This study is the third part of a paper series investigating the polarimetric radar properties of melting hail and application of those properties for operational polarimetric hail detection and ...determination of its size. The results of theoretical simulations in Part I were used to develop a hail size discrimination algorithm (HSDA) described in Part II. The HSDA uses radar reflectivity Z, differential reflectivity Z
DR, and cross-correlation coefficient ρ
hv along with melting-level height within a fuzzy-logic scheme to distinguish among three hail size classes: small hail (with diameter D < 2.5 cm), large hail (2.5 < D < 5.0 cm), and giant hail (D > 5.0 cm). The HSDA validation is performed using radar data collected by numerous WSR-88D sites and more than 3000 surface hail reports obtained from the Severe Hazards Analysis and Verification Experiment (SHAVE). The original HSDA version was modified in the process of validation, and the modified algorithm demonstrates probability of detection of 0.594, false-alarm ratio of 0.136, and resulting critical success index (CSI) equal to 0.543. The HSDA outperformed the current operational single-polarization hail detection algorithm, which only provides a single hail size estimate per storm and is characterized by CSI equal to 0.324. It is shown that HSDA is particularly sensitive to the quality of Z
DR measurements, which might be affected by possible radar miscalibration and anomalously high differential attenuation.
The results of the analysis of long-term radar research of the hailstorms over the central part of the Northern Caucasus are presented. Radar observations which formed the basis of experimental ...material were carried out continuously from the moment of the first radar echo registration until complete dissipation of the hailstorm. The computerized system of collecting, processing and the analysis of the radar information was used. Time discretization of the radar parameters of the full spatial observation averaged 3 min. Statistical sampling of radar data included 392 hail cells, for each of which the time distributions of the radar parameters both measured and calculated using the computerized system were compiled. Distribution of the hailstorms first radar echo formation zones over the observation region was compiled. Areas with the maximum frequency of the hailstorms first radar echo formation were defined. The hailstorm trajectories were analyzed. Four main types of hail cell trajectories were selected, which included 86 % of the supercells and 64 % of the long-lived multicells. The dynamic parameters of the hail core formation and development were analyzed. The hail storm characteristics of the Northern Caucasus are compared to the hail storms of Mendoza, Argentina, and Alberta, Canada. The bases of the organization of regional hail suppression services which use the rocket technology of cloud seeding are presented. The results of the cloud seeding operations during recent years are shown.
Damaging hailstorms are rare but are significant meteorological phenomena from the point of view of economic losses in central Europe. Because of the high spatial and temporal variability of hail, ...the proper detection of hail occurrences is almost impossible using ground station reports alone. An alternate approach uses information from weather radars. Several algorithms that use single-polarisation radar data have been developed for hail detection. In the present study, seven algorithms were tested on well documented recent hail events from Czechia and southwest Germany from 2002 to 2011. The study aimed to find the optimal threshold values for the applications of these techniques over the Czech territory and for evaluating the climatology of hail events. The results showed that the Waldvogel technique and the NEXRAD severe hail algorithm were the most accurate methods for hail detection over the area of interest. A combined criterion was proposed based on a combination of previously tested techniques. The precision of this “combi-criterion” was demonstrated for a severe hail event. The abilities of the tested criteria to provide information about a hail-fall area distribution and hail damage risk over the Czech territory were shown and discussed.
•Seven algorithms for hail detection with single-polarisation radar data were tested.•New combi-criterion was created for large hail detection on the Czech territory.•Radar-based hail risk over Czechia is presented.•Values up to 1 hail day per year were found for the Czech territory.
Spectral (bin) microphysics models are used to simulate polarimetric radar variables in melting hail. Most computations are performed in a framework of a steady-state, one-dimensional column model. ...Vertical profiles of radar reflectivity factorZ, differential reflectivityZ
DR, specific differential phaseK
DP, specific attenuationAh
, and specific differential attenuationA
DPare modeled at S, C, and X bands for a variety of size distributions of ice particles aloft. The impact of temperature lapse rate, humidity, vertical air velocities, and ice particle density on the vertical profiles of the radar variables is also investigated. Polarimetric radar signatures of melting hail depend on the degree of melting or the height of the radar resolution volume with respect to the freezing level, which determines the relative fractions of partially and completely melted hail (i.e., rain). Simulated vertical profiles of radar variables are very sensitive to radar wavelength and the slope of the size distribution of hail aloft, which is correlated well with maximal hail size. Analysis of relative contributions of different parts of the hail/rain size spectrum to the radar variables allows explanations of a number of experimentally observed features such as large differences inZof hail at the three radar wavelengths, unusually high values ofZ
DRat C band, and relative insensitivity of the measurements at C and X bands to the presence of large hail exceeding 2.5 cm in diameter. Modeling results are consistent with S- and C-band polarimetric radar observations and are utilized in Part II for devising practical algorithms for hail detection and determination of hail size as well as attenuation correction and rainfall estimation in the presence of hail.
