scholarly journals On the Influence of Raindrop Collision Outcomes on Equilibrium Drop Size Distributions

2012 ◽  
Vol 69 (5) ◽  
pp. 1534-1546 ◽  
Author(s):  
Olivier P. Prat ◽  
Ana P. Barros ◽  
Firat Y. Testik
Keyword(s):  
Drop Size ◽  
Number Concentration ◽  
Drop Diameter ◽  
Size Distributions ◽  
Left Hand ◽  
Dynamical Simulation ◽  
Drop Number ◽  
Raindrop Size ◽  
Drop Size Distributions ◽  
The Impact

Abstract The objective of this study is to evaluate the impact of a new parameterization of drop–drop collision outcomes based on the relationship between Weber number and drop diameter ratios on the dynamical simulation of raindrop size distributions. Results of the simulations with the new parameterization are compared with those of the classical parameterizations. Comparison with previous results indicates on average an increase of 70% in the drop number concentration and a 15% decrease in rain intensity for the equilibrium drop size distribution (DSD). Furthermore, the drop bounce process is parameterized as a function of drop size based on laboratory experiments for the first time in a microphysical model. Numerical results indicate that drop bounce has a strong influence on the equilibrium DSD, in particular for very small drops (<0.5 mm), leading to an increase of up to 150% in the small drop number concentration (left-hand side of the DSD) when compared to previous modeling results without accounting for bounce effects.

scholarly journals On the Shape–Slope Relation of Drop Size Distributions in Convective Rain

2005 ◽  
Vol 44 (7) ◽  
pp. 1146-1151 ◽  
Author(s):  
Axel Seifert
Keyword(s):  
Size Distribution ◽  
Gamma Distribution ◽  
Drop Size ◽  
Empirical Relation ◽  
Size Distributions ◽  
Shape Parameters ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Drop Size Distributions ◽  
Good Agreement

Abstract The relation between the slope and shape parameters of the raindrop size distribution parameterized by a gamma distribution is examined. The comparison of results of a simple rain shaft model with an empirical relation based on disdrometer measurements at the surface shows very good agreement, but a more detailed discussion reveals some difficulties—for example, deviations from the gamma shape and the overestimation of collisional breakup.

scholarly journals On the Variability of Drop Size Distributions over Areas

2015 ◽  
Vol 72 (4) ◽  
pp. 1386-1397 ◽  
Author(s):  
A. R. Jameson ◽  
M. L. Larsen ◽  
A. B. Kostinski
Keyword(s):  
Drop Size ◽  
Network Size ◽  
Drop Diameter ◽  
Size Distributions ◽  
Physical Explanation ◽  
Spatial Correlation Function ◽  
Drop Size Distributions ◽  
The Fourier Transform ◽  
D Values ◽  
Physical Reasons

Abstract Past studies of the variability of drop size distributions (DSDs) have used moments of the distribution such as the mass-weighted mean drop size as proxies for the entire size distribution. In this study, however, the authors separate the total number of drops Nt from the DSD leaving the probability size distributions (PSDs); that is, DSD = Nt × PSD. The variability of the PSDs are then considered using the frequencies of size [P(D)] values at each different drop diameter P(PD | D) over an ensemble of observations collected using a network of 21 optical disdrometers. The relative dispersions RD of P(PD | D) over all the drop diameters are used as a measure of PSD variability. An intrinsic PSD is defined as an average over one or more instruments excluding zero drop counts. It is found that variability associated with an intrinsic PSD fails to characterize its true variability over an area. It is also shown that this variability is not due to sampling limitations but rather originates for physical reasons. Furthermore, this variability increases with the expansion of the network size and with increasing drop diameter. A physical explanation is that the network acts to integrate the Fourier transform of the spatial correlation function from smaller toward larger wavelengths as the network size increases so that the contributions to the variance by all spatial wavelengths being sampled also increases. Consequently, RD and, hence, PSD variability will increase as the size of the area increases.

Effect of Dispersed Phase Viscosity on Emulsification in Turbulence Flow

2013 ◽  
Vol 446-447 ◽  
pp. 571-575 ◽  
Author(s):  
Chen Wei Liu ◽  
Ming Zhong Li
Keyword(s):  
Experimental Study ◽  
Drop Size ◽  
Dispersed Phase ◽  
Drop Diameter ◽  
Volume Distribution ◽  
Size Distributions ◽  
Sauter Mean Diameter ◽  
Turbulence Flow ◽  
Mean Diameter ◽  
Drop Size Distributions

