Snowfall variability as seen by a weather radar

Wednesday, 17 December 2014: 10:50 AM
Alexis Berne, Swiss Federal Institute of Technology Lausanne, Lausanne, Switzerland
Snowfall is highly variable in space and time because of the interactions between (cold) cloud microphysics and turbulent atmospheric dynamics. In comnplex terrain, this variability is amplified but remains poorly understood mainly due to a lack of monitoring capabilities. This contribution deals with the characterization and the quantification of the variability of snowfall at small scales (up to 10 km) in the Swiss Alps as seen by a Doppler polarimetric weather radar.

The focus is first on the comparison of the horizontal variability in snowfall close to the surface (as seen by a radar) and in the snow accumulation on the ground (derived from aerial laser scans). The results show that the latter is larger than the former, pointing towards small-scale topographically induced winds as the main factor controlling the variability of snow accumulation. Second, the average vertical structure of snowfall is investigated using the polarimetric radar variables collected in vertical scans in the atmosphere. The main features of the vertical structure are related to the dominant microphysical processes at work.

These results are a (preliminray) step forward to better understand the variability of snowfall at small scales in complex terrain, and illustrate the need for additional effort to collect snowfall observations from a variety of sensors