Hail involving very large hailstones (maximum diameter ≥ 4 cm) is rare but is one of the most hazardous weather phenomena in Poland. The most useful of the numerous weather radar reflectivity ...indicators are automated hail detection algorithms and reflectivity criteria, which can be easily implemented in operational weather warning systems. Since the temperature at which large hail forms is known, the vertically integrated liquid water content (VIL) can be calculated for the corresponding temperature layer. This paper presents four new VIL-based hail indicators using hail formation temperatures determined by the isotherms from ERA5. We compared these indicators with the 8 km Constant Altitude Plan Position Indicator (CAPPI) and the Waldvogel hail detection method by linking the detected cells to ESWD reports. Based on the VILs, we aimed to determine which layer within the VIL integration was the most useful for large hail prediction. In the case of the VILs, the layer between −12 and −25 °C was the best for hail detection. We also analysed the lead times of these indicators to assess their potential for implementation in the operational warning system in Poland. Using data from the European Severe Weather Database and the Polish radar system, we found that most incidents involving very large hailstones were linked to supercell storms with distinctive reflectivity signatures. The best hail indicator was the Waldvogel et al. (1979) hail detection technique, which had a lead time of approximately 17,5 min. The VIL had a near-zero lead time.
•Vertically Integrated Liquid (VIL)-based hail detection algorithm was performed for isotherms derived from ERA5 reanalysis.•Four layers between the different isotherms were compared of the hail detection skill.•Most of the storms with reflectivity of at least 56 dBZ at a height of 8 km was severe weather-producing storms.•The most severe storms had larger area of high value of the VILs.•The VIL method is not a good indicator of the low-topped storms.
Severe hailstorms produce over $1 billion in insured losses annually in the United States, yet details of a given storm's hail threat (e.g., maximum hailstone size and total hailfall) remain ...challenging to forecast. Previous research suggests that, in addition to maximum updraft speed, the storm-relative airflow could be equally important for hail formation and growth. This study is a first step toward determining how changes in environmental wind shear and subsequent changes in simulated supercell storm structure affect hail growth. Using Cloud Model 1 (CM1) with 500-m horizontal and 250-m vertical grid spacing, 20 idealized simulations are performed in which the thermodynamic profile remains fixed but the environmental hodograph is systematically altered. Hail growth is quantified using the hail mass mixing ratio from composites of storms over the last hour of simulation time. Hailstone growth "pseudotrajectories" are computed from these storm composites to determine favorable embryo source regions. Results indicate that increased deep-layer east-west shear elongates the storm's updraft in that direction, providing 1) increased volumes over which microphysically relevant hail processes can act, 2) increased hailstone residence times within the updraft, and 3) a larger potential embryo source region; together, these lead to increased hail mass. Increased low-level north-south shear, which results in hodographs with increased 0-3-km storm-relative helicity, also elongates the updraft in the north-south direction. However, hail mass is reduced owing to a separation of favorable embryo source regions (which shift southward) and available hydrometeors to serve as embryos (which shift northward).
Abstract
Observed proximity soundings from Europe are used to highlight how well environmental parameters discriminate different kind of severe thunderstorm hazards. In addition, the skill of ...parameters in predicting lightning and waterspouts is also tested. The research area concentrates on central and western European countries and the years 2009–15. In total, 45 677 soundings are analyzed including 169 associated with extremely severe thunderstorms, 1754 with severe thunderstorms, 8361 with nonsevere thunderstorms, and 35 393 cases with nonzero convective available potential energy (CAPE) that had no thunderstorms. Results indicate that the occurrence of lightning is mainly a function of CAPE and is more likely when the temperature of the equilibrium level drops below −10°C. The probability for large hail is maximized with high values of boundary layer moisture, steep mid- and low-level lapse rates, and high lifting condensation level. The size of hail is mainly dependent on the deep layer shear (DLS) in a moderate to high CAPE environment. The likelihood of tornadoes increases along with increasing CAPE, DLS, and 0–1-km storm-relative helicity. Severe wind events are the most common in high vertical wind shear and steep low-level lapse rates. The probability for waterspouts is maximized in weak vertical wind shear and steep low-level lapse rates. Wind shear in the 0–3-km layer is the best at distinguishing between severe and extremely severe thunderstorms producing tornadoes and convective wind gusts. A parameter WMAXSHEAR multiplying square root of 2 times CAPE (WMAX) and DLS turned out to be the best in distinguishing between nonsevere and severe thunderstorms, and for assessing the severity of convective phenomena.
Abstract
The central east coast of Australia is frequently impacted by large hail and damaging winds associated with severe convective storms, with individual events recording damages exceeding AUD 1 ...billion. These storms present a significant challenge for forecasting because of their development in seemingly marginal environments. They often have been observed to intensify upon approaching the coast, with case studies and climatological analyses indicating that interactions with the sea breeze are key to this process. The relative importance of the additional lifting and vorticity along the sea-breeze front in comparison with the change to a cooler, moister air mass with stronger low-level shear behind the front has yet to be investigated. Here, the role of the sea-breeze air mass is isolated using idealized numerical simulations of storms developing in a horizontally homogeneous environment. The base-state substitution (BSS) modeling technique is utilized to introduce the sea-breeze air mass following initial storm development. Relative to a simulation without BSS, the storm is longer lived and more intense, ultimately developing supercell characteristics including increased updraft rotation, deviant motion to the left of the mean wind vector, and a strong reflectivity gradient on the inflow edge. Separately simulating the changes in the thermodynamic and wind fields reveals that the enhanced storm longevity and intensity are primarily due to the latter. The change in the low-level environmental winds slows gust-front propagation, allowing the storm to continue to ingest warm, potentially buoyant environmental air. At the same time, increased low-level shear promotes the development of persistent updraft rotation that causes the storm to make a transition from a multicell to a supercell.
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