SnowPappus v1.0, a blowing-snow model for large-scale applications of the Crocus snow scheme

Abstract

Wind-induced snow transport has a strong influence on snow spatial variability, especially at spatial scales between 1 and 500 m in alpine environments. Thus, the evolution of operational snow modelling systems towards 100–500 m resolutions requires representing this process at these resolutions over large domains and entire snow seasons. We developed SnowPappus, a parsimonious blowing-snow model coupled to the state-of-the-art Crocus snow model able to cope with these requirements. SnowPappus simulates blowing-snow occurrence, horizontal transport flux and sublimation rate at each grid cell as a function of 2D atmospheric forcing and snow surface properties. Then, it computes a mass balance using an upwind scheme to provide eroded or accumulated snow amounts to Crocus. Parameterizations used to represent the different processes are described in detail and discussed against existing literature. A point-scale evaluation of blowing-snow fluxes was conducted, mainly at the Col du Lac Blanc observatory in the French Alps. Evaluations showed that SnowPappus performs as well as the currently operational scheme SYTRON in terms of blowing-snow occurrence detection, while the latter does not give access to spatialized information. Evaluation of the simulated suspension fluxes highlighted a strong sensitivity to the suspended particle's terminal fall speed. Proper calibrations allow the model to reproduce the correct order of magnitude of the mass flux in the suspension layer. Numerical performances of gridded simulations of Crocus coupled with SnowPappus were assessed, showing the feasibility of using it for operational snow forecast at the scale of the entire French Alps.