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

2010 ◽  
Vol 49 (4) ◽  
pp. 632-645 ◽  
Author(s):  
Shengjie Niu ◽  
Xingcan Jia ◽  
Jianren Sang ◽  
Xiaoli Liu ◽  
Chunsong Lu ◽  
...  
Keyword(s):  
Terminal Velocity ◽  
Systematic Change ◽  
Drop Diameter ◽  
Size Distributions ◽  
Fall Velocity ◽  
Convective Clouds ◽  
Stratiform Clouds ◽  
The Difference ◽  
Raindrop Size ◽  
Rain Rates

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 (36°N, 106°16′E). 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.

scholarly journals Effects of Altitude on Maximum Raindrop Size and Fall Velocity as Limited by Collisional Breakup

2013 ◽  
Vol 70 (4) ◽  
pp. 1129-1134 ◽  
Author(s):  
Federico Porcù ◽  
Leo Pio D’Adderio ◽  
Franco Prodi ◽  
Clelia Caracciolo
Keyword(s):  
Terminal Velocity ◽  
Size Distributions ◽  
Fall Velocity ◽  
Rainfall Events ◽  
Air Density ◽  
X Band ◽  
Full Knowledge ◽  
Raindrop Size ◽  
Limiting Value ◽  
Different Altitudes

Abstract Coalescence and breakup of drops are recognized as the main mechanisms determining raindrop size distributions on the ground. Full knowledge of these processes is hindered by the challenging difficulties both in the laboratory and tunnel experiments and during observations in the open air. In real rain breakup is mainly due to collision between drops of different sizes (collisional breakup) and occurs when the collisional kinetic energy (CKE) is not absorbed by the colliding drops. In this work, the authors observe and measure the dependence on altitude of the occurrence of collisional breakup in real rainfall events, and then estimate the corresponding limit terminal velocities of drops and their size when breakup significantly takes place. Data from Pludix, an X-band microwave disdrometer, were collected at three locations at different elevations: collisional breakup position in the power spectrum of Pludix increases toward higher frequencies with increasing altitude. Terminal velocities and sizes of the drops at breakup were determined consequently, with drop sizes resulting in 4.55 ± 0.35, 4.02 ± 0.32, and 3.16 ± 0.3 mm for altitudes of 15, 950, and 3300 m MSL, respectively. The authors computed the CKE of the colliding drops at the breakup, finding an upper limiting value of about 1.22 × 10−5 J for all three altitudes. This shows that most dominant collisional breakup signature occurs at similar CKE values for all three locations, corresponding to different drop diameters at different altitudes because of the effect of air density on the drop terminal velocity.

scholarly journals Possible Effects of Collisional Breakup on Mixed-Phase Deep Convection Simulated by a Spectral (Bin) Cloud Model

2005 ◽  
Vol 62 (6) ◽  
pp. 1917-1931 ◽  
Author(s):  
Axel Seifert ◽  
Alexander Khain ◽  
Ulrich Blahak ◽  
Klaus D. Beheng
Keyword(s):  
Cloud Model ◽  
Deep Convection ◽  
Sensitivity Study ◽  
Mixed Phase ◽  
Convective Clouds ◽  
Hebrew University ◽  
Raindrop Size ◽  
Convective Cells ◽  
Rain Rates ◽  
Rain Formation

Abstract The effects of the collisional breakup of raindrops are investigated using the Hebrew University Cloud Model (HUCM). The parameterizations, which are combined in the new breakup scheme, are those of Low and List, Beard and Ochs, as well as Brown. A sensitivity study reveals strong effects of collisional breakup on the precipitation formation in mixed-phase deep convective clouds for strong as well as for weak precipitation events. Collisional breakup reduces the number of large raindrops, increases the number of small raindrops, and, as a consequence, decreases surface rain rates and considerably reduces the speed of rain formation. In addition, it was found that including breakup can lead to a more intense triggering of secondary convective cells. But a statistical comparison with observed raindrop size distributions shows that the parameterizations might systematically overestimate collisional breakup.

