scholarly journals Identification of the Melting Layer through Dual-Polarization Radar Measurements at Vertical Incidence

2006 ◽  
Vol 23 (6) ◽  
pp. 829-839 ◽  
Author(s):  
Luca Baldini ◽  
Eugenio Gorgucci
Keyword(s):  
Standard Deviation ◽  
Case Studies ◽  
Doppler Radar ◽  
Convective Precipitation ◽  
Doppler Velocity ◽  
Polarimetric Radar ◽  
Dual Polarization ◽  
Physical Processes ◽  
Melting Layer ◽  
Radar Measurements

Abstract Features of the melting layer of precipitation such as height and thickness are important in many meteorological applications. Doppler radar observations with a vertically pointing antenna have often been used in order to derive these features and to investigate the physical processes governing formation of the precipitation. This paper presents a technique to detect the characteristics of the melting layer based on the standard deviation of polarimetric radar measurements taken at vertical incidence. Using two case studies with stratiform and convective precipitation, the proposed technique is compared with conventional techniques based on reflectivity and mean Doppler velocity profiles. Data presented in this paper were obtained by the coherent dual-polarization C-band radar, Polar 55C, in Rome, Italy, during the summer and the fall of 2004.

scholarly journals Multi-sensor analysis of convective activity in central Italy during the HyMeX SOP 1.1

2016 ◽  
Vol 9 (2) ◽  
pp. 535-552 ◽  
Author(s):  
N. Roberto ◽  
E. Adirosi ◽  
L. Baldini ◽  
D. Casella ◽  
S. Dietrich ◽  
...  
Keyword(s):  
Case Studies ◽  
Hydrological Cycle ◽  
Central Italy ◽  
Lightning Activity ◽  
Convective Precipitation ◽  
Coefficient Of Determination ◽  
Dual Polarization ◽  
Radar Measurements ◽  
Sensor Analysis ◽  
Raindrop Size

Abstract. A multi-sensor analysis of convective precipitation events that occurred in central Italy in autumn 2012 during the HyMeX (Hydrological cycle in the Mediterranean experiment) Special Observation Period (SOP) 1.1 is presented. Various microphysical properties of liquid and solid hydrometeors are examined to assess their relationship with lightning activity. The instrumentation used consisted of a C-band dual-polarization weather radar, a 2-D video disdrometer, and the LINET lightning network. Results of T-matrix simulation for graupel were used to (i) tune a fuzzy logic hydrometeor classification algorithm based on Liu and Chandrasekar (2000) for the detection of graupel from C-band dual-polarization radar measurements and (ii) to retrieve graupel ice water content. Graupel mass from radar measurements was related to lightning activity. Three significant case studies were analyzed and linear relations between the total mass of graupel and number of LINET strokes were found with different slopes depending on the nature of the convective event (such as updraft strength and freezing level height) and the radar observational geometry. A high coefficient of determination (R2 = 0.856) and a slope in agreement with satellite measurements and model results for one of the case studies (15 October 2012) were found. Results confirm that one of the key features in the electrical charging of convective clouds is the ice content, although it is not the only one. Parameters of the gamma raindrop size distribution measured by a 2-D video disdrometer revealed the transition from a convective to a stratiform regime. The raindrop size spectra measured by a 2-D video disdrometer were used to partition rain into stratiform and convective classes. These results are further analyzed in relation to radar measurements and to the number of strokes. Lightning activity was not always recorded when the precipitation regime was classified as convective rain. High statistical scores were found for relationships relating lightning activity to graupel aloft.

scholarly journals Quantitative Precipitation Estimation of the Epic 2013 Colorado Flood Event: Polarization Radar-Based Variational Scheme

2016 ◽  
Vol 55 (7) ◽  
pp. 1477-1495 ◽  
Author(s):  
Wei-Yu Chang ◽  
Jothiram Vivekanandan ◽  
Kyoko Ikeda ◽  
Pay-Liam Lin
Keyword(s):  
Power Law ◽  
Rain Rate ◽  
Flood Event ◽  
Polarimetric Radar ◽  
Dual Polarization ◽  
Observational Error ◽  
Quantitative Precipitation Estimation ◽  
Precipitation Estimation ◽  
Radar Measurements ◽  
Event Based

