Large Eddy Simulations of summertime Arctic stratus during ASCOS

Due to a lack of observational data and hence suitable parameterizations, large scale numerical models often perform badly in their simulation of the Arctic. One major factor for their poor simulation of the summertime boundary layer has been attributed to a lack of understanding of the structure of Arctic stratus clouds and the complex feedback mechanisms which link these to the boundary layer structure and surface. Summertime Arctic stratus differ from their mid-latitude counterparts - on which current parameterizations are based - in several respects, with the result that the surface radiation balance is very poorly represented. With the Arctic region currently experiencing a rapid temperature rise the ability of models to correctly simulate Arctic stratus is necessary to help determine future changes in Arctic climate.

Using the unique dataset collected during the ASCOS field campaign, quasi-idealised simulations of Arctic stratus have been carried out to examine their dynamical and microphysical characteristics. These simulations were performed using the UK Met Office's Large Eddy Model (LEM) with a single moment liquid and double moment precipitation, cloud ice, snow and graupel, bulk microphysics scheme. Simulations are compared with the dynamical structure of the clouds observed with the NOAA MMCR Doppler cloud radar and the results of several sensitivity tests will be shown. Future modelling will involve further large eddy simulations using a bin resolved microphysical scheme and with a single column version of the Met Office's Unified Model to guide development of future Arctic cloud parameterizations.