scholarly journals Polarimetric Radar Observations of Biological Scatterers in Hurricanes Irene (2011) and Sandy (2012)

2013 ◽  
Vol 30 (12) ◽  
pp. 2754-2767 ◽  
Author(s):  
Matthew S. Van Den Broeke
Keyword(s):  
Tropical Cyclones ◽  
Elevation Angle ◽  
Bird Species ◽  
Hurricane Sandy ◽  
Polarimetric Radar ◽  
Biological Transport ◽  
Radar Observations ◽  
Hurricane Irene ◽  
Constant Altitude ◽  
Differential Reflectivity

Abstract Biological scatterers, consisting of birds and insects, may become trapped near the circulation center of tropical cyclones, particularly if a well-developed eyewall is present. These scatterers may be observed using weather radar, where they may appear to the radar operator as areas of light precipitation. Polarimetric radar characteristics of these scatterers, informed by additional observations of known bioscatter, include a combination of very high differential reflectivity (3–7.9 dB) and very low copolar correlation coefficient (0.3–0.8). Polarimetric radar observations of bioscatter are presented for Hurricane Irene (2011) and Hurricane Sandy (2012). In these storms, the bioscatter signature first appeared at the 0.5° elevation angle at a distance of 100–120 km from the radar. The signature appeared on successively higher tilts as the circulation center neared the radar, and its areal coverage in constant altitude plan position indicator (CAPPI) slices was primarily governed by the distribution of convection in the eye and by the timing of landfall. The highest altitude at which the signature appears may represent the inversion level within certain tropical cyclone eyes. For Hurricane Irene, inland observations of oceanic bird species support biological transport. Knowledge of the bioscatter signature has value to meteorologists monitoring tropical cyclones within the range of a polarimetric radar, possible value for estimating inversion height changes within the eyes of well-structured tropical cyclones, and value to biologists who wish to estimate the magnitude of biological transport in tropical cyclones.

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.

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 Extreme Rainfall from Landfalling Tropical Cyclones in the Eastern United States: Hurricane Irene (2011)

2016 ◽  
Vol 17 (11) ◽  
pp. 2883-2904 ◽  
Author(s):  
Maofeng Liu ◽  
James A. Smith
Keyword(s):  
United States ◽  
Tropical Cyclones ◽  
Extreme Rainfall ◽  
Hurricane Sandy ◽  
Mountainous Terrain ◽  
Eastern United States ◽  
Rainfall Distribution ◽  
Extratropical Transition ◽  
Hurricane Irene ◽  
Landfalling Tropical Cyclones

Abstract Hurricane Irene produced catastrophic rainfall and flooding in portions of the eastern United States from 27 to 29 August 2011. Like a number of tropical cyclones that have produced extreme flooding in the northeastern United States, Hurricane Irene was undergoing extratropical transition during the period of most intense rainfall. In this study the rainfall distribution of landfalling tropical cyclones is examined, principally through analyses of radar rainfall fields and high-resolution simulations using the Weather Research and Forecasting (WRF) Model. In addition to extratropical transition, the changing storm environment at landfall and orographic precipitation mechanisms can be important players in controlling the distribution of extreme rainfall. Rainfall distribution from landfalling tropical cyclones is examined from a Lagrangian perspective, focusing on times of landfall and extratropical transition, as well as interactions of the storm circulation with mountainous terrain. WRF simulations capture important features of rainfall distribution, including the pronounced change in rainfall distribution during extratropical transition. Synoptic-scale analyses show that a deep baroclinic zone developed and strengthened in the left-front quadrant of Irene, controlling rainfall distribution over the regions experiencing most severe flooding. Numerical experiments were performed with WRF to examine the role of mountainous terrain in altering rainfall distribution. Analyses of Hurricane Irene are placed in a larger context through analyses of Hurricane Hannah (2008) and Hurricane Sandy (2012).

scholarly journals Continuous Monitoring of Differential Reflectivity Bias for C-Band Polarimetric Radar Using Online Solar Echoes in Volume Scans

2019 ◽  
Vol 11 (22) ◽  
pp. 2714
Author(s):  
Chu ◽  
Liu ◽  
Zhang ◽  
Kou ◽  
Li
Keyword(s):  
High Frequency ◽  
Continuous Monitoring ◽  
Information Science ◽  
Elevation Angle ◽  
Gaussian Model ◽  
Likelihood Estimation ◽  
Polarimetric Radar ◽  
Time Calibration ◽  
Calibration Methods ◽  
Differential Reflectivity

