Raindrop Size Distribution in Different Climatic Regimes from Disdrometer and Dual-Polarized Radar Analysis
15 Jan 2003-Journal of the Atmospheric Sciences (American Meteorological Society)-Vol. 60, Iss: 2, pp 354-365
TL;DR: In this article, the application of polarimetric radar data to the retrieval of raindrop size distribution parameters and rain rate in samples of convective and stratiform rain types is presented.
Abstract: The application of polarimetric radar data to the retrieval of raindrop size distribution parameters and rain rate in samples of convective and stratiform rain types is presented. Data from the Colorado State University (CSU), CHILL, NCAR S-band polarimetric (S-Pol), and NASA Kwajalein radars are analyzed for the statistics and functional relation of these parameters with rain rate. Surface drop size distribution measurements using two different disdrometers (2D video and RD-69) from a number of climatic regimes are analyzed and compared with the radar retrievals in a statistical and functional approach. The composite statistics based on disdrometer and radar retrievals suggest that, on average, the two parameters (generalized intercept and median volume diameter) for stratiform rain distributions lie on a straight line with negative slope, which appears to be consistent with variations in the microphysics of stratiform precipitation (melting of larger, dry snow particles versus smaller, rimed ic...
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TL;DR: In this article, the authors present a review of the many aspects of precipitation measurement that are relevant to providing an accurate global assessment of this important environmental parameter, including ground data, satellite estimates and numerical models.
403 citations
TL;DR: In this paper, a synthetic polarimetric algorithm has been developed for rainfall estimation, which results in significant reduction in the rms errors of hourly rain estimates when compared with the conventional nonpolarimetric relation.
Abstract: As part of the Joint Polarization Experiment (JPOLE), the National Severe Storms Laboratory conducted an operational demonstration of the polarimetric utility of the Norman, Oklahoma (KOUN), Weather Surveillance Radar-1988 Doppler (WSR-88D). The capability of the KOUN radar to estimate rainfall is tested on a large dataset representing different seasons and different types of rain. A dense gauge network—the Agricultural Research Service (ARS) Micronet—is used to validate different polarimetric algorithms for rainfall estimation. One-hour rain totals are estimated from the KOUN radar using conventional and polarimetric algorithms and are compared with hourly accumulations measured by the gauges. Both point and areal rain estimates are examined. A new “synthetic” rainfall algorithm has been developed for rainfall estimation. The use of the synthetic polarimetric algorithm results in significant reduction in the rms errors of hourly rain estimates when compared with the conventional nonpolarimetric relation: 1.7 times for point measurements and 3.7 times for areal rainfall measurements.
289 citations
TL;DR: In this paper, the relationship between raindrop-size distributions and radar reflectivity-rainfall rate (Z-R) relationships is revisited, this time from the combined approach of rain-forming physical processes that shape the RDSD, and a formulation of the RDP into the simplest free parameters of the rain intensity R, rainwater content W, and median volume drop diameter D0.
Abstract: In this work the longstanding question of the connections between raindrop-size distributions (RDSDs) and radar reflectivity-rainfall rate (Z-R) relationships is revisited, this time from the combined approach of rain-forming physical processes that shape the RDSD, and a formulation of the RDSD into the simplest free parameters of the rain intensity R, rainwater content W, and median volume drop diameter D0. This is accomplished through a theoretical analysis, using a gamma RDSD, of D0-R and W-R relations implied by the coefficients and exponents in empirical Z-R relations. The results provide a means by which these Z-R relations can be classified. The most dramatic of these classifications involves the relation between D0 and W, which shows a remarkable ordering with the rain types.
269 citations
TL;DR: In this paper, a self-consistency approach was proposed to reduce the impact of variability in the drop size distribution and raindrop shape on the quality of the radar reflectivity Z. The proposed scheme was tested on a large polarimetric dataset obtained during the Joint Polarization Experiment in Oklahoma and yielded an accura...
