An extreme number of sensors in one spot
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?
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)!”
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?
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.
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.