Location

Mammoth Mountain, CA - eastern Sierra Nevada

A complex system of sensors and automatic data logging devices monitor snow and energy budget conditions at a cooperative site midway up Mammoth Mountain (37 deg. 37 min. N, 119 deg. 2 min. W) at about 2940 meters (9645 feet) in the eastern Sierra Nevada of California. Researchers and research staff also make a variety of manual measurements at the site, which has operated at the current location in Mammoth Mountain Ski Area since 1987. The site lies well out of the way of ski area operation and recreational ski traffic so that the snow remains undisturbed from accumulation through melting. The site’s position, on the east side of the Sierra crest near the headwaters of the San Joaquin River, makes environmental conditions sensitive to different types of storms, which typically result in an enormous amount of precipitation and severe winds. These weather conditions, along with ease of winter access via the ski area, make this an ideal spot for monitoring alpine snow. Measurements include meteorological variables that affect energy transfer over the snow and its mass balance, snow properties as the pack evolves during the snow season and conditions in the soil under the snow cover. The participants in snow research and weather monitoring at the site include the University of California, Donald Bren School of Environmental Science and Management; the U.S. Army's Cold Regions Research and Engineering Laboratory (CRREL); the University of California's Sierra Nevada Aquatic Research Laboratory (SNARL); and Mammoth Mountain Ski Area (MMSA).

History and Research

The U.S. Forest Service (USFS), California Cooperative Snow Survey (CCSS) and MMSA have monitored snow and weather conditions on Mammoth Mountain since the 1960s for ski area planning and operation, water resources assessment and avalanche-hazard evaluation. Snow physics research on Mammoth Mountain began in the mid-1970s as Jeff Dozier's research group at the University of California, Santa Barbara (UCSB) sought a more permanent home for their field efforts. Between 1977 and 1987, the UCSB researchers carried out their research measurements at the original snow study site, located about 300 meters to the south of the current site. Dozier’s research team chose the original location because of the ease of winter access and opportunity to locate near a USFS meteorological station and a CCSS snow course and snow pillow (Davis and Marks, 1980).

Original Snow Study Site

In the early days, before reliable digital data loggers and ready-made sensors designed for the rugged conditions in alpine environments, snow scientists had to build their own instruments, support structures and data logging systems. Mainly through trial and error, the UCSB researchers established an infrastructure that could survive wind speeds over 50 ms^-1, severe icing and snow depths over 9 meters (and its associated compressive stresses during settlement). Incremental improvements to the original site eventually enabled measurement of most components of the energy and mass balances of a snow cover (Davis et al., 1984). Highlights from the early work included development of instrumentation for alpine snow measurements, preliminary measurements of the solar reflectance properties of snow and new techniques for measuring the properties of snow correlating to its remote sensing signature (e.g., snow wetness – Davis and Dozier, 1984, Davis et al., 1985; snow textural properties – Dozier et al., 1987; and Davis et al., 1987; and microwave properties – Davis et al., 1987; Davis and Dozier, 1989).

In 1987 snow studies began at a new location, again selected by UCSB researchers. The ski area management had announced to the research team plans to install a new lift near the first site that would have compromised the integrity of the area for snow research. Although the ski area later decided not to build the lift, their construction crew generously built a large instrument platform at the new site. Again over several years, incremental improvements to the infrastructure, sensing configuration and computing facilities brought the site to state-of-the art for alpine snow research. In 1991 a steel cargo container, partially buried in the ground and outfitted inside as a small laboratory, replaced the old plywood "Santa Claus" shack that allowed researchers to access the base of the snow cover in the winter. Additional modifications to the tower structure have included a steel I-beam with a 14-meter cable way for moving instruments in the air over the snow, and new masts and mounts for various sensors.

Current Snow Study Site

Early research at the new site in the late 1980s and early 1990s concentrated primarily on snow chemistry and remote sensing of snow using measurements in the solar and microwave spectral regions. Studies on contaminants in snow focused in part on the processes removing soluble trace species from snow (Bales et al., 1993). This work took advantage of the new snow melt lysimeters, made from chemically inert polyurethane, and provided field validation of results from laboratory studies carried out at the nearby facility SNARL (Bales et al. 1989). The results of these studies added theory of the behavior of trace chemical species (Harrington and Bales, 1998) to a detailed model of the physical processes within snow and energy transfer over snow (Jordan, 1991). Also in this time period and extending to the present, the site has served as a base for investigations involving improved measurements of snow from remote sensors. In the solar spectral region, studies at the site and studies over the larger area of Mammoth Mountain characterized the spectral reflectance of snow and its links to snow properties (Davis et al., 1993) and developed techniques for estimating grain sizes and fractional extent from imaging spectrometer measurements (Nolin and Dozier, 1993; Nolin et al., 1993; Painter et al., 1998). In 1996, a joint collaboration between UCSB and CRREL showed that an L-band, Frequency Modulated Continuous Wave radar could make measurements that allowed estimation of snow depth to within about 6 percent, even when the surface of the pack had liquid water present (Rosenthal et al., submitted).

