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1. Estimating Snow Sublimation in Complex Terrain: A Season of Intensive Field Measurements and the Role of Vertical Water Vapor Flux Divergence

   https://doi.org/10.1175/JHM-D-25-0022.1  

   Schwat, Eli; Hogan, Daniel; Paw_U, Kyaw Tha; Cox, Christopher J; Butterworth, Brian J; Gutmann, Ethan; Vano, Julie A; Lundquist, Jessica D (October 2025, Journal of Hydrometeorology)

   Abstract Understanding the role of snow sublimation in the alpine water balance is critical to predicting future water resource availability. During winter 2022–23, the Sublimation of Snow campaign in Colorado’s East River watershed used 12 eddy covariance (EC) instruments (2–20-m height) to measure sublimation and micrometeorology on the valley floor. ECs measured 33–42 mm of snow water equivalent sublimated (8%–10% of seasonal peak snow accumulation). Midwinter sublimation was driven by blowing snow and springtime sublimation by positive net radiation. During blowing snow, EC water vapor fluxes increased with height between 3 and 10 m, on average by 26% and by up to 200% during individual events (positive vertical turbulent flux divergence). During nonblowing snow conditions, fluxes decreased with height between 3 and 20 m, on average by 36% (negative vertical turbulent flux divergence). Estimates of transport terms in a water vapor conservation equation suggest that positive divergence arose from blowing snow sublimation and negative divergence arose from vertical water vapor advection, although horizontal advection remains unquantified, limiting our conclusions. We found that keeping one instrument functional over the entire winter is more important than having instruments at multiple heights. Seasonal uncertainty in measured total sublimation due to instrument height is estimated at ±12% due to blowing snow sublimation and water vapor advection; however, for shorter deployments, this uncertainty may be larger. The optimal instrument height for estimating total sublimation, 10 m at our site, is likely to vary by location, and further work is needed to understand the role of advection. Significance StatementMountain snowpacks act as water reservoirs for populations worldwide, and snow sublimation, which is rarely measured, removes water from those reservoirs. A recent measurement campaign offered the unique opportunity to compare sublimation measurements from 12 instruments, which reveal that sublimation estimates vary both across a winter season and with instrument height. Sublimation rates are higher during times with blowing snow compared to times without. During blowing snow, higher instruments (above 5 m) measure 26% more sublimation than lower instruments. Otherwise, higher instruments (above 10 m) measure 36% less sublimation. This work concludes that when measuring alpine sublimation, instrument height can introduce uncertainty, particularly if instruments are deployed for short periods of time. To best estimate total sublimation, instruments should be deployed over an entire winter season. 

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2. The role of sublimation as a driver of climate signals in the water isotope content of surface snow: laboratory and field experimental results

   https://doi.org/10.5194/tc-15-4949-2021  

   Hughes, Abigail G; Wahl, Sonja; Jones, Tyler R; Zuhr, Alexandra; Hörhold, Maria; White, James_W C; Steen-Larsen, Hans Christian (January 2021, The Cryosphere)

   Abstract. Ice core water isotope records from Greenland and Antarctica are a valuableproxy for paleoclimate reconstruction, yet the processes influencing theclimate signal stored in the isotopic composition of the snow are beingchallenged and revisited. Apart from precipitation input, post-depositionalprocesses such as wind-driven redistribution and vapor–snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal subsequently stored in the ice. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor–snow exchange is an important driving mechanism. Here we investigate how vapor–snow exchange processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under forced sublimation show an increase in snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer due to sublimation, with an attenuated signal down to 3 cm snow depth over the course of 4–6 d. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Our observations confirm that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 d field experiments at the East Greenland Ice Core Project site (northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation contribute to the climate signal recorded in the water isotopes in surface snow, in both laboratory and field settings. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such, particularly in regions of low accumulation. 

