scholarly journals Hydrometeor Shape Variability in Snowfall as Retrieved from Polarimetric Radar Measurements

2020 ◽  
Vol 59 (9) ◽  
pp. 1503-1517
Author(s):  
Sergey Y. Matrosov ◽  
Alexander V. Ryzhkov ◽  
Maximilian Maahn ◽  
Gijs de Boer
Keyword(s):  
Aspect Ratio ◽  
Doppler Radar ◽  
Particle Model ◽  
Polarimetric Radar ◽  
Aspect Ratios ◽  
Air Temperatures ◽  
Radar Measurements ◽  
Differential Reflectivity ◽  
Particle Shapes

AbstractA polarimetric radar–based method for retrieving atmospheric ice particle shapes is applied to snowfall measurements by a scanning Ka-band radar deployed at Oliktok Point, Alaska (70.495°N, 149.883°W). The mean aspect ratio, which is defined by the hydrometeor minor-to-major dimension ratio for a spheroidal particle model, is retrieved as a particle shape parameter. The radar variables used for aspect ratio profile retrievals include reflectivity, differential reflectivity, and the copolar correlation coefficient. The retrievals indicate that hydrometeors with mean aspect ratios below 0.2–0.3 are usually present in regions with air temperatures warmer than approximately from −17° to −15°C, corresponding to a regime that has been shown to be favorable for growth of pristine ice crystals of planar habits. Radar reflectivities corresponding to the lowest mean aspect ratios are generally between −10 and 10 dBZ. For colder temperatures, mean aspect ratios are typically in a range between 0.3 and 0.8. There is a tendency for hydrometeor aspect ratios to increase as particles transition from altitudes in the temperature range from −17° to −15°C toward the ground. This increase is believed to result from aggregation and riming processes that cause particles to become more spherical and is associated with areas demonstrating differential reflectivity decreases with increasing reflectivity. Aspect ratio retrievals at the lowest altitudes are consistent with in situ measurements obtained using a surface-based multiangle snowflake camera. Pronounced gradients in particle aspect ratio profiles are observed at altitudes at which there is a change in the dominant hydrometeor species, as inferred by spectral measurements from a vertically pointing Doppler radar.

scholarly journals Atmospheric Ice Particle Shape Estimates from Polarimetric Radar Measurements and In Situ Observations

2017 ◽  
Vol 34 (12) ◽  
pp. 2569-2587 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Carl G. Schmitt ◽  
Maximilian Maahn ◽  
Gijs de Boer
Keyword(s):  
Aspect Ratio ◽  
Particle Shape ◽  
Characteristic Size ◽  
In Situ Measurements ◽  
Department Of Energy ◽  
Depolarization Ratio ◽  
Suggested Approach ◽  
Aspect Ratios ◽  
Radar Measurements

AbstractA remote sensing approach to retrieve the degree of nonsphericity of ice hydrometeors using scanning polarimetric Ka-band radar measurements from a U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program cloud radar operated in an alternate transmission–simultaneous reception mode is introduced. Nonsphericity is characterized by aspect ratios representing the ratios of particle minor-to-major dimensions. The approach is based on the use of a circular depolarization ratio (CDR) proxy reconstructed from differential reflectivity ZDR and copolar correlation coefficient ρhυ linear polarization measurements. Essentially combining information contained in ZDR and ρhυ, CDR-based retrievals of aspect ratios are fairly insensitive to hydrometeor orientation if measurements are performed at elevation angles of around 40°–50°. The suggested approach is applied to data collected using the third ARM Mobile Facility (AMF3), deployed to Oliktok Point, Alaska. Aspect ratio retrievals were also performed using ZDR measurements that are more strongly (compared to CDR) influenced by hydrometeor orientation. The results of radar-based retrievals are compared with in situ measurements from the tethered balloon system (TBS)-based video ice particle sampler and the ground-based multiangle snowflake camera. The observed ice hydrometeors were predominantly irregular-shaped ice crystals and aggregates, with aspect ratios varying between approximately 0.3 and 0.8. The retrievals assume that particle bulk density influencing (besides the particle shape) observed polarimetric variables can be deduced from the estimates of particle characteristic size. Uncertainties of CDR-based aspect ratio retrievals are estimated at about 0.1–0.15. Given these uncertainties, radar-based retrievals generally agreed with in situ measurements. The advantages of using the CDR proxy compared to the linear depolarization ratio are discussed.

scholarly journals Velocity-Based EDR Retrieval Techniques Applied to Doppler Radar Measurements from Rain: Two Case Studies

