Sensitivity of CICE/CESM Arctic ice extent and characteristics to a seasonal evolution of snow density and snow depth biases

In this study we introduce a seasonally evolving snow density to the Community Ice CodE (CICE). After introducing density evolution alongside a depth bias correction previously reported, we observe an increase in the seasonal cycle of ice extent in both stand alone and atmospheric coupled simulations. We determine snow density evolution and snow depth bias with situ measurements taken starting in the latter half of the 20th century. For the Period 1950-1991 we use the Russian Arctic Ocean snow observations from drifting stations, acquired through NSIDC. During these campaigns, a seasonal evolution of snow density was observed, whereby the autumn snow cover was significantly less dense than the late winter and spring snow cover. In relation to the constant snow density used by CICE, we find the autumn snow density is as much as one third lower. By late winter, the in situ measurements of snow density approach the values used by CICE. When we correct for this bias we find a similarly reduced thermal conductivity. We therefore can introduce the effects of a seasonal snow density evolution to CICE by manipulating the thermal conductivity of snow. This allows us to limit the effects of this investigation on other model processes while retaining the effects on energy transfer between the atmosphere and ice cover. We use the same method for snow depth bias correction. We observe similar responses to our seasonal snow density evolution in both the stand alone and coupled atmosphere - ice simulations. Most notably, we observe an increase in the seasonal cycle in ice extent. We find that while the winter Arctic ice cover remains essentially unchanged, the summer Arctic ice extent decreases on the order of ten percent in both the stand alone and coupled atmosphere simulation. In addition, we find that the ice thickness is reduced across the Arctic in both simulations, with an enhanced effect in the coupled atmosphere - ice model integration. While the ice state between the ice only and active atmosphere integrations reacts similarly to our snow density evolution, we find that the processes controlling the response vary between the stand alone and coupled configurations. As such, we determine the importance of feedback mechanisms present in the coupled atmosphere simulation. In this investigation, we determine that the introduction of a seasonal snow density to CICE results in an enhanced seasonality in Arctic ice cover, with moderate decease in summer ice extent.