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Alexander Khain - One of the best experts on this subject based on the ideXlab platform.

  • hydrometeor mixing ratio retrievals for storm scale radar data assimilation utility of current relations and potential benefits of polarimetry
    Monthly Weather Review, 2016
    Co-Authors: Jacob T Carlin, Alexander V Ryzhkov, Jeffrey C Snyder, Alexander Khain
    Abstract:

    AbstractThe assimilation of radar data into storm-scale numerical weather prediction models has been shown to be beneficial for successfully modeling convective storms. Because of the difficulty of directly assimilating reflectivity (Z), hydrometeor mixing ratios, and sometimes Rainfall Rate, are often retrieved from Z observations using retrieval relations, and are assimilated as state variables. The most limiting (although widely employed) cases of these relations are derived, and their assumptions and limitations are discussed.To investigate the utility of these retrieval relations for liquid water content (LWC) and ice water content (IWC) in rain and hail as well as the potential for improvement using polarimetric variables, two models with spectral bin microphysics coupled with a polarimetric radar operator are used: a one-dimensional melting hail model and the two-dimensional Hebrew University Cloud Model. The relationship between LWC and Z in pure rain varies spatially and temporally, with biases c...

  • spectral bin microphysics coupled with a mesoscale model mm5 part ii simulation of a cape rain event with a squall line
    Monthly Weather Review, 2005
    Co-Authors: Barry Lynn, Alexander Khain, Jimy Dudhia, Daniel Rosenfeld, Andrei Pokrovsky, Axel Seifert
    Abstract:

    Abstract Spectral (bin) microphysics (SBM) has been implemented into the three-dimensional fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). The new model was used to simulate a squall line that developed over Florida on 27 July 1991. It is shown that SBM reproduces precipitation Rate, rain amounts, and location, radar reflectivity, and cloud structure much better than bulk parameterizations currently implemented in MM5. Sensitivity tests show the importance of (i) raindrop breakup, (ii) in-cloud turbulence, (iii) different aerosol concentrations, and (iv) inclusion of scavenging of aerosols. Breakup decreases average and maximum Rainfall. In-cloud turbulence enhances particle drop collision Rates and increases rain Rates. A “continental” aerosol concentration produces a much larger maximum Rainfall Rate versus that obtained with “maritime” aerosol concentration. At the same time accumulated rain is larger with maritime aerosol concentration. The scavenging of aerosols by nucleati...

Sandra E Yuter - One of the best experts on this subject based on the ideXlab platform.

  • relations between radar reflectivity liquid water content and Rainfall Rate during the map sop
    Quarterly Journal of the Royal Meteorological Society, 2003
    Co-Authors: Martin Hagen, Sandra E Yuter
    Abstract:

    SUMMARY Raindrop size distribution data obtained from two Joss‐Waldvogel disdrometers located at Locarno-Monti, Switzerland during the Mesoscale Alpine Programme (MAP) Special Observation Period are analysed to obtain appropriate relationships of radar ree ectivity, Z, with both water content, W, and surface Rainfall, R, for use in MAP applications. The disdrometer data are accumulated into 10-minute samples to reduce sampling error associated with the »1 m 3 sample volume of the instruments. Based on previous studies, relations of the form W D qZ .4=7/ and Z D aR 1:5 are assumed and the coefe cients q and a are estimated from the data. The combined dataset of 10-minute samples from the two disdrometers and the 10-minute data divided into two independent subsets yielded similar mean values of the coefe cients. The recommended relationships are W D 3:4Z .4=7/ and Z D 216R 1:5 . The uncertainties in these mean relationships as expressed in terms of §1 standard deviation are approximately equivalent to a §4.4 dBZ error for the Z‐W relationship, and to a §2.4 dBZ error for the Z‐R relationship.

Toshiaki Kozu - One of the best experts on this subject based on the ideXlab platform.

  • raindrop axis ratios fall velocities and size distribution over sumatra from 2d video disdrometer measurement
    Atmospheric Research, 2013
    Co-Authors: Walter Randeu, Hiroyuki Hashiguchi, Toshiaki Kozu, Toyoshi Shimomai, Michael Schonhuber
    Abstract:

    Abstract Raindrop axis ratio, falling velocity and size distribution are important in broad list of applications. However, they are not frequently observed in the equatorial region. This paper elucidated the characteristics of raindrop axis ratio, falling velocity and size distribution based on 2D-Video Disdrometer (2DVD) data that have been collected in the equatorial Indonesia, particularly at Kototabang (hereafter called KT), west Sumatra, Indonesia (0.20°S, 100.32°E, 864 m above sea level). A comprehensive follow-up of the previous study on the natural variability of raindrop size distributions (DSDs) is presented. Precipitation was classified through 1.3-GHz wind profiler observation. The dependence of raindrop falling velocity and axis ratio on Rainfall type was not clearly observed. Overall, measured raindrop fall velocities were in good agreement with Gunn–Kinzer's data. Raindrop axis ratio at KT was more spherical than that of artificial rain and equilibrium model, and close to the values reported in the turbulent high shear zone of surface layer which can be partially due to the effect of the instrument errors (e.g., location and container shape). Of some natural variations of DSD investigated, the dependence of DSD on Rainfall Rate and Rainfall type as well as diurnal variation was clearly visible. A striking contrast between the stratiform and convective rains is that the size distributions from the stratiform (convective) rains tend to narrow (broaden) with increasing Rainfall Rates. For Rainfall Rate R D m values in the morning hours than their counterparts in the evening. Rainfall type dependence and diurnal variation of DSD lead to significant variation of Z–R relations so that they must be considered to increase the accuracy of Z–R conversion from weather radar in this region. Consistent with the previous study, lack of seasonal DSD variability was also found in this work that would be due to significant local convective and orographic effect at this region throughout the year. However, D m values in our result were larger than the typical orographic DSD.

