A Comparison Study of Summer-season Land Surface Climatology in CFSv2 with Two Experimental Runs Using a Different Atmospheric Model and Ocean Components

To examine the impact of upgrades in atmospheric and oceanic components on land surface water and energy predictions in the National Centers and Environmental Prediction's (NCEP) latest fully-coupled Climate Forecast System version 2 (CFSv2), two summer-time T126 CFS experiments are carried out over a 23-yr period with 10 ensemble members, whose initial conditions are from mid-April to early May. In the first experiment, the atmosphere and ocean model in CFSv2 are replaced with its corresponding early version to assess the combined impact from the two upgrades. In the second experiment, the ocean component in the first experiment is replaced with observed Sea Surface Temperature (SST) to examine the impact from the atmospheric model enhancement and ocean-atmosphere interaction. The experimental CFS shares the same Noah land model with the CFSv2. Results from the two experimental runs are compared to each other, to those obtained from the CFSv2 run with 12 ensemble members whose initial conditions cover the same period of time, as well as to the available observations. The comparisons are based on the ensemble means.

Inter-comparisons of seasonal means in surface precipitation, evaporation, 2-m temperature, downward and net radiation, and the skills in predicting precipitation and 2-m temperature anomalies show that there are some similarities and notable differences, suggesting that the upgrades in model physics and the interactions among the earth system components have a large impact on seasonal energy and water predictions.