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 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 Estimation of Melting-Layer Cooling Rate from Dual-Polarization Radar: Spectral Bin Model Simulations

2019 ◽  
Vol 58 (7) ◽  
pp. 1485-1508 ◽  
Author(s):  
Jacob T. Carlin ◽  
Alexander V. Ryzhkov
Keyword(s):  
Cooling Rate ◽  
Phase Changes ◽  
Strongly Correlated ◽  
Polarimetric Radar ◽  
Differential Phase Shift ◽  
Model Simulations ◽  
Melting Snow ◽  
Melting Layer ◽  
Bright Band ◽  
Differential Reflectivity

AbstractDiabatic cooling from hydrometeor phase changes in the stratiform melting layer is of great interest to both operational forecasters and modelers for its societal and dynamical consequences. Attempts to estimate the melting-layer cooling rate typically rely on either the budgeting of hydrometeor content estimated from reflectivity Z or model-generated lookup tables scaled by the magnitude of Z in the bright band. Recent advances have been made in developing methods to observe the unique polarimetric characteristics of melting snow and the additional microphysical information they may contain. However, to date no work has looked at the thermodynamic information available from the polarimetric radar brightband signature. In this study, a one-dimensional spectral bin model of melting snow and a coupled polarimetric operator are used to study the relation between the polarimetric radar bright band and the melting-layer cooling rate. Simulations using a fixed particle size distribution (PSD) and variable environmental conditions show that the height and thickness of the bright band and the maximum brightband Z and specific differential phase shift are all sensitive to the ambient environment, while the differential reflectivity is relatively insensitive. Additional simulations of 2700 PSDs based on in situ observations above the melting layer indicate that the maximum Z, , and within the melting layer are poorly correlated with the maximum cooling rate while is strongly correlated. Finally, model simulations suggest that, in addition to riming, concurrent changes in aggregation and precipitation intensity and the associated cooling may plausibly cause observed sagging brightband signatures.

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 Examining Polarimetric Radar Observations of Bulk Microphysical Structures and Their Relation to Vortex Kinematics in Hurricane Arthur (2014)

2017 ◽  
Vol 145 (11) ◽  
pp. 4521-4541 ◽  
Author(s):  
Anthony C. Didlake ◽  
Matthew R. Kumjian
Keyword(s):  
Tropical Cyclone ◽  
Lower Layer ◽  
Polarimetric Radar ◽  
Arthur Prior ◽  
Radar Observations ◽  
Melting Layer ◽  
Ice Particles ◽  
Planar Crystal ◽  
Differential Reflectivity ◽  
Left Quadrant

Dual-polarization radar observations were taken of Hurricane Arthur prior to and during landfall, providing needed insight into the microphysics of tropical cyclone precipitation. A total of 30 h of data were composited and analyzed by annuli capturing storm features (eyewall, inner rainbands, and outer rainbands) and by azimuth relative to the deep-layer environmental wind shear vector. Polarimetric radar variables displayed distinct signatures indicating a transition from convective to stratiform precipitation in the downshear-right to downshear-left quadrants, which is an organization consistent with the expected kinematic asymmetry of a sheared tropical cyclone. In the downshear-right quadrant, vertical profiles of differential reflectivity ZDR and copolar correlation coefficient ρHV were more vertically stretched within and above the melting layer at all annuli, which is attributed to convective processes. An analysis of specific differential phase KDP indicated that nonspherical ice particles had an increased presence in two layers: just above the melting level and near 8-km altitude. Here, convective updrafts generated ice particles in the lower layer, which were likely columnar crystals, and increased the available moisture in the upper layer, leading to increased planar crystal growth. A sharp transition in hydrometeor population occurred downwind in the downshear-left quadrant where ZDR and ρHV profiles were more peaked within the melting layer. Above the melting layer, these signatures indicated reduced ice column counts and shape diversity owing to aggregation in a predominantly stratiform regime. The rainband quadrants exhibited a sharper transition compared to the eyewall quadrants owing to weaker winds and longer distances that decreased azimuthal mixing of ice hydrometeors.

