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.

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.

Microphysical and Polarimetric Radar Modeling of Hydrometeor Refreezing

2021 ◽  
Author(s):  
Dana M. Tobin ◽  
Matthew R. Kumjian
Keyword(s):  
Polarimetric Radar ◽  
Horizontal Polarization ◽  
Radar Signature ◽  
Liquid Portion ◽  
Linear Depolarization Ratio ◽  
Bin Microphysics ◽  
Ice Shell ◽  
Differential Reflectivity ◽  
The Impact ◽  
Polar Correlation

AbstractA unique polarimetric radar signature indicative of hydrometeor refreezing during ice pellet events has been documented in several recent studies, yet the underlying microphysical causes remain unknown. The signature is characterized by enhancements in differential reflectivity (ZDR), specific differential phase (KDP), and linear depolarization ratio (LDR), and a reduction in co-polar correlation coefficient (ρhv) within a layer of decreasing radar reflectivity factor at horizontal polarization (ZH). In previous studies, the leading hypothesis for the observed radar signature is the preferential refreezing of small drops. Here, a simplified, one-dimensional, explicit bin microphysics model is developed to simulate the refreezing of fully melted hydrometeors, and coupled with a polarimetric radar forward operator to quantify the impact of preferential refreezing on simulated radar signatures. The modeling results demonstrate that preferential refreezing is insufficient by itself to produce the observed signatures. In contrast, simulations considering an ice shell growing asymmetrically around a freezing particle (i.e., emulating a thicker ice shell on the bottom of a falling particle) produce realistic ZDR enhancements, and also closely replicate observed features in ZH, KDP, LDR, and ρhv. Simulations that assume no increase in particle wobbling with freezing produce an even greater ZDR enhancement, but this comes at the expense of reducing the LDR enhancement. It is suggested that the polarimetric refreezing signature is instead strongly related to both the distribution of the unfrozen liquid portion within a freezing particle, and the orientation of this liquid with respect to the horizontal.

scholarly journals A Dual-Polarization Radar Signature of Hydrometeor Refreezing in Winter Storms

2013 ◽  
Vol 52 (11) ◽  
pp. 2549-2566 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Alexander V. Ryzhkov ◽  
Heather D. Reeves ◽  
Terry J. Schuur
Keyword(s):  
Horizontal Polarization ◽  
Winter Storms ◽  
Radar Signature ◽  
Long Duration ◽  
Pros And Cons ◽  
Radar Measurements ◽  
Microphysical Processes ◽  
Differential Reflectivity ◽  
Potential Use ◽  
Unique Signature

AbstractPolarimetric radar measurements in winter storms that produce ice pellets have revealed a unique signature that is indicative of ongoing hydrometeor refreezing. This refreezing signature is observed within the low-level subfreezing air as an enhancement of differential reflectivity ZDR and specific differential phase KDP and a decrease of radar reflectivity factor at horizontal polarization ZH and copolar correlation coefficient ρhv. It is distinct from the overlying melting-layer “brightband” signature and suggests that unique microphysical processes are occurring within the layer of hydrometeor refreezing. The signature is analyzed for four ice-pellet cases in central Oklahoma as observed by two polarimetric radars. A statistical analysis is performed on the characteristics of the refreezing signature for a case of particularly long duration. Several hypotheses are presented to explain the appearance of the signature, along with a summary of the pros and cons for each. It is suggested that preferential freezing of small drops and local ice generation are plausible mechanisms for the appearance of the ZDR and KDP enhancements. Polarimetric measurements and scattering calculations are used to retrieve microphysical information to explore the validity of the hypotheses. The persistence and repetitiveness of the signature suggest its potential use in operational settings to diagnose the transition between freezing rain and ice pellets.

scholarly journals The Impact of Raindrop Collisional Processes on the Polarimetric Radar Variables

2014 ◽  
Vol 71 (8) ◽  
pp. 3052-3067 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Olivier P. Prat
Keyword(s):  
Electromagnetic Scattering ◽  
Vertical Profiles ◽  
Polarimetric Radar ◽  
Horizontal Polarization ◽  
One Dimensional ◽  
Microphysical Process ◽  
Warm Rain ◽  
Microphysical Processes ◽  
Differential Reflectivity ◽  
The Impact

Abstract The impact of the collisional warm-rain microphysical processes on the polarimetric radar variables is quantified using a coupled microphysics–electromagnetic scattering model. A one-dimensional bin-microphysical rain shaft model that resolves explicitly the evolution of the drop size distribution (DSD) under the influence of collisional coalescence and breakup, drop settling, and aerodynamic breakup is coupled with electromagnetic scattering calculations that simulate vertical profiles of the polarimetric radar variables: reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, and specific differential phase KDP. The polarimetric radar fingerprint of each individual microphysical process is quantified as a function of the shape of the initial DSD and for different values of nominal rainfall rate. Results indicate that individual microphysical processes (collisional processes, evaporation) display a distinctive signature and evolve within specific areas of ZH–ZDR and ZDR–KDP space. Furthermore, a comparison of the resulting simulated vertical profiles of the polarimetric variables with radar and disdrometer observations suggests that bin-microphysical parameterizations of drop breakup most frequently used are overly aggressive for the largest rainfall rates, resulting in very “tropical” DSDs heavily skewed toward smaller drops.

