Abstract : K.1
High resolution NWP modelling of the atmospheric conditions across VATNAJ├ľKULL (Iceland)

Laura Rontu, Friedrich Obleitner, Sander Tijm, Christoph Zingerle, Stefan Gollvik
laura.rontu@fmi.fi
Finnish Meteorological Institute

We investigate the potential of an operational NWP model to reproduce the near surface atmospheric conditions, as well as the energy and mass balance of snow and ice across an ice sheet and its environment. Our study is based on the application of an updated version of the High Resolution Limited Area Model (HIRLAM) for the simulation of a mesoscale glacio-meteorological experiment, carried out on Europe's largest ice cap (Vatnaj├Âkull, Iceland) during the melt period of 1996. The observations comprise synoptic data, tethered balloon and radio soundings plus detailed measurements of the micrometeorological profiles, turbulence and radiation from 15 automatic weather stations across the ice sheet. Snow pit and stake measurements and satellite images provide glaciologically relevant data.

To our knowledge, this data set has not been utilized for evaluation of mesoscale NWP models. We will compare the HIRLAM output with the screen-level observations across the ice sheet (time series, basic statistics, scores over the area). Specific studies at single sites will focus on the characteristics and evolution of the atmospheric boundary layer above snow and ice, including topographically and synoptically induced effects. Special emphasis will be given to parameters like accumulation (precipitation), melt rates, albedo, turbulent fluxes, katabatic flow and mesoscale flow characteristics. These validation studies are considered as valuable steps towards further improvement of the model and its glaciologically oriented applications.

The modelling concept is based on nesting of fine-scale hydrostatic HIRLAM experiments into the downscaled ERA40 (ECMWF) analyses. The fine-scale simulations are run with various options of (surface) data assimilation, physical parameterizations and model vertical resolution. Compared to the reference HIRLAM, we test modified parameterizations over permanent snow/continental ice and the impact of enhanced observational data.