Abstract: Techniques for the absolute calibration of radar reflectivity Z and differential reflectivity ZDR measured with dual-polarization weather radars are examined herein. Calibration of Z is based on the idea of self-consistency among Z, ZDR, and the specific differential phase KDP in rain. Extensive spatial and temporal averaging is used to derive the average values of ZDR and KDP for each 1 dB step in Z. Such averaging substantially reduces the standard error of the KDP estimate so the technique can be used for a wide range of rain intensities, including light rain. In this paper, the performance of different consistency relations is analyzed and a new self-consistency methodology is suggested. The proposed scheme substantially reduces the impact of variability in the drop size distribution and raindrop shape on the quality of the Z calibration. The new calibration technique was tested on a large polarimetric dataset obtained during the Joint Polarization Experiment in Oklahoma and yielded an accura...
223 citations
Cites background from "Raindrop Size Distribution in Diffe..."
...18 Bringi et al. (2003) suggested using Eq....
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...19 The dependencies of the raindrop axis ratio on its equivolume diameter for equilibrium shapes defined by (17), “oscillating” raindrop shapes as specified by Bringi et al. (2003), and the ones defined by (19) are shown in Fig....
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TL;DR: In this paper, data from three 2D video disdrometers and an S-band polarimetric radar are used to characterize rain microphysics in Oklahoma and a method of sorting and averaging based on two parameters (SATP) is proposed.
Abstract: In this paper, data from three 2-dimensional video disdrometers (2DVDs) and an S-band polarimetric radar are used to characterize rain microphysics in Oklahoma. Sampling errors from the 2DVD measurements are quantified through side-by-side comparisons. In an attempt to minimize the sampling errors, a method of sorting and averaging based on two parameters (SATP) is proposed. The shape–slope (μ–Λ) relation of a constrained gamma (C-G) model is then refined for the retrieval of drop size distributions (DSDs) from polarimetric radar measurements. An adjustable term that is based on observed radar reflectivity and differential reflectivity is introduced to make the C-G DSD model more applicable. Radar retrievals using this improved DSD model are shown to provide good agreement with disdrometer observations and to give reasonable results, including in locations near the leading edge of convection where poorly sampled large drops are often observed.
219 citations
References
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TL;DR: In this paper, a three-parameter gamma distribution was used for dual-measurement techniques to determine rainfall rate, and the relationship between pairs of integral rainfall parameters using a three parameter gamma drop size distribution was investigated.
Abstract: Empirical analyses are shown to imply variation in the shape or analytical form of the raindrop size distribution consistent with that observed experimentally and predicted theoretically. These natural variations in distribution shape are demonstrated by deriving relationships between pairs of integral rainfall parameters using a three parameter gamma drop size distribution and comparing the expressions with empirical. There comparisons produce values for the size distribution parameters which display a systematic dependence of one of the parameters on another between different rainfall types as well as from moment to moment within a given rainfall type. The implications of this finding are explored in terms of the use of a three-parameter gamma distribution in dual-measurement techniques to determine rainfall rate.
1,237 citations
"Raindrop Size Distribution in Diffe..." refers background or methods in this paper
...R relations from the Tropics to the continental (e.g., Ulbrich 1983)....
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...The DSD can be characterized by three parameters such as characteristic diameter, concentration, and DSD shape, and analytic forms such as the gamma or lognormal distributions have been widely used (e.g., Ulbrich 1983; Feingold and Levin 1986)....
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Book•
15 Oct 2001TL;DR: A detailed introduction to the principles of Doppler and polarimetric radar, focusing in particular on their use in the analysis of weather systems, is provided in this article, where the authors discuss background topics such as electromagnetic scattering, polarization, and wave propagation.
Abstract: This 2001 book provides a detailed introduction to the principles of Doppler and polarimetric radar, focusing in particular on their use in the analysis of weather systems. The design features and operation of practical radar systems are highlighted throughout the book in order to illustrate important theoretical foundations. The authors begin by discussing background topics such as electromagnetic scattering, polarization, and wave propagation. They then deal in detail with the engineering aspects of pulsed Doppler polarimetric radar, including the relevant signal theory, spectral estimation techniques, and noise considerations. They close by examining a range of key applications in meteorology and remote sensing. The book will be of great use to graduate students of electrical engineering and atmospheric science as well as to practitioners involved in the applications of polarimetric radar systems.
1,043 citations
TL;DR: In this paper, the potential use of differential reflectivity measurements at orthogonal polarizations to determine rain-fall rate was examined, which involves measurements of ZH and ZV, the radar reflectivity factors due to horizontally and vertically polarized incident waves respectively.
