Intensive field campaign on snow microstructure evolution at a low-elevation alpine site

Dataset of snowpack properties combined with atmospheric forcing are necessary to evaluate snow models. Here, we followed the evolution of the snowpack at Col de Porte, a regular snow observation site located near Grenoble at 1350 m, with detailed measurements of the snow microstructure and related properties. The goals were 1/ to test the feasibility of using X-ray tomography for regular snowpack monitoring, 2/ to carry out an inter-comparison of different instruments for density and specific surface area (SSA) measurements, and 3/ to provide new dataset of snow properties including snow microstructure and meteorological forcing for model driving and evaluation for a low-elevation alpine environment. Over the winters 2021-2022 and 2022-2023, the standard observation program was complemented by SnowMicroPen measurements, SSA measurements with two optical instruments (DUFISSS and HISSGraS), and 3D imaging using a cold laboratory X-ray tomograph located next to the snow field. Measurements were performed weekly to bi-weekly. For tomography, snow were collected in cylinders of 4 cm diameter and 15 cm height. The scans were performed at two resolutions: 10 microns (50 min scan per cm) and 42 microns (3 min scan per cm). We present the evolution of the snowpack in relation to the weather conditions. Snow heights were well below average for the second winter, with several total snowpack disappearances, from mid-February on. Both winters showed regular rain-on-snow and melt events throughout the winter, offering suited data to evaluate wet snow and liquid water flow in models, especially. An inter-comparison of density and SSA estimates from tomography, SnowMicroPen and optical instruments is provided. Finally, we present a preliminary comparison of the snowpack evolution between measurements and the snowpack model Crocus.