scholarly journals Evaluation of the New Version of the Laser-Optical Disdrometer, OTT Parsivel2

2014 ◽  
Vol 31 (6) ◽  
pp. 1276-1288 ◽  
Author(s):  
Ali Tokay ◽  
David B. Wolff ◽  
Walter A. Petersen
Keyword(s):  
Drop Size ◽  
Heavy Rain ◽  
Rain Gauges ◽  
Raindrop Size Distribution ◽  
Goddard Space Flight Center ◽  
Absolute Bias ◽  
Fall Speed ◽  
The Difference ◽  
Raindrop Size ◽  
Rain Rates

Abstract A comparative study of raindrop size distribution measurements has been conducted at NASA’s Goddard Space Flight Center where the focus was to evaluate the performance of the upgraded laser-optical OTT Particle Size Velocity (Parsivel2; P2) disdrometer. The experimental setup included a collocated pair of tipping-bucket rain gauges, OTT Parsivel (P1) and P2 disdrometers, and Joss–Waldvogel (JW) disdrometers. Excellent agreement between the two collocated rain gauges enabled their use as a relative reference for event rain totals. A comparison of event total showed that the P2 had a 6% absolute bias with respect to the reference gauges, considerably lower than the P1 and JW disdrometers. Good agreement was also evident between the JW and P2 in hourly raindrop spectra for drop diameters between 0.5 and 4 mm. The P2 drop concentrations mostly increased toward small sizes, and the peak concentrations were mostly observed in the first three measurable size bins. The P1, on the other hand, underestimated small drops and overestimated the large drops, particularly in heavy rain rates. From the analysis performed, it appears that the P2 is an improvement over the P1 model for both drop size and rainfall measurements. P2 mean fall velocities follow accepted terminal fall speed relationships at drop sizes less than 1 mm. As a caveat, the P2 had approximately 1 m s−1 slower mean fall speed with respect to the terminal fall speed near 1 mm, and the difference between the mean measured and terminal fall speeds reduced with increasing drop size. This caveat was recognized as a software bug by the manufacturer and is currently being investigated.

Refinements to Ice Particle Mass Dimensional and Terminal Velocity Relationships for Ice Clouds. Part I: Temperature Dependence

2007 ◽  
Vol 64 (4) ◽  
pp. 1047-1067 ◽  
Author(s):  
Andrew J. Heymsfield ◽  
Aaron Bansemer ◽  
Cynthia H. Twohy
Keyword(s):  
Weather Forecast ◽  
Terminal Velocity ◽  
Fall Velocity ◽  
Cross Sectional ◽  
Convective Clouds ◽  
Particle Mixing ◽  
Particle Dimension ◽  
Mass Dimension ◽  
Forecast Models ◽  
Ice Water

Abstract This two-part study attempts to find appropriate mass dimension and terminal velocity relationships that, when considered together with particle size distributions (PSD), agree with coincident measurements of ice water content (IWC), and with variables related to higher moments such as the mean mass-weighted fall speed. Reliable relationships are required for improving microphysical parameterizations for weather forecast models and developing methods for evaluating them, subjects addressed in detail in Part II of this study. Here, a range of values from 1.5 to 2.3 is assumed for the exponent b in the mass dimension relationship, m = aDb, where D is the maximum particle dimension, to bound its likely value for sizes above about 100 μm. Measured IWC and size spectra are used to find appropriate values for the coefficient a. It is demonstrated that all values of the exponent b, with appropriate a coefficients, can fit the IWC measurements. Coincident information on particle cross-sectional areas with the m(D) relationships is used to develop general fall velocity relationships of the form Vt = ADB. These assessments use five midlatitude, synoptically generated ice layers, and 10 low-latitude, convectively generated ice cloud layers, spanning the temperature range from −60° to 0°C. The coefficients a and A and exponent B are represented in terms of the exponent b and are shown to be temperature-dependent for the synoptic clouds and relatively independent of it in the convective clouds, a result of particle mixing through the cloud column. Consistency is found with earlier results and with analytic considerations. It is found that the fall velocity is inversely proportional to the air density to approximately the exponent 0.54, close to values assumed in earlier studies.

