S-Band Dual-Polarization Radar Observations of Winter Storms

2011 ◽  
Vol 50 (4) ◽  
pp. 844-858 ◽  
Author(s):  
Patrick C. Kennedy ◽  
Steven A. Rutledge
Keyword(s):  
Particle Growth ◽  
Dual Polarization ◽  
Winter Storms ◽  
Radar Observations ◽  
Surface Precipitation ◽  
Colorado State University ◽  
Local Maxima ◽  
Temperature Isotherm ◽  
State Water ◽  
Differential Reflectivity

AbstractThis study is based on analyses of dual-polarization radar observations made by the 11-cm-wavelength Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) system during four significant winter storms in northeastern Colorado. It was found that values of specific differential phase KDP often reached local maxima of ∼0.15°–0.4° km−1 in an elevated layer near the −15°C environmental temperature isotherm. The passage of these elevated positive KDP areas is shown to be linked to increased surface precipitation rates. Calculations using a microwave scattering model indicate that populations of highly oblate ice particles with moderate bulk densities and diameters in the ∼0.8–1.2-mm range can generate KDP (and differential reflectivity ZDR) values that are consistent with the radar observations. The persistent correlation between the enhanced KDP level and the −15°C temperature regime suggests that rapidly growing dendrites likely played a significant role in the production of the observed KDP patterns. The detection of organized regions of S-band KDP values greater than ∼0.1°–0.2° km−1 in winter storms may therefore be useful in identifying regions of active dendritic particle growth, as a precursor to aggregate snowfall.

scholarly journals Wideband Reception and Processing for Dual-Polarization Radars with Dual Transmitters

2007 ◽  
Vol 24 (1) ◽  
pp. 95-101 ◽  
Author(s):  
Sutanay Choudhury ◽  
V. Chandrasekar
Keyword(s):  
Doppler Radar ◽  
Negative Impact ◽  
Spectral Width ◽  
Parameter Estimates ◽  
Dual Polarization ◽  
Mean Velocity ◽  
Colorado State University ◽  
State Water ◽  
Differential Reflectivity ◽  
The Impact

Abstract Oversampling pulsed Doppler radar returns at a rate larger than the pulse bandwidth, whitening the range samples, and subsequent averaging has been pursued as a potential way to decrease the measured standard deviation of signal parameter estimates. It has been shown that the application of oversampling, whitening, and subsequent averaging improves the quality of reflectivity, mean velocity, and spectral width estimates in agreement with theory. Application of this procedure to a dual-polarization radar with dual transmitters is evaluated in this paper. Oversampled data collected from the Colorado State University (CSU)-University of Chicago–Illinois State Water Survey (CHILL) radar using a wideband receiver are analyzed to evaluate the performance of dual-polarization parameter estimators, such as differential reflectivity and differential phase. The negative impact of relative phase characteristics of the transmitted pulses in two polarizations on the copolar correlation, and subsequently on polarimetric parameter estimation, is analyzed. CSU-CHILL radar’s transmitted pulse sampling capability is used to evaluate the impact of the transmitted waveform’s mismatch on whitening and estimation.

scholarly journals Polarimetric Radar Signatures of Dendritic Growth Zones within Colorado Winter Storms

2015 ◽  
Vol 54 (12) ◽  
pp. 2365-2388 ◽  
Author(s):  
Robert S. Schrom ◽  
Matthew R. Kumjian ◽  
Yinghui Lu
Keyword(s):  
Electromagnetic Scattering ◽  
Polarimetric Radar ◽  
Front Range ◽  
Horizontal Polarization ◽  
Winter Storms ◽  
Radar Observations ◽  
Colorado State University ◽  
Radar Signature ◽  
Radar Signatures ◽  
Differential Reflectivity