scholarly journals X-Band Dual-Polarization Radar Observations of Snow Growth Processes of a Severe Winter Storm: Case of 12 December 2013 in South Korea

2019 ◽  
Vol 36 (7) ◽  
pp. 1217-1235 ◽  
Author(s):  
S. Allabakash ◽  
S. Lim ◽  
V. Chandrasekar ◽  
K. H. Min ◽  
J. Choi ◽  
...  
Keyword(s):  
Polarimetric Radar ◽  
Atmospheric Conditions ◽  
Severe Winter ◽  
Dual Polarization ◽  
Winter Storm ◽  
Horizontal Polarization ◽  
Growth Processes ◽  
Radar Observations ◽  
X Band ◽  
Radar Signatures

AbstractThe characteristics of microphysical processes of a severe winter storm that occurred on the Korean Peninsula on 12 December 2013 was studied in this work for the first time via X-band dual-polarization weather radar observations. A new range–height indicator (RHI) scan-based quasi-vertical profile methodology, in which polarimetric radar variables were averaged at each height of the RHI scan, was introduced to investigate the snow microphysics, and the obtained polarimetric radar signatures served as fingerprints of the dendritic growth, aggregation, and riming processes. Enhanced differential reflectivity (Zdr) and specific differential phase shift (Kdp) bands were detected near the −15°C isotherm, which signified the growth of dendrites or platelike crystals. The observed correlation between the increases in the reflectivity factor at horizontal polarization Zh and copolar correlation coefficient ρhv and the decreases in Zdr and Kdp magnitudes at lower heights suggested the occurrence of the aggregation process. The combination of high Zh and low Zdr values with turbulent atmospheric conditions observed at the ground level indicated the occurrence of the riming process. In addition, the negative Kdp and Zdr values combined with high Zh and ρhv magnitudes (observed near the end of the snow event) indicated the formation of graupel particles. The polarimetric radar signatures obtained for the snow growth processes were evident from ground observations and agreed well with the results of the Weather Research and Forecasting Model and Modern-Era Retrospective Analysis for Research and Applications data. Furthermore, the spatial variability of Zh methodology was implemented to describe both aggregates and rimed ice particles.

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 High-Resolution Polarimetric Radar Observations of Snow-Generating Cells

2014 ◽  
Vol 53 (6) ◽  
pp. 1636-1658 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Steven A. Rutledge ◽  
Roy M. Rasmussen ◽  
Patrick C. Kennedy ◽  
Mike Dixon
Keyword(s):  
High Resolution ◽  
Radar Data ◽  
Radiosonde Data ◽  
Polarimetric Radar ◽  
Front Range ◽  
Ice Crystal ◽  
Horizontal Polarization ◽  
X Band ◽  
Northern Colorado ◽  
Differential Reflectivity

AbstractHigh-resolution X-band polarimetric radar data were collected in 19 snowstorms over northern Colorado in early 2013 as part of the Front Range Orographic Storms (FROST) project. In each case, small, vertically erect convective turrets were observed near the echo top. These “generating cells” are similar to those reported in the literature and are characterized by ~1-km horizontal and vertical dimensions, vertical velocities of 1–2 m s−1, and lifetimes of at least 10 min. In some cases, these generating cells are enshrouded by enhanced differential reflectivity ZDR, indicating a “shroud” of pristine crystals enveloping the larger, more isotropic particles. The anticorrelation of radar reflectivity factor at horizontal polarization ZH and ZDR suggests ongoing aggregation or riming of particles in the core of generating cells. For cases in which radiosonde data were collected, potential instability was found within the layer in which generating cells were observed. The persistence of these layers suggests that radiative effects are important, perhaps by some combination of cloud-top cooling and release of latent enthalpy through depositional and riming growth of particles within the cloud. The implications for the ubiquity of generating cells and their role as a mechanism for ice crystal initiation and growth are discussed.

scholarly journals Polarimetric Signatures above the Melting Layer in Winter Storms: An Observational and Modeling Study

2013 ◽  
Vol 52 (3) ◽  
pp. 682-700 ◽  
Author(s):  
Jelena Andrić ◽  
Matthew R. Kumjian ◽  
Dušan S. Zrnić ◽  
Jerry M. Straka ◽  
Valery M. Melnikov
Keyword(s):  
Electromagnetic Scattering ◽  
Vertical Profiles ◽  
Polarimetric Radar ◽  
Winter Storm ◽  
Differential Phase Shift ◽  
Winter Storms ◽  
One Dimensional ◽  
Melting Layer ◽  
Differential Reflectivity ◽  
General Profile