The measurement error of differential reflectivity (ZDR), especially systematic ZDR bias, is a fundamental issue for the application of polarimetric radar data. Several calibration methods have been proposed and applied to correct ZDR bias. However, recent studies have shown that ZDR bias is time-dependent and can be significantly different on two adjacent days. This means that the frequent monitoring of ZDR bias is necessary, which is difficult to achieve with existing methods. As radar sensitivity has gradually been enhanced, large amounts of online solar echoes have begun to be observed in volume-scan data. Online solar echoes have a high frequency, and a known theoretical value of ZDR (0 dB) could thus allow the continuous monitoring of ZDR bias. However, online solar echoes are also affected by low signal-to-noise ratio and precipitation attenuation for short-wavelength radar. In order to understand the variation of ZDR bias in a C-band polarimetric radar at the Nanjing University of Information Science and Technology (NUIST-CDP), we analyzed the characteristics of online solar echoes from this radar, including the daily frequency of occurrence, the distribution along the radial direction, precipitation attenuation, and fluctuation caused by noise. Then, an automatic method based on online solar echoes was proposed to monitor the daily ZDR bias of the NUIST-CDP. In the proposed method, a one-way differential attenuation correction for solar echoes and a maximum likelihood estimation using a Gaussian model were designed to estimate the optimal daily ZDR bias. The analysis of three months of data from the NUIST-CDP showed the following: (1) Online solar echoes occurred very frequently regardless of precipitation. Under the volume-scan mode, the average number of occurrences was 15 per day and the minimum number was seven. This high frequency could meet the requirements of continuous monitoring of the daily ZDR bias under precipitation and no-rain conditions. (2) The result from the proposed online solar method was significantly linearly correlated with that from the vertical pointing method (observation at an elevation angle of 90°), with a correlation coefficient of 0.61, suggesting that the proposed method is feasible. (3) The day-to-day variation in the ZDR bias was relatively large, and 32% of such variations exceeded 0.2 dB, meaning that a one-time calibration was not representative in time. Accordingly, continuous calibration will be necessary. (4) The ZDR bias was found to be largely influenced by the ambient temperature, with a large negative correlation between the ZDR bias and the temperature.

Influence of Ground Clutter Contamination on Polarimetric Radar Parameters

2009 ◽  
Vol 26 (2) ◽  
pp. 251-269 ◽  
Author(s):  
Katja Friedrich ◽  
Urs Germann ◽  
Pierre Tabary
Keyword(s):  
Reference Data ◽  
Critical Level ◽  
Elevation Angle ◽  
Convective Precipitation ◽  
Polarimetric Radar ◽  
Mountain Ranges ◽  
Ground Clutter ◽  
The Mean ◽  
Rain Events ◽  
Differential Reflectivity

Abstract The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Zh), differential reflectivity (Zdr), correlation coefficient (ρhυ), and differential propagation phase (ϕdp) was examined. This study aims to derive the critical level of ground clutter contamination for Zh, Zdr, ρhυ, and ϕdp at which ground clutter influence exceeds predefined precision thresholds. Reference data with minimal ground clutter contamination consist of eight precipitation fields measured during three rain events characterized by stratiform and convective precipitation. Data were collected at an elevation angle of 0.8° by the Météo-France operational, polarimetric Doppler C-band weather radar located in Trappes, France, ∼30 km southwest of Paris. Nine different ground clutter signatures, ranging from point targets to more complex signatures typical for mountain ranges or urban obstacles, were added to the precipitation fields. This is done at the level of raw in-phase and quadrature component data in the two polarimetric channels. For each ground clutter signature, 30 simulations were conducted in which the mean reflectivity of ground clutter within the resolution volume varied between being 30 dB higher to 30 dB lower than the mean reflectivity of precipitation. Differences in Zh, Zdr, ρυ, and ϕdp between simulation and reference were shown as a function of ratio between ground clutter and precipitation intensities. As a result of this study, horizontal reflectivity showed the lowest sensitivity to ground clutter contamination. Furthermore, a precision of 1.7 dBZ in Zh is achieved on average when the precipitation and ground clutter intensities are equal. Requiring a precision of 0.2 dB in Zdr and 3° in ϕdp, the reflectivity of precipitation needs to be on average ∼5.5 and ∼6 dB, respectively, higher compared to the reflectivity of ground clutter. The analysis also indicates that the highest sensitivity to the nine clutter signatures was derived for ρhυ. To meet a predefined precision threshold of 0.02, reflectivity of precipitation needs to be ∼13.5 dB higher than the reflectivity of ground clutter.

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.

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.

In Situ and Radar Observations of the Low Reflectivity Ribbon in Supercells during VORTEX2

2018 ◽  
Vol 146 (1) ◽  
pp. 307-327 ◽  
Author(s):  
Casey B. Griffin ◽  
Christopher C. Weiss ◽  
Anthony E. Reinhart ◽  
Jeffrey C. Snyder ◽  
Howard B. Bluestein ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Potential Temperature ◽  
Three Dimensional ◽  
Polarimetric Radar ◽  
Radar Observations ◽  
Narrow Region ◽  
Differential Reflectivity ◽  
The Vertical Distribution ◽  
Doppler Analysis

Abstract During the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) field campaign, mobile radars observed a previously undocumented feature: the low-reflectivity ribbon (LRR). The LRR was characterized by reduced reflectivity ZH and differential reflectivity ZDR through a narrow region extending from the intersection of the hook and forward-flank regions of supercells. This study synthesizes kinematic and polarimetric radar observations with in situ measurements taken by the “StickNet” observing network. StickNet data have been used to establish that the LRR is associated with a localized minimum in pseudoequivalent potential temperature Pronounced drops in are observed by nine separate probes in three different supercell thunderstorms. Both single- and dual-Doppler analyses are used to examine the two- and three-dimensional structures of the winds within the LRR, revealing that the LRR is associated with cyclonic vertical vorticity aloft. Polarimetric radar observations are used to study the hydrometeor characteristics and the processes that cause those hydrometers to be present. Special consideration is given to the analysis of the vertical distribution of traditional and polarimetric variables, as well as the evolution of the kinematic fields retrieved by dual-Doppler analysis. The combination of thermodynamic, kinematic, and inferred microphysical observations supports a hypothesis that the LRR comprises sparse, large hail.

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

2017 ◽  
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 to estimate the full Doppler spectrum, as well a melting scheme which allows to represent 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.

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