Distributions of Raindrop Sizes and Fall Velocities in a Semiarid Plateau Climate: Convective versus Stratiform Rains

Abstract

Joint size and fall velocity distributions of raindrops were measured with a Particle Size and Velocity (PARSIVEL) precipitation particle disdrometer in a field experiment conducted during July and August 2007 at a semiarid continental site located in Guyuan, Ningxia Province, China (368N, 1068169E). Data from both stratiform and convective clouds are analyzed. Comparison of the observed raindrop size distributions shows that the increase of convective rain rates arises from the increases of both drop concentration and drop diameter while the increase of the rain rate in the stratiform clouds is mainly due to the increase of median and large drop concentration. Another striking contrast between the stratiform and convective rains is that the size distributions from the stratiform (convective) rains tend to narrow (broaden) with increasing rain rates. Statistical analysis of the distribution pattern shows that the observed size distributions from both rain types can be well described by the gamma distribution. Examination of the raindrop fall velocity reveals that the difference in air density leads to a systematic change in the drop fall velocity while organized air motions (updrafts and downdrafts), turbulence, drop breakup, and coalescence likely cause the large spread of drop fall velocity, along with additional systematic deviation from terminal velocity at certain raindrop diameters. Small (large) drops tend to have superterminal (subterminal) velocities statistically, with the positive deviation from the terminal velocity of small drops being much larger than the negative deviation of large drops.

Statistical Characteristics of Raindrop Size Distribution in the Meiyu Season Observed in Eastern China

“…DSD measure-ments carried out around the world show that they vary both spatially and temporally and over a wide range (e.g., Bringi et al 2003;Uijlenhoet et al 2003;Ulbrich and Atlas 2007;Lee et al 2009;Radhakrishna et al 2009;Marzano et al 2010;Niu et al 2010;Thurai et al 2010;Tokay and Bashor 2010;). The differences in DSD characteristics have been found to be associated with precipitation types, atmospheric conditions, and geographical locations or climatic regimes (Rosenfeld and Ulbrich 2003).…”

Quantitative precipitation estimation based on high-resolution numerical weather prediction and data assimilation with WRF – a performance test

“…Germann et al, 2009;Rossa et al, 2009), the investigation of the usefulness of additional observations on the spacetime structure of rainfall (e.g. Lee and Zawadzki, 2005;Lee et al, 2007;Berenguer and Zawadzki, 2008;Niu et al, 2010;Tapiador et al, 2010) and a detailed understanding of radar signals and their interaction with hydrometeors to retrieve their microphysical properties (e.g. Dotzek and Beheng, 2001;Brandes et al, 2004aBrandes et al, , 2004bPeters et al, 2005;Cao et al, 2008).…”

Precipitation Sensitivity to the Mean Radius of Drop Spectra: Comparison of Single- and Double-Moment Bulk Microphysical Schemes

“…In Figure 9, test 1M_10 is characterized by an unrealistic and very low concentration of raindrops [41,42]. The maximum concentrations of rain do not exceed 0.04 m .…”

“…Very low concentrations of raindrops significantly reduced the collection of cloud droplets (Figure 7) leading to a small mass contribution to the further development of the rain field. Other sensitivity tests generated substantially higher rain concentrations, while experiment 1M_30 overestimates the concentration of raindrops by ~60,000 m −3 [42,43]. Niu et al [42] used an observed dataset of raindrops with raindrop number concentration that do not exceed 1500 m .…”