Seasonal Evolution of Alpine Snow Stratigraphy: Multi-Year High-Resolution SnowMicroPen Measurements at Weissfluhjoch

Abstract. Snow density and specific surface area are key properties controlling snowpack mechanical behavior, thermal conductivity, and snow metamorphism. They are crucial parameters in several fields, including avalanche prediction, snow hydrology, and climate modeling. Yet long-term high-resolution in situ observations of their seasonal evolution remain rare. Here we present a ten-year record of daily SnowMicroPen (SMP) measurements collected at the WSL Institute for Snow and Avalanche Research (WSL/SLF) Weissfluhjoch research site (2536 m a.s.l., Davos, Switzerland) spanning winters 2015–2016 to 2024–2025. The SMP measures resistance penetration force and, through parametrization, allows retrieval of density and specific surface area (SSA) at high vertical (millimeter) resolution. Comparison against independent measurements (density cutter, IceCube, etc.) reveals two systematic sources of error. First, an offset in the SMP force signal causes an overestimation of new snow density, and second, temperatures above −0.6±0.2 °C result in a strong nonphysical increase in SSA. The overall SMP measurement uncertainties are 40.1 kg m⁻³ for the density and 7.05 m² kg⁻¹ for SSA, both in close agreement with previous studies, supporting existing parameterizations to remain valid. The presented 10-year SMP measurements reveal seasonal and inter-annual densification and SSA evolution of alpine snow stratigraphies at unprecedented temporal and spatial (vertical) resolution, providing a unique dataset for improved theoretical descriptions of snow metamorphism, snow optical and mechanical properties, and snowpack model development.