Research on energy and mass budgets of an alpine snow cover, characteristics of the spectral reflectance of snow, remote sensing of snow, distribution of snow accumulation and relationships between weather factors and avalanche activity continue today. A forthcoming book chapter on validation of snow models (Davis et al., submitted) makes use of the data sets to illustrate examples of modeling accuracies and inaccuracies. Continuing UCSB graduate research assesses the impact of the angular distribution of snow reflectance on snow mapping. This effort relates to other remote sensing efforts. Some instrumentation at the site will characterize atmospheric properties simultaneously with acquisitions by remote sensing instruments aboard the NASA satellite Terra. The ground based atmospheric characterization facilitates an improved atmospheric correction of data acquired by Moderate-resolution Imaging Spectroradiometer (MODIS), the Multi-angle Imaging Spectro-Radiometer (MISR), and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Recent results analyzing measurements of snow accumulation at the site and seven other locations on Mammoth Mountain confirms the usefulness of techniques to interpolate snowfall over wider areas for snow hydrology. The ski patrol at MMSA has tied measurements from the site into their weather meso-net to support avalanche control work.

Today the cooperative research site continues to provide an excellent base of activities extending over the area of Mammoth Mountain and the Sierra region. Instrumentation at the site includes radiometers for measuring incoming and outgoing radiation; sensors for measuring air temperature, relative humidity and wind speed and direction; tipping-bucket gages for measuring precipitation; temperature sensors at various depths in the soil and snowpack; boards for collecting storm-snowfall; and snowmelt lysimeters with conductance meters. Also a camera points at the suite of radiometers in order to monitor their condition remotely. The site also continues to offer a superb resource for field classes studying snow science or snow hydrology.

Data Management

A Campbell CR7 data logger records environmental measurements from all instruments at the site. UCSB downloads and archives data from the data logger and images from a remote camera on an hourly basis. Software at UCSB automatically reviews the data to check quality (e.g., whether data values are within specified ranges, etc.). If the program detects bad data, it flags before ingestion in the UCSB database. All data then flow into the MMSA database, a Microsoft Access relational database management system (RDBMS). UCSB finally transfers the data to an SQL Server 7 RDBMS and makes them available via the Internet, along with images of the radiometers and their background.
 
 

References

Bales, R.C., Davis, R.E., Stanley, D.A., 1989, Ion elution through shallow homogeneous

snow, Water Resources Research, 25(8): 1869-1877.

Bales R.C., Davis R.E., and Williams M.W., 1993, Tracer release in melting snow - diurnal and seasonal patterns, Hydrological Processes, 7(4): 389-401.

Davis, R.E. and Marks, D., 1980, Undisturbed measurement of the energy and mass balance of deep alpine snowcover, Proceedings of the Western Snow Conference, 48: 62-67.

Davis, R.E., Dozier, J., 1984, Snow wetness measurement by fluorescent dye dilution, Journal of Glaciology, 30(106): 362-363

Davis, R. E., Dozier, J. & Marks, D., 1984, Micrometeorological measurements and instrumentation in support of remote sensing observations of an alpine snow cover, Proceedings of the Western Snow Conference, 51: 161-164.

Davis, R.E., Dozier, J., LaChapelle, E.R., Perla, R., 1985, Field and laboratory measurements of snow liquid water by dilution, Water Resources Research, 21(9): 1415-1420.

Davis, R.E., Dozier, J., Perla, R., 1987, Measurement of snow grain properties, In NATO Advanced Institute on Seasonal Snowcovers: Physics, Chemistry, Hydrology, Les Arcs, France, July 13-25, 1986. Edited by H.G. Jones and W.J. Orville-Thomas. Dordrecht, Holland, D. Reidel Publishing Co., 1987, p.63-74.

Davis, R.E., Dozier, J., Chang, A.T.C., 1987, Snow property measurements correlative to

microwave emission at 35 GHz, IEEE Transactions on Geoscience and Remote Sensing, GE-25(6): 751-757.

Dozier, J., Davis, R.E., Perla, R., 1987, On the objective analysis of snow microstructure, International Association of Hydrological Sciences. IAHS publication No.162, Avalanche formation, movement and effects, Davos Symposium, Sep. 14-19, 1986. Edited by B. Salm and H. Gubler, 49-59.

Davis, R.E., Dozier, J., 1989, Stereological characterization of dry alpine snow for microwave remote sensing, Advances in Space Research, 9(1): 245-251.

Davis, R.E., Nolin, A.W., Jordan, R., Dozier, J., 1993, Towards predicting temporal changes of the spectral signature of snow in visible and near-infrared wavelengths, Annals of Glaciology, 17:143-148.

Davis, R. E., R. Jordan, G. G. Koenig, Snow cover modeling and validation, In: Model Validation in Hydrologic Science, M.G. Anderson and P.D. Bates, Eds., John Wiley and Sons, (in review).

Harrington, R., Bales, R.C., 1998, Interannual, seasonal, and spatial patterns of meltwater and solute fluxes in a seasonal snowpack, Water Resources Research, 34(4): 823-831.

Jordan, R., 1991, A one-dimensional temperature model for a snow cover, technical documentation for SNTHERM.89, Special Report 91-16, U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H.

Kattelmann, R. C., 1997, Snowpack characteristics of an alpine site in the Sierra Nevada, Proceedings of the Western Snow Conference, 65: 363-365.

Nolin, A.W., Dozier, J., 1993, Estimating snow grain size using AVIRIS data, Remote Sensing of Environment, 44(2-3): 231-238.

Nolin, A.W., Dozier, J., Mertes, L.A.K., 1993, Mapping alpine snow using a spectral mixture modeling technique, Annals of Glaciology,.17:121-124.

Painter, T. H., Roberts, D. A., Green, R. O., Dozier, J. 1998, The effect of grain size on spectral mixture analysis of snow-covered area from AVIRIS data, Remote Sensing of Environment, 65: 320-332.

Rosenthal, W., Yankielun, N., Davis, R. E., Alpine snow measurements from aerial FMCW radar, Cold Regions Science and Technology, submitted.