Measurements and Modeling of the Full Rain Drop Size Distribution

Abstract

The raindrop size distribution (DSD) is fundamental for quantitative precipitation estimation (QPE) and in numerical modeling of microphysical processes. Conventional disdrometers cannot capture the small drop end, in particular the drizzle mode which controls collisional processes as well as evaporation. To overcome this limitation, the DSD measurements were made using (i) a high-resolution (50 microns) meteorological particle spectrometer to capture the small drop end, and (ii) a 2D video disdrometer for larger drops. Measurements were made in two climatically different regions, namely Greeley, Colorado, and Huntsville, Alabama. To model the DSDs, a formulation based on (a) double-moment normalization and (b) the generalized gamma (GG) model to describe the generic shape with two shape parameters was used. A total of 4550 three-minute DSDs were used to assess the size-resolved fidelity of this model by direct comparison with the measurements demonstrating the suitability of the GG distribution. The shape stability of the normalized DSD was demonstrated across different rain types and intensities. Finally, for a tropical storm case, the co-variabilities of the two main DSD parameters (normalized intercept and mass-weighted mean diameter) were compared with those derived from the dual-frequency precipitation radar onboard the global precipitation mission satellite.

The Latitudinal Variability of Oceanic Rainfall Properties and Its Implication for Satellite Retrievals: 1. Drop Size Distribution Properties

“…The latitudinal variability of the σ m -D m and R-D m relationships were found to be large, especially for D m > 1.5 mm. Interestingly, our σ m -D m distribution derived from all oceanic DSDs from all latitudes was found to be very similar to that derived from a recent analysis of continental DSDs (Thurai et al, 2019), suggesting that land/ocean differences in DSDs might not translate into an large impact on this distribution. In particular, the R-D m relationships obtained in the S-highlat and N-polar bands clearly stood out as very different from the mean R-D m relationship when data from all latitudes are included, from the currently assumed GPM relationships, and from the relationships obtained in other latitude bands.…”

“…As can be seen in Figure 9a, the W14 relationship falls very close to the lower bound σ m -D m relationship derived in our study. The exact same conclusion was also recently reached in a detailed analysis of a 12,177 1-min continental DSD data set (Thurai et al, (Figure 6 in Thurai et al, 2019) is also remarkably similar to that of Figure 9a.…”

Effect of disdrometer type on rain drop size distribution characterisation: a new dataset for south-eastern Australia

“…The first two bin sizes for particle diameters (0-0.125 and 0.125-0.250) are systematically left empty. More details on the measurement procedure are described in Battaglia et al (2010), Jaffrain et al (2011), Tokay et al (2013) and Angulo-Martinez et al (2018). It is worth noting that a new version of the instrument was released by OTT in 2011 (Parsivel 2 ), which incorporates some modifications from the version described herein , including sensitivity to drop sizes in the lower and upper ranges.…”

“…First a series of filtering procedures was applied: (i) data corresponding to error flags were discarded; (ii) only data corresponding to WMO synoptic weather codes 4677 and 4680 for rainfall (drizzle, rain) were retained; (iii) following Jaffrain and Berne (2011), PSVD data needed to fall between ±50 % of the Atlas et al (1973) drop velocity model to be retained. For the Thies LPM instruments, the upper bin classes for velocities (> 10 m s −1 ) have no upper limit, but these data were retained; (iv) minute data must meet the occurrence of more than 10 particles in three different bins Tokay et al, 2013); (v) only rainfall rates > 0.1 mm h −1 were considered for further analysis; and (vi) contrary to Angulo-Martinez et al (2018), the first bin diameter size for the LPM was used as, ultimately, users of this instrument will consider all available data to derive integrated DSD variables. The postprocessed data following these sequential steps are further described as "quality" data.…”

Large Sample Comparison of Parameter Estimates in Gamma Raindrop Distributions

“…While not yet widely available, the technology to measure drop size quite accurately across nearly the full drop size 2 of 11 spectrum is now available and will continue to improve over time. Presently, meteorological particle spectrometers may be used to measure small drop size (100 microns to 1.5 mm) with a resolution of 50 microns [15]. Additionally, third generation 2D-video disdrometers may be used to measure larger drops (0.7 mm and larger) with a resolution of 170 microns [15,16].…”