An Analysis of Errors in Drop Size Distribution Retrievals and Rain Bulk Parameters with a UHF Wind Profiling Radar and a Two-Dimensional Video Disdrometer

2008 ◽  
Vol 25 (12) ◽  
pp. 2282-2292 ◽  
Author(s):  
Laura Kanofsky ◽  
Phillip Chilson
Keyword(s):  
Error Analysis ◽  
Size Distribution ◽  
Drop Size ◽  
Ambient Air ◽  
Drop Size Distribution ◽  
Rainfall Rate ◽  
Doppler Velocity ◽  
Drop Diameter ◽  
Fall Speed ◽  
Air Motion

Abstract Vertically pointed wind profiling radars can be used to obtain measurements of the underlying drop size distribution (DSD) for a rain event by means of the Doppler velocity spectrum. Precipitation parameters such as rainfall rate, radar reflectivity factor, liquid water content, mass-weighted mean drop diameter, and median volume drop diameter can then be calculated from the retrieved DSD. The DSD retrieval process is complicated by the presence of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding. In this note, error analysis is presented to quantify the effect of each of those factors on rainfall rate. The error analysis results are then applied to two precipitation events to better interpret the rainfall-rate retrievals. It was found that a large source of error in rain rate is due to unaccounted-for vertical air motion. For example, in stratiform rain with a rainfall rate of R = 10 mm h−1, a mesoscale downdraft of 0.6 m s−1 can result in a 34% underestimation of the estimated value of R. The fall speed relationship selection and source of air density information both caused negligible errors. Errors due to velocity thresholding become more important in the presence of significant contamination near 0 m s−1, such as ground clutter. If particles having an equivalent volume diameter of 0.8 mm and smaller are rejected, rainfall rate errors from −4% to −10% are possible, although these estimates depend on DSD and rainfall rate.

Characterization of Vertical Velocity and Drop Size Distribution Parameters in Widespread Precipitation at ARM Facilities

2012 ◽  
Vol 51 (2) ◽  
pp. 380-391 ◽  
Author(s):  
Scott E. Giangrande ◽  
Edward P. Luke ◽  
Pavlos Kollias
Keyword(s):  
Standard Deviation ◽  
Size Distribution ◽  
Great Plains ◽  
Rainfall Rate ◽  
Doppler Velocity ◽  
Small Scale ◽  
Drop Diameter ◽  
Dual Frequency ◽  
Raindrop Size Distribution ◽  
Air Motion

AbstractExtended, high-resolution measurements of vertical air motion and median volume drop diameter D0 in widespread precipitation from three diverse Atmospheric Radiation Measurement Program (ARM) locations [Lamont, Oklahoma, Southern Great Plains site (SGP); Niamey, Niger; and Black Forest, Germany] are presented. The analysis indicates a weak (0–10 cm−1) downward air motion beneath the melting layer for all three regions, a magnitude that is to within the typical uncertainty of the retrieval methods. On average, the hourly estimated standard deviation of the vertical air motion is 0.25 m s−1 with no pronounced vertical structure. Profiles of D0 vary according to region and rainfall rate. The standard deviation of 1-min-averaged D0 profiles for isolated rainfall rate intervals is 0.3–0.4 mm. Additional insights into the form of the raindrop size distribution are provided using available dual-frequency Doppler velocity observations at SGP. The analysis suggests that gamma functions better explain paired velocity observations and radar retrievals for the Oklahoma dataset. This study will be useful in assessing uncertainties introduced in the measurement of precipitation parameters from ground-based and spaceborne remote sensors that are due to small-scale variability.