Systematic experimental study has been performed to examine the effects of dispersed phase viscosity on emulsification in turbulence flow. It is found that the volume drop size distributions widen as dispersed phase viscosity increased; at lower dispersed phase viscosity, both Sauter mean diameter and the maximum stable diameter increase with the viscosity, while at higher dispersed phase viscosity, Sauter mean diameter and the maximum stable diameter decreasing and increasing, respectively. It has also been found that linear relation between the Sauter mean diameter and the maximum stable drop diameter is still valid for the emulsions which show a bimodal volume distribution, and the proportional constant decreases as dispersed phase viscosity increases.

scholarly journals Retrieval of Arbitrarily Shaped Raindrop Size Distributions from Wind Profiler Measurements

2005 ◽  
Vol 22 (4) ◽  
pp. 433-442 ◽  
Author(s):  
Takahisa Kobayashi ◽  
Ahoro Adachi
Keyword(s):  
Drop Size ◽  
Large Data ◽  
Doppler Spectrum ◽  
Wind Profiler ◽  
Size Distributions ◽  
Vertical Profiles ◽  
Large Variability ◽  
Median Volume ◽  
Raindrop Size ◽  
Drop Size Distributions

Abstract An efficient iterative retrieval method for arbitrarily shaped raindrop size distributions (ITRAN) is developed for Doppler spectra measured with a wind profiler. A measured Doppler spectrum is a convolution of the precipitation spectrum and the turbulent spectrum. Deconvolution of the Doppler spectra is achieved through repeated convolutions. The developed method assumes no prior shape of drop size distributions and automatically obtains raindrop size distributions; additionally, it can be applied to large data volumes. Furthermore, it is insensitive to initial values. The method was applied to both simulated and observed spectra. Derived drop size distributions agree with simulated values. Narrower turbulent spectral widths yield better results. Integral values of median volume diameter (D0), liquid water content (LWC), and radar reflectivity factor are estimated with errors of less than 10%. Accurate vertical profiles of raindrop size distributions result when this method is applied to wind profiler data. The technique performed very well with most observed spectra. Some recovered spectra departed from the corresponding measured spectra, for cases in which a clear-air peak could not be accurately reproduced because of uncertainties in the location of the minimum position between the clear-air echo and the precipitation echo. Statistical relationships between LWC and integral rainfall parameters yield interesting features. The median volume diameter is statistically independent of the LWC and is associated with the large variability of the total number of drops, NT, between events. Vertical profiles from one event show a clear inverse relationship between NT and D0

Examination of the μ–Λ Relation Suggested for Drop Size Distribution Parameters

2007 ◽  
Vol 24 (5) ◽  
pp. 847-855 ◽  
Author(s):  
Dmitri N. Moisseev ◽  
V. Chandrasekar
Keyword(s):  
Gamma Distribution ◽  
Method Of Moments ◽  
Drop Size ◽  
Size Distributions ◽  
Data Filtering ◽  
Wide Range ◽  
Distribution Parameters ◽  
Raindrop Size ◽  
Drop Size Distributions ◽  
Physical Correlations

Abstract Raindrop size distributions are often assumed to follow a three-parameter gamma distribution. Since rain intensity retrieval from radar observations is an underdetermined problem, there is great interest in finding physical correlations between the parameters of the gamma distribution. One of the more common approaches is to measure naturally occurring drop size distributions (DSDs) using a disdrometer and to find DSD parameters by fitting a gamma distribution to these observations. Often the method of moments is used to retrieve the parameters of a gamma distribution from disdrometer observations. In this work the effect of the method of moments and data filtering on the relation between the parameters of the DSD is investigated, namely, the shape μ and the slope Λ parameters. For this study the disdrometer observations were simulated. In these simulations the gamma distribution parameters Nw, D0, and μ were randomly selected from a wide range of values that are found in rainfall. Then, using simulated disdrometer measurements, DSD parameters were estimated using the method of moments. It is shown that the statistical errors associated with data filtering of disdrometer measurements might produce a spurious relation between μ and Λ parameters. It is also shown that three independent disdrometer measurements can be used to verify the existence of such a relation.

Observed Bulk Hook Echo Drop Size Distribution Evolution in Supercell Tornadogenesis and Tornadogenesis Failure

2021 ◽  
Author(s):  
Kristofer S. Tuftedal ◽  
Michael M. French ◽  
Darrel M. Kingfield ◽  
Jeffrey C. Snyder
Keyword(s):  
Drop Size ◽  
Thermodynamic Characteristics ◽  
Radar Data ◽  
Number Concentration ◽  
Size Distributions ◽  
Polarimetric Radar ◽  
Dual Polarization ◽  
Near Surface ◽  
Microphysical Processes ◽  
Drop Size Distributions

