称重与人工观测降水量的差异

为了更好地使用降水观测数据，对引起称重观测和人工观测的差异原因进行分析，选取北京市15个国家级地面观测站2012年11月—2014年1月称重式降水传感器与人工观测降水量业务资料，探讨称重观测与人工观测累积降水量的差异，并细化为对固态降水和液态降水两种降水类型进行相关性研究。结果表明:称重观测与人工观测日降水量相关系数为0.9990, 88.0%的对比次数中, 两者日降水量差值满足业务要求；在出现固态降水时，称重观测较人工观测降水量偏大，在出现液态降水时，称重观测较人工观测降水量偏小；两者在日降水量等级判断差异较小，小量降水时称重观测的能力较优；防风圈可显著提高称重观测固态降水的捕捉率，而称重观测内筒蒸发对夏季降水测量有一定影响。

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.