Windfield and snowdrift modelling over complex mountainous terrain

The transport of snow by wind is an important factor for avalanche danger as well as ecology and hydrology in mountainous environments. Investigations of airflow and snowdrift are carried out using field data and model.

Field experiment for airflow and snow deposition/accumulation studies were held at the Gaudergrat ridge, located near Davos, accumulation and erosion studies. In the summer 2003 a large scale field experiment, Gaudex 2003, took place there in collaboration with the University of Leeds.  During this field campaign, more than 30 measurement devices were placed around the Gaudergrat in order to collect airflow data at a very small scale. These data are used  to compare and validate the numerical models.

The wind field data required to initialise and drive the snow transport model are provided by the meteorological model ARPS.
ARPS is developed at the Center for Analysis and Prediction of Storms, at the University of Oklahoma. This model can handle simulations ranging from regional scales down to micro-scales. The numerical forecast component of the ARPS is a three-dimensional, nonhydrostatic compressible model in generalized terrain-following coordinates, using finite differences and can be used in a Large-Eddy Simulations configuration.

As transport of snow mostly occurs in the first meters of the atmospheric boundary layer, snowdrift modelling requires high resolution windfields.  Consequently ARPS has been adapted for microscales simulations, with a finest horizontal resolution of 25 meters in order to resolve the complex topography.

Windfields simulations are higly sensitive to initial and boundary conditions, for this reason ARPS is now coupled to Meteoswiss model aLMo in order to produce initial and boundary conditions for ARPS runs. aLMo outputs have a horizontal resoltion of 7km, thus Arps computations are realised using nesting domains with a decreasing resolution down to 25m.
Part of the computations are run at the Swiss National Supercomputing Centre (CSCS).

Windfield computed with ARPS over the Gaudergrat ridge, at 3m above the surface, on Aug.18, 2003. The resolution is 25m. The red crosses show the Gaudex measurement sites.

Links

ARPS (http://www.caps.ou.edu/ARPS/index_flash.html)

aLMo(http://www.meteoswiss.ch/web/en/weather/models/almo.html)

CSCS (http://www.cscs.ch/)

GAUDEX 2003 (http://homepages.see.leeds.ac.uk/~lecjlg/gaudex/index.htm)