Evaluation of Two Radar-Based Hail Detection Algorithms (original) (raw)
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Development and behaviour of a radar-based operational tool for hailstorms identification
Atmospheric Research, 2007
Hailstorms are a common meteorological phenomenon in Spain which causes substantial economic damage especially in spring and summer. During 2000 and 2001, a radar-based application for convective monitoring was developed at STAP (Forecasting and Analysis Techniques Department); in order to improve this nowcasting tool, it is needed to include an advanced procedure to estimate the presence of hail as a complementary module in the operational application. A preliminary study, carried out during 2001, showed that the Waldvogel technique, VIL (vertical integrated liquid) density and the hail detection algorithm (HDA) are the methodologies which proved more accurate in our latitudes.
Meteorological Applications
This study investigated the radar-derived parameters in hail-producing storms and compared two hail-detection approaches in order to select the optimal method for real-time hail detection for the southern part of Romania. A statistical analysis of radar parameters was made, and the thresholds for radar-deriver parameters in hailproducing storms were determined. In addition, the hail storms' life cycle and diurnal and seasonal cycles of hail occurrence were investigated. The first algorithm developed in this study was based on the logistic regression model (LRM); the second one on the vertically integrated liquid (VIL) density algorithm. These algorithms were tested for the convective seasons (May-September) of 2014 and 2015. For the construction of the LRM, the composite reflectivity (CR), VIL and echo-top high (ET) were used as predictors for the probability of hail occurrence determination for 43 hail events observed at the synoptic station located in the radar-coverage area. The obtained statistics showed a marked diurnal cycle of hail occurrence with a maximum in the afternoon hours (1500-1800 LT), and the highest occurrence frequency of hail falls was in June. The results revealed that 93% of hail events occurred with 60 dBZ CR, 87% with 13 km ET, 100% with 55 kg/m 2 VIL and 100% with 4.5 g/m 3 VIL density. For the two hail-detection methods' performance comparison, a twoby-two contingency table was constructed and several statistical scores calculated. The LRM algorithm performed better than the VIL density algorithm.
Atmospheric Research, 2009
In order to identify hail into thunderstorms identified with radar data, different kinds of techniques are use based. This paper will evaluate some of these methodologies for the case of the Ebro valley (NE Spain), in order to obtain the best method to identify hail at surface. To achieve this end, an analysis of the 2004 and 2005 hail seasons has been undertaken using C-band radar, MM5 meteorological model outputs and ground observations provided by two hailpad networks. These data were integrated, identifying, characterizing and tracking the convective cells, and obtaining for each one different hail probability equations by means of various radar techniques. Kinetic energy flux was found to be the best parameter for distinguishing between hail and no-hail precipitation, although there was found to exist no significant difference between the various methods used. Moreover, the high correlations between radar parameters obtained by means of cell analyses led us to reduce the initial number of variables in new radar parameters. These new variables are defined and provide new improved models of the intensity of the storm.
Environmental & Socio-economic Studies
Hail involving very large hailstones (maximum diameter ≥ 5 cm), is a rare but very hazardous phenomenon in Poland, and can be forecast using reflectivity signatures. Every year, Poland experiences from one to over a dozen storms with such large hailstones. Despite the current recommendations regarding polarimetric techniques used in hail risk monitoring, Poland does not have a fully polarimetric radar network. Therefore it is essential to check hail detection capabilities using only reflectivity techniques based on individual radar systems involving hail detection algorithms such as Waldvogel et al. (1979) or Vertically Integrated Liquid thresholds connected with manual signature analysis to get better warning decisions. This study is aimed to determine the reflectivity features, thresholds and lead times for nowcasting of severe storms with very large hailstones in Poland, using data from the Polish radar system and from the European Severe Weather Database for the period 2007–2015...
Weather and Forecasting, 2007
Radar data were analyzed for severe thunderstorms that produced severe hail (Ͼ19 mm diameter) across the central and northern plains of the United States during the 2001-04 convective seasons. Results showed a strongly linear relationship between the 50-dBZ echo height and the height of the melting level-so strong that a severe hail warning methodology was successfully deployed at the National Weather Service Warning and Forecast Offices in North Dakota and Iowa. Specifically, for each of 183 severe hailstorms, the 50-dBZ echo height near the hail event time was plotted against the depth of the environmental melting level. Linear regression revealed a coefficient of determination of 0.86, which suggested a strong linear relationship between the 50-dBZ echo height and the melting-level depth for the severe hail producing storms. As the height of the melting level increased, the expected 50-dBZ echo height increased. A severe warning criterion for large hail was based on the 10th percentile from the linear regression, producing a probability of detection of 90% and a false alarm rate of 22%. Additional analysis found that the 50-dBZ echo-height technique performs very well for weakly to moderately sheared thunderstorm environments. However, for strongly sheared, supercell-type environments, signatures such as weak-echo regions and three-body scatter spikes led to more rapid severe thunderstorm detection in many cases.
Verification of an algorithm (DWSR 2500C) for hail detection
Atmosfera
The aim of this paper is to determine the real-time forecast and warning critera for hail events, using height of maximum reflectivity (Hmax), vertically integrated liquid water (VIL), hail occurrence probability (HailP) and reflectivity radar products (PPIZ). In addition, criteria were sought for use in estimating the size of hail stones. The study is based on data supplied by the Bucharest C-band weather radar along with observation data during the 2001-2008 period. The following radar products: HailP, Hmax, (PPIZ) and VIL, have been determined for each hail event reported by the weather station. A number of 320 cases have been analyzed when hail was determined for 20 weather stations in Muntenia area, Romania. One related result is that in situations when the 0 °C isotherm is between 3000 and 4000 m, the frequency of hail events certified on the ground is 50%. Another conclusion is that if the maximum reflectivity appears at heights between 7000 and 8000 m, there is an approximat...
Erad 2014-EIGHTH European Conference on Radar in Meteorology and Hydrology
2014
Supercell thunderstorms typically produce hail. The largest hail is commonly found at the edges of the updrafts, which allow sufficient growth time for hail to reach large sizes (Miller et al. 1988). An algorithm for hail recognition with the single polarization WSR-88D (Weather Surveillance Radar-Doppler) has been in use since early 1990s (Witt et al. 1994). Dual polarization radar capabilities allow measurements of differential reflectivity (ZDR), the correlation coefficient (ρhv), and differential phase (Φdp), which deliver additional information about scatterers. Studies by Balakrishnan and Zrnic (1990) of hail producing thunderstorms reveal low ZDR (about 0 dB) and reduced ρhv (as low as 0.8) in hail cores. These features are explained with tumbling non-spherical hailstones: the correlation coefficient drops because the scatterers are not spherical and ZDR is low because they tumble. Further works reveal variety of hail cases with reflectivities in a wide interval from ~ 30 to ...