Sorin Burcea

A Cloud-to-Ground Lightning Climatology for Romania

Abstract The first study of the characteristics of cloud-to-ground (CG) lightning in Romania, based on the data recorded by the Romanian National Lightning Detection Network (RNLDN), is presented. The data, more than 1.75 million CG flashes, covers the entirety of Romania and were recorded between January 2003 and December 2005 and January and December 2007. The spatial analyses (total and positive flash density, the percentage of positive flashes, and negative and positive peak currents) were done with a resolution of 20 km. The average spatial distribution shows a maximum (3.06 flashes km−2 yr−1) over the south slopes of the central meridional Carpathians possibly associated with the Romanian Plain convergence zone. The mean monthly variation shows maximum CG lightning between May and September (98%) and minimum values in December and January. High values (>0.028 km−2 yr−1) for positive CG lightning density are observed in southwestern and central Romania. The monthly distribution of positive flashes sh...

Hail Climatology and Trends in Romania: 1961–2014

AbstractA climatology and trend of hail events in Romania are presented using hail data spanning the years 1961–2014. Hail observations from weather stations and model reanalysis data were used to document the spatial and temporal distributions, variabilities, and environments of hail events. The results show that hail occurs most frequently in mountainous areas, while the smallest average number of hail days per year is found in the southeast. Herein, the convective season was defined as April–September, given that 94.2% of all mean monthly hail days were identified in this period. During the convective season the hail events prevail with most of these occurring in the afternoon and evening hours between 1000 and 1800 UTC. The severe hail events occur, overall, between 1400 and 1600 UTC, while in the southwest severe hail occurs later between 1600 and 1900 UTC. The spatial distribution of the convective parameters is consistent with the spatial distribution of hail days, revealing that hail is not favore...

Detection of hail through the three-body scattering signatures and its effects on radar algorithms observed in Romania

The Romanian National Meteorological Administration (NMA) radar network consists of five S-band and four C-band radars. Observation of convection in Romania through the Doppler radar network offered a new perspective in understanding the climatologic risk of certain regions and mesoscale environments. Highly organized convective systems, such as supercells, are better observed and their subsequent threat can be better anticipated during the nowcasting process using Doppler velocity fields and detection algorithmssuch as mesocyclones (MESO) and tornadic vortex signature (TVS). However, for warning purposes,these tools cannot be used without a subjective validation because of the associated errors and limitations of radar observations. In this paper several cases are presented where the presence of large hail inside the storm produced a radar artifact named three-body scatter signature (TBSS) that disturbed the Doppler velocity field. The cases presented were observed with S-band radars and were associated with hail reports on the ground. The first case shows a TBSS whose radial Doppler velocities are negative due to the falling hydrometeors. The second case is a less frequent event; there the Doppler velocities in the TBSS region are positive due to the updraft. The third case has both positive and negative values in the TBSS region; it is ocurred in a supercell that affected the city of Varna in Bulgaria with large hail. The positive values were associated with the overhang region in the rotational updraft at upper heights, while the negative values in the regions outside the rotational updraft at lower heights, were associated with the downdrafts. Features produced by the TBSS have perturbed the output of the MESO and TVS algorithms by introducing false strong values of wind shear that have been interpreted as rotation. Thus false mesocyclonic and tornadic vortex signatures were generated. In some of the cases large hail and weak tornadoes were reported, so the presence of a TBSS was a challenge for the nowcasters. In the last part of the paper we analyze the link between the TBSS appearance with reports of large hail at the ground in 2009 within the coverage area of the Romanian S-band radars, which also cover parts of Hungary, Bulgaria, the Republic of Moldova and Serbia. The results show that the TBSS artifact is a strong indicator of large size hail.