The Arctic atmosphere in CCSM4: Evaluation of key variables

Changes to Arctic Climate observed in the present day have lead to increased focus on understanding and predicting Arctic climate processes and their future states. Of climate models used to analyze future Arctic climate, the fourth version of the National Center for Atmospheric Research's (NCAR) Community Climate System Model (CCSM4) is among the most popular. Included in CCSM4 are several component models, including the Community Atmosphere Model version four (CAM4), the Los Alamos Sea Ice Model (CICE), the Community Land Model (CLM), and the Parallel Ocean Program Ocean Model, version two (POP2). In preparation for the Intergovernmental Panel on Climate Change's (IPCC) fifth Assessment Report (AR5), several CCSM4 simulations have been completed. Included are six ensemble runs with monthly mean output, and a high frequency output run featuring output at three-hourly, six-hourly and daily frequencies, depending on the variable. In this work, we utilize the CCSM4 AR5 simulations to evaluate the ability of CCSM4 to accurately portray the present-day Arctic Climate (1981-2005). Included in this analysis are comparisons of observed and simulated Arctic (70-90 N) atmospheric surface temperature, sea level pressure, cloud occurrence and phase, energy budget, hydrological cycle, and lower tropospheric stability. The high-frequency output simulation provides added insight into things such as variability of surface temperature and pressure extremes and lower-tropospheric stability not evident from monthly means of these variables. In this presentation we will illustrate the model's strengths and weaknesses in simulating the above-listed features of the Arctic Atmosphere through direct comparison with observations and reanalysis products. We will also provide interpretation of results and potential implications on simulation of future climate, along with discussion on atmospheric variability within these simulations.