scholarly journals Statistical Characteristics of Multipeak Raindrop Size Distributions at the Surface and Aloft in Different Rain Regimes

2009 ◽  
Vol 137 (10) ◽  
pp. 3501-3518 ◽  
Author(s):  
B. Radhakrishna ◽  
T. Narayana Rao
Keyword(s):  
Southwest Monsoon ◽  
Statistical Characteristics ◽  
Drop Diameter ◽  
Size Distributions ◽  
Warm Rain ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Two Peaks ◽  
First Time ◽  
Key Questions

Abstract Two years (∼672 h) of lower-atmospheric wind profiler (LAWP) and 4 yr (∼733 h) of Joss–Waldvogel disdrometer measurements are utilized to study the multipeak (MP) occurrence statistics at the surface and aloft. For the first time, an attempt has been made to address several key questions regarding MPs: their occurrence statistics and their dependency on height, season, and type of precipitation. MPs are not exceptional; rather, they are observed at all altitudes, albeit with different occurrence percentages. The occurrence of MPs seems to be height dependent, and this dependency varies with the type of rain system. The occurrence percentage of bimodal echo (two peaks) is high above (below) the melting level (ML) in convection (in other types of rain). The percentage occurrence of bimodal echo in warm rain is similar to that in cold rain, but only below the ML. The spectrum with more than two peaks appears to be predominantly in convection, particularly above 4 km. The MP statistics on the surface DSD derived from disdrometer data also support the profiler statistics qualitatively (occurrence is more likely in convection); however, the magnitudes of the percentage of occurrence are different at the surface and aloft. The peaks in the raindrop size distribution (DSD) spectra exist predominantly in drop diameter ranges of 0.45–0.65 and 0.9–1.3 mm in all types of rain, consistent with earlier numerical and observational studies. The MP occurrence does not have seasonal dependence aloft, but shows some variation at the surface with a larger percentage of the occurrences in the southwest monsoon. However, peaks in the surface DSD exist at same diameters in both monsoon seasons.

scholarly journals Drop-Size Distributions in Thunderstorms Measured by Optical Disdrometers during VORTEX2

2013 ◽  
Vol 141 (4) ◽  
pp. 1182-1203 ◽  
Author(s):  
Katja Friedrich ◽  
Evan A. Kalina ◽  
Forrest J. Masters ◽  
Carlos R. Lopez
Keyword(s):  
Particle Size ◽  
Wind Speed ◽  
Size Distributions ◽  
Fall Velocity ◽  
Near Surface ◽  
Weather Radars ◽  
Raindrop Size Distribution ◽  
Strong Winds ◽  
Raindrop Size ◽  
Surface Buoyancy

Abstract When studying the influence of microphysics on the near-surface buoyancy tendency in convective thunderstorms, in situ measurements of microphysics near the surface are essential and those are currently not provided by most weather radars. In this study, the deployment of mobile microphysical probes in convective thunderstorms during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) is examined. Microphysical probes consist of an optical Ott Particle Size and Velocity (PARSIVEL) disdrometer that measures particle size and fall velocity distributions and a surface observation station that measures wind, temperature, and humidity. The mobile probe deployment allows for targeted observations within various areas of the storm and coordinated observations with ground-based mobile radars. Quality control schemes necessary for providing reliable observations in severe environments with strong winds and high rainfall rates and particle discrimination schemes for distinguishing between hail, rain, and graupel are discussed. It is demonstrated how raindrop-size distributions for selected cases can be applied to study size-sorting and microphysical processes. The study revealed that the raindrop-size distribution changes rapidly in time and space in convective thunderstorms. Graupel, hailstones, and large raindrops were primarily observed close to the updraft region of thunderstorms in the forward- and rear-flank downdrafts and in the reflectivity hook appendage. Close to the updraft, large raindrops were usually accompanied by an increase in small-sized raindrops, which mainly occurred when the wind speed and standard deviation of the wind speed increased. This increase in small drops could be an indicator of raindrop breakup.