AbstractX-band polarimetric radar observations of winter storms in northeastern Colorado on 20–21 February, 9 March, and 9 April 2013 are examined. These observations were taken by the Colorado State University–University of Chicago–Illinois State Water Survey (CSU-CHILL) radar during the Front Range Orographic Storms (FROST) project. The polarimetric radar moments of reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, and specific differential phase KDP exhibited a range of signatures at different times near the −15°C temperature level favored for dendritic ice crystal growth. In general, KDP was enhanced in these regions with ZDR decreasing and ZH increasing toward the ground, suggestive of aggregation (or riming). The largest ZDR values (~3.5–5.5 dB) were observed during periods of significant low-level upslope flow. Convective features observed when the upslope flow was weaker had the highest KDP (>1.5° km−1) and ZH (>20 dBZ) values. Electromagnetic scattering calculations using the generalized multiparticle Mie method were used to determine whether these radar signatures were consistent with dendrites. Particle size distributions (PSDs) of dendrites were retrieved for a variety of cases using these scattering calculations and the radar observations. The PSDs derived using stratiform precipitation observations were found to be reasonably consistent with previous PSD observations. PSDs derived where riming may have occurred likely had errors and deviated significantly from these previous PSD observations. These results suggest that this polarimetric radar signature may therefore be useful in identifying regions of rapidly collecting dendrites, after considering the effects of riming on the radar variables.

A New Dual-Polarization Radar Rainfall Algorithm: Application in Colorado Precipitation Events

2011 ◽  
Vol 28 (3) ◽  
pp. 352-364 ◽  
Author(s):  
R. Cifelli ◽  
V. Chandrasekar ◽  
S. Lim ◽  
P. C. Kennedy ◽  
Y. Wang ◽  
...  
Keyword(s):  
Estimation Algorithm ◽  
State University ◽  
Dual Polarization ◽  
Rainfall Estimation ◽  
Radar Rainfall ◽  
Colorado State University ◽  
Differential Phase ◽  
Precipitation Estimation ◽  
The One ◽  
Differential Reflectivity

Abstract The efficacy of dual-polarization radar for quantitative precipitation estimation (QPE) has been demonstrated in a number of previous studies. Specifically, rainfall retrievals using combinations of reflectivity (Zh), differential reflectivity (Zdr), and specific differential phase (Kdp) have advantages over traditional Z–R methods because more information about the drop size distribution (DSD) and hydrometeor type are available. In addition, dual-polarization-based rain-rate estimators can better account for the presence of ice in the sampling volume. An important issue in dual-polarization rainfall estimation is determining which method to employ for a given set of polarimetric observables. For example, under what circumstances does differential phase information provide superior rain estimates relative to methods using reflectivity and differential reflectivity? At Colorado State University (CSU), an optimization algorithm has been developed and used for a number of years to estimate rainfall based on thresholds of Zh, Zdr, and Kdp. Although the algorithm has demonstrated robust performance in both tropical and midlatitude environments, results have shown that the retrieval is sensitive to the selection of the fixed thresholds. In this study, a new rainfall algorithm is developed using hydrometeor identification (HID) to guide the choice of the particular rainfall estimation algorithm. A separate HID algorithm has been developed primarily to guide the rainfall application with the hydrometeor classes, namely, all rain, mixed precipitation, and all ice. Both the data collected from the S-band Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) radar and a network of rain gauges are used to evaluate the performance of the new algorithm in mixed rain and hail in Colorado. The evaluation is also performed using an algorithm similar to the one developed for the Joint Polarization Experiment (JPOLE). Results show that the new CSU HID-based algorithm provides good performance for the Colorado case studies presented here.

scholarly journals A Comparison of X-Band Polarization Parameters with In Situ Microphysical Measurements in the Comma Head of Two Winter Cyclones

2016 ◽  
Vol 55 (12) ◽  
pp. 2549-2574 ◽  
Author(s):  
Joseph A. Finlon ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
David M. Plummer ◽  
Brian F. Jewett ◽  
...  
Keyword(s):  
Sample Volume ◽  
Dual Polarization ◽  
Axis Ratio ◽  
Winter Storms ◽  
Frequency Distributions ◽  
X Band ◽  
Data Points ◽  
Measured Polarization ◽  
Differential Reflectivity

