Pangaean climates: Megamonsoons of the megacontinent

The climate for a highly idealized geographic representation of the megacontinent of Pangaea, corresponding to the period 250–200 m.y. ago, is explored using a low-resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth, with a provision for sea-ice formation and decay. Soil moisture is included as a predicted variable on the continent. Because there are large uncertainties about key factors that might influence the Pangaean climate, sensitivity experiments are used to examine the climate for two different mean elevations (0 and 1000 m), two different snowcover prescriptions, and two different levels of implied greenhouse heating and solar luminosity (modern CO₂ concentration and modern solar luminosity; fivefold increase in modern CO₂ concentration and a 1% decrease in modern solar luminosity). In all of the experiments, the large bipolar land masses of Laurasia and Gondwanaland, joined near the equator in the west and separated by the Tethys Sea in the east, exhibit extreme continentality, with hot summers, cold winters, and large-scale summer and winter monsoon circulations. Year-round or seasonal aridity is simulated for all but the eastern coastal regions, the tropical western coast, and the regions poleward of 40° latitude. The simulated climate of the idealized Pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late Permian and Triassic. However, the model results serve mainly to indicate the importance of various climate-forming factors (geography, topography, heating). Detailed comparisons will require new experiments, with better models and more accurate geologic boundary conditions.