary albedo, the difference is also small (Figures 3 (a1)–(c1)). The f45_L26 experiment has a planetary albedo of 0.440, being 0.005 higher than that of f19_L26 and 0.006 higher than that of f05_L26, which corresponds to a difference in global-mean shortwave reflection of 2.25 and 2.70 W m −2 , respectively. The cloud longwave radiation effects
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