scholarly journals Estimation of rain kinetic energy from radar reflectivity and/or rain rate based on a scaling formulation of the raindrop size distribution

2012 ◽  
Vol 48 (4) ◽  
Author(s):  
Nan Yu ◽  
Brice Boudevillain ◽  
Guy Delrieu ◽  
Remko Uijlenhoet
Keyword(s):  
Kinetic Energy ◽  
Size Distribution ◽  
Rain Rate ◽  
Radar Reflectivity ◽  
Raindrop Size Distribution ◽  
Raindrop Size

scholarly journals Raindrop size distributions and radar reflectivity–rain rate relationships for radar hydrology

2001 ◽  
Vol 5 (4) ◽  
pp. 615-628 ◽  
Author(s):  
R. Uijlenhoet
Keyword(s):  
Size Distribution ◽  
Power Law ◽  
Rain Rate ◽  
Radar Reflectivity ◽  
Size Distributions ◽  
Raindrop Size Distribution ◽  
Special Cases ◽  
Fundamental Reason ◽  
Radar Measurements ◽  
Raindrop Size

Abstract. The conversion of the radar reflectivity factor Z(mm6m-3) to rain rate R(mm h-1 ) is a crucial step in the hydrological application of weather radar measurements. It has been common practice for over 50 years now to take for this conversion a simple power law relationship between Z and R. It is the purpose of this paper to explain that the fundamental reason for the existence of such power law relationships is the fact that Z and R are related to each other via the raindrop size distribution. To this end, the concept of the raindrop size distribution is first explained. Then, it is demonstrated that there exist two fundamentally different forms of the raindrop size distribution, one corresponding to raindrops present in a volume of air and another corresponding to those arriving at a surface. It is explained how Z and R are defined in terms of both these forms. Using the classical exponential raindrop size distribution as an example, it is demonstrated (1) that the definitions of Z and R naturally lead to power law Z–R relationships, and (2) how the coefficients of such relationships are related to the parameters of the raindrop size distribution. Numerous empirical Z–R relationships are analysed to demonstrate that there exist systematic differences in the coefficients of these relationships and the corresponding parameters of the (exponential) raindrop size distribution between different types of rainfall. Finally, six consistent Z–R relationships are derived, based upon different assumptions regarding the rain rate dependence of the parameters of the (exponential) raindrop size distribution. An appendix shows that these relationships are in fact special cases of a general Z–R relationship that follows from a recently proposed scaling framework for describing raindrop size distributions and their properties. Keywords: radar hydrology, raindrop size distribution, radar reflectivity–rain rate relationship

scholarly journals Evaluation of Gamma Raindrop Size Distribution Assumption through Comparison of Rain Rates of Measured and Radar-Equivalent Gamma DSD

2014 ◽  
Vol 53 (6) ◽  
pp. 1618-1635 ◽  
Author(s):  
Elisa Adirosi ◽  
Eugenio Gorgucci ◽  
Luca Baldini ◽  
Ali Tokay
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Rain Rate ◽  
Hydrological Cycle ◽  
Drop Size Distribution ◽  
Dual Polarization ◽  
Raindrop Size Distribution ◽  
Radar Measurements ◽  
Raindrop Size ◽  
Rain Rates

AbstractTo date, one of the most widely used parametric forms for modeling raindrop size distribution (DSD) is the three-parameter gamma. The aim of this paper is to analyze the error of assuming such parametric form to model the natural DSDs. To achieve this goal, a methodology is set up to compare the rain rate obtained from a disdrometer-measured drop size distribution with the rain rate of a gamma drop size distribution that produces the same triplets of dual-polarization radar measurements, namely reflectivity factor, differential reflectivity, and specific differential phase shift. In such a way, any differences between the values of the two rain rates will provide information about how well the gamma distribution fits the measured precipitation. The difference between rain rates is analyzed in terms of normalized standard error and normalized bias using different radar frequencies, drop shape–size relations, and disdrometer integration time. The study is performed using four datasets of DSDs collected by two-dimensional video disdrometers deployed in Huntsville (Alabama) and in three different prelaunch campaigns of the NASA–Japan Aerospace Exploration Agency (JAXA) Global Precipitation Measurement (GPM) ground validation program including the Hydrological Cycle in Mediterranean Experiment (HyMeX) special observation period (SOP) 1 field campaign in Rome. The results show that differences in rain rates of the disdrometer DSD and the gamma DSD determining the same dual-polarization radar measurements exist and exceed those related to the methodology itself and to the disdrometer sampling error, supporting the finding that there is an error associated with the gamma DSD assumption.