Abstract: The potential use of differential reflectivity measurements at orthogonal polarizations to determine rain-fall rate is examined. The method involves measurements of ZH and ZV, the radar reflectivity factors due to horizontally and vertically polarized incident waves respectively. The differential reflectivity, ZDR = 10 log (ZH/ZV), which should be precisely determinate, occurs as a result of the distortion of raindrops as they fall at terminal velocity. The approximate theory of Gans for electromagnetic scattering by spheroids is applied to the distorted raindrops. Assuming a general exponential form for the raindrop size distribution, equations are derived relating the distribution parameters to the measurements. The determination of rainfall rate follows directly. Finally, the sensitivity of the distribution parameters to radar inaccuracies is examined, and several methods of implementing the measurements are suggested. It is concluded that good estimates of rainfall rate using a single non-att...
623 citations
"Raindrop Size Distribution in Diffe..." refers background in this paper
...Since the early articles by Seliga and Bringi (1976, 1978), a long-standing goal in radar polarimetric research has been the retrieval of the raindrop size distribution using measurements of reflectivity (Zh), differential reflectivity (Zdr), and specific differential phase (Kdp)....
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TL;DR: In this article, it is shown mathematically that it is appropriate to normalize by N 0 √ √ LWC/Dm4 with respect to particle concentration and by Dm with regard to drop diameter, where N 0* is defined as the intercept parameter that would have an exponential DSD with the same LWC and Dm as the real one.
Abstract: The shape of the drop size distribution (DSD) reflects the physics of rain. The DSD is the result of the microphysical processes that transform the condensed water into rain. The question of the DSD is also central in radar meteorology, because it rules the relationships between the radar reflectivity and the rainfall rate R. Normalizing raindrop spectra is the only way to identify the shape of the distribution. The concept of normalization of DSD developed in this paper is founded upon two reference variables, the liquid water content LWC and the mean volume diameter Dm. It is shown mathematically that it is appropriate to normalize by N0* ∝ LWC/Dm4 with respect to particle concentration and by Dm with respect to drop diameter. Also, N0* may be defined as the intercept parameter that would have an exponential DSD with the same LWC and Dm as the real one. The major point of the authors' approach is that it is totally free of any assumption about the shape of the DSD. This new normalization has be...
553 citations
TL;DR: In this paper, the equilibrium shape of raindrops has been determined from Laplace's equation using an internal hydrostatic pressure with an external aerodynamic pressure based on measurements for a sphere but adjusted for the effect of distortion.
Abstract: The equilibrium shape of raindrops has been determined from Laplace's equation using an internal hydrostatic pressure with an external aerodynamic pressure based on measurements for a sphere but adjusted for the effect of distortion. The drop shape was calculated by integration from the upper pole with the initial curvature determined by iteration on the drop volume. The shape was closed at the lower pole by adjusting either the pressure drag or the drop weight to achieve an overall force balance. Model results provide bounds on the axis ratio of raindrops with an uncertainty of about 1% and very good agreement with extensive wind tunnel measurements for moderate to large water drops. The model yields the peculiar asymmetric shape of raindrops: a singly curved surface with a flattened base and a maximum curvature just below the major axis. A close match was found between model shapes and profiles obtained from photos of water drops for diameters up to 5 mm. Coefficients are provided for computing...
549 citations
"Raindrop Size Distribution in Diffe..." refers background or methods in this paper
...(1999) for 1 , D (equivalent diameter) , 4 mm, which accounts for transverse oscillations and the equilibrium axis ratio model of Beard and Chuang (1987) for D , 1 and D ....
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...Simulations using gamma fits to measured drop size distributions (see section 3) and scattering calculations at 2.8 GHz of Zh, Zdr, and Kdp assuming, (i) mean axis ratio versus D fit of Andsager et al. (1999) for 1 # D # 4 mm, and Beard and Chuang (1987) for D , 1 and D ....
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...Drop shapes are usually modeled as oblate spheroidal with axis ratio (ratio of minor to major axes, r 5 b/a) corresponding to equilibrium shapes that result from a balance between hydrostatic, surface tension, and aerodynamic forces (e.g., Green 1975; Beard and Chuang 1987)....
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