Caveats about Regional Climate Model outputs

Sea Ice in RegCM4 simulations

The RegCM4 regional model is unable to model sea ice. It does not contain a frozen land cover type over water in winter, nor any code describing how frozen seawater behaves. In the GCM-driven simulations, it uses the skin temperature from the atmospheric component of the GCM as the sea surface temperature (SST). This gives it a temperature that is more reflective of what the air temperature over the water would be if it were frozen, even though the water is open in the model.

We don't use the actual SST from the ocean model in the GCM because it is pegged to the freezing temperature of salt water any time there is ice, and that would lead to warm open ocean water in RegCM in the winter, and that would be sub-optimal.

However, in the simulations driven by the ERA-Int reanalysis, that was the only available option at the time. As a result, there is a notable warm bias, particularly in winter, over the oceans and nearby land in high-latitude regions in these simulations.