Comparative Analysis of Precipitation Between Weighing Gauge and Manual Gauge

Precipitation data play an important role in meteorological observation and relative applications. In order to accelerate CMA meteorological modernization, nearly 1000 weighing gauges are put into use in relative quantities national meteorological stations as an alternative observation device different from manual gauge for precipitation. Although field intercomparison experiments are carried out before the usage of weighing guage, there still exist some doubts on this kind of instrument, particularly in liquid precipitation measurements.
    Based on 1064 groups of precipitation data observed by weighing gauge and manual gauge at 15 national meteorological stations in Beijing during November 2012 to January 2014, several analyses are carried out to find out differences between two precipitation observation methods. 1064 precipitation processes include 253 snowfalls or sleets and 811 rainfalls. The error of accumulated precipitation for 14 stations meets requirements of operation. Also, the deviation of quantitative precipitation value obtained by weighing gauge and manual gauge also is within the margin of error, with 88.0% coverage rate of analyzed precipitation. In terms of the comparison, the average daily precipitation observed by weighing gauge is 0.04 mm smaller, and the RMSE (root mean square error) is 0.54 mm. Corresponding to different precipitation patterns, results make difference. For snowfall measurement, the quantitative value of precipitation obtained by manual gauge is 0.12 mm smaller and the RMSE is 0.51 mm. But for rainfall measurement, the quantitative value of precipitation obtained by manual gauge is 0.19 mm larger and the RMSE is 0.64 mm. For each significant precipitation process, the judgment of precipitation grade with weighing gauge and manual gauges is very close. But, more light rain phenomena can be detected by weighing gauge, typically when the quantitative value of daily precipitation is under 0.2 mm. The weighing gauge is shielded with Tretyakov wind shield, while manual gauge is unshielded. Results show that weighing gauge could capture more precipitation than manual gauge for solid precipitation, while effects of Tretyakov wind shield are not significant for liquid precipitation. Also, it's found that evaporation from the container of weighing gauge could reduce the precipitation of rainfall. The daily precipitation between weighing gauge and manual gauge is obviously linearly related with the correlation coefficient of 0.9990. In detail, the correlation coefficient is 0.9984 for solid precipitation and 0.9992 for liquid precipitation, respectively.
    In general, weighing gauge is satisfactory for measuring all kinds of precipitation, showing considerable advantages over manual gauge when measuring snowfall, and it can minimize some potential errors in manual methods of precipitation measurement.