AbstractThe accuracy of rain-rate estimation using polarimetric radar measurements has been improved as a result of better characterization of radar measurement quality and rain microphysics. In the literature, a variety of power-law relations between polarimetric radar measurements and rain rate are described because of the dynamic or varying nature of rain microphysics. A variational technique that concurrently takes into account radar observational error and dynamically varying rain microphysics is proposed in this study. Rain-rate estimation using the variational algorithm that uses event-based observational error and background rain climatological values is evaluated using observing system simulation experiments (OSSE), and its performance is demonstrated in the case of an epic Colorado flood event. The rain event occurred between 11 and 12 September 2013. The results from OSSE show that the variational algorithm with event-based observational error consistently estimates more accurate rain rate than does the “R(ZHH, ZDR)” power-law algorithm. On the contrary, the usage of ad hoc or improper observational error degrades the performance of the variational method. Furthermore, the variational algorithm is less sensitive to the observational error of differential reflectivity ZDR than is the R(ZHH, ZDR) algorithm. The variational quantitative precipitation estimation (QPE) retrieved more accurate rainfall estimation than did the power-law dual-polarization QPE in this particular event, despite the fact that both algorithms used the same dual-polarization radar measurements from the Next Generation Weather Radar (NEXRAD).

scholarly journals Velocity-Based EDR Retrieval Techniques Applied to Doppler Radar Measurements from Rain: Two Case Studies

2019 ◽  
Vol 36 (9) ◽  
pp. 1693-1711 ◽  
Author(s):  
A. C. P. Oude Nijhuis ◽  
C. M. H. Unal ◽  
O. A. Krasnov ◽  
H. W. J. Russchenberg ◽  
A. G. Yarovoy
Keyword(s):  
Case Studies ◽  
Doppler Radar ◽  
Energy Dissipation Rate ◽  
Accurate Estimation ◽  
Retrieval Technique ◽  
Sonic Anemometers ◽  
Radar Measurements ◽  
Rain Events ◽  
Kolmogorov Constant

In this article, five velocity-based energy dissipation rate (EDR) retrieval techniques are assessed. The EDR retrieval techniques are applied to Doppler measurements from Transportable Atmospheric Radar (TARA)—a precipitation profiling radar—operating in the vertically fixed-pointing mode. A generalized formula for the Kolmogorov constant is derived, which gives potential for the application of the EDR retrieval techniques to any radar line of sight (LOS). Two case studies are discussed that contain rain events of about 2 and 18 h, respectively. The EDR values retrieved from the radar are compared to in situ EDR values from collocated sonic anemometers. For the two case studies, a correlation coefficient of 0.79 was found for the wind speed variance (WSV) EDR retrieval technique, which uses 3D wind vectors as input and has a total sampling time of 10 min. From this comparison it is concluded that the radar is able to measure EDR with a reasonable accuracy. Almost no correlation was found for the vertical wind velocity variance (VWVV) EDR retrieval technique, as it was not possible to sufficiently separate the turbulence dynamics contribution to the radar Doppler mean velocities from the velocity contribution of falling raindrops. An important cause of the discrepancies between radar and in situ EDR values is thus due to insufficient accurate estimation of vertical air velocities.

scholarly journals Observations of Ash, Ice, and Lightning within Pyrocumulus Clouds Using Polarimetric NEXRAD Radars and the National Lightning Detection Network

2017 ◽  
Vol 145 (12) ◽  
pp. 4899-4910 ◽  
Author(s):  
Kendell T. LaRoche ◽  
Timothy J. Lang
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Case Studies ◽  
Correlation Coefficient ◽  
Convective Cloud ◽  
Past Research ◽  
Polarimetric Radar ◽  
Dual Polarization ◽  
Lightning Detection ◽  
Differential Reflectivity

A pyrocumulus is a convective cloud that can develop over a wildfire. Under certain conditions, pyrocumulus clouds become vertically developed enough to produce lightning. NEXRAD dual-polarization weather radar and upgraded National Lightning Detection Network (NLDN) data were used to analyze 10 case studies of ash plumes and pyrocumulus clouds from 2013 that either did or did not produce detected lightning. Past research has shown that pyrocumulus cases are most likely to produce lightning when there is a decrease in differential reflectivity (toward 0 dB) and an increase in the correlation coefficient (to >0.8), as measured by polarimetric radar, due to the transition from pure smoke/ash to frozen hydrometeors. All pyrocumulus cases that produced lightning in this study displayed the polarimetric characteristics of rimed ice within their respective clouds. Time series analysis of radar-inferred ash and rimed ice volumes within ash plumes and pyrocumulus clouds showed that NLDN-detected lightning occurred only after the cloud contained significant amounts of precipitation-sized rimed ice. The results suggest that the recently dual-pol-enabled NEXRADs and the more sensitive NLDN network can be used to explore ash plume and pyrocumulus microphysical structure and lightning production.