scholarly journals From model to radar variables: a new forward polarimetric radar operator for COSMO

2018 ◽  
Vol 11 (7) ◽  
pp. 3883-3916 ◽  
Author(s):  
Daniel Wolfensberger ◽  
Alexis Berne
Keyword(s):  
Phase Shift ◽  
Solid Phase ◽  
Weather Prediction ◽  
Doppler Spectrum ◽  
Polarimetric Radar ◽  
Dual Frequency ◽  
Differential Phase Shift ◽  
Radar Observations ◽  
Differential Phase ◽  
Differential Reflectivity

Abstract. In this work, a new forward polarimetric radar operator for the COSMO numerical weather prediction (NWP) model is proposed. This operator is able to simulate measurements of radar reflectivity at horizontal polarization, differential reflectivity as well as specific differential phase shift and Doppler variables for ground based or spaceborne radar scans from atmospheric conditions simulated by COSMO. The operator includes a new Doppler scheme, which allows estimation of the full Doppler spectrum, as well a melting scheme which allows representing the very specific polarimetric signature of melting hydrometeors. In addition, the operator is adapted to both the operational one-moment microphysical scheme of COSMO and its more advanced two-moment scheme. The parameters of the relationships between the microphysical and scattering properties of the various hydrometeors are derived either from the literature or, in the case of graupel and aggregates, from observations collected in Switzerland. The operator is evaluated by comparing the simulated fields of radar observables with observations from the Swiss operational radar network, from a high resolution X-band research radar and from the dual-frequency precipitation radar of the Global Precipitation Measurement satellite (GPM-DPR). This evaluation shows that the operator is able to simulate an accurate Doppler spectrum and accurate radial velocities as well as realistic distributions of polarimetric variables in the liquid phase. In the solid phase, the simulated reflectivities agree relatively well with radar observations, but the simulated differential reflectivity and specific differential phase shift upon propagation tend to be underestimated. This radar operator makes it possible to compare directly radar observations from various sources with COSMO simulations and as such is a valuable tool to evaluate and test the microphysical parameterizations of the model.

scholarly journals On the Use of Radiosondes in Freezing Precipitation

2018 ◽  
Vol 35 (3) ◽  
pp. 459-472 ◽  
Author(s):  
Sean Waugh ◽  
Terry J. Schuur
Keyword(s):  
Response Times ◽  
Radar Data ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
Storm Event ◽  
Polarimetric Radar ◽  
Winter Storm ◽  
Winter Storms ◽  
Model Initialization ◽  
Source Of Error

AbstractRadiosonde observations are used the world over to provide critical upper-air observations of the lower atmosphere. These observations are susceptible to errors that must be mitigated or avoided when identified. One source of error not previously addressed is radiosonde icing in winter storms, which can affect forecasts, warning operations, and model initialization. Under certain conditions, ice can form on the radiosonde, leading to decreased response times and incorrect readings. Evidence of radiosonde icing is presented for a winter storm event in Norman, Oklahoma, on 24 November 2013. A special sounding that included a particle imager probe and a GoPro camera was flown into the system producing ice pellets. While the iced-over temperature sensor showed no evidence of an elevated melting layer (ML), complementary Particle Size, Image, and Velocity (PASIV) probe and polarimetric radar observations provide clear evidence that an ML was indeed present. Radiosonde icing can occur while passing through a layer of supercooled drops, such as frequently found in a subfreezing layer that often lies below the ML in winter storms. Events that have warmer/deeper MLs would likely melt any ice present off the radiosonde, minimizing radiosonde icing and allowing the ML to be detected. This paper discusses the hypothesis that the absence of an ML in the radiosonde data presented here is more likely to occur in winter storms that produce ice pellets, which tend to have cooler/shallower MLs. Where sounding data do appear to be compromised by icing, polarimetric radar data might be used to identify MLs for nowcasting purposes and numerical model initialization.

scholarly journals High-Resolution Vertical Profiles of X-Band Polarimetric Radar Observables during Snowfall in the Swiss Alps

