Abstract
Raindrop size distributions (DSDs) are the microphysical characteristics of raindrop spectra. Rainfall characterization is important to: (1) provide information on extreme rate, thus, it has an impact on rainfall related hazard; (2) provide data for indirect observation, model and forecast; (3) calibrate and validate the parameters in radar reflectivity-rainfall intensity (Z-R) relationships (quantitative estimate precipitation, QPE) and the mechanism of precipitation erosivity. In this study, the one-year datasets of raindrop spectra were measured by an OTT Parsivel-2 Disdrometer placed in Yulin, Shaanxi Province, China. At the same time, four TE525MM Gauges were also used in the same location to check the disdrometer-measured rainfall data. The theoretical formula of raindrop kinetic energy-rainfall intensity (KE-R) relationships was derived based on the DSDs to characterize the impact of precipitation characteristics and environmental conditions on KE-R relationships in semi-arid areas. In addition, seasonal rainfall intensity curves observed by the disdrometer of the area with application to erosion were characterized and estimated. The results showed that after quality control (QC), the frequencies of raindrop spectra data in different seasons varied, and rainfalls with R within 0.5–5 mm/h accounted for the largest proportion of rainfalls in each season. The parameters in Z-R relationships (Z = aRb) were different for rainfall events of different seasons (a varies from 78.3–119.0, and b from 1.8–2.1), and the calculated KE-R relationships satisfied the form of power function KE = ARm, in which A and m are parameters derived from rainfall shape factor μ. The sensitivity analysis of parameter A with μ demonstrated the applicability of the KE-R formula to different precipitation processes in the Yulin area.
Highlights
Characteristics of precipitation show the impact of meteorological conditions [1], and the measurement of quantitative distribution of precipitation is important for studying the mechanism of global climate and environmental change [2]
The DSDs are of importance to enhance the accuracy of quantitative precipitation estimation (QPE) by weather radar, and raindrop spectra have been used to calculate radar reflectivity factors in many studies [3,4,5,6]
Raindrop spectra can be measured by many methods, e.g., as done by Das et al, Waldvogel et al, Schönhuber et al and Liu et al [3,7,8,9], and these different methods vary in measurement principles and precision of data
Summary
Characteristics of precipitation show the impact of meteorological conditions [1], and the measurement of quantitative distribution of precipitation is important for studying the mechanism of global climate and environmental change [2]. Raindrop size distributions (DSDs) show the microphysical properties of a rainfall event and vary with precipitation both in time and space. Raindrop spectra can be measured by many methods, e.g., as done by Das et al, Waldvogel et al, Schönhuber et al and Liu et al [3,7,8,9], and these different methods vary in measurement principles and precision of data. Liu et al [9] measured the precipitation in Nanjing, China and compared four different methods of rainfall to conclude that the disdrometer and other methods are consistent within the range of medium particle size. Zhang et al [10] used three different methods to analyze the DSD characteristics in Zhuhai, China and found that the disdrometer had limitations in measuring small raindrops when compared to other methods. The study on the seasonal variation of rainfall characteristics in semi-arid areas of China using a raindrop disdrometer is very limited
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