AbstractThe time preceding supercell tornadogenesis and tornadogenesis “failure” has been studied extensively to identify differing attributes related to tornado production or lack thereof. Studies from the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX) found that air in the rear-flank downdraft (RFD) regions of non- and weakly tornadic supercells had different near-surface thermodynamic characteristics than that in strongly tornadic supercells. Subsequently, it was proposed that microphysical processes are likely to have an impact on the resulting thermodynamics of the near-surface RFD region. One way to view proxies to microphysical features, namely drop size distributions (DSDs), is through use of polarimetric radar data. Studies from the second VORTEX used data from dual-polarization radars to provide evidence of different DSDs in the hook echoes of tornadic and non-tornadic supercells. However, radar-based studies during these projects were limited to a small number of cases preventing result generalizations. This study compiles 68 tornadic and 62 non-tornadic supercells using Weather Surveillance Radar–1988 Doppler (WSR-88D) data to analyze changes in polarimetric radar variables leading up to, and at, tornadogenesis and tornadogenesis failure. Case types generally did not show notable hook echo differences in variables between sets, but did show spatial hook echo quadrant DSD differences. Consistent with past studies, differential radar reflectivity factor (ZDR) generally decreased leading up to tornadogenesis and tornadogenesis failure; in both sets, estimated total number concentration increased during the same times. Relationships between DSDs and the near-storm environment, and implications of results for nowcasting tornadogenesis, also are discussed.

The impact of multi-frequency and forced disturbances upon drop size distributions in prilling

2010 ◽  
Vol 65 (11) ◽  
pp. 3474-3484 ◽  
Author(s):  
C.J. Gurney ◽  
M.J.H. Simmons ◽  
V.L. Hawkins ◽  
S.P. Decent
Keyword(s):  
Drop Size ◽  
Size Distributions ◽  
Drop Size Distributions ◽  
The Impact

Quantitative Evaluation of Polarimetric Estimates from Scanning Weather Radars using a Vertically Pointing Micro Rain Radar

2020 ◽  
Author(s):  
Ricardo Reinoso-Rondinel ◽  
Marc Schleiss
Keyword(s):  
Drop Size ◽  
Limited Attention ◽  
Size Distributions ◽  
Weather Radars ◽  
X Band ◽  
Microphysical Processes ◽  
Drop Size Distributions ◽  
Differential Reflectivity ◽  
The Impact ◽  
Rain Radar

AbstractConventionally, micro rain radars (MRRs) have been used as a tool to calibrate reflectivity from weather radars, estimate the relation between rainfall rate and reflectivity, and study microphysical processes in precipitation. However, limited attention has been given to the reliability of the retrieved drop size distributions DSDs from MRRs. This study sheds more light on this aspect by examining the sensitivity of retrieved DSDs to the assumptions made to map Doppler spectra into size distributions, and investigates the capability of an MRR to assess polarimetric observations from operational weather radars. For that, an MRR was installed near the Cabauw observatory in the Netherlands, between the IDRA X-band radar and the Herwijnen operational C-band radar. The measurements of the MRR from November 2018 to February 2019 were used to retrieve DSDs and simulate horizontal reflectivity Ze, differential reflectivity ZDR, and specific differential phase KDP in rain. Attention is given to the impact of aliased spectra and right-hand side truncation on the simulation of polarimetric variables. From a quantitative assessment, the correlations of Ze and ZDR between the MRR and Herwijnen radar were 0.93 and 0.70, respectively, while those between the MRR and IDRA were 0.91 and 0.69. However, Ze and ZDR from the Herwijnen radar showed slight biases of 1.07 and 0.25 dB. For IDRA, the corresponding biases were 2.67 and -0.93 dB. Our results show that MRR measurements are advantageous to inspect the calibration of scanning radars and validate polarimetric estimates in rain, provided that the DSDs are correctly retrieved and controlled for quality assurance.

Controls on the space-time variability of raindrop size distributions

2021 ◽  
Author(s):  
Remko Uijlenhoet
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Space Time ◽  
Drop Size Distribution ◽  
Time Variability ◽  
Statistical Interpretation ◽  
Size Distributions ◽  
Scaling Exponents ◽  
Raindrop Size ◽  
Drop Size Distributions