scholarly journals Drop Axis Ratios from a 2D Video Disdrometer

2005 ◽  
Vol 22 (7) ◽  
pp. 966-978 ◽  
Author(s):  
Merhala Thurai ◽  
V. N. Bringi
Keyword(s):  
Equilibrium Shape ◽  
Terminal Velocity ◽  
Drop Diameter ◽  
Fall Velocity ◽  
Axis Ratio ◽  
Axisymmetric Mode ◽  
Spreading Function ◽  
Radar Applications ◽  
Linear Fit ◽  
The Mean

Abstract Results from an experiment to measure the drop shapes using a 2D video disdrometer (2DVD) are reported. Under calm conditions, drops were generated from a hose located on a bridge 80 m above ground, this height being sufficient to allow drop oscillations to reach a steady state. The disdrometer data had to be carefully processed so as to eliminate the drops mismatched by the instrument and to remove the system spreading function. The total number of drops analyzed was around 115 000. Their axis ratio distributions were obtained for diameters ranging from 1.5 to 9 mm. The mean axis ratio decreases with increasing drop diameter, in agreement with the upper bound of the Beard and Chuang equilibrium shape model. The inferred mode of oscillation appears to be dominated by the oblate–prolate axisymmetric mode for the diameter range of 1.5 to 9 mm. The mean axis ratio agrees well with two empirically fitted formulas reported in earlier studies. In addition, a linear fit was applied to the data for radar applications relating to rain retrievals from dual-polarization measurements. The 2DVD data taken in moderate stratiform rain were also analyzed in a similar way and the results agree with the artificially generated drop experiment, at least up to 4 mm. No data for larger diameters were available for stratiform precipitation. Finally, the fall velocity was examined in terms of drop diameter. The results closely follow an empirical formula fitted to the Gunn and Kinzer data as well as the Beard and Pruppacher data including a slight decrease in the terminal velocity with a diameter beyond 7 mm.

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 Decadal Variation in Raindrop Size Distributions in Busan, Korea

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Cheol-Hwan You ◽  
Dong-In Lee
Keyword(s):  
Drop Size ◽  
Annual Rainfall ◽  
Size Distributions ◽  
Decadal Variation ◽  
Gamma Model ◽  
Radar Rainfall ◽  
Precipitation Occurrence ◽  
Raindrop Size ◽  
Using Data ◽  
Rain Rates

This paper investigated the variability of raindrop size distributions (DSDs) in Busan, Korea, using data from two different disdrometers: a precipitation occurrence sensor system (POSS) and a particle size velocity (Parsivel) optical disdrometer. DSDs were simulated using a gamma model to assess the intercomparability of these two techniques. Annual rainfall amount was higher in 2012 than in 2002, as were the annually averagedDm(which was 0.1 mm greater in 2012) and the frequency of convective rain. Severe rainfall (greater than 20 mm h−1) occurred more frequently and with a largerDmin 2012. The values ofDmfrom July, August, and December, 2012, were much greater than from other months when compared with 2002. Larger raindrops contributed to the higher rain rates that were observed in the morning during 2012, whereas relatively smaller raindrops dominated in the afternoon. These results suggest that the increase in raindrop size that has been observed in Busan may continue in the future; however, more research will be required if we are to fully understand this phenomenon. Rainfall variables are highly dependent on drop size and so should be recalculated using the newest DSDs to allow more accurate polarimetric radar rainfall estimation.

Sign in / Sign up

Export Citation Format

Share Document