  • an overview of the precipitation retrieval algorithm for the dual frequency precipitation radar dpr on the global precipitation measurement gpm mission s core satellite
    Earth Observing Missions and Sensors: Development Implementation and Characterization II, 2012
    Co-Authors: Toshio Iguchi, Takuji Kubota, Naofumi Yoshida, Shinta Seto, Robert Meneghini, Jun Awaka, Toshiaki Kozu, V Chandra, Liang Liao, Simone Tanelli
    Abstract:

    This paper describes the planned level 2 algorithm that retrieves precipitation profiles from data to be obtained by the Dual-frequency Precipitation Radar (DPR) on the core satellite of the Global Precipitation Measurement (GPM) mission. The general idea behind the algorithms is to determine general characteristics of the precipitation, correct for attenuation and estimate profiles of the precipitation water content, Rainfall Rate and, when dual-wavelength data are available, information on the particle size distributions in rain and snow. It is particularly important that dual-wavelength data will provide better estimates of Rainfall and snowfall Rates than the TRMM PR data by using the particle size information and the capability of estimating the height at which the precipitation transitions from solid to liquid.

  • diurnal variation of rain attenuation obtained from measurement of raindrop size distribution in equatorial indonesia
    IEEE Transactions on Antennas and Propagation, 2009
    Co-Authors: Marzuki Marzuki, Hiroyuki Hashiguchi, Toshiaki Kozu, Walter Randeu, Toyoshi Shimomai, Yoshiaki Shibagaki
    Abstract:

    The measured rain Rate, raindrop size distribution (DSD), and the ITU-R model over the frequency range from 1-100 GHz have been used to elucidate the cumulative Rainfall Rate and the variability of rain attenuation at Kototabang. Rain Rate and DSD are recorded from ground-based optical rain gauge and disdrometer measurements, respectively. Considerable differences between the recorded data and the ITU-R model are observed at small time percentage. The specific rain attenuation obtained from the DSD measurement shows diurnal variation with the largest attenuation observed in the morning hours. This characteristic is due to the raindrop spectra of rain events in this period containing more small-sized drops (<2 mm) than at others as described by the largest contribution of these drops on the specific rain attenuation. The diurnal variation is serious for frequencies higher than 60 GHz especially in very extreme rain.

P Tabary - One of the best experts on this subject based on the ideXlab platform.

  • the new french operational polarimetric radar Rainfall Rate product
    Journal of Applied Meteorology and Climatology, 2013
    Co-Authors: Jordi Figueras I Ventura, P Tabary
    Abstract:

    AbstractIn 2012 the Meteo France metropolitan operational radar network consists of 24 radars operating at C and S bands. In addition, a network of four X-band gap-filler radars is being deployed in the French Alps. The network combines polarimetric and nonpolarimetric radars. Consequently, the operational radar Rainfall algorithm has been adapted to process both polarimetric and nonpolarimetric data. The polarimetric processing chain is available in two versions. In the first version, now operational, polarimetry is only used to correct for attenuation and filter out clear-air echoes. In the second version there is a more extensive use of polarimetry. In particular, the specific differential phase Kdp is used to estimate Rainfall Rate in intense rain. The performance of the three versions of radar Rainfall algorithms (conventional, polarimetric V1, and polarimetric V2) at different frequency bands (S, C, and X) is evaluated by processing radar data of significant events offline and comparing hourly radar...

Robin J Hogan - One of the best experts on this subject based on the ideXlab platform.

  • a variational scheme for retrieving Rainfall Rate and hail reflectivity fraction from polarization radar
    Journal of Applied Meteorology and Climatology, 2007
    Co-Authors: Robin J Hogan
    Abstract:

    Polarization radar offers the promise of much more accuRate Rainfall-Rate R estimates than are possible from radar reflectivity factor Z alone, not only by better characterization of the drop size distribution, but also by more reliable correction for attenuation and the identification of hail. However, practical attempts to implement retrieval algorithms have been hampered by the difficulty in coping with the inherent noise in the polarization parameters. In this paper, a variational retrieval scheme is described that overcomes these problems by employing a forward model for differential reflectivity Zdr and differential phase shift dp and iteratively refining the coefficient a in the relationship Z aR b such that the difference between the forward model and the measurements is minimized in a least squares sense. Two methods are used to ensure that a varies smoothly in both range and azimuth. In range, a is represented by a set of cubic-spline basis functions; in azimuth, the retrieval at one ray is used as a constraint on the next. The result of this smoothing is that the retrieval is tolerant of random errors in Zdr of up to 1 dB and in dp of up to 5°. Correction for attenuation is achieved simply and effectively by including its effects in the forward model. If hail is present then the forward model is unable to match the observations of Zdr and dp simultaneously. This enables a first pass of the retrieval to be used to identify the radar pixels that contain hail, followed by a second pass in which the fraction of the Z in those gates that is due to hail is retrieved, this time with the scheme being able to forward-model both Zdr and dp accuRately. The scheme is tested on S-band radar data from southern England in cases of rain, spherical hail, oblate hail, and mixtures of rain and hail. It is found to be robust and stable, even in the presence of differential phase shift on backscatter.