2019 ◽  
Vol 36 (9) ◽  
pp. 1693-1711 ◽  
Author(s):  
A. C. P. Oude Nijhuis ◽  
C. M. H. Unal ◽  
O. A. Krasnov ◽  
H. W. J. Russchenberg ◽  
A. G. Yarovoy
Keyword(s):  
Case Studies ◽  
Doppler Radar ◽  
Energy Dissipation Rate ◽  
Accurate Estimation ◽  
Retrieval Technique ◽  
Sonic Anemometers ◽  
Radar Measurements ◽  
Rain Events ◽  
Kolmogorov Constant

In this article, five velocity-based energy dissipation rate (EDR) retrieval techniques are assessed. The EDR retrieval techniques are applied to Doppler measurements from Transportable Atmospheric Radar (TARA)—a precipitation profiling radar—operating in the vertically fixed-pointing mode. A generalized formula for the Kolmogorov constant is derived, which gives potential for the application of the EDR retrieval techniques to any radar line of sight (LOS). Two case studies are discussed that contain rain events of about 2 and 18 h, respectively. The EDR values retrieved from the radar are compared to in situ EDR values from collocated sonic anemometers. For the two case studies, a correlation coefficient of 0.79 was found for the wind speed variance (WSV) EDR retrieval technique, which uses 3D wind vectors as input and has a total sampling time of 10 min. From this comparison it is concluded that the radar is able to measure EDR with a reasonable accuracy. Almost no correlation was found for the vertical wind velocity variance (VWVV) EDR retrieval technique, as it was not possible to sufficiently separate the turbulence dynamics contribution to the radar Doppler mean velocities from the velocity contribution of falling raindrops. An important cause of the discrepancies between radar and in situ EDR values is thus due to insufficient accurate estimation of vertical air velocities.

Removing the Barriers to Next Generation'S Dielectric Films: In Situ Void-Free Planarized Films

1990 ◽  
Vol 203 ◽  
Author(s):  
J.R. Monkowski ◽  
M.A. Logan ◽  
L.F. Wright
Keyword(s):  
Aspect Ratio ◽  
Ion Chromatography ◽  
Field Measurements ◽  
Dielectric Films ◽  
Breakdown Field ◽  
Scanning Electron Micrographs ◽  
Aspect Ratios ◽  
New Process ◽  
Scanning Electron

ABSTRACTIn the next generation of semiconductor devices, minimum dimensions will be smaller, aspect ratios (height to width) of devices features will be larger, and BPSG dielectrics will be challenged to deal with these changes. A new process, which integrates deposition, flow, and anneal of BPSG films, and allows void-free filling of high-aspect-ratio trenches with excellent surface planarization, is presented in this paper. Scanning electron micrographs are used to show the extent of film coverage and planarization. Additional characterization includes ion chromatography, ellipsometry, stress measurements, and breakdown field measurements.

Solidification Processing Routes to High Aspect Ratio Reinforcements in γ-TiAl

1990 ◽  
Vol 194 ◽  
Author(s):  
J. J. Valencia ◽  
J. P. A. Löfvander ◽  
J. Rösler ◽  
C. G. Levi ◽  
R. Mehrabian
Keyword(s):  
Solid Solution ◽  
Aspect Ratio ◽  
Creep Strength ◽  
High Aspect Ratio ◽  
Anisotropic Growth ◽  
Solidification Processing ◽  
Aspect Ratios ◽  
The Matrix ◽  
Solute Strengthening

AbstractAdditions of ∼5%B1 and ∼9%Ta to binary γ-TiAl result in the formation of a monoboride isomorphous with TiB but containing Ta in solid solution. This boride exhibits strongly anisotropic growth from the melt, producing rod-like primary phases which are of potential interest for creep strengthening of the γ matrix. Fibrous borides with aspect ratios larger than ∼20 and volume fractions of ∼0.12 have been produced in arc-melted Ti-48AI-9Ta-4.3B alloys. Creep testing at 1255 K indicates that these “in-situ” composites have much higher creep strength than γ-TiAl, but the contribution of the reinforcements is relatively small compared with the solute-strengthening of the matrix.

scholarly journals A Variational Approach for Retrieving Raindrop Size Distribution from Polarimetric Radar Measurements in the Presence of Attenuation

2013 ◽  
Vol 52 (1) ◽  
pp. 169-185 ◽  
Author(s):  
Qing Cao ◽  
Guifu Zhang ◽  
Ming Xue
Keyword(s):  
Variational Approach ◽  
Simulated Data ◽  
Real Data ◽  
Radar Data ◽  
Polarimetric Radar ◽  
University Of Oklahoma ◽  
Raindrop Size Distribution ◽  
Radar Measurements ◽  
Raindrop Size ◽  
Differential Reflectivity