The Effect of Drop-Size Distribution Variability on Radiometric Estimates of Rainfall Rates for Frequencies from 3 to 10 GHz

1991 ◽  
Vol 30 (7) ◽  
pp. 1025-1033 ◽  
Author(s):  
A. R. Jameson
Keyword(s):  
Absorption Coefficient ◽  
Size Distribution ◽  
Drop Size ◽  
Radiative Transfer Equation ◽  
Microwave Frequency ◽  
Drop Size Distribution ◽  
Rainfall Rate ◽  
Field Of View ◽  
Ice Clouds ◽  
Microwave Frequencies

Abstract The substantial upwelling microwave radiation emitted by rain, as well as the relative simplicity of radiometers, guarantees their continuing important role in measuring rain from space. However, for frequencies greater than around 20 GHz, ice clouds overlying rain often scatter much of the upwelling radiation out of the field of view. In addition, at these frequencies raindrops scatter so well that oven when a few more are added to an already low concentration of drops, the additional drops actually scatter away more radiation than they contribute to the field of view. Because of these two effects, the direct measurement of rainfall rate at high microwave frequencies using upwelling radiation is restricted to low rainfall rates. In contrast, from 3 to 10 GHz emissions from raindrops and from clouds dominate the radiative transfer equation. Because emission and absorption are reciprocal, the combined absorption coefficient of the cloud and the rain can be estimated from the upwelling radiation at these frequencies. After extracting the component due to rain (ka), it may be used to estimate the rainfall rate ξ(R). It is important, therefore, that R depend as strongly as possible on ka. The physical link between R and ka varies depending upon the microwave frequency. The weaker the relation the more sensitive ka and ξ(R) are to variations in the drop-size distribution. In this study it is shown that the scatter in ka and ξ(R), in response to variations in the drop-size distribution, is greatest at 8 and smallest at 3 GHz.

scholarly journals Phase Space Parameterization of Rain: The Inadequacy of Gamma Distribution

2014 ◽  
Vol 53 (2) ◽  
pp. 548-562 ◽  
Author(s):  
Massimiliano Ignaccolo ◽  
Carlo De Michele
Keyword(s):  
Phase Space ◽  
Size Distribution ◽  
Gamma Distribution ◽  
Goodness Of Fit ◽  
Drop Size ◽  
Cartesian Product ◽  
Drop Size Distribution ◽  
Drop Diameter ◽  
Goodness Of Fit Test ◽  
Kolmogorov Smirnov

AbstractThe authors test the adequacy of gamma distribution to describe the statistical variability of raindrop diameters in 1-min disdrometer data using the Kolmogorov–Smirnov goodness-of-fit test. The results do not support the use of this distribution, with a percentage of rejected cases that increases with the sample size. A different parameterization of the drop size distribution is proposed that does not require any particular functional form and is based on the adoption of statistical moments. The first three moments, namely the mean, standard deviation, and skewness, are sufficient to characterize the distribution of the drop diameter at the ground. These parameters, together with the drop count, form a 4-tuple, which fully describes the variability of the drop size distribution. The Cartesian product of this 4-tuple of parameters is the rainfall phase space. Using disdrometer data from 10 different locations, invariant, location-independent properties of rainfall are identified.

scholarly journals The Interdependence of Spray Characteristics and Evaporation History of Fuel Sprays in Stagnant Air

1983 ◽  
Author(s):  
J. S. Chin ◽  
R. Durrett ◽  
A. H. Lefebvre
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Simple Calculation ◽  
Drop Size Distribution ◽  
Drop Diameter ◽  
Transient Effects ◽  
Spray Characteristics ◽  
Full Account ◽  
Mass Evaporation ◽  
Time Required

A simple calculation method based on an evaporation analysis proposed previously [1] [2] is used to predict the variation of JP-5 fuel spray characteristics (median drop diameter, Dm, and drop-size distribution parameter, n) with time during evaporation in stagnant hot air. The method takes full account of transient effects occurring during the heat-up period. The results show that Dm increases with time, and so also does n, indicating that the drop-size distribution narrows with passage of time. The time to vaporize any given fraction of the spray mass is found to be proportional to D2mo. The effect of the initial value of n, no, is that a spray having a large value of no will reach its 90% evaporation point faster, but a smaller value of no will give a shorter 20% evaporation time. Based on these calculations, a general method for estimating the time required for any liquid fuel to attain any given percentage of spray mass evaporation in stagnant air is proposed.

