The Evolution of Three-Peak Raindrop Size Distributions in One-Dimensional Shaft Models. Part II: Multiple Pulse Rain

Abstract

The release of multiple pulses of rain with durations of 120 s < T < 600 s and pulse repetition periods of 240 s < &tau < 1200 s at the top of one-dimensional shafts, followed by drop coalescence and breakup during the fall, leads to the arrival of drops in overlapping packages at the ground, with the largest drops first in the individual packages. When the drop spectra are averaged over time, three-peak distributions (3PDs) are found. More frequent and shorter pulses produce 3PDs that resemble three-peak equilibrium distributions (3PED) for steady warm rain closer than less frequent longer pulses because overlapping pulses lead to more interactions between large and small drops. When a 3PED is released at shaft top, it disappears because different size drops fall at different speeds, and then must be recreated by drop interactions. These multiple pulses replicate trends measured during nonsteady tropical rain better than single pulses. A ?pulse interference diameter,? based on the parameterization of single pulse rain, describes how much interaction occurs between pulses.