AbstractThis study presents a two-dimensional variational approach to retrieving raindrop size distributions (DSDs) from polarimetric radar data in the presence of attenuation. A two-parameter DSD model, the constrained-gamma model, is used to represent rain DSDs. Three polarimetric radar measurements—reflectivity ZH, differential reflectivity ZDR, and specific differential phase KDP—are optimally used to correct for the attenuation and retrieve DSDs by taking into account measurement error effects. Retrieval results with simulated data demonstrate that the proposed algorithm performs well. Applications to real data collected by the X-band Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) radars and the C-band University of Oklahoma–Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME) also demonstrate the efficacy of this approach.

scholarly journals Can a Unique Model Describe the Raindrop Shape–Size Relation? A Clue from Polarimetric Radar Measurements

2009 ◽  
Vol 26 (9) ◽  
pp. 1829-1842 ◽  
Author(s):  
Eugenio Gorgucci ◽  
V. Chandrasekar ◽  
Luca Baldini
Keyword(s):  
Axial Ratio ◽  
Radar Data ◽  
Polarimetric Radar ◽  
Drop Shape ◽  
Climatic Regions ◽  
Unique Shape ◽  
Initial Drop ◽  
Radar Measurements ◽  
Differential Reflectivity ◽  
Size Relation

Abstract A method is proposed to retrieve raindrop shape–size relations from the radar measurements of reflectivity factor Zh, differential reflectivity Zdr, and specific differential phase Kdp at S band. This procedure is obtained using a domain defined by the two variables Kdp/Zh and Zdr where the drop size distribution (DSD) variability is collapsed onto a line and any variation is essentially due to the drop shape variability. To obtain information on the raindrop shape–size relation underlying a set of radar observations, this domain is studied in conjunction with another domain describing the relation between the drop axial ratio (or shape) and its equivolumetric diameter. Using an initial drop shape and choosing a set of DSDs described by a normalized gamma model, polarimetric radar measurements are produced by simulation. An averaged curve of Kdp/Zh versus Zdr is obtained and compared with the same curve obtained from the radar data. By changing the initial axial ratio relation, a procedure of minimization between the two curves is developed to derive the underlying drop shape–size relation governing the radar measurements under consideration. Three sets of radar data collected in different climatic regions are analyzed to evaluate whether there is a unique shape–size relation.

Influence of Particle Shape and Contact Parameters on DEM-Simulated Bulk Density of Wheat

2020 ◽  
Vol 63 (6) ◽  
pp. 1657-1672
Author(s):  
Marvin C. Petingco ◽  
Mark E. Casada ◽  
Ronaldo G. Maghirang ◽  
Oladiran O. Fasina ◽  
Zhengpu Chen ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Bulk Density ◽  
Particle Shape ◽  
Static Friction ◽  
Rolling Friction ◽  
Particle Model ◽  
Dem Simulation ◽  
Aspect Ratios ◽  
Ellipsoidal Particles ◽  
Contact Parameters

HighlightsDecreasing aspect ratio and improved geometrical smoothness of particles increased DEM-predicted bulk density of wheat.Among the three particle models, the 5-sphere ellipsoidal particle was the best option to represent wheat particles, as indicated by the simulated bulk densities that best agreed with the experiments.Among the contact parameters, the wheat-to-wheat coefficient of static friction and wheat-surface coefficient of rolling friction had the greatest influence on simulated bulk density.Abstract. The discrete element method (DEM) has been shown to be an effective tool for simulating the behavior of granular material. The accuracy of simulations depends highly on the contact models, particle physical parameters, and contact parameters used. The objectives of this study were to determine the influence of particle shape and contact parameters on simulated wheat bulk density and to develop an effective wheat particle model for DEM simulation of filling a container using EDEM software. Grain characteristics, including single-kernel weight, kernel density, kernel dimensions, aspect ratio, and bulk density, were determined for three size fractions of wheat used in the experiments. Three categories of particle models (5-sphere pseudo-ellipsoidal, 7-sphere pseudo-ellipsoidal, and ASG-generated) with varying aspect ratios and geometrical smoothness were tested in the simulations. Results showed that DEM-simulated bulk density of wheat increased with lower aspect ratio and greater geometrical smoothness of pseudo-ellipsoidal particles (7-sphere versus 5-sphere). Increasing the number of spheres to approximately 30 for better representation of wheat kernel shape, using ASG-generated particles, did not reproduce the trend of greater simulated bulk density seen in the experiments. Among the six contact parameters, the wheat-wheat coefficient of static friction and wheat-surface coefficient of rolling friction had the most significant effect on the simulated bulk density. Among the different sets of particle models, the 5-sphere pseudo-ellipsoidal particles, having aspect ratios close to that of wheat kernels in each size fraction, were found to be the most practical and appropriate particle model for use in DEM simulation of wheat bulk density. This study contributes to better understanding of the influence of particle shape and contact parameters on DEM-simulated bulk density and provides a calibrated particle model for use in simulating container filling operations. Keywords: Bulk density, Contact parameters, DEM, Particle shape, Wheat.

