Global Precipitation Measurement Cold Season Precipitation Experiment (GCPEX): For Measurement’s Sake, Let It Snow

Abstract

As a component of Earth’s hydrologic cycle, and especially at higher latitudes, falling snow creates snowpack accumulation that in turn provides a large proportion of the freshwater resources required by many communities throughout the world. To assess the relationships between remotely sensed snow measurements with in situ measurements, a winter field project, termed the Global Precipitation Measurement (GPM) Cold Season Precipitation Experiment (GCPEx), was carried out in the winter of 2011/12 in Ontario, Canada. Its goal was to provide information on the precipitation microphysics and processes associated with cold season precipitation to support GPM snowfall retrieval algorithms that make use of a dual-frequency precipitation radar and a passive microwave imager on board the GPM core satellite and radiometers on constellation member satellites. Multiparameter methods are required to be able to relate changes in the microphysical character of the snow to measureable parameters from which precipitation detection and estimation can be based. The data collection strategy was coordinated, stacked, high-altitude, and in situ cloud aircraft missions with three research aircraft sampling within a broader surface network of five ground sites that in turn were taking in situ and volumetric observations. During the field campaign 25 events were identified and classified according to their varied precipitation type, synoptic context, and precipitation amount. Herein, the GCPEx field campaign is described and three illustrative cases detailed.

Rain or snow: hydrologic processes, observations, prediction, and research needs

“…These are more advanced than the sensors onboard the TRMM spacecraft and permit better quantification of the physical properties of precipitating particles, particularly over land at middle to high latitudes (Hou et al, 2014). Algorithms for the GPM mission are still under development, and are partly being driven by data collected during the GPM Cold-season Experiment (GCPEx) (Skofronick-Jackson et al, 2015). Using airborne sensors to simulate GPM and DPR measurements, one of the questions that the GCPEx hoped to address concerned the potential capability of data from the DPR and GMI to discriminate falling snow from rain or clear air (Skofronick-Jackson et al, 2015).…”

“…Algorithms for the GPM mission are still under development, and are partly being driven by data collected during the GPM Cold-season Experiment (GCPEx) (Skofronick-Jackson et al, 2015). Using airborne sensors to simulate GPM and DPR measurements, one of the questions that the GCPEx hoped to address concerned the potential capability of data from the DPR and GMI to discriminate falling snow from rain or clear air (Skofronick-Jackson et al, 2015). The initial results reported by the GCPEx study echo some of the challenges recognized for ground-based single-polarized radar detection of snowfall.…”

“…The relationship between radar reflectivity and snow-fall is not unique. For the GPM mission, it will be necessary to include more variables from dual-frequency radar measurements, multiple-frequency passive microwave measurements, or a combination of radar and passive microwave measurement (Skofronick-Jackson et al, 2015).…”

“…The recent GPM mission Cold-season Precipitation Experiment (GCPEx) is an example of such a campaign in noncomplex terrain, where simultaneous observations using arrays of both airborne and ground-based sensors were used to measure and characterize both solid and liquid precipitation (e.g., Skofronick-Jackson et al, 2015). Similar intensive field campaigns are needed in complex terrain that is frequently characterized by highly dynamic and spatially variable hydrometeorological conditions.…”

A variational technique to estimate snowfall rate from coincident radar, snowflake, and fall-speed observations

“…These estimates have proven valuable for assessing snowfall budgets in remote regions (Palerme et al, 2014;Kulie et al, 2016), providing data for testing global climate models (Palerme et al, 2016;Christensen et al, 2016), and evaluating the performance of ground-based radar measurements of snowfall (Norin et al, 2015). The Global Precipitation Mission continues the global monitoring of snowfall with dual-frequency Ka-band and Ku-band radar and extensive ground measurement activities (Skofronick-Jackson et al, 2015).…”