2013 ◽  
Vol 52 (2) ◽  
pp. 378-394 ◽  
Author(s):  
Marc Schneebeli ◽  
Nicholas Dawes ◽  
Michael Lehning ◽  
Alexis Berne
Keyword(s):  
Water Vapor ◽  
High Water ◽  
Snow Accumulation ◽  
Swiss Alps ◽  
Vertical Profiles ◽  
Polarimetric Radar ◽  
High Accumulation ◽  
Melting Layer ◽  
Mountainous Regions ◽  
X Band

AbstractAn X-band polarimetric radar was deployed in the eastern Swiss Alps at an altitude of 2133 m. Radar measurements were complemented with several weather stations deployed in an altitude range from 1500 to 3100 m as well as with a fixed GPS ground station that was used to infer integrated water vapor estimates. Around 8000 vertical profiles of polarimetric radar observables above the melting layer collected during two months are analyzed. First, the behavior of the mean profiles of reflectivity at horizontal polarization Zh, differential reflectivity Zdr, copolar cross correlation ρhv, and specific differential phase shift Kdp are interpreted from a microphysical point of view. It is shown that the whole evolution of snowflakes, from pristine crystals at temperatures around −30°C to dendritic crystals around −15°C, to large aggregates around 0°C, is well captured by the polarimetric radar variables. In a second step, the profiles are analyzed as functions of high and low water vapor and snow accumulation conditions. It is found that the vertical profiles of polarimetric radar variables have distinct features in low versus high water vapor conditions. High water vapor conditions appear to favor the occurrence of crystal aggregates at high altitudes/low temperatures. It is shown with a hydrometeor identification scheme that graupel-like particles are found to be dominant right above the melting layer for snow events with high accumulation intensities. The present analyses show that measurements from X-band dual-polarization radar can be useful to characterize the dominant microphysical processes during precipitation in mountainous regions.

scholarly journals Freezing of Raindrops in Deep Convective Updrafts: A Microphysical and Polarimetric Model

2012 ◽  
Vol 69 (12) ◽  
pp. 3471-3490 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Scott M. Ganson ◽  
Alexander V. Ryzhkov
Keyword(s):  
Electromagnetic Scattering ◽  
Drop Size ◽  
Sharp Decrease ◽  
Supercooled Liquid ◽  
Freezing Process ◽  
Polarimetric Radar ◽  
Linear Depolarization Ratio ◽  
Bin Microphysics ◽  
Differential Reflectivity ◽  
The Impact

Abstract Polarimetric radar observations of convective storms routinely reveal positive differential reflectivity ZDR extending above the 0°C level, indicative of the presence of supercooled liquid particles lofted by the storm’s updraft. The summit of such “ZDR columns” is marked by a zone of enhanced linear depolarization ratio LDR or decreased copolar cross-correlation coefficient ρhv and a sharp decrease in ZDR that together mark a particle freezing zone. To better understand the relation between changes in the storm updraft and the observed polarimetric variables, it is necessary to first understand the physics governing this freezing process and the impact of freezing on the polarimetric variables. A simplified, one-dimensional explicit bin microphysics model of stochastic drop nucleation by an immersed foreign particle and subsequent deterministic freezing is developed and coupled with an electromagnetic scattering model to explore the impact of the freezing process on the polarimetric radar variables. As expected, the height of the ZDR column is closely related to the updraft strength and initial drop size distribution. Additionally, the treatment of the stochastic nucleation process can also affect the depth of the freezing zone, underscoring the need to accurately depict this process in parameterizations. Representation of stochastic nucleation and deterministic freezing for each drop size bin yields better agreement between observations and the modeled vertical profiles of the surface reflectivity factor ZH and ZDR than bulk microphysics schemes. Further improvements in the representation of the LDR cap, the observed ZDR gradient in the freezing zone, and the magnitude of the ρhv minimum may require inclusion of accretion, which was not included in this model.

