An extreme number of sensors in one spot | Aspen Global Change Institute

Reprinted with permission from Mountain Views Chronicle (Vol. 16, 2022)

Thanks to Eli Schwat, University of Washington, for editorial help.

Did you ever return home from fieldwork and think to yourself: did I hang that temperature sensor the right height above the ground? Am I measuring the wind in the best location? Did I just accidentally bias my entire study because I have no idea how representative my measurements are of the 20 m cube I’m standing in, let alone the whole valley?

From October 1st-15th, a team of scientists from the National Center for Atmospheric Research, University of Washington, and Aspen Global Change Institute deployed an extensive array of near-surface atmospheric instrumentation in Gothic, Colorado. This project involves extremely dense instrumentation for near-surface atmospheric measurements to quantify the physical processes involved in snow sublimation. To endure the harsh winter in this area of the Rocky Mountains, this instrumentation will be tended to throughout the winter by members of the team staying in Gothic to ensure that all measurements are repeatedly gathered. Together the instrumentation is designed to quantify sublimation of snow during the winter months. This image shows the research team beginning to install a snow pillow, an instrument that measures the total water equivalent of the snowpack sitting above it, while our outreach team gathers audio and visuals for future educational materials. The tower in the back left is one of four installed during this deployment which allows for a gradient of measurements between 0-20 m above the ground. Photo: Emilio Mateo, AGCI Climate Science Fellow. Emilio is working to display this research on the sublimation of snow in the Colorado Rocky Mountains to a broader audience through photography, outreach videos, and educational materials.

These questions have long kept me up at night. Meanwhile, Julie Vano (at the Aspen Global Change Institute) stays up at night worrying about water in the Colorado River, a topic that should keep you up at night too. In recent years, streamflow has been less than one would expect given the snow measurements used for forecasts. Since approximately 70% of Colorado river streamflow originates as snowmelt, a difference between expected and received water from snow matters greatly to water managers and water users. But why the discrepancy? Ethan Gutmann (NCAR) stares out his window and wonders if maybe the snow blew away. All three of us are collectively wondering – what is happening to the water now, and what should we expect in the future?

Blowing snow can increase the amount of snow lost to the atmosphere, which can change the water available for runoff, but how do we measure it? Working together, Julie, Ethan, and I put out an SOS to the National Science Foundation that we needed help. SOS isn’t just a distress signal: it’s an acronym for Sublimation of Snow, the process by which ice within the snow matrix turns into water vapor and is potentially blown away to another watershed. Sublimation is extremely tricky to measure. Rebecca Mott (SLF, Switzerland) reviewed studies on sublimation from across the globe and found values reporting losses ranging anywhere from 10% to 90% of snowfall (Mott et al., 2018). While some of this variability can be attributed to location at which snow measurements are taken (we expect to lose more snow to sublimation in places that are dry and windy, like Colorado, and less in places that are moist and wet, like western Washington) we still see wide variation between different methods used to estimate sublimation at a given spot.

The solution to the sublimation challenge: “Let’s try to put every type of measurement we can think of together in one spot and compare them very carefully (Fig. 1)!”

Figure 1. Sketches from proposal asking for every way to measure sublimation that I could think of.

Ideally, we wanted to arrange them in a “control triangular prism” and try to track every snowflake inside that control volume. Ideally, we wanted to deploy these instruments in a valley where the Department of Energy (DOE, SAIL https://sail.lbl.gov/about/) and the National Oceanographic and Atmospheric Administration (NOAA, SPLASH, https://psl.noaa.gov/splash/) were already intensely measuring weather at the valley scale at the valley scale and where the Rocky Mountain Biological Laboratory (RMBL) has been conducting ecology-related research for over 50 years.

To our great delight and excitement, our proposal was selected after rigorous NSF review, and NCAR’s Earth Observing Laboratory (EOL) designated the community instruments of their Integrated Surface Flux System (ISFS) to come together in our envisioned triangle to study sublimation. Their team of scientists and engineers, led by Steve Oncley, had the expertise to turn my sketches into reality (Fig. 2, Fig. 3). From across University of Washington, UCAR, and the Aspen Global Change Institute, we assembled a team of our own. The sensors were deployed, as hoped, near RMBL in October 2022. Shortly thereafter snow fell, and now we’re ready, at least to the best of our ability, to track that snow’s fate, using an extreme number of sensors, all basically in one spot. With the support of our experienced team, we can now begin to explore what happens to snow in near real time, and we can continue to wonder, and maybe even begin to answer, what should we expect in the future?

Figure 2. Looking up at the 20 m tower during October field deployment. On left, temperature and relative humidity sensors every 1 m, sonic anemometers (to measure aid movement) at every 4 m. Image Credit: Emilio Mateo/AGCI.

To learn more about the SOS project, visit: https://www.eol.ucar.edu/field_projects/sos.

To view near real-time data visit: http://datavis.eol.ucar.edu/ncharts/projects/SOS/noqc_geo.

Figure 3. One of the 10 m towers with snow on the ground, Oct. 30, 2022.
Image Credit: Isabel Suhr, NCAR.

LITERATURE CITED

Mott, R., Vionnet, V., & Grünewald, T. 2018. The seasonal snow cover dynamics: Review on wind-driven coupling processes. Frontiers in Earth Science, 6(197).

Jessica Lundquist, University of Washington, is the Principal Investigator on the Sublimation of Snow Project.

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