scholarly journals Bragg Scatter Detection by the WSR-88D. Part I: Algorithm Development

2017 ◽  
Vol 34 (3) ◽  
pp. 465-478 ◽  
Author(s):  
Lindsey M. Richardson ◽  
Jeffrey G. Cunningham ◽  
W. David Zittel ◽  
Robert R. Lee ◽  
Richard L. Ice ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Relative Humidity ◽  
Richardson Number ◽  
Automated Detection ◽  
Dual Polarization ◽  
Convective Boundary ◽  
Ground Clutter ◽  
Radar Calibration ◽  
Visual Confirmation ◽  
Differential Reflectivity

AbstractStudies have shown that echo returns from clear-air Bragg scatter (CABS) can be used to detect the height of the convective boundary layer and to assess the systematic differential reflectivity (ZDR) bias for a radar site. However, these studies did not use data from operational Weather Surveillance Radar-1988 Doppler (WSR-88D) or data from a large variety of sites. A new algorithm to automatically detect CABS from any operational WSR-88D with dual-polarization capability while excluding contamination from precipitation, biota, and ground clutter is presented here. Visual confirmation and tests related to the sounding parameters’ relative humidity slope, refractivity gradient, and gradient Richardson number are used to assess the algorithm. Results show that automated detection of CABS in operational WSR-88D data gives useful ZDR bias information while omitting the majority of contaminated cases. Such an algorithm holds potential for radar calibration efforts and Bragg scatter studies in general.

scholarly journals Convective Boundary Layer Depth Estimation from S-Band Dual-Polarization Radar

2018 ◽  
Vol 35 (8) ◽  
pp. 1723-1733 ◽  
Author(s):  
John R. Banghoff ◽  
David J. Stensrud ◽  
Matthew R. Kumjian
Keyword(s):  
Boundary Layer ◽  
New York ◽  
Convective Boundary Layer ◽  
Depth Estimation ◽  
Dual Polarization ◽  
Layer Depth ◽  
Reasonable Estimate ◽  
Convective Boundary ◽  
Using Data ◽  
Differential Reflectivity

AbstractThis study investigates Bragg scatter signatures in dual-polarization radar observations, which are defined by low differential reflectivity values, as a proxy for convective boundary layer (CBL) depth. Using data from the WSR-88D in Twin Lakes, Oklahoma (KTLX), local minima in quasi-vertical profiles of are found to provide a reasonable estimate of CBL depth when compared with depth estimates from upper-air soundings from Norman, Oklahoma (KOUN), during 2014. The 243 Bragg scatter and upper-air sounding CBL depth estimates have a correlation of 0.90 and an RMSE of 254 m. Using Bragg scatter as a proxy for CBL depth was expanded to other seasons and locations—performing well in Wilmington, Ohio; Fairbanks, Alaska; Tucson, Arizona; Minneapolis, Minnesota; Albany, New York; Portland, Oregon; and Tampa, Florida—showing its potential usefulness in monitoring CBL depth throughout the year in a variety of geographic locations and meteorological conditions.

scholarly journals Some Observational Evidence for Dry Soils Supporting Enhanced Relative Humidity at the Convective Boundary Layer Top

2012 ◽  
Vol 13 (4) ◽  
pp. 1347-1358 ◽  
Author(s):  
D. Westra ◽  
G. J. Steeneveld ◽  
A. A. M. Holtslag
Keyword(s):  
Boundary Layer ◽  
Relative Humidity ◽  
Conceptual Framework ◽  
Convective Boundary Layer ◽  
Land Surface ◽  
Layer Growth ◽  
Observational Evidence ◽  
Cloud Formation ◽  
Semiarid Region ◽  
Convective Boundary

Abstract The tendency of the relative humidity at the top of a clear convective boundary layer (RHtop) is studied as an indicator of cloud formation over a semiarid region within the conceptual framework introduced by Ek and Holtslag. Typically the tendency of RHtop increases if the evaporative fraction at the land surface increases, which supports boundary layer moistening but only when boundary layer growth is limited by atmospheric factors. This regime was supported by Cabauw observations in the original study. Here, new observational evidence that the tendency of RHtop can also increase as the surface becomes more dry, as is consistent with another regime of the conceptual framework, is provided. The observations used are from the African Monsoon Multidisciplinary Analyses (AMMA) intensive observational campaign near Niamey, Niger, 20–25 June 2006. In addition, the authors evaluate whether various versions of the Weather Research and Forecasting single-column model confirm the different regimes of the conceptual framework for a typical day in the AMMA campaign. It appears that the model confirms that dryer soils can support cloud formation.

scholarly journals Use of Ground Clutter to Monitor Polarimetric Radar Calibration