Influence of Downstream Distance on the Spray Characteristics of Pressure-Swirl Atomizers

1986 ◽  
Vol 108 (1) ◽  
pp. 219-224 ◽  
Author(s):  
J. S. Chin ◽  
D. Nickolaus ◽  
A. H. Lefebvre
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Fuel Injection ◽  
Injection Pressure ◽  
Ambient Air ◽  
Drop Size Distribution ◽  
Axial Distance ◽  
Spray Characteristics ◽  
Full Account ◽  
Pressure Swirl

An analytical study is made of the factors that are responsible for the observed changes in fuel spray characteristics with axial distance downstream of a pressure-swirl nozzle. To simplify the analysis the effect of fuel evaporation is neglected, but full account is taken of the effects of spray dispersion and drop acceleration (or deceleration). Equations are derived and graphs are presented to illustrate the manner and extent to which the variations of mean drop size and drop-size distribution with axial distance are governed by such factors as ambient air pressure and velocity, fuel injection pressure, initial mean drop size, and initial drop-size distribution.

Disdrometer Gravitational Sorting Signature in a Mediterranean Environment

2020 ◽  
Author(s):  
Takis Kasparis ◽  
Silas Michaelides ◽  
John Lane
Keyword(s):  
Size Distribution ◽  
Sea Level ◽  
Drop Size ◽  
Meteorological Station ◽  
Drop Size Distribution ◽  
Negative Slope ◽  
Drop Diameter ◽  
Scatter Plot ◽  
Mediterranean Environment ◽  
Mean Sea Level

<p>The motivation behind this research was initially the observation and the subsequent modelling of the gravitational sorting of precipitation in disdrometer-based spectra. The gravitational sorting signature (GSS) is expected to be observed when every drop impact measured by the disdrometer is time tagged and then displayed as a scatter plot diagram of drop diameter (D) versus time (t). The resulting D-t diagrams exhibit marked diagonal features and gravitational sorting signatures are characterized by a negative slope. However, because of the way that manufacturers and researchers process disdrometer data, this signature is typically wiped out. </p><p>This research is based on the assumption that if a rain producing cloud that goes through a complete rain process from start to end, remains fixed (no advection) over a disdrometer site, then some GSS should occur; if advection dominates, then GSS may not be observable.  In this latter case, the precipitating cloud may move over the disdrometer. In this paper, two cases are presented one in which GSS was detected and another in which GSS was absent.</p><p>The disdrometer data used in this study were recorded by using a Joss-Waldvogel impact disdrometer located on the roof of a building of the meteorological station at Athalassa, Cyprus (35.15°N, 33.40°, 161.0 m above Mean Sea Level, MSL). The Joss-Waldvogel impact disdrometer used is able to record drop diameters from 0.3mm to 5.5mm in ten-second intervals, allowing for the establishment of the Drop Size Distribution (DSD) representing this range of drop sizes.</p>

Evaluation of GPM Dual-Frequency Precipitation Radar Algorithms to Estimate Drop Size Distribution Parameters, Using Ground-Based Measurement over the Central Andes of Peru

2021 ◽  
Author(s):  
Carlos Del Castillo-Velarde ◽  
Shailendra Kumar ◽  
Jairo M. Valdivia-Prado ◽  
Aldo S. Moya-Álvarez ◽  
Jose Luis Flores-Rojas ◽  
...  
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Central Andes ◽  
Drop Size Distribution ◽  
Dual Frequency ◽  
Precipitation Radar ◽  
Distribution Parameters

Dispersed phase holdup and drop size distribution in pulsed plate columns

1988 ◽  
Vol 66 (2) ◽  
pp. 232-240 ◽  
Author(s):  
A. Prabhakar ◽  
G. Sriniketan ◽  
Y. B. G. Varma
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Drop Size Distribution ◽  
Dispersed Phase
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