Variability of rainfall rate and raindrop size distributions in heavy rain

Abstract

[1] A stochastic model of rainfall rate is used to examine the temporal variability of rainfall during heavy convective rain periods. The model represents the microstructure of rainfall rate at time scales that are important for land surface processes associated with infiltration and runoff production. The representation of rainfall rate is based on a marked point process model of raindrop size distributions, which yields a gamma raindrop spectrum with parameters that are time-varying stochastic processes. Raindrop size distribution observations from a Joss-Waldvogel disdrometer in Princeton, New Jersey, during the period May-October 2006 are used along with the stochastic model to examine rainfall rate variability. Analyses focus on a sample of 60-min time periods in which heavy convective rainfall occurred. Central elements of the analyses entail examination of the relationships between rainfall rate and the time-varying model parameters that characterize the raindrop size distribution. We also examine the dependence structure among these processes. ''Scaling law'' formulations of raindrop size distributions are used to examine variability of raindrop size distributions. Analyses of the Princeton heavy rainfall periods also point to seasonal and diurnal heterogeneities as important elements of the distribution of extreme rainfall rates. Convective intensity, as reflected in cloud-to-ground lightning observations, plays an important role in the distribution of extreme rainfall rates and the evolution of raindrop size distributions associated with heavy rainfall.

Extending the life of wind turbine blade leading edges by reducing the tip speed during extreme precipitation events

“…For a convective rain event the rain intensity at 1 minute intervals can be more than 10 times the intensity measured at 60 minutes intervals. Based on disdrometer observation during thunderstorms in New Jersey, USA, it was shown that raindrop size distribution and rainfall intensity in heavy rain can be 15 described from a Gamma distribution (Smith et al, 2009). Similar results are found in tropical rainfall during the monsoon season in Malaysia (Hong et al, 2015).…”

Drop size distributions and kinetic energy rates in variable intensity rainfall

“…As an illustration (Figure 1), a convective storm of 30 min during the rainy season of summer 2006 at Princeton, New Jersey, was characterized by rainfall intensities ranging from 0 to 120 mm/h [Smith et al, 2009]. For that event, 40% of the total rainfall amount was delivered in a short period of 7 min of intense rain (between the 20th to the 27th min).…”

“…These data sets regroup information from several storms, measured at different periods and at various temporal resolutions, and using different methods and devices. For the first time, the study of Smith et al [2009] provided data on temporal variability of rainfall intensity and the corresponding DSDs at 1-min intervals, at both the seasonal and the single-storm scale at the same location. This offered the opportunity to look into the nature of the relationship between convective rainfall characteristics at these two interesting scales at a given location and during the same season.…”

“…Different appropriate mathematical models are applied to describe the DSD in terms of probability density functions: lognormal distribution [Park et al, 1983;Feingold and Levin, 1986;Quimpo and Brohi, 1986], gamma function [Takeuchi, 1978;Ulbrich, 1983;Willis, 1984;Narayana Rao et al, 2006;Smith et al, 2009], and Weibull distribution [Best, 1950b;Mualem and Assouline, 1986;Assouline and Mualem, 1989]. The Weibull distribution in the study of Assouline and Mualem [1989] was derived from a ''uniform random fragmentation'' model [Tenchov and Yanev, 1986] assuming that the probability for a drop breakup is proportional to its volume, as suggested by the experimental results of Low and List [1982].…”

“…Temporal variability in rainfall intensity is reflected in the DSD and affects the rainfall kinetic energy during the event. Smith et al (2009) reported on 1-min interval rainfall intensity and corresponding DSD variability during a storm on 22 July 2006 at Princeton, New Jersey. They reported also on DSD characteristics of heavy convective rainfall events during the whole summer.…”