scholarly journals Influence of the Subgrid Variability of the Raindrop Size Distribution on Radar Rainfall Estimators

2012 ◽  
Vol 51 (4) ◽  
pp. 780-785 ◽  
Author(s):  
Joël Jaffrain ◽  
Alexis Berne
Keyword(s):  
Size Distribution ◽  
Rain Rate ◽  
Power Laws ◽  
Radar Data ◽  
Sampling Uncertainty ◽  
Radar Rainfall ◽  
Differential Phase Shift ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Pixel Scale

AbstractThis work aims at quantifying the variability of the parameters of the power laws used for rain-rate estimation from radar data, on the basis of raindrop size distribution measurements over a typical weather radar pixel. Power laws between the rain rate and the reflectivity or the specific differential phase shift are fitted to the measured values, and the variability of the parameters is analyzed. At the point scale, the variability within this radar pixel cannot be solely explained by the sampling uncertainty associated with disdrometer measurements. When parameters derived from point measurements are applied at the radar pixel scale, the resulting error in the rain amount varies between −2% and +15%.

scholarly journals Characteristics of Raindrop Size Distribution on the Eastern Slope of the Tibetan Plateau in Summer

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 562
Author(s):  
Yingjue Wang ◽  
Jiafeng Zheng ◽  
Zhigang Cheng ◽  
Bingyun Wang
Keyword(s):  
Tibetan Plateau ◽  
Size Distribution ◽  
Rain Rate ◽  
The Tibetan Plateau ◽  
Eastern Slope ◽  
Microphysical Properties ◽  
Raindrop Size Distribution ◽  
Plateau Area ◽  
Raindrop Size ◽  
Rain Rates

Precipitation microphysics over the Tibetan Plateau (TP) remain insufficiently understood, due to the lack of observations and studies. This paper presents a comprehensive investigation of the raindrop size distribution (DSD) for rainfall that happened on the eastern slope of TP in summer. DSD differences between different rain types and under different rain rates are investigated. Confidential empirical relationships between the gamma shape and slope parameters, and between reflectivity and rain rate are proposed. DSD properties in this area are also compared with those in other areas. The results indicate that the stratiform and convective rains contribute to different rain duration and amount, with diverse rainfall macro- and microphysical properties. The rain spectra of two rain types can become broader with higher concentrations as the rain rate increases. DSDs in this area are different to those in other areas. The stratiform DSD is narrower than that in the non-plateau area. The two rain types of this area both have higher number concentrations for 0.437–1.625 mm raindrops than those of the mid-TP. The relationships of shape–slope parameters and reflectivity–rain rate in this area are also different from those in other areas. The rain spectra in this area can produce a larger slope parameter under the same shape parameter than in the mid-TP. The convective rain can produce a smaller rain rate under the same reflectivity. The accuracy proposed reflectivity–rain rate relationship in application to quantitative rainfall estimation is also discussed. The results show that the relationship has an excellent performance when the rain rate exceeds 1 mm h−1.

scholarly journals Raindrop Size Distribution and Radar Parameters in Coastal Tropical Rain Systems of Northeastern Brazil

2012 ◽  
Vol 51 (11) ◽  
pp. 1960-1970 ◽  
Author(s):  
Ricardo Sarmento Tenório ◽  
Marcia Cristina da Silva Moraes ◽  
Henri Sauvageot
Keyword(s):  
Size Distribution ◽  
Rain Rate ◽  
The Other ◽  
Northeastern Brazil ◽  
Drop Diameter ◽  
Coastal Site ◽  
Raindrop Size Distribution ◽  
The Mean ◽  
Raindrop Size ◽  
Bearing System