scholarly journals Hydrometeor Shape Variability in Snowfall as Retrieved from Polarimetric Radar Measurements

2020 ◽  
Vol 59 (9) ◽  
pp. 1503-1517
Author(s):  
Sergey Y. Matrosov ◽  
Alexander V. Ryzhkov ◽  
Maximilian Maahn ◽  
Gijs de Boer
Keyword(s):  
Aspect Ratio ◽  
Doppler Radar ◽  
Particle Model ◽  
Polarimetric Radar ◽  
Aspect Ratios ◽  
Air Temperatures ◽  
Radar Measurements ◽  
Differential Reflectivity ◽  
Particle Shapes

AbstractA polarimetric radar–based method for retrieving atmospheric ice particle shapes is applied to snowfall measurements by a scanning Ka-band radar deployed at Oliktok Point, Alaska (70.495°N, 149.883°W). The mean aspect ratio, which is defined by the hydrometeor minor-to-major dimension ratio for a spheroidal particle model, is retrieved as a particle shape parameter. The radar variables used for aspect ratio profile retrievals include reflectivity, differential reflectivity, and the copolar correlation coefficient. The retrievals indicate that hydrometeors with mean aspect ratios below 0.2–0.3 are usually present in regions with air temperatures warmer than approximately from −17° to −15°C, corresponding to a regime that has been shown to be favorable for growth of pristine ice crystals of planar habits. Radar reflectivities corresponding to the lowest mean aspect ratios are generally between −10 and 10 dBZ. For colder temperatures, mean aspect ratios are typically in a range between 0.3 and 0.8. There is a tendency for hydrometeor aspect ratios to increase as particles transition from altitudes in the temperature range from −17° to −15°C toward the ground. This increase is believed to result from aggregation and riming processes that cause particles to become more spherical and is associated with areas demonstrating differential reflectivity decreases with increasing reflectivity. Aspect ratio retrievals at the lowest altitudes are consistent with in situ measurements obtained using a surface-based multiangle snowflake camera. Pronounced gradients in particle aspect ratio profiles are observed at altitudes at which there is a change in the dominant hydrometeor species, as inferred by spectral measurements from a vertically pointing Doppler radar.

scholarly journals WRF–SBM Simulations of Melting-Layer Structure in Mixed-Phase Precipitation Events Observed during LPVEx

2014 ◽  
Vol 53 (12) ◽  
pp. 2710-2731 ◽  
Author(s):  
Takamichi Iguchi ◽  
Toshihisa Matsui ◽  
Wei-Kuo Tao ◽  
Alexander P. Khain ◽  
Vaughan T. J. Phillips ◽  
...  
Keyword(s):  
Liquid Water ◽  
Large Diameter ◽  
Mixed Phase ◽  
Doppler Velocity ◽  
Gradual Change ◽  
Phase Precipitation ◽  
Melting Layer ◽  
Validation Experiment ◽  
Radar Measurements ◽  
Precipitation Events

AbstractTwo mixed-phase precipitation events were observed on 21 September and 20 October 2010 over the southern part of Finland during the Light Precipitation Validation Experiment (LPVEx). These events have been simulated using the Weather Research and Forecasting Model coupled with spectral bin microphysics (WRF–SBM). The detailed ice-melting scheme with prognosis of the liquid water fraction during melting enables explicit simulation of microphysical properties in the melting layer. First, the simulations have been compared with C-band 3D radar measurements for the purpose of evaluating the overall profiles of cloud and precipitation. The simulation has some artificial convective patterns and errors in the forecast displacement of the precipitation system. The overall overestimation of reflectivity is consistent with a bias toward the range characterized by large-diameter droplets in the surface drop size distribution. Second, the structure of the melting bands has been evaluated against vertically pointing K-band radar measurements. A peak in reflectivity and a gradual change in Doppler velocity are observed and similarly simulated in the common temperature range from approximately 0° to 3°C. The effectiveness of the time-dependent melting scheme has been justified by intercomparison with a corresponding simulation using an instantaneous melting scheme. A weakness of the new melting scheme is that melting particles having high liquid water fractions on the order of 80%–90% cannot be simulated. This situation may cause underestimation of radar reflectivity in the melting layer because of the assumptions of melting-particle structure used to calculate the scattering properties.

