Abstract
Abstract. It has recently been shown that at high rainfall intensities, small raindrops may fall with much larger velocities than would be expected from their diameters. These were argued to be fragments of recently broken-up larger drops. In this paper we quantify the effect of this phenomenon on raindrop size distribution measurements from a Joss-Waldvogel disdrometer, a 2-D Video Distrometer, and a vertically-pointing Doppler radar. Probability distributions of fall velocities have been parameterized, where the parameters are functions of both rainfall intensity and drop size. These parameterizations have been used to correct Joss-Waldvogel disdrometer measurements for this phenomenon. The effect of these corrections on fitted scaled drop size distributions are apparent but not major. Fitted gamma distributions for three different types of rainfall have been used to simulate drop size measurements. The effect of the high-velocity small drops is shown to be minor. Especially for the purpose of remote sensing of rainfall using radar, microwave links, or optical links, the errors caused by using the slightly different retrieval relations will be masked completely by other error sources.
Highlights
It has recently been shown that in heavy rain, small drops do not all travel at their theoretical terminal fall velocity (Montero-Martınez et al, 2009)
Because the correction scheme depends on the rainfall intensity R, and the corrected drop size distributions (DSDs) will yield a different R than the original, iteration of the method is required
We have fitted lognormal distributions of velocity ratios to the data presented in Fig. 2 of Montero-Martınez et al (2009). The parameters of these distributions depend on both drop size and rainfall intensity
Summary
A recent break-up of a larger drop, which travels at a much greater velocity (e.g. Beard, 1976). Montero-Martınez et al (2009) state in their conclusions that this deviation may have severe effects on drop size distributions (DSDs) derived from Joss-Waldvogel disdrometer (JWD), 2-D Video Distrometer (2DVD), and vertically-pointing Doppler radar measurements, and the subsequently derived radar reflectivity– rainfall intensity relations. We do not focus on the origin of the reported high-velocity raindrops, but we attempt to quantify the severity of the mentioned effects, taking the observations of Montero-Martınez et al (2009) as starting point This will be done by simulating disdrometer measurements using a known drop size distribution, in a manner similar to that of Salles and Creutin (2003). It is necessary to quantify the probability distribution of velocities for a given drop size at a given rainfall intensity To this end, an attempt is made to parameterize the distributions of fall velocities as given by Montero-Martınez et al (2009) in Sect.
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