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 hail‐producing 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/m² VIL and 100% with 4.5 g/m³ VIL density. For the two hail‐detection methods’ performance comparison, a two‐by‐two contingency table was constructed and several statistical scores calculated. The LRM algorithm performed better than the VIL density algorithm.

Acta Geophysica Open Access Published: 01 April 2016 Changes in the Large-Scale Atmospheric Circulation over Romania Between 1961 and 2010 on Seasonal Basis Nicu Barbu¹, Cristina Burada³, Sabina Stefan¹ & Florinela Georgescu² Acta Geophysica volume 64, pages 510–520 (2016)Cite this article 290 Accesses 7 Citations Metrics details Abstract The aim of this paper is to investigate the trends and shifts of the circulation types over Romania for 50-year period (1961–2010) on seasonal basis. In order to achieve this, two objective catalogues, namely GWT and WLK, from COST733 Action were employed. Daily circulation types were grouped according to the cyclonicity and anticyclonicity and were used to calculate the seasonal occurrence frequency of cyclonic and anticyclonic types. The trend of seasonal time series was investigated by using Mann–Kendall test and the shifts points were determined by using Pettitt test. 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The goal of this article is to investigate how the Romanian air space would be affected by a potential large eruption of Vesuvius volcano. In order to characterize the potential impact of such an event on the Romanian air space, we simulated the ash plume transport from a hypothetical explosive eruption with a significant magnitude, that is, Volcanic Explosivity Index (VEI 4). The volcanic ash cloud transport towards Romania was described by using the mass distribution from the HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) for Volcanic Ash numerical model. To assess the dominant air circulation types, an adaptation of the WetterLagenKlassification (WLK) classification scheme was used. The results emphasized that a long‐wave trough and southwesterly flow in upper levels would favour the direct transport of volcanic ash cloud towards the Romanian air space. Non‐negative matrix factorization method has been used to identify the atmospheric layer with the maximum values of mass. The simulation results reveal that the maximum values of averaged mass were obtained at an altitude around 7 km.

Three case studies of Saharan dust intrusions over southern Romania were performed. For these studies the database from the ceilometers located at Magurele and Strejnic was used. In addition, the meteorological conditions were analyzed using the WLK Catalogue based on the Objektive Wetterlagenklassifikation classification of the weather types [1]. This catalogue uses information from three basic tropospheric levels: 925, 700 and 500 hPa, and information on the precipitable water content over the entire atmosphere column. Geopotential fields at 925hPa and 500hPa are used for establishing the cyclonicity or anticyclonicity, while the U and V components of wind at 700hPa for establishing the dominant direction of the wind flow. For better understanding of the atmospheric parameters we performed HYSPLIT dispersion and trajectories analysis in conjunction with DREAM model output data.