The Utility of X-Band Polarimetric Radar for Quantitative Estimates of Rainfall Parameters

2005 ◽  
Vol 6 (3) ◽  
pp. 248-262 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
David E. Kingsmill ◽  
Brooks E. Martner ◽  
F. Martin Ralph
Keyword(s):  
Rain Attenuation ◽  
Polarimetric Radar ◽  
Differential Phase Shift ◽  
Differential Phase ◽  
X Band ◽  
Drop Size Distributions ◽  
Russian River ◽  
Phase Shift Data ◽  
Reflectivity Data ◽  
Differential Reflectivity

Abstract The utility of X-band polarimetric radar for quantitative retrievals of rainfall parameters is analyzed using observations collected along the U.S. west coast near the mouth of the Russian River during the Hydrometeorological Testbed project conducted by NOAA’s Environmental Technology and National Severe Storms Laboratories in December 2003 through March 2004. It is demonstrated that the rain attenuation effects in measurements of reflectivity (Ze) and differential attenuation effects in measurements of differential reflectivity (ZDR) can be efficiently corrected in near–real time using differential phase shift data. A scheme for correcting gaseous attenuation effects that are important at longer ranges is introduced. The use of polarimetric rainfall estimators that utilize specific differential phase and differential reflectivity data often provides results that are superior to estimators that use fixed reflectivity-based relations, even if these relations were derived from the ensemble of drop size distributions collected in a given geographical region. Comparisons of polarimetrically derived rainfall accumulations with data from the high-resolution rain gauges located along the coast indicated deviation between radar and gauge estimates of about 25%. The ZDR measurements corrected for differential attenuation were also used to retrieve median raindrop sizes, D0. Because of uncertainties in differential reflectivity measurements, these retrievals are typically performed only for D0 > 0.75 mm. The D0 estimates from an impact disdrometer located at 25 km from the radar were in good agreement with the radar retrievals. The experience of operating the transportable polarimetric X-band radar in the coastal area that does not have good coverage by the National Weather Service radar network showed the value of such radar in filling the gaps in the network coverage. The NOAA X-band radar was effective in covering an area up to 40–50 km in radius offshore adjacent to a region that is prone to flooding during wintertime landfalling Pacific storms.

A Polarimetric Radar Analysis of Ice Microphysical Processes in Melting Layers of Winter Storms Using S-Band Quasi-Vertical Profiles

2020 ◽  
Vol 59 (4) ◽  
pp. 751-767 ◽  
Author(s):  
Erica M. Griffin ◽  
Terry J. Schuur ◽  
Alexander V. Ryzhkov
Keyword(s):  
Cold Season ◽  
Vertical Profiles ◽  
Horizontal Polarization ◽  
Winter Storms ◽  
Differential Phase ◽  
High Vertical Resolution ◽  
Microphysical Processes ◽  
Statistical Relationships ◽  
Reflectivity Data ◽  
Differential Reflectivity

AbstractQuasi-vertical profiles (QVPs) obtained from a database of U.S. WSR-88D data are used to document polarimetric characteristics of the melting layer (ML) in cold-season storms with high vertical resolution and accuracy. A polarimetric technique to define the top and bottom of the ML is first introduced. Using the QVPs, statistical relationships are developed to gain insight into the evolution of microphysical processes above, within, and below the ML, leading to a statistical polarimetric model of the ML that reveals characteristics that reflectivity data alone are not able to provide, particularly in regions of weak reflectivity factor at horizontal polarization ZH. QVP ML statistics are examined for two regimes in the ML data: ZH ≥ 20 dBZ and ZH < 20 dBZ. Regions of ZH ≥ 20 dBZ indicate locations of MLs collocated with enhanced differential reflectivity ZDR and reduced copolar correlation coefficient ρhv, while for ZH < 20 dBZ a well-defined ML is difficult to discern using ZH alone. Evidence of large ZDR up to 4 dB, backscatter differential phase δ up to 8°, and low ρhv down to 0.80 associated with lower ZH (from −10 to 20 dBZ) in the ML is observed when pristine, nonaggregated ice falls through it. Positive correlation is documented between maximum specific differential phase KDP and maximum ZH in the ML; these are the first QVP observations of KDP in MLs documented at S band. Negative correlation occurs between minimum ρhv in the ML and ML depth and between minimum ρhv in the ML and the corresponding enhancement of ZH (ΔZH = ZHmax − ZHrain).

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