AbstractPolarimetric radar observations above the melting layer in winter storms reveal enhanced differential reflectivity ZDR and specific differential phase shift KDP, collocated with reduced copolar correlation coefficient ρhv; these signatures often appear as isolated “pockets.” High-resolution RHIs and vertical profiles of polarimetric variables were analyzed for a winter storm that occurred in Oklahoma on 27 January 2009, observed with the polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D) in Norman. The ZDR maximum and ρhv minimum are located within the temperature range between −10° and −15°C, whereas the KDP maximum is located just below the ZDR maximum. These signatures are coincident with reflectivity factor ZH that increases toward the ground. A simple kinematical, one-dimensional, two-moment bulk microphysical model is developed and coupled with electromagnetic scattering calculations to explain the nature of the observed polarimetric signature. The microphysics model includes nucleation, deposition, and aggregation and considers only ice-phase hydrometeors. Vertical profiles of the polarimetric radar variables (ZH, ZDR, KDP, and ρhv) were calculated using the output from the microphysical model. The base model run reproduces the general profile and magnitude of the observed ZH and ρhv and the correct shape (but not magnitude) of ZDR and KDP. Several sensitivity experiments were conducted to determine if the modeled signatures of all variables can match the observed ones. The model was incapable of matching both the observed magnitude and shape of all polarimetric variables, however. This implies that some processes not included in the model (such as secondary ice generation) are important in producing the signature.

scholarly journals Comparisons of Electromagnetic Scattering Properties of Real Hailstones and Spheroids

2019 ◽  
Vol 58 (1) ◽  
pp. 93-112 ◽  
Author(s):  
Zhiyuan Jiang ◽  
Matthew R. Kumjian ◽  
Robert S. Schrom ◽  
Ian Giammanco ◽  
Tanya Brown-Giammanco ◽  
...  
Keyword(s):  
Electromagnetic Scattering ◽  
3D Structure ◽  
Laser Scanner ◽  
The United States ◽  
Dipole Approximation ◽  
Horizontal Polarization ◽  
Differential Phase ◽  
Irregular Shapes ◽  
Linear Depolarization Ratio ◽  
Differential Reflectivity

AbstractSevere (>2.5 cm) hail causes >$5 billion in damage annually in the United States. However, radar sizing of hail remains challenging. Typically, spheroids are used to represent hailstones in radar forward operators and to inform radar hail-sizing algorithms. However, natural hailstones can have irregular shapes and lobes; these details significantly influence the hailstone’s scattering properties. The high-resolution 3D structure of real hailstones was obtained using a laser scanner for hail collected during the 2016–17 Insurance Institute for Business and Home Safety (IBHS) Hail Field Study. Plaster casts of several record hailstones (e.g., Vivian, South Dakota, 2010) were also scanned. The S-band scattering properties of these hailstones were calculated with the discrete dipole approximation (DDA). For comparison, scattering properties of spheroidal approximations of each hailstone (with identical maximum and minimum dimensions and mass) were calculated with the T matrix. The polarimetric radar variables have errors when using spheroids, even for small hail. Spheroids generally have smaller variations in the polarimetric variables than the real hailstones. This increased variability is one reason why the correlation coefficient tends to be lower in observations than in forward-simulated cases using spheroids. Backscatter differential phase δ also is found to have large variance, particularly for large hailstones. Irregular hailstones with a thin liquid layer produce enhanced and more variable values for reflectivity factor at horizontal polarization ZHH, differential reflectivity ZDR, specific differential phase KDP, linear depolarization ratio (LDR), and δ compared with dry hailstones; is also significantly reduced.

scholarly journals Polarimetric Radar Observations from a Waterspout-Producing Thunderstorm

2015 ◽  
Vol 30 (2) ◽  
pp. 329-348 ◽  
Author(s):  
Matthew S. Van Den Broeke ◽  
Cynthia A. Van Den Broeke
Keyword(s):  
Lake Michigan ◽  
Convective Cell ◽  
Great Lakes Region ◽  
Polarimetric Radar ◽  
Air Mass ◽  
Radar Observations ◽  
Potential Source ◽  
Western Lake ◽  
Low Levels ◽  
Differential Reflectivity

Abstract A family of four waterspouts was produced by a convective cell over western Lake Michigan on 12 September 2013. This storm initiated along a boundary north of a mesolow in a low-level cold-air advection regime, and developed supercell characteristics once the second waterspout was in progress. Polarimetric characteristics of the storm, and of the development of supercell character, are presented. These observations represent the first documented polarimetric radar observations of waterspout-producing convection in the Great Lakes region. Unusually high differential reflectivity values accompanied this storm and its initiating boundary. The high values along the boundary are partially explained by a high density of dragonflies. High differential reflectivity values were present through much of the storm of interest despite very low aerosol concentration at low levels in the lake-influenced air mass. Finally, this case illustrates the importance of environmental awareness on waterspout-favorable days, especially when boundaries are nearby to serve as a potential source of enhanced environmental vertical vorticity.

Sign in / Sign up

Export Citation Format

Share Document