Obtaining sub-daily new snow density from automated measurements in high mountain regions

Abstract

Abstract. The density of new snow is sometimes monitored by meteorological or hydrological services at daily time intervals, or occasionally measured in local field studies. However, meteorological conditions and thus settling of the freshly deposited snow rapidly alter the new snow density until measurement. Physically based snow models and now-casting 10 applications make use of hourly weather data to determine the water equivalent of the snowfall and snow depth. In previous studies, a number of empirical parameterizations were developed to approximate the new snow density by meteorological parameters. These parameterizations are largely based on new snow measurements derived from local in-situ measurements.In this study a data set of automated snow measurements at four stations located in the European Alps is analysed for several winter seasons. Hourly new snow densities are calculated from the height of new snow and the water equivalent of snowfall. 15Considering the settling of the new snow and the old snow pack, the average hourly new snow density is 68 kgm -3 with a standard deviation of 9 kgm -3 . Seven existing parameterizations for estimating new snow densities were tested against these data, and most calculations overestimate the hourly automated measurements. Two of the tested parameterizations were capable of simulating low new snow densities observed at sheltered inner-alpine stations. The observed variability in new snow density from the automated measurements could not be described with satisfactory statistical significance by any of the 20 investigated parameterizations, but relationships between new snow density and wet bulb temperature are partly visible in the automated measurements data. Wind speed is a crucial parameter for the inter-station variability of new snow density, with higher new snow density at more windy locations. Whereas snow measurements using ultrasonic devices and snow pillows are appropriate for calculating station mean new snow densities, we recommend instruments with higher accuracy e.g. optical devices for better investigations of the variability of new snow densities on sub daily intervals. 25Hydrol. Earth Syst. Sci. Discuss., https://doi

Shift in seasonal snowpack melt-out date due to light-absorbing particles at a high-altitude site in Central Himalaya

“…Precipitation was not explicitly measured at this location, but is estimated similar to the method described in Svensson et al (2021), yielding an estimate of the amount of precipitation in mm SWE (PP). The positive changes in snow depth (SD + ) are integrated over the periods in question and the density of the new snow is assumed to be 100 kg m -3 (Helfricht, et al, 2018). The estimated total PP for season 1 and season 2 are 290 and 460 mm, respectively.…”

“…Where SDis the absolute change in SD (mm) when it decreases, i is the number of day during the snow season and n is the number of days since the start of the snow layer, ns and w are the density of new snow (100 kg m -3 ) (Helfricht, et al, 2018) and liquid water (1000 kg m -3 ), respectively. Average ECeq is thus the sum of ECeq in the layer d plus the ECeq that is in layer d from the ablated snow.…”