Modelling the vertical structure of the central Arctic boundary layer : ASCOS case studies

Atmospheric models have difficulty reproducing the near-persistent layer of low-level cloud that occurs in the central Arctic during the summer months. A temperature inversion somewhere between the surface and 1-2km is common during all seasons in the Arctic and it has been suggested that model difficulties in characterising the low cloud may be related to a model's ability to resolve this inversion. A comprehensive set of in-situ and remote-sensing atmospheric measurements were made over the central Arctic Ocean during August and September 2008 as part of the Arctic Summer Cloud Ocean Study (ASCOS). These measurements are used to evaluate the success of the Met Office Unified Model in reproducing the observed vertical cloud and temperature structure in its global operational forecasts. A single column version of the model is then used to determine any problematic parameterisations and to test improvements to them.