<p>It has been stated that "the study of drop-size distributions, with its roots in both land-surface processes [e.g. interception, erosion, infiltration and surface runoff] and atmospheric remote sensing [e.g. radar meteorology], provides an important element to an integrated program of hydrometeorological research" (Smith, 1993). Although raindrop size distributions have been studied from a scientific perspective since the early 20th century, it was not until the mid-1990s that researchers realized that all parameterizations for the drop size distribution published until then could be summarized in the form of a scaling law, which provided "a general phenomenological formulation for drop size distribution" (Sempere Torres et al., 1994). The main implication of the proposed expression is that the integral rainfall variables (such as rain rate and radar reflectivity) are related by power laws, in agreement with experimental evidence. The proposed formulation naturally leads to a general methodology for scaling all raindrop size data in a unique plot, which yields more robust fits of the drop size distribution. Here, we provide a statistical interpretation of the law’s scaling exponents in terms of different modes of control on the space-time variability of drop size distributions, namely size-control vs. number-control, inspired by the work of Smith and De Veaux (1994). Also, an attempt will be made toward interpreting the values of the scaling exponents and the shape of the scaled drop size distribution in terms of the underlying (micro)physical processes.</p><p>REFERENCES</p><p>Smith, J. A., 1993: Precipitation. In Maidment, D. R., editor, Handbook of Hydrology, pages 3.1–3.47. McGraw-Hill, New York.</p><p>Sempere Torres, D., J.M. Porrà, and J.-D. Creutin, 1994: A general formulation for raindrop size distribution. J. Appl. Meteor., 33, 1494–1502.</p><p>Smith, J.A. and R.D. De Veaux, 1994: A stochastic model relating rainfall intensity to raindrop processes. Water Resour. Res., 30, 651–664.</p>

Drop Shapes, Model Comparisons, and Calculations of Polarimetric Radar Parameters in Rain

2007 ◽  
Vol 24 (6) ◽  
pp. 1019-1032 ◽  
Author(s):  
M. Thurai ◽  
G. J. Huang ◽  
V. N. Bringi ◽  
W. L. Randeu ◽  
M. Schönhuber
Keyword(s):  
Drop Size ◽  
Resonance Region ◽  
Oblate Spheroid ◽  
Size Distributions ◽  
Spherical Drop ◽  
X Band ◽  
Median Volume ◽  
Drop Size Distributions ◽  
The Impact ◽  
Good Agreement

Drop shapes derived from a previously conducted artificial rain experiment using a two-dimensional video disdrometer (2DVD) are presented. The experiment involved drops falling over a distance of 80 m to achieve their terminal velocities as well as steady-state oscillations. The previous study analyzed the measured axis ratios (i.e., ratio of maximum vertical to maximum horizontal chord) as a function of equivolumetric spherical drop diameter (Deq) for over 115 000 drops ranging from 1.5 to 9 mm. In this paper, the actual contoured shapes of the drops are reported, taking into account the finite quantization limits of the instrument. The shapes were derived from the fast line-scanning cameras of the 2DVD. The drops were categorized into Deq intervals of 0.25-mm width and the smoothed contours for each drop category were superimposed on each other to obtain their most probable shapes and their variations due to drop oscillations. The most probable shapes show deviation from oblate spheroids for Deq > 4 mm, the larger drops having a more flattened base, in good agreement with the equilibrium (nonoblate) shape model of Beard and Chuang. Deviations were noted from the Beard and Chuang model shapes for diameters larger than 6 mm. However, the 2DVD measurements of the most probable contour shapes are the first to validate the Beard and Chuang model shapes for large drops, and further to demonstrate the differences from the equivalent oblate shapes. The purpose of this paper is to document the differences in radar polarization parameters and the range of error incurred when using the equivalent oblate shapes versus the most probable contoured shapes measured with the 2DVD especially for drop size distributions (DSDs) with large median volume diameters (>2 mm). The measured contours for Deq > 1.5 mm were fitted to a modified conical equation, and scattering calculations were performed to derive the complex scattering amplitudes for forward and backscatter for H and V polarizations primarily at 5.34 GHz (C band) but also at 3 GHz (S band) and 9 GHz (X band). Calculations were also made to derive the relevant dual-polarization radar parameters for measured as well as model-based drop size distributions. When comparing calculations using the contoured shapes against the equivalent oblate spheroid shapes, good agreement was obtained for cases with median volume diameter (D0) less than around 2 mm. Small systematic differences in the differential reflectivity (Zdr) values of up to 0.3 dB were seen for the larger D0 values when using the oblate shapes, which can be primarily attributed to the shape differences in the resonance region, which occurs in the 5.5–7-mm-diameter range at C band. Lesser systematic differences were present in the resonance region at X band (3–4 mm). At S band, the impact of shape differences in the polarimetric parameters were relatively minor for D0 up to 2.5 mm. Unusual DSDs with very large D0 values (>3 mm) (e.g., as can occur along the leading edge of severe convective storms or aloft due localized “big drop” zones) can accentuate the Zdr difference between the contoured shape and the oblate spheroid equivalent, especially at C band. For attenuation-correction schemes based on differential propagation phase, it appears that the equivalent oblate shape approximation is sufficient using a fit to the axis ratios from the 80-m fall experiment given in this paper. For high accuracy in developing algorithms for predicting D0 from Zdr, it is recommended that the fit to the most probable contoured shapes as given in this paper be used especially at C band.

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