Kinetic Energy Flux Associated with Natural and Simulated Rainfall Events and Instrumentation Used in the Evaluation.

摘要

There have been many studies that focus on the evaluation of the raindrop-size distribution and the parameters that are based upon this distribution, ranging from radar reflectivity to kinetic energy flux at the surface. The main focus of this study was to analyze several naturally occurring and simulated rainfall events using rainfall detection equipment such as a Rain Imaging System and a Parsivel Disdrometer to determine how critical accurate observation of the drop-size distribution is in the assessment of the kinetic energy. Some of the objectives were to evaluate the accuracy of each instrument and, for each event, to determine the total kinetic energy flux at the surface as well as some of the attributes that affect it.;It was found that the moderate to heavy rainfall events maintain a higher kinetic energy flux, while the lighter events tend to maintain much lower fluxes. It was shown that the kinetic energy flux is not solely a function of rainfall rate; rather, it is also largely a function of the drop-size distribution. While analyzing the distributions, it was noticed that events with similar storm structures tended to have very similar drop-size distributions as well as maximum drop sizes. Also discovered in this analysis was that the kinetic energy flux calculated using the rainfall rate, as is used for the RUSLE equation, is a reasonable estimate when compared with the summed kinetic energy flux.;Another finding was that using the Gunn and Kinzer (1949) equation for determining drop-terminal velocity provided an accurate parameterization. This was completed by comparing kinetic energy flux using theoretical-terminal velocity and actual velocity, as measured by the disdrometer. Using rainfall simulators it was possible to compare the simulated distribution to that of the naturally occurring distribution and to calibrate the instrumentation to ensure that accuracy was being achieved; however, it was found that the Rain Imaging System did not perform with satisfactory results. It did appear, however, that the gravity-fed rainfall simulator produced a drop-size distribution that was very similar to the distribution in naturally occurring rainfall events. When using a drop-redistribution screen to obtain the distribution, it was discovered that the screen height above the ground may reduce the drops potential to reach terminal velocity as the drops adhere and then drip from the screen at lower heights causing the kinetic energy flux to be underestimated.