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The measurement of accurate full drop size distribution (DSD) is critical for its precise modeling and hydrometeorological application. However, its measurement hinders from instrumental limitation. We explored a way of constructing full DSDs by combining the 2D-Video Distrometer (2DVD) and Meteorological Particle Spectrometer (MPS) measurements based on instrumental uncertainty statistics, while other existing methods use a fixed critical diameter and weighting. First, the median relative bias (RB) of number concentration for each diameter between the two distrometers is used to determine the diameter range of their merging. Second, the weighting factors within the range were derived from normalized standard deviations of MPS and 2DVD number concentration by diameter during quasi-homogeneous microphysical process. The accuracy of derived full DSD is verified with the rainfall rate (R) and radar reflectivity (Z) from other independent instruments such as PLUVIO and Precipitation Occurrence Sensor System (POSS) that provide the best possible reference of R and Z. The new method is superior to the existing methods, providing relatively lower error statistics during summer rainfall events in 2022. Additionally, the impact of the new method is analyzed on DSD variability using double-moment scaling normalization to derive a stable generic function. Four different triple-moment normalization methods are also employed to describe the reduction of DSD variability. The results demonstrate that the new full DSD significantly reduces DSD variability and better provides stable generic function of DSDs. 

A method to retrieve the moments of rain drop size distributions (DSDs) from X-band dual-polarimetric radars is tested using data from a warm rain event that occurred near Incheon, Republic of Korea. The method involves the use of attenuation-corrected radar reflectivity ( Zh ) for horizontal polarization, attenuation-corrected differential reflectivity ( Zdr ), and the specific attenuation ( Ah ) for horizontal polarization. The method was previously tested for an event in Greeley, CO, USA, and had resulted in very encouraging results. In this article, we apply the same method to an isolated warm rain cell and examine the height profiles of the retrieved moments. We show that the application of the method results in very plausible results in terms of the dominant microphysical processes associated with warm rain events. 

We examine several different features of DSDs based on data and observations from two mid-latitude coastal locations: (a) the Delmarva peninsula, USA, and (b) Incheon, South Korea. In each case, the full DSD spectra were obtained from two collocated disdrometers. Two events from location (a) and one event from location (b) are presented. For (a), observations and retrievals from NASA’s S-band polarimetric radar are included in the analyses as well as retrieved DSD parameters from the dual-wavelength precipitation radar onboard the Global Precipitation Measurement satellite. For (b), the disdrometer-based DSD data are compared with measurements from another sensor. Our main aim is to examine the underlying shape of the DSDs and their representation by the generalized gamma model. 

The raindrop size distribution (DSD) is vital for applications such as quantitative precipitation estimation, understanding microphysical processes, and validation/improvement of two-moment bulk microphysical schemes. We trace the history of the DSD representation and its linkage to polarimetric radar observables from functional forms (exponential, gamma, and generalized gamma models) and its normalization (un-normalized, single/double-moment scaling normalized). The four-parameter generalized gamma model is a good candidate for the optimal representation of the DSD variability. A radar-based disdrometer was found to describe the five archetypical shapes (from Montreal, Canada) consisting of drizzle, the larger precipitation drops and the ‘S’-shaped curvature that occurs frequently in between the drizzle and the larger-sized precipitation. Similar ‘S’-shaped DSDs were reproduced by combining the disdrometric measurements of small-sized drops from an optical array probe and large-sized drops from 2DVD. A unified theory based on the double-moment scaling normalization is described. The theory assumes the multiple power law among moments and DSDs are scaling normalized by the two characteristic parameters which are expressed as a combination of any two moments. The normalized DSDs are remarkably stable. Thus, the mean underlying shape is fitted to the generalized gamma model from which the ‘optimized’ two shape parameters are obtained. The other moments of the distribution are obtained as the product of power laws of the reference moments M3 and M6 along with the two shape parameters. These reference moments can be from dual-polarimetric measurements: M6 from the attenuation-corrected reflectivity and M3 from attenuation-corrected differential reflectivity and the specific differential propagation phase. Thus, all the moments of the distribution can be calculated, and the microphysical evolution of the DSD can be inferred. This is one of the major findings of this article.