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Building on the results and recommendations of previous inter-comparisons, the WMO Solid Precipitation Intercomparison Experiment (WMO-SPICE) will focus on the performance of modern automated sensors measuring solid precipitation. The WMO-SPICE will investigate and report the measurement and reporting of the following parameters:
  • a) Precipitation amount, precipitation intensity, and precipitation type (liquid, solid, mixed), over various time periods (minutes, hours, days, season);
  • b) Snow on the ground (snow depth); as snow depth measurements are closely tied to snowfall measurements, the intercomparison will address the linkages between them.

As a key outcome, recommendations will be made to the WMO Members, WMO programmes, manufacturers and the scientific community, on the ability to accurately measure solid precipitation, on the use of automatic instruments, and the improvements possible. The results of the experiment will inform those Members that wish to automate their manual observations.

While spatial measurements and global coverage are part of the observation considerations, these issues are beyond the scope of this intercomparison and while important, it must be addressed in other ways. However, the results of this intercomparison will contribute to improved spatial and temporal estimates of precipitation.

Solid precipitation is one of the more complex parameters to be observed and measured by automatic sensors. The measurement of precipitation has been the subject of a multitude of studies, but there have been limited coordinated assessments of the ability and reliability of automatic sensors to accurately measure solid precipitation. The WMO Solid Precipitation Measurement Inter-comparison" - Final Report B.E. Goodison (Canada), P.Y.T. Louie (Canada) and D. Yang (China), 1998, focused on the instruments in use in national networks at the time of the intercomparison, primarily manual methods of observation. The assessment of automatic sensors/systems for snow depth and snowfall measurement was not a central part of the study, and no intercomparison stations were included in the Arctic or Antarctic.

Since then, an increasing percentage of precipitation data used in a variety of applications have been obtained using automatic instruments and stations, including the measurement of snow depth, and many new applications (e.g., climate change, nowcasting, water supply, complex terrain, avalanche warnings, etc) have emerged. At the same time, many of the new techniques used for the measurement of solid precipitation are of non-catchment type, e.g. light scattering, microwave backscatter, mass and heat transfer, etc.

Additionally, during the development of proposals for satellite sensors to measure solid precipitation, the issue of validation and calibration of such products using in-situ measurements (network or reference stations) identified the availability of reliable measurements of solid precipitation at automatic stations as a key input in assessing measurements in cold climates.

The modern data processing capabilities, data management and data assimilation techniques provide the means for better assessment and error analysis.

Snow Gauge and wind shield.

Double Alter Shield.

DFIR Shield.