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3. Sublimation of Snow

   https://doi.org/10.1175/BAMS-D-23-0191.1  

   Lundquist, Jessica D; Vano, Julie; Gutmann, Ethan; Hogan, Daniel; Schwat, Eli; Haugeneder, Michael; Mateo, Emilio; Oncley, Steve; Roden, Chris; Osenga, Elise; et al (June 2024, Bulletin of the American Meteorological Society)

   Abstract Snow is a vital part of water resources, and sublimation may remove 10%–90% of snowfall from the system. To improve our understanding of the physics that govern sublimation rates, as well as how those rates might change with the climate, we deployed an array of four towers with over 100 instruments from NCAR’s Integrated Surface Flux System from November 2022 to June 2023 in the East River watershed, Colorado, in conjunction with the U.S. Department of Energy’s Surface Atmosphere Integrated Field Laboratory (SAIL) and the National Oceanic and Atmospheric Administration (NOAA)’s Study of Precipitation, the Lower Atmosphere and Surface for Hydrometeorology (SPLASH) campaigns. Mass balance observations, snow pits, particle flux sensors, and terrestrial lidar scans of the evolving snowfield demonstrated how blowing snow influences sublimation rates, which we quantified with latent heat fluxes measured by eddy-covariance systems at heights 1–20 m above the snow surface. Detailed temperature profiles at finer resolutions highlighted the role of the stable boundary layer. Four-stream radiometers indicated the important role of changing albedo in the energy balance and its relationship to water vapor losses. Collectively, these observations span scales from seconds to seasons, from boundary layer turbulence to valley circulation to mesoscale meteorology. We describe the field campaign, highlights in the observations, and outreach and education products we are creating to facilitate cross-disciplinary dialogue and convey relevant findings to those seeking to better understand Colorado River snow and streamflow. 

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4. The Maximum Entropy Production (MEP) Method for Modeling Surface Energy Budget – Theory and Applications to Arctic Regions

   Wang, Jingfeng.; Sharif, Husayn E.; Ivanov, Valeriy Y.; Zhou, Wenbo; Sheshukov, Alexsey; Mazepa, Valeriy. (December 2019, Agu)

   The Maximum Entropy Production (MEP) method for modeling surface energy budget has been developed and validated at local, regional and global scale including the Arctic regions. The MEP model has solid theoretical foundation built on the Bayesian probability theory, information theory, non-equilibrium thermodynamics and boundary layer turbulence theory. Its formulation has advantageous features including closing energy budget at any space-time scales, independence of moisture and temperature gradient, wind speed and surface roughness, and free of tunable empirical parameters. Application of the MEP model has been covering all types of land covers including Arctic permafrost tundra, sea ice and snow surfaces. Recent tests using field experimental observations suggest that the MEP model using fewer input data and model parameters is able to simulate surface energy budget accurately. It is a more efficient alternative to the classical Penman-Monteith model of potential evapotranspiration. The MEP method has potential to influence the study of Arctic water-energy cycles and climate change. 

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5. Observations and simulations of the seasonal evolution of snowpack cold content and its relation to snowmelt and the snowpack energy budget

   https://doi.org/10.5194/tc-12-1595-2018  

   Jennings, Keith S.; Kittel, Timothy G.; Molotch, Noah P. (January 2018, The Cryosphere)

   Abstract. Cold content is a measure of a snowpack's energy deficit and is a linear function of snowpack mass and temperature. Positive energy fluxes into a snowpack must first satisfy the remaining energy deficit before snowmelt runoff begins, making cold content a key component of the snowpack energy budget. Nevertheless, uncertainty surrounds cold content development and its relationship to snowmelt, likely because of a lack of direct observations. This work clarifies the controls exerted by air temperature, precipitation, and negative energy fluxes on cold content development and quantifies the relationship between cold content and snowmelt timing and rate at daily to seasonal timescales. The analysis presented herein leverages a unique long-term snow pit record along with validated output from the SNOWPACK model forced with 23 water years (1991–2013) of quality controlled, infilled hourly meteorological data from an alpine and subalpine site in the Colorado Rocky Mountains. The results indicated that precipitation exerted the primary control on cold content development at our two sites with snowfall responsible for 84.4 and 73.0% of simulated daily gains in the alpine and subalpine, respectively. A negative surface energy balance – primarily driven by sublimation and longwave radiation emission from the snowpack – during days without snowfall provided a secondary pathway for cold content development, and was responsible for the remaining 15.6 and 27.0% of cold content additions. Non-zero cold content values were associated with reduced snowmelt rates and delayed snowmelt onset at daily to sub-seasonal timescales, while peak cold content magnitude had no significant relationship to seasonal snowmelt timing. These results suggest that the information provided by cold content observations and/or simulations is most relevant to snowmelt processes at shorter timescales, and may help water resource managers to better predict melt onset and rate. 

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