Adjusting precipitation amounts from Geonor and Pluvio automated weighing gauges to preserve continuity of observations in Canada

Abstract

Since the early 2000s, the Geonor and Pluvio automated weighing gauges have been part of the standard configuration of climate monitoring Reference Climate Stations (RCS) and the Meteorological Service of Canada Surface Weather and Climate Network (MSC SWCN). To more closely reflect true precipitation amounts, 15-minute observations from 312 Geonor and 34 Pluvio gauges were used to recover small amounts of 0.2 mm or less that were inadvertently filtered from 2002 until December 2013 by the hourly data-archiving CODECON algorithm. The precipitation data were quality controlled to remove spurious outliers and new derived hourly amounts were adjusted for wind undercatch according to the hourly 10-m wind speed, and dry bulb temperature. The recovered small amounts averaged for each month at individual stations were up to 16 mm in January, 10 mm in April, 8 mm in July, and 11 mm in October. The medians of average monthly adjustments for the wind undercatch were 74%, 38%, less than 1%, and 7% of the unadjusted amounts for January, April, July and October, respectively. Preliminary comparison of the monthly total precipitation amounts from parallel-adjusted automated and manual observations at 59 sites showed monthly amounts from the automated gauges generally higher during cold months in the Prairies and the North. Occasional large outliers in adjusted amounts at coastal stations in Newfoundland and Labrador and Quebec, and in the Prairies in winds greater than 9 m s⁻¹, suggest that the measured amounts were possibly already augmented by blowing snow. Further research is needed to determine how to adjust precipitation during very windy snowstorms. The adjusted hourly data sets were aggregated into the daily and monthly amounts for the climatological day ending at 06 GMT and 07 LST for compatibility with the two major observing programs at the principal aviation and cooperative networks.

Keywords:

• Precipitation observations
• automated weighing gauges
• Geonor and Pluvio
• wind undercatch adjustment
• transfer functions

Acknowledgements

The authors would like thank the internal reviewers C. Smith, D. Yang, X. Wang (Science & Technology, ECCC) and two anonymous reviewers for their helpful comments, and to acknowledge contributions about climate observation archiving procedures and automated gauge characteristics from the MSC scientists D. Halliwell, C. Paterson, D. Boudreau, G. Tsim, A. Shabbar, C. Hampel, L. Cudlip, M. Elie, J. Sowiak, M. Shephard and P. Wong.

Disclosure statement

No potential conflict of interest was reported by the authors.