After a little bit more work on fiddling with CO2 levels, I've managed to get global average temperatures closer to what I was hoping for. I also reduced the planet radius from earth’s value to mine (3100 mi), which probably helps equator-to-pole heat transfer.

300 ppm (22.9 C)
scaled_T42_8mo_scaled.png

180 ppm (19.8 C)
scaled_T42_R_180ppm.png

120 ppm (16.7 C)
scaled_T42_R_120ppm.png

After doing a number of these with different parameters—and looking at the results from Nikolai and discussions with Tiluchi—it’s pretty clear that the ITCZ doesn’t seem to fluctuate quite as much as it should from summer to winter. Even over land it typically doesn’t deviate more than +/- 10 degrees from the equator and, when it does, it tends to be somewhat dry as compared to the areas over the ocean; this latter quality is illustrated really nicely by Nikolai’s figure here where large swaths of land in the tropics have underestimated precipitation while the oceans are overestimated. There’s probably some systematic error with pressures going on here, but I’ve not dug deeply enough to sort out what that might be.

In any case, at this point things are probably good enough to estimate the extent of glaciation on my final continent and finish the topography there before coming back and doing a final pass(es) in ExoPlaSim.