Characteristics of the raindrop distributions in RICO shallow cumulus

The physical properties of rain spectra are generally modeled using analytical distribution, commonly the Gamma law and to a lesser extent the Lognormal law. The majority of studies of the literature focusing on the characterization of rain distribution are based on deep convective cloud observations, mostly at ground level. This study focuses on shallow cumulus rain distribution at every level in the cloudy boundary layer using airborne in situ measurements made with both the PMS-OAP-260X and the PMS-2DP instruments during the RICO field experiment. Sampled spectra analyzed at the scale of LES resolution (100 m) are found to be relatively broad, with values of the shape parameter – υ for the Gamma law and σg for the Lognormal law, respectively – of the order of 1–3 and 1.5–2. The dependence of the shape parameters on the rain variable is examined, and a parameterization of the shape parameters υ and σg in function of a power law of the rainwater content and raindrop number concentration is proposed.