AbstractA dataset on raindrop size distribution (DSD) gathered in a coastal site of the Alagoas state in northeastern Brazil is used to analyze some differences between continental and maritime rainfall parameters. The dataset is divided into two subsets. One is composed of rainfall systems coming from the continent and moving eastward (i.e., offshore), representing the continental subset. The other is composed of rainfall systems that developed over the sea and are moving westward (i.e., inshore), representing the maritime subset. The mean conditional rain rate (i.e., for rain rate R > 0) is found to be higher for maritime (4.6 mm h−1) than for continental (3.2 mm h−1) conditions. The coefficient of variation of the conditional rain rate is lower for the maritime (1.75) than for the continental (2.25) subset. The continental and maritime DSDs display significant differences. For drop diameter D smaller than about 2 mm, the number of drops is higher for maritime rain than for continental rain. This reverses for D > 2 mm, in such a way that radar reflectivity factor Z for the maritime case is lower than for the continental case at the same rain rate. These results show that, to estimate precipitation by radar in the coastal area of northeastern Brazil, coefficients of the Z–R relation need to be adapted to the direction of motion of the rain-bearing system, inshore or offshore.

scholarly journals Quantification of the Small-Scale Spatial Structure of the Raindrop Size Distribution from a Network of Disdrometers

2012 ◽  
Vol 51 (5) ◽  
pp. 941-953 ◽  
Author(s):  
Joël Jaffrain ◽  
Alexis Berne
Keyword(s):  
Spatial Structure ◽  
Size Distribution ◽  
Rain Rate ◽  
Quantitative Estimation ◽  
Total Concentration ◽  
Small Scale ◽  
Raindrop Size Distribution ◽  
Crucial Information ◽  
Raindrop Size ◽  
Remote Sensing Techniques

AbstractThe spatial structure of the raindrop size distribution (DSD) conveys crucial information for reliable quantitative estimation of rainfall using remote sensing techniques. To investigate this question, a network of 16 optical disdrometers has been deployed over a typical weather radar pixel (~1 × 1 km2) in Lausanne, Switzerland. A set of 36 rainfall events has been classified according to three types: convective, transitional, and frontal. In a first step, the spatial structure of the DSD is quantified using spatial correlation for comparison with the literature, showing good agreement with previous studies. The spatial structure of important quantities related to the DSD—namely, the total concentration of drops Nt, the mass-weighted diameter Dm, and the rain rate R—is quantified using variograms. Results clearly highlight that DSD fields are organized and not randomly distributed even at a scale below 1 km. Moreover, convective-type rainfall exhibits larger variability of the DSD than do transitional and frontal rainfall. The temporal resolution is shown to have an influence on the results: increasing time steps tend to decrease the spatial variability. This study presents a possible application of such information by quantifying the error associated with the use of point measurements as areal estimates at larger scales. Analyses have been conducted for different sizes of domain ranging from 100 × 100 to 1000 × 1000 m2. As expected, this error is increasing with the size of the domain. For instance, for a domain of ~1000 × 1000 m2, the error associated with rain-rate estimates is on the order of 25% for all types of rain.

scholarly journals Raindrop Size Distribution and Rain Characteristics of the 2017 Great Hunan Flood Observed with a Parsivel2 Disdrometer

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1556
Author(s):  
Li Luo ◽  
Ling Wang ◽  
Tao Huo ◽  
Mingxuan Chen ◽  
Jianli Ma ◽  
...  
Keyword(s):  
Size Distribution ◽  
Radar Reflectivity ◽  
Hunan Province ◽  
Maximum Diameter ◽  
Rainfall Erosivity ◽  
Intense Rainfall ◽  
Raindrop Size Distribution ◽  
Hourly Rainfall ◽  
The Mean ◽  
Raindrop Size

Disdrometer observations obtained by an OTT Parsivel2 during the 2017 Great Hunan Flood from 1:00 a.m. LST 23 June 2017 to 4:00 a.m. LST 2 July 2017 in Changsha, Hunan Province, southern China, are analyzed to diagnose characteristics of raindrop size distribution (DSD). This event was characterized by a large number of small- to medium-sized raindrops (diameters smaller than 1.5 mm) and the mean median volume diameter (D0) is about 1.04 mm. The median values of rain rate R (1.57 mm h−1), liquid water content W (0.10 g m−3), and radar reflectivity Z (25.7 dBZ) are smaller than that of the 2013 Great Colorado Flood. This event was composed of two intense rainfall periods and a stratiform period, and notable distinctions of rainfall microphysics among the three rainfall episodes are observed. Two intense rainfall periods were characterized by widespread and intense convection rains with a surface reflectivity of 48.8~56.7 dBZ. A maximum diameter of raindrops up to 7.5 mm was observed, as well as high concentrations of small and midsize drops, resulting in large rainfall amounts during the two intense rainfall episodes. The mean radar reflectivity of 22.6 dBZ, total rainfall of 17.85 mm and the maximum raindrop of approximately 4.25 mm were observed during the stratiform rainfall episode. The composite DSD for each rainfall episode peaked at 0.56 mm but higher concentrations of raindrops appeared in the two intense rainfall episodes. The Z-R relationships derived from the disdrometer measurements reflect the unusual characteristics of DSD during the flood. As a result, the standard NEXRAD Z-R relationship (Z = 300R1.4) strongly underestimated hourly rainfall by up to 27.5%. In addition, the empirical relations between rainfall kinetic energy (KE) versus rainfall intensity (R) and mean mass diameter (Dm) are also derived using DSDs to further investigate the impacts of raindrop properties on the rainfall erosivity.

scholarly journals Perbandingan Parameter Distribusi Butiran Hujan Arah Vertikal antara Fase Aktif dan Tidak Aktif Osilasi Madden Julian Menggunakan Metode Dual-Frequency Radar

2017 ◽  
Vol 6 (1) ◽  
pp. 81-88
Author(s):  
Meri Yoseva ◽  
Mutya Vonnisa ◽  
Marzuki Marzuki
Keyword(s):  
Boundary Layer ◽  
Size Distribution ◽  
Radar Reflectivity ◽  
Madden Julian Oscillation ◽  
Dual Frequency ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Coupling Processes

Distribusi ukuran butiran hujan atau raindrop size distribution (DSD) arah vertikal antara fase aktif dan tidak aktif Madden Julian oscillation (MJO) di Kototabang, Sumatera Barat, telah dibandingkan. Perbandingan dilakukan melalui parameter DSD yang dihitung menggunakan data Equatorial Atmosphere Radar (EAR) yang dikopling dengan data Boundary Layer Radar (BLR) selama proyek Coupling Processes In The Equatorial Atmosphere (CPEA)-I (10 April - 9 Mei 2004). Estimasi parameter DSD menggunakan metode dual-frequency. DSD dimodelkan dengan distribusi gamma dan parameternya didapatkan menggunakan metode momen. Dari penelitian ini terlihat bahwa intensitas curah hujan yang tinggi lebih banyak terjadi pada fase MJO tidak aktif dibandingkan dengan fase aktif. Perbedaan parameter DSD antara fase MJO aktif dan tidak aktif lebih jelas terlihat pada hujan dengan intensitas tinggi (R ≥ 20 mm/h). DSD selama fase tidak aktif mengandung lebih banyak butiran hujan berukuran besar daripada fase aktif. Hal ini ditandai dengan nilai Λ yang lebih kecil dan µ yang lebih besar selama fase tidak aktif. Banyaknya butiran hujan yang berukuran besar ini berdampak kepada nilai radar reflectivity (Z) dimana pada fase tidak aktif nilainya lebih besar dibandingkan pada fase aktif MJO. Dengan demikian, proses fisika yang menghasilkan butiran hujan yang berukuran besar dominan terjadi pada fase tidak aktif MJO. Kata kunci: raindrop size distribution (DSD), Madden Julian oscillation (MJO), dual frekuensi,Kototabang, Equatorial Atmosphere Radar (EAR)

Sign in / Sign up

Export Citation Format

Share Document