scholarly journals Doppler Radar Observations of Anticyclonic Tornadoes in Cyclonically Rotating, Right-Moving Supercells

2016 ◽  
Vol 144 (4) ◽  
pp. 1591-1616 ◽  
Author(s):  
Howard B. Bluestein ◽  
Michael M. French ◽  
Jeffrey C. Snyder ◽  
Jana B. Houser
Keyword(s):  
Case Studies ◽  
Doppler Radar ◽  
Environmental Parameters ◽  
Radar Data ◽  
Doppler Velocity ◽  
Weighted Mean ◽  
Radar Observations ◽  
Azimuthal Shear ◽  
The Right ◽  
Gust Front

Abstract Supercells dominated by mesocyclones, which tend to propagate to the right of the tropospheric pressure-weighted mean wind, on rare occasions produce anticyclonic tornadoes at the trailing end of the rear-flank gust front. More frequently, mesoanticyclones are found at this location, most of which do not spawn any tornadoes. In this paper, four cases are discussed in which the formation of anticyclonic tornadoes was documented in the plains by mobile or fixed-site Doppler radars. These brief case studies include the analysis of Doppler radar data for tornadoes at the following dates and locations: 1) 24 April 2006, near El Reno, Oklahoma; 2) 23 May 2008, near Ellis, Kansas; 3) 18 March 2012, near Willow, Oklahoma; and 4) 31 May 2013, near El Reno, Oklahoma. Three of these tornadoes were also documented photographically. In all of these cases, a strong mesocyclone (i.e., vortex signature characterized by azimuthal shear in excess of ~5 × 10−3 s−1 or a 20 m s−1 change in Doppler velocity over 5 km) or tornado was observed ~10 km away from the anticyclonic tornado. In three of these cases, the evolution of the tornadic vortex signature in time and height is described. Other features common to all cases are noted and possible mechanisms for anticyclonic tornadogenesis are identified. In addition, a set of estimated environmental parameters for these and other similar cases are discussed.

scholarly journals Quantification of Precipitation Using Polarimetric Radar Measurements during Several Typhoon Events in Southern China

2020 ◽  
Vol 12 (12) ◽  
pp. 2058
Author(s):  
Qiulei Xia ◽  
Wenjuan Zhang ◽  
Haonan Chen ◽  
Wen-Chau Lee ◽  
Lei Han ◽  
...  
Keyword(s):  
Southern China ◽  
Rain Gauge ◽  
Polarimetric Radar ◽  
Dual Polarization ◽  
Radar Rainfall ◽  
Flood Warning ◽  
Microphysical Properties ◽  
Raindrop Size Distribution ◽  
Precipitation Estimation ◽  
Radar Measurements

Accurate quantitative precipitation estimation (QPE) during typhoon events is critical for flood warning and emergency management. Dual-polarization radar has proven to have better performance for QPE, compared to traditional single-polarization radar. However, polarimetric radar applications have not been extensively investigated in China, especially during extreme events such as typhoons, since the operational dual-polarization system upgrade only happened recently. This paper extends a polarimetric radar rainfall system for local applications during typhoons in southern China and conducts comprehensive studies about QPE and precipitation microphysics. Observations from S-band dual-polarization radar in Guangdong Province during three typhoon events in 2017 are examined to demonstrate the enhanced radar rainfall performance. The microphysical properties of hydrometeors during typhoon events are analyzed through raindrop size distribution (DSD) data and polarimetric radar measurements. The stratiform precipitation in typhoons presents lower mean raindrop diameter and lower raindrop concentration than that of the convection precipitation. The rainfall estimates from the adapted radar rainfall algorithm agree well with rainfall measurements from rain gauges. Using the rain gauge data as references, the maximum normalized mean bias ( N M B ) of the adapted radar rainfall algorithm is 20.27%; the normalized standard error ( N S E ) is less than 40%; and the Pearson’s correlation coefficient ( C C ) is higher than 0.92. For the three typhoon events combined, the N S E and N M B are 36.66% and -15.78%, respectively. Compared with several conventional radar rainfall algorithms, the adapted algorithm based on local rainfall microphysics has the best performance in southern China.

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