The mesoscale configurations are analysed associated withthesplitting process of convective cells responsible for severe weather phenomena in the south-eastern part of Romania. The analysis was performed using products from the S-band Doppler weather radar located in Medgidia. The cases studied were chosen to cover various synoptic configurations when the cell splitting process occurs. To detect the presence and intensity of the tropospheric jet, the Doppler velocity field and vertical wind profiles derived from radar algorithms were used. The relative Doppler velocity field was used to study relative flow associated with convective cells. Trajectories and rotational characteristics associated with convective cells were obtained from reflectivity and relative Doppler velocity fields at various elevations. This analysis highlights the main dynamic features associated with the splitting process of convective cells: the tropospheric jet and vertical moisture flow associated with the configuration of the flow relative to the convective cells for the lower and upper tropospheric layers. These dynamic characteristics seen in the Doppler based velocity field and in the relative Doppler velocity field to the storm can indicate further evolution of convective developments, with direct implications to very short range forecast (nowcasting). 1. Introduction In south-eastern Romania, in the convective season (from May to September), severe weather phenomena develop frequently and evolve [1–5], sometimes leading to significant damages. Analysis of severe convective events and their structure, at least for certain classes of phenomena (isolated convective cells), taking into account the mesoscale configuration can improve the nowcasting procedures. Using an S-band Doppler radar (10？cm wavelength), we see that the