scholarly journals A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications

2019 ◽  
Vol 76 (1) ◽  
pp. 305-332 ◽  
Author(s):  
Edwin L. Dunnavan ◽  
Zhiyuan Jiang
Keyword(s):  
Aspect Ratio ◽  
Particle Shape ◽  
Ratio Distribution ◽  
Aspect Ratios ◽  
Shape Uncertainty ◽  
Aspect Ratio Distribution ◽  
Spheroidal Geometry ◽  
Orientation Parameters ◽  
General Method

Abstract The orientation of falling ice particles directly influences estimates of microphysical and radiative bulk quantities as well as in situ retrievals of size, shape, and mass. However, retrieval efforts and bulk calculations often incorporate very basic orientations or ignore these effects altogether. To address this deficiency, this study develops a general method for projecting bulk distributions of particle shape for arbitrary orientations. The Amoroso distribution provides the most general bulk aspect ratio distribution for gamma-distributed particle axis lengths. The parameters that govern the behavior of this aspect ratio distribution depend on the assumed relationship between mass, maximum dimension, and aspect ratio. Individual spheroidal geometry allows for eccentricity quantities to linearly map onto ellipse analogs, whereas aspect ratio quantities map nonlinearly. For particles viewed from their side, this analytic distinction leads to substantially larger errors in projected aspect ratio than for projected eccentricity. Distribution transformations using these mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientation parameters. This shape uncertainty is maximized for distributions of highly eccentric particles and for particles like aggregates that are thought to fall with large canting-angle deviations. As a result, the methods used to report projected aspect ratios and the corresponding values should be questioned.

Improving Parameterization of Rain Microphysics with Disdrometer and Radar Observations

2006 ◽  
Vol 63 (4) ◽  
pp. 1273-1290 ◽  
Author(s):  
Guifu Zhang ◽  
Juanzhen Sun ◽  
Edward A. Brandes
Keyword(s):  
Doppler Radar ◽  
Numerical Models ◽  
Distribution Model ◽  
Model Parameterization ◽  
Raindrop Size Distribution ◽  
Single Moment ◽  
Radar Measurements ◽  
Raindrop Size ◽  
Analysis System ◽  
Differential Reflectivity

Abstract Disdrometer observations indicate that the raindrop size distribution (DSD) can be represented by a constrained-gamma (CG) distribution model. The model is used to retrieve DSDs from polarization radar measurements of reflectivity and differential reflectivity and to characterize rain microphysics and physical processes such as evaporation, accretion, and precipitation. The CG model parameterization is simplified to a single parameter for application in single-moment numerical models. This simplified parameterization is applied in the Variational Doppler Radar Analysis System (VDRAS) using Kessler-type parameterizations for model initialization and forecasting. Results are compared to those for the Marshall–Palmer (MP) DSD model. It is found that the simplified CG model parameterization better preserves the stratiform rain and produces better forecasts than the MP model parameterization.

scholarly journals Ice Hydrometeor Shape Estimations Using Polarimetric Operational and Research Radar Measurements

Atmosphere ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 97 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Depolarization Ratio ◽  
Model Uncertainties ◽  
Shape Information ◽  
Ice Cloud ◽  
Cloud Radar ◽  
Weather Radars ◽  
Aspect Ratios ◽  
Radar Systems ◽  
Radar Measurements ◽  
Differential Reflectivity

A polarimetric radar method to estimate mean shapes of ice hydrometeors was applied to several snowfall and ice cloud events observed by operational and research weather radars. The hydrometeor shape information is described in terms of their aspect ratios, r, which represent the ratio of particle minor and major dimensions. The method is based on the relations between depolarization ratio (DR) estimates and aspect ratios. DR values, which are a proxy for circular depolarization ratio, were reconstructed from radar variables of reflectivity factor, Ze, differential reflectivity, ZDR, and copolar correlation coefficient ρhv, which are available from radar systems operating in either simultaneous or alternate transmutation of horizontally and vertically polarized signals. DR-r relations were developed for retrieving aspect ratios and their sensitivity to different assumptions and model uncertainties were discussed. To account for changing particle bulk density, which is a major contributor to the retrieval uncertainty, an approach is suggested to tune the DR-r relations using reflectivity-based estimates of characteristic hydrometeor size. The analyzed events include moderate snowfall observed by an operational S-band weather radar and a precipitating ice cloud observed by a scanning Ka-band cloud radar at an Arctic location. Uncertainties of the retrievals are discussed.

Sign in / Sign up

Export Citation Format

Share Document