Print Email Facebook Twitter Understanding wind-driven melt of patchy snow cover Title Understanding wind-driven melt of patchy snow cover Author van der Valk, L.D. (TU Delft Water Resources; Wageningen University & Research) Teuling, Adriaan J. (Wageningen University & Research) Girod, Luc (Universitetet i Oslo) Pirk, Norbert (Universitetet i Oslo) Stoffer, Robin (Wageningen University & Research) van Heerwaarden, Chiel C. (Wageningen University & Research) Date 2022 Abstract The representation of snow processes in most large-scale hydrological and climate models is known to introduce considerable uncertainty into the predictions and projections of water availability. During the critical snowmelt period, the main challenge in snow modeling is that net radiation is spatially highly variable for a patchy snow cover, resulting in large horizontal differences in temperatures and heat fluxes. When a wind blows over such a system, these differences can drive advection of sensible and latent heat from the snow-free areas to the snow patches, potentially enhancing the melt rates at the leading edge and increasing the variability of subgrid melt rates. To get more insight into these processes, we examine the melt along the upwind and downwind edges of a 50 m long snow patch in the Finseelvi catchment, Norway, and try to explain the observed behavior with idealized simulations of heat fluxes and air movement over patchy snow. The melt of the snow patch was monitored from 11 June until 15 June 2019 by making use of height maps obtained through the photogrammetric structure-from-motion principle. A vertical melt of 23 ± 2.0 cm was observed at the upwind edge over the course of the field campaign, whereas the downwind edge melted only 3 ± 0.4 cm. When comparing this with meteorological measurements, we estimate the turbulent heat fluxes to be responsible for 60 % to 80 % of the upwind melt, of which a significant part is caused by the latent heat flux. The melt at the downwind edge approximately matches the melt occurring due to net radiation. To better understand the dominant processes, we represented this behavior in idealized direct numerical simulations, which are based on the measurements on a single snow patch by and resemble a flat, patchy snow cover with typical snow patch sizes of 15, 30, and 60 m. Using these simulations, we found that the reduction of the vertical temperature gradient over the snow patch was the main cause of the reductions in vertical sensible heat flux over distance from the leading edge, independent of the typical snow patch size. Moreover, we observed that the sensible heat fluxes at the leading edge and the decay over distance were independent of snow patch size as well, which resulted in a 15 % and 25 % reduction in average snowmelt for, respectively, a doubling and quadrupling of the typical snow patch size. These findings lay out pathways to include the effect of highly variable turbulent heat fluxes based on the typical snow patch size in large-scale hydrological and climate models to improve snowmelt modeling. To reference this document use: http://resolver.tudelft.nl/uuid:c3b5b5cc-cf56-4ec3-8304-bf2a09c66a42 DOI https://doi.org/10.5194/tc-16-4319-2022 ISSN 1994-0416 Source The Cryosphere, 16 (10), 4319-4341 Part of collection Institutional Repository Document type journal article Rights © 2022 L.D. van der Valk, Adriaan J. Teuling, Luc Girod, Norbert Pirk, Robin Stoffer, Chiel C. van Heerwaarden Files PDF tc_16_4319_2022.pdf 8.03 MB Close viewer /islandora/object/uuid:c3b5b5cc-cf56-4ec3-8304-bf2a09c66a42/datastream/OBJ/view