2012 ◽  
Vol 29 (2) ◽  
pp. 159-176 ◽  
Author(s):  
L. Borowska ◽  
D. Zrnic
Keyword(s):  
Environmental Factors ◽  
Heavy Precipitation ◽  
Cold Season ◽  
Polarimetric Radar ◽  
Operational Monitoring ◽  
Ground Clutter ◽  
X Band ◽  
Hot Days ◽  
Radar Calibration ◽  
Differential Reflectivity

Abstract It is suggested that urban ground clutter can have a role in monitoring calibration of reflectivity factor ZH and differential reflectivity ZDR on polarimetric radars. The median and average values of these variables are considered. Analysis of data from 1 month of cold season in Germany (X-band radar) and 3.5 hot days in Oklahoma (S-band radar) is presented. In the presence of up to moderate rain or snow a reflectivity threshold suffices for separating significant clutter from precipitation observed with an X-band radar. The same threshold was suitable on observations with an S-band radar in Oklahoma because heavy precipitation was not present. The tests suggest the scheme is worthy considering for operational monitoring of ZH as its median values at both locations were within the quantization interval of 0.5 dB. Environmental factors that can influence reflectivities from clutter are examined. The effects on ZDR can be significant. These are quantified in the data and possible uses for calibration and monitoring radar status are indicated.

scholarly journals Structures of Bragg Scatter Observed with the Polarimetric WSR-88D

2013 ◽  
Vol 30 (7) ◽  
pp. 1253-1258 ◽  
Author(s):  
Valery M. Melnikov ◽  
Richard J. Doviak ◽  
Dusan S. Zrnić ◽  
David J. Stensrud
Keyword(s):  
Boundary Layer ◽  
Signal Processing ◽  
Data Collection ◽  
Convective Boundary Layer ◽  
Dual Polarization ◽  
Detection Capability ◽  
Convective Boundary ◽  
Boundary Layer Turbulence ◽  
Fine Structures

Abstract Enhancements to signal processing and data collection in the dual-polarization Weather Surveillance Radar-1988 Doppler (WSR-88D) to increase its detection capability yield observations of “fine” structures from Bragg scatterers. Several types of the fine structures observed in and above the boundary layer are discussed. These Bragg scatter structures include the top of the convective boundary layer, nonprecipitating clouds, strong convective plumes above the boundary layer, and a layer of weak reflections associated with decaying boundary layer turbulence. A conclusion that data from polarimetric WSR-88Ds can be used to obtain the depth of the convective boundary layer is made.

Dual-Polarization Radar Characteristics of an Apartment Fire

2009 ◽  
Vol 26 (10) ◽  
pp. 2257-2269 ◽  
Author(s):  
Thomas A. Jones ◽  
Sundar A. Christopher ◽  
Walt Petersen
Keyword(s):  
Correlation Coefficients ◽  
Ground Level ◽  
Significant Degree ◽  
Substantial Contribution ◽  
Bragg Scattering ◽  
Dual Polarization ◽  
Ground Clutter ◽  
Fire Debris ◽  
Close Range ◽  
Differential Reflectivity

Abstract Dual-polarimetric microwave wavelength radar observations of an apartment fire in Huntsville, Alabama, on 3 March 2008 are examined to determine the radar-observable properties of ash and fire debris lofted into the atmosphere. Dual-polarimetric observations are collected at close range (<20 km) by the 5-cm (C band) Advanced Radar for Meteorological and Operational Research (ARMOR) radar operated by the University of Alabama in Huntsville. Precipitation radars, such as ARMOR, are not sensitive to aerosol-sized (D < 10 μm) smoke particles, but they are sensitive to the larger ash and burnt debris embedded within the smoke plume. The authors also assess if turbulent eddies caused by the heat of the fire cause Bragg scattering to occur at the 5-cm wavelength. In this example, the mean reflectivity within the debris plume from the 1.3° elevation scan was 9.0 dBZ, with a few values exceeding 20 dBZ. The plume is present more than 20 km downstream of the fire, with debris lofted at least 1 km above ground level into the atmosphere. Velocities up to 20 m s−1 are present within the plume, indicating that the travel time for the debris from its source to the maximum range of detection is less than 20 min. Dual-polarization observations show that backscattered radiation is dominated by nonspherical, large, oblate targets as indicated by nonzero differential reflectivity values (mean = 1.7 dB) and low correlation coefficients (0.49). Boundary layer convective rolls are also observed that have very low reflectivity values (−6.0 dBZ); however, differential reflectivity is much larger (3.2 dB). This is likely the result of noise, because ARMOR differential reflectivity is not reliable for reflectivity values <0 dBZ. Also, copolar correlation is even lower compared to the debris plume (0.42). The remainder of the data mainly consists of atmospheric and ground-clutter noise. The large differential phase values coupled with positive differential reflectivity strongly indicate that the source of much of the return from the debris plume is particle scattering. However, given the significant degree of noise present, a substantial contribution from Bragg scattering cannot be entirely ruled out.

scholarly journals An integrated approach to monitor the calibration stability of operational dual-polarization radars

2016 ◽  
Author(s):  
Mattia Vaccarono ◽  
Renzo Bechini ◽  
Venkatachalam Chandrasekar ◽  
Roberto Cremonini ◽  
Claudio Cassardo
Keyword(s):  
Weather Prediction ◽  
Weather Radar ◽  
Integrated Approach ◽  
The Sun ◽  
Dual Polarization ◽  
Ground Clutter ◽  
Hardware Failures ◽  
Radar Calibration ◽  
The Stability ◽  
Self Consistency

Abstract. The stability of the weather radar calibration is a mandatory aspect for quantitative applications, such as rainfall estimation, short-term weather prediction and initialization of numerical atmospheric and hydrological models. Over the years, calibration monitoring techniques based on external sources have been developed, specifically the calibration using the Sun, and the calibration based on ground clutter returns. In this paper, these two techniques are integrated and complemented with a self-consistency procedure and an intercalibration technique. The aim of the integrated approach is to implement a robust method for online monitoring, able to detect significant changes in the radar calibration. The physical consistency of polarimetric radar observables is exploited using the self-consistency approach, based on the expected correspondence between the dual-polarization power and phase measurements in rain. This technique allows to provide a reference absolute value for the radar calibration, from which eventual deviations may be detected using the other procedures. In particular, the ground clutter calibration is implemented on both polarization channels (horizontal and vertical) and for each radar scan, allowing to monitor the polarimetric variables and promptly recognize hardware failures. The Sun calibration allows to monitor the calibration and sensitivity of the radar receiver, in addition to the antenna pointing accuracy. It is also applied using observations collected during the standard operational scans, but requires longer integration times (several days) in order to accumulate a sufficient amount of data. Finally, an intercalibration technique is developed and performed to compare co-located measurements collected in rain by two radars on overlapping regions. The integrated approach is performed on the C-band weather radar network in northwestern Italy, during July–October 2014. The set of methods considered is shown to provide a robust online tool to monitor the stability of the radar calibration. The attainable accuracy for the calibration of the radar reflectivity is about 1 dB, which is considered adequate for most quantitative applications.

scholarly journals An integrated approach to monitoring the calibration stability of operational dual-polarization radars

2016 ◽  
Vol 9 (11) ◽  
pp. 5367-5383 ◽  
Author(s):  
Mattia Vaccarono ◽  
Renzo Bechini ◽  
Chandra V. Chandrasekar ◽  
Roberto Cremonini ◽  
Claudio Cassardo
Keyword(s):  
Weather Prediction ◽  
Weather Radar ◽  
Integrated Approach ◽  
The Sun ◽  
Dual Polarization ◽  
Ground Clutter ◽  
Hardware Failures ◽  
Radar Calibration ◽  
The Stability ◽  
Self Consistency

Abstract. The stability of weather radar calibration is a mandatory aspect for quantitative applications, such as rainfall estimation, short-term weather prediction and initialization of numerical atmospheric and hydrological models. Over the years, calibration monitoring techniques based on external sources have been developed, specifically calibration using the Sun and calibration based on ground clutter returns. In this paper, these two techniques are integrated and complemented with a self-consistency procedure and an intercalibration technique. The aim of the integrated approach is to implement a robust method for online monitoring, able to detect significant changes in the radar calibration. The physical consistency of polarimetric radar observables is exploited using the self-consistency approach, based on the expected correspondence between dual-polarization power and phase measurements in rain. This technique allows a reference absolute value to be provided for the radar calibration, from which eventual deviations may be detected using the other procedures. In particular, the ground clutter calibration is implemented on both polarization channels (horizontal and vertical) for each radar scan, allowing the polarimetric variables to be monitored and hardware failures to promptly be recognized. The Sun calibration allows monitoring the calibration and sensitivity of the radar receiver, in addition to the antenna pointing accuracy. It is applied using observations collected during the standard operational scans but requires long integration times (several days) in order to accumulate a sufficient amount of useful data. Finally, an intercalibration technique is developed and performed to compare colocated measurements collected in rain by two radars in overlapping regions. The integrated approach is performed on the C-band weather radar network in northwestern Italy, during July–October 2014. The set of methods considered appears suitable to establish an online tool to monitor the stability of the radar calibration with an accuracy of about 2 dB. This is considered adequate to automatically detect any unexpected change in the radar system requiring further data analysis or on-site measurements.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

2020 ◽  
Vol 45 (4) ◽  
pp. 373-383
Author(s):  
Nepal Chandra Roy ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Thermal Boundary Layer ◽  
Volume Fraction ◽  
Convection Flow ◽  
Mixed Convection Flow

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

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