Abstract : 3K.7
Measurement and simulation of the energy and mass balance of snow at an Alpine valley site

Helmut Aschauer, Friedrich Obleitner, Johannes Vergeiner, Stefan Emeis
Institute of Meteorology and Geophysics, University of Innsbruck, Austria

This investigation is based on data that were collected at a mid valley location in the Unterinntal valley (Austria) during winter 2005/2006. The measurements were performed within a comprehensive field campaign (ALPNAP) focussing on air pollution and noise aspects in relation to the specific meteorological and topographical conditions in Alpine valleys. In this context, the evolution of snow plays an important role too, e.g. with respect to the strength and persistence of inversions. This is of particular interest in view of the exceptional situation during winter 2005/2006, which was characterized by an almost unbroken snow cover throughout the whole province.

A one-dimensional mass and energy balance model is used to simulate the evolution of the snow pack and its interaction with the atmosphere and the underlying soil. Profiles of snow temperature and density, grain size, or liquid water content are predicted by numerically solving for the governing equations of the relevant processes. The model is driven by half-hourly values of the basic meteorological parameters including the short-wave and atmospheric long-wave radiation components. Precipitation input is derived from nearby climate data and local snow pit investigations. Validation of the simulation results is based on comparison with independent measurement data.

During the accumulation period (04Dec2005 until 09Feb2006) about 40cm of snow were build up. During this period, the energy balance was characterized by a net loss due to radiation and the prevalence of evaporation, which was offset by the positive contributions from turbulent sensible and conductive soil heat fluxes. During the melt period, the snow pack experienced enhanced energy input, which was mainly associated to the now positive radiation budget and the more pronounced soil heat flux towards the surface. The initial ablation rates were significantly enhanced as soon as melt water and solar radiation approached the snow-soil interface.