AbstractSince the advent of dual-polarization radar, methods of classifying hydrometeors by type from measured polarization variables have been developed. The deterministic approach of existing hydrometeor classification algorithms of assigning only one dominant habit to each radar sample volume does not properly consider the distribution of habits present in that volume, however. During the Profiling of Winter Storms field campaign, the “NSF/NCAR C-130” aircraft, equipped with in situ microphysical probes, made multiple passes through the comma heads of two cyclones as the Mobile Alabama X-band dual-polarization radar performed range–height indicator scans in the same plane as the C-130 flight track. On 14–15 February and 21–22 February 2010, 579 and 202 coincident data points, respectively, were identified when the plane was within 10 s (~1 km) of a radar gate. For all particles that occurred for times within different binned intervals of radar reflectivity ZHH and of differential reflectivity ZDR, the reflectivity-weighted contribution of each habit and the frequency distributions of axis ratio and sphericity were determined. This permitted the determination of habits that dominate particular ZHH and ZDR intervals; only 40% of the ZHH–ZDR bins were found to have a habit that contributes over 50% to the reflectivity in that bin. Of these bins, only 12% had a habit that contributes over 75% to the reflectivity. These findings show the general lack of dominance of a given habit for a particular ZHH and ZDR and suggest that determining the probability of specific habits in radar volumes may be more suitable than the deterministic methods currently used.

scholarly journals Characteristic Analysis of the Downburst in Greely, Colorado on 30 July 2017 Using WPEA Method and X-Band Radar Observations

Atmosphere ◽  
2018 ◽  
Vol 9 (9) ◽  
pp. 348 ◽  
Author(s):  
Hao Wang ◽  
Venkatachalam Chandrasekar ◽  
Jianxin He ◽  
Zhao Shi ◽  
Lijuan Wang
Keyword(s):  
Phase Distribution ◽  
Potential Temperature ◽  
Ground Surface ◽  
Dual Polarization ◽  
Characteristic Analysis ◽  
Radar Observations ◽  
X Band ◽  
Future Events ◽  
Low Altitude ◽  
Differential Reflectivity

As a manifestation of low-altitude wind shear, a downburst is a localized, strong downdraft that can lead to disastrous wind on the ground surface. For effective pre-warning and forecasting of downbursts, it is particularly critical to understand relevant weather features that occur before and during a downburst process. It is important to identify the macroscopic features associated with the downburst weather process before considering fine-scale observations because this would greatly increase the accuracy and timeliness of forecasts. Therefore, we applied the wind-vector potential-temperature energy analysis (WPEA) method and CSU-CHILL X-band dual-polarization radar to explore the features of the downburst process. Here it was found that prior to the occurrence of the downburst of interest, the specific areas that should be monitored in future events could be determined by studying the atmospherically unstable areas using the WPEA method. Combining the WPEA method with dual-polarization radar observations, we can better distinguish the phase distribution of the hydrometeor in the process and greatly enhance the judgment of the possibility of the downburst. From exploration of the microphysical features of the downburst, we further found that ‘Zdr (differential reflectivity) column’ can be regarded as an important early warning indicator of the location of the downburst. Finally, a schematic of the formation process of the downburst according to the analyses was produced.

scholarly journals Connecting Microphysical Processes in Colorado Winter Storms with Vertical Profiles of Radar Observations

2016 ◽  
Vol 55 (8) ◽  
pp. 1771-1787 ◽  
Author(s):  
Robert S. Schrom ◽  
Matthew R. Kumjian
Keyword(s):  
Dendritic Growth ◽  
Doppler Velocity ◽  
Front Range ◽  
Horizontal Polarization ◽  
Winter Storms ◽  
Radar Observations ◽  
Velocity Magnitude ◽  
Microphysical Processes ◽  
Project Data ◽  
Differential Reflectivity

AbstractTo better connect radar observations to microphysical processes, the authors analyze concurrent polarimetric radar observations at vertical incidence and roughly side incidence during the Front Range Orographic Storms (FROST) project. Data from three events show signatures of riming, aggregation, and dendritic growth. Riming and the growth of graupel are suggested by negative differential reflectivity ZDR and vertically pointing Doppler velocity magnitude |VR| > 2.0 m s−1; aggregation is indicated by maxima in the downward-relative gradient of radar reflectivity at horizontal polarization ZH below the −15°C isotherm and positive downward-relative gradients in |VR| when averaged over time. A signature of positive downward-relative gradients in ZH, negative downward-relative gradients in |VR|, and maxima in ZDR is observed near −15°C during all three events. This signature may be indicative of dendritic growth; preexisting, thick platelike crystals fall faster and grow slower than dendrites, allowing for |VR| to shift toward the slower-falling, rapidly growing dendrites. To test this hypothesis, simplified calculations of the ZH and |VR| gradients are performed for a range of terminal fall speeds of dendrites and isometric crystals. The authors prescribe linear profiles of ZH for the dendrites and isometric crystals, with the resulting profiles and gradients of |VR| determined from a range of particle fall speeds. Both the observed ZH and |VR| gradients are reproduced by the calculations for a large range of fall speeds. However, more observational data are needed to fully constrain these calculations and reject or support explanations for this signature.

scholarly journals The Value of Dual-Polarization Radar in Diagnosing the Complex Microphysical Evolution of an Intense Snowband

2014 ◽  
Vol 95 (12) ◽  
pp. 1825-1834 ◽  
Author(s):  
Joseph C. Picca ◽  
David M. Schultz ◽  
Brian A. Colle ◽  
Sara Ganetis ◽  
David R. Novak ◽  
...  
Keyword(s):  
New York ◽  
New England ◽  
Spatial Scales ◽  
Radar Reflectivity ◽  
Mixed Phase ◽  
Dual Polarization ◽  
Winter Storms ◽  
Snow Crystals ◽  
Differential Reflectivity

The northeast U.S. extratropical cyclone of 8–9 February 2013 produced blizzard conditions and more than 0.6–0.9 m (2–3 ft) of snow from Long Island through eastern New England. A surprising aspect of this blizzard was the development and rapid weakening of a snowband to the northwest of the cyclone center with radar ref lectivity factor exceeding 55 dBZ. Because the radar reflectivity within snowbands in winter storms rarely exceeds 40 dBZ, this event warranted further investigation. The high radar reflectivity was due to mixed-phase microphysics in the snowband, characterized by high differential reflectivity (ZDR > 2 dB) and low correlation coefficient (CC < 0.9), as measured by the operational dual-polarization radar in Upton, New York (KOKX). Consistent with these radar observations, heavy snow and ice pellets (both sleet and graupel) were observed. Later, as the reflectivity decreased to less than 40 dBZ, surface observations indicated a transition to primarily high-intensity dry snow, consistent with lower-tropospheric cold advection. Therefore, the rapid decrease of the 50+ dBZ reflectivity resulted from the transition from higher-density, mixed-phase precipitation to lower-density, dry-snow crystals and aggregates. This case study indicates the value that dual-polarization radar can have in an operational forecast environment for determining the variability of frozen precipitation (e.g., ice pellets, dry snow aggregates) on relatively small spatial scales.

scholarly journals Polarimetric Spectral Filter for Adaptive Clutter and Noise Suppression

2009 ◽  
Vol 26 (2) ◽  
pp. 215-228 ◽  
Author(s):  
Dmitri N. Moisseev ◽  
V. Chandrasekar
Keyword(s):  
Noise Suppression ◽  
State University ◽  
Spectral Filter ◽  
Colorado State University ◽  
Ground Clutter ◽  
Observation Volume ◽  
Spectral Decompositions ◽  
Different Types ◽  
State Water ◽  
Differential Reflectivity

Abstract In this paper, spectral decompositions of differential reflectivity, differential phase, and copolar correlation coefficient are used to discriminate between weather and nonweather signals in the spectral domain. This approach gives a greater flexibility for discrimination between different types of scattering sources present in a radar observation volume. A spectral filter, which removes nonweather signals, is defined based on this method. The performance of this filter is demonstrated on the Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) observations. It is shown that the resulting filter parameters are adaptively defined for each range sample and do not require an assumption on spectral properties of ground clutter.

Performance of the Hail Differential Reflectivity (HDR) Polarimetric Radar Hail Indicator

2007 ◽  
Vol 46 (8) ◽  
pp. 1290-1301 ◽  
Author(s):  
Tracy K. Depue ◽  
Patrick C. Kennedy ◽  
Steven A. Rutledge
Keyword(s):  
Elevation Angle ◽  
Maximum Diameter ◽  
State University ◽  
Polarimetric Radar ◽  
Colorado State University ◽  
Surface Wetness ◽  
Critical Success ◽  
State Water ◽  
Linear Depolarization Ratio ◽  
Differential Reflectivity

Abstract A series of poststorm surveys were conducted in the wake of hailstorms observed by the Colorado State University–University of Chicago–Illinois State Water Survey (CSU-CHILL) S-Band polarimetric radar. Information on hail characteristics (maximum diameter, building damage, apparent hailstone density, etc.) was solicited from the general-public storm observers that were contacted during the surveys; the locations of their observations were determined using GPS equipment. Low-elevation angle radar measurements of reflectivity, differential reflectivity ZDR, and linear depolarization ratio (LDR) were interpolated to the ground-observer locations. Relationships between the hail differential reflectivity parameter HDR and the observer-reported hail characteristics were examined. It was found that HDR thresholds of 21 and 30 dB were reasonably successful (critical success index values of ∼0.77) in respectively identifying regions where large (>19 mm in diameter) and structurally damaging hail were observed. The LDR characteristics in the observed hail areas were also examined. Because of sensitivities to variations in the hailstone bulk ice density, degree of surface wetness, and shape irregularities, the basic correlation between LDR magnitude and hail diameter was poor. However, when the reported hail diameters exceeded ∼25 mm, LDR levels below ∼−24 dB were uncommon.

Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part I: Mostly Stratiform Clouds

2015 ◽  
Vol 54 (9) ◽  
pp. 1944-1969 ◽  
Author(s):  
Xiaoqin Jing ◽  
Bart Geerts ◽  
Katja Friedrich ◽  
Binod Pokharel
Keyword(s):  
Radar Data ◽  
Control Area ◽  
Target Area ◽  
Dual Polarization ◽  
Stratiform Clouds ◽  
Orographic Clouds ◽  
Close Range ◽  
Glaciogenic Seeding ◽  
Differential Reflectivity ◽  
The Impact

AbstractThe impact of ground-based glaciogenic seeding on wintertime orographic, mostly stratiform clouds is analyzed by means of data from an X-band dual-polarization radar, the Doppler-on-Wheels (DOW) radar, positioned on a mountain pass. This study focuses on six intensive observation periods (IOPs) during the 2012 AgI Seeding Cloud Impact Investigation (ASCII) project in Wyoming. In all six storms, the bulk upstream Froude number below mountaintop exceeded 1 (suggesting unblocked flow), the clouds were relatively shallow (with bases below freezing), some liquid water was present, and orographic flow conditions were mostly steady. To examine the silver iodide (AgI) seeding effect, three study areas are defined (a control area, a target area upwind of the crest, and a lee target area), and comparisons are made between measurements from a treated period and those from an untreated period. Changes in reflectivity and differential reflectivity observed by the DOW at low levels during seeding are consistent with enhanced snow growth, by vapor diffusion and/or aggregation, for a case study and for the composite analysis of all six IOPs, especially at close range upwind of the mountain crest. These low-level changes may have been affected by natural changes aloft, however, as evident from differences in the evolution of the echo-top height in the control and target areas. Even though precipitation in the target region is strongly correlated with that in the control region, the authors cannot definitively attribute the change to seeding because there is a lack of knowledge about natural variability, nor can the outcome be generalized, because the sample size is small.

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