An evaluation of the U.K. Met Office Unified Model over the central Arctic Ocean during ASCOS

Recent years have produced record minimum sea ice extents over the Arctic Ocean and temperatures are rising faster than the global mean. It is therefore important to predict future changes in Arctic climate accurately. Currently, surface flux and cloud parameterization schemes in both regional and global models tend to perform poorly over sea ice, leading to significant errors in the surface energy balance. Short range weather forecasts produced by the Met Office Unified Model are evaluated with in-situ observations to highlight errors in parameterized physical processes in the climate version of the model without the complications of large biases caused by errors in simulated circulation. The observations were made over pack ice at 87°N during August and September 2008 as part of the Arctic Summer Cloud Ocean Study (ASCOS). The comprehensive data set includes turbulent flux profiles, surface radiation fluxes, vertical temperature, wind and humidity profiles, radiosonde measurements and cloud property observations from remote sensing instruments. The focus of this study is to use the observations to evaluate the performance of the model's surface turbulent flux parameterization scheme and find reasons for any significant errors that are found.