Abstract
Abstract. The World Meteorological Organization (WMO) Solid Precipitation Intercomparison Experiment (SPICE) involved extensive field intercomparisons of automated instruments for measuring snow during the 2013/2014 and 2014/2015 winter seasons. A key outcome of SPICE was the development of transfer functions for the wind bias adjustment of solid precipitation measurements using various precipitation gauge and wind shield configurations. Due to the short intercomparison period, the data set was not sufficiently large to develop and evaluate transfer functions using independent precipitation measurements, although on average the adjustments were effective at reducing the bias in unshielded gauges from −33.4 % to 1.1 %. The present analysis uses data collected at eight SPICE sites over the 2015/2016 and 2016/2017 winter periods, comparing 30 min adjusted and unadjusted measurements from Geonor T-200B3 and OTT Pluvio2 precipitation gauges in different shield configurations to the WMO Double Fence Automated Reference (DFAR) for the evaluation of the transfer function. Performance is assessed in terms of relative total catch (RTC), root mean square error (RMSE), Pearson correlation (r), and percentage of events (PEs) within 0.1 mm of the DFAR. Metrics are reported for combined precipitation types and for snow only. The evaluation shows that the performance varies substantially by site. Adjusted RTC varies from 54 % to 123 %, RMSE from 0.07 to 0.38 mm, r from 0.28 to 0.94, and PEs from 37 % to 84 %, depending on precipitation phase, site, and gauge configuration (gauge and wind screen type). Generally, windier sites, such as Haukeliseter (Norway) and Bratt's Lake (Canada), exhibit a net under-adjustment (RTC of 54 % to 83 %), while the less windy sites, such as Sodankylä (Finland) and Caribou Creek (Canada), exhibit a net over-adjustment (RTC of 102 % to 123 %). Although the application of transfer functions is necessary to mitigate wind bias in solid precipitation measurements, especially at windy sites and for unshielded gauges, the variability in the performance metrics among sites suggests that the functions be applied with caution.
Highlights
The World Meteorological Organization (WMO) Solid Precipitation Intercomparison Experiment (SPICE) was a Commission for Instruments and Methods of Observation (CIMO) initiative to assess and compare instruments and methods for measuring solid precipitation (Nitu et al, 2012, 2018)
The impact and the performance of transfer functions used for adjusting precipitation can be examined by comparing the accumulation time series for unadjusted and adjusted data to the reference
Where more than one gauge with the same shield configuration was present at a site, and where more than one wind speed height was available, results for only one gauge and wind speed height were selected for illustrative purposes
Summary
The World Meteorological Organization (WMO) Solid Precipitation Intercomparison Experiment (SPICE) was a Commission for Instruments and Methods of Observation (CIMO) initiative to assess and compare instruments and methods for measuring solid precipitation (Nitu et al, 2012, 2018). SPICE was motivated by the need for accurate and homogenized solid precipitation measurements. Such measurements are required for climate trend analysis in northern regions (e.g. Førland and Hanssen-Bauer, 2000; Yang and Ohata, 2001, Scaff et al, 2015). Following historical works on adjusting the systematic undercatch of solid precipitation measurements due to wind (Goodison, 1978; Sevruk et al, 1991, 2009; Goodison et al, 1998; Smith, 2009; Wolff et al, 2015; Kochendorfer et al, 2017a; Buisán et al, 2017), a methodology and a set of widely applicable transfer functions for the adjustment of high-resolution (i.e. 30 min) precipitation measurements was developed. Because of the symbioses between the Kochendorfer et al (2017b) SPICE work and this evaluation, the SPICE methodology is described below in more detail and referred to as K2017b
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