scholarly journals A Preliminary Analysis of Spatial Variability of Raindrop Size Distributions during Stratiform Rain Events

2009 ◽  
Vol 48 (2) ◽  
pp. 270-283 ◽  
Author(s):  
Choong Ke Lee ◽  
Gyu Won Lee ◽  
Isztar Zawadzki ◽  
Kyung-Eak Kim
Keyword(s):  
Spatial Variability ◽  
Characteristic Number ◽  
Radar Reflectivity ◽  
Rainfall Rate ◽  
Size Distributions ◽  
Number Density ◽  
Ratio Error ◽  
Raindrop Size ◽  
Rain Events ◽  
Highly Correlated

Abstract The spatial variability of raindrop size distributions (DSDs) and precipitation fields is investigated utilizing disdrometric measurements from the four Precipitation Occurrence Sensor Systems (POSS) and radar reflectivity fields from S-band dual-polarization radar and vertically pointing X-band radar. The spatial cross correlation of the moments of DSDs, their ratio, error in rainfall estimate, and normalization parameters are quantified using a “noncentered” correlation function. The time-averaged spatial autocorrelation function of observed radar reflectivity factor (Ze) is smaller than that of estimated rainfall rate from Ze because of power-law R–Z transformation with its exponent larger than unity. The important spatial variability of DSDs and rain integral fields is revealed by the significant differences among average DSDs and leads to an average fractional error of 25% in estimating rainfall accumulation during an event. The spatial correlation of the reflectivity from POSS is larger than that of Ze because of larger measurement noise in Ze. The higher moments of DSDs are less correlated in space than lower moments. The correlation of rainfall estimate error is higher than that of estimated rainfall rate and of rainfall rate calculated from DSDs. The correlation of the characteristic number density is low (0.87 at 1.3-km distance), suggesting that the assumed homogeneity of the characteristic number density in space could result in larger errors in the retrieval of DSDs and rain-related parameters. However, the characteristic diameter is highly correlated in space.

scholarly journals Characterization of disdrometer uncertainties and impacts on estimates of snowfall rate and radar reflectivity

2013 ◽  
Vol 6 (4) ◽  
pp. 6329-6369
Author(s):  
N. B. Wood ◽  
T. S. L'Ecuyer ◽  
F. L. Bliven ◽  
G. L. Stephens
Keyword(s):  
Three Dimensional ◽  
Cold Season ◽  
Radar Reflectivity ◽  
Size Distributions ◽  
Truncated Form ◽  
Microphysical Properties ◽  
Uncertainty Model ◽  
Uncertainty Estimates ◽  
Geometry Effects ◽  
Highly Correlated

Abstract. Estimates of snow microphysical properties obtained by analyzing collections of individual particles are often limited to short time scales and coarse time resolution. Retrievals using disdrometer observations coincident with bulk measurements such as radar reflectivity and snowfall amounts may overcome these limitations; however, retrieval techniques using such observations require uncertainty estimates not only for the bulk measurements themselves, but also for the simulated measurements modeled from the disdrometer observations. Disdrometer uncertainties arise due to sampling and analytic errors and to the discrete, potentially truncated form of the reported size distributions. Imaging disdrometers such as the Snowflake Video Imager and 2-D Video Disdrometer provide remarkably detailed representations of snow particles, but view limited projections of their three-dimensional shapes. Particle sizes determined by such instruments underestimate the true dimensions of the particles in a way that depends, in the mean, on particle shape, also contributing to uncertainties. An uncertainty model that accounts for these uncertainties is developed and used to establish their contributions to simulated radar reflectivity and snowfall rate. Viewing geometry effects are characterized by a parameter, φ, that relates disdrometer-observed particle size to the true maximum dimension of the particle. Values and uncertainties for φ are estimated using idealized ellipsoidal snow particles. The model is applied to observations from seven snow events from the Canadian CloudSat CALIPSO Validation Project (C3VP), a mid-latitude cold season cloud and precipitation field experiment. Typical total uncertainties are 4 dBZ for reflectivity and 40–60% for snowfall rate, are highly correlated, and are substantial compared to expected observational uncertainties. The dominant sources of errors are viewing geometry effects and the discrete, truncated form of the size distributions. While modeled Ze-S relationships are strongly affected by assumptions about snow particle mass properties, such relationships are only modestly sensitive to φ owing to partially compensating effects on both the reflectivity and snowfall rate.

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 Variability of rainfall rate and raindrop size distributions in heavy rain

2009 ◽  
Vol 45 (4) ◽  
Author(s):  
James A. Smith ◽  
Eric Hui ◽  
Matthias Steiner ◽  
Mary Lynn Baeck ◽  
Witold F. Krajewski ◽  
...  
Keyword(s):  
Heavy Rain ◽  
Rainfall Rate ◽  
Size Distributions ◽  
Raindrop Size

scholarly journals Approaches to radar reflectivity bias correction to improve rainfall estimation in Korea

2016 ◽  
Vol 9 (5) ◽  
pp. 2043-2053 ◽  
Author(s):  
Cheol-Hwan You ◽  
Mi-Young Kang ◽  
Dong-In Lee ◽  
Jung-Tae Lee
Keyword(s):  
Bias Correction ◽  
Drop Size ◽  
Radar Reflectivity ◽  
Size Distributions ◽  
Rainfall Estimation ◽  
Rainfall Events ◽  
Rain Events ◽  
Single Polarization ◽  
Pass Through ◽  
Drop Size Distributions

Abstract. Three methods for determining the reflectivity bias of single polarization radar using dual polarization radar reflectivity and disdrometer data (i.e., the equidistance line, overlapping area, and disdrometer methods) are proposed and evaluated for two low-pressure rainfall events that occurred over the Korean Peninsula on 25 August 2014 and 8 September 2012. Single polarization radar reflectivity was underestimated by more than 12 and 7 dB in the two rain events, respectively. All methods improved the accuracy of rainfall estimation, except for one case where drop size distributions were not observed, as the precipitation system did not pass through the disdrometer location. The use of these bias correction methods reduced the RMSE by as much as 50 %. Overall, the most accurate rainfall estimates were obtained using the overlapping area method to correct radar reflectivity.

scholarly journals Struktur Vertikal Distribusi Butiran Hujan di Kototabang Berdasarkan Pengamatan Micro Rain Radar (MRR)

2016 ◽  
Vol 5 (4) ◽  
pp. 287-296
Author(s):  
Indah Rahayu ◽  
Marzuki Marzuki ◽  
Hiroyuki Hashiguchi ◽  
Toyoshi Shimomai
Keyword(s):  
Size Distribution ◽  
Rain Gauge ◽  
Radar Reflectivity ◽  
Rainfall Rate ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Rain Radar

Distribusi ukuran butiran hujan atau raindrop size distribution (RDSD) arah vertikal dari ketinggian 0,15 km hingga 4,65 km di Kototabang, Sumatera Barat, telah diteliti melalui pengamatan Micro Rain Radar (MRR) selama Januari-Desember 2012. Intensitas curah hujan (rainfall rate) dari Optical Rain Gauge (ORG) dan RDSD dari Parsivel digunakan untuk menguji kinerja MRR. Pengujian memperlihatkan bahwa MRR berfungsi dengan baik dimana intensitas curah hujan dari ORG berkorelasi dengan baik dengan MRR (r = 0,98) dan RDSD dari MRR secara umum juga memperlihatkan pola dan nilai yang sama dengan yang didapatkan Parsivel.  Selanjutnya, RDSD dari MRR dimodelkan dengan distribusi gamma dan parameternya didapatkan menggunakan metode momen.  Terlihat bahwa pertumbuhan RDSD di Kototabang dari ketinggian 4,65 km hingga 0,15 km sangat kuat yang kemungkinan disebabkan oleh proses tumbukan-penggabungan.  Hal ini ditandai dengan peningkatan konsentrasi butiran berukuran besar dengan penurunan ketinggian.  Peningkatan konsentrasi butiran hujan berukuran besar terhadap penurunan ketinggian berpengaruh kepada parameter-parameter hujan seperti radar reflectivity (Z) dan rainfall rate (R) yang menyebabkan peningkatan koefisien A (Z= ARb) terhadap penurunan ketinggian.  Dengan demikian, penggunaan persamaan Z-R yang konstan untuk setiap ketinggian bagi radar meteorologi di kawasan tropis khususnya Sumatera Barat tidak  tepat.Kata kunci: raindrop size distribution, MRR, Kototabang, distribusi gamma.

Scaling of raindrop size distributions and classification of radar reflectivity–rain rate relations in intense Mediterranean precipitation

2011 ◽  
Vol 402 (3-4) ◽  
pp. 179-192 ◽  
Author(s):  
Pieter Hazenberg ◽  
Nan Yu ◽  
Brice Boudevillain ◽  
Guy Delrieu ◽  
Remko Uijlenhoet
Keyword(s):  
Rain Rate ◽  
Radar Reflectivity ◽  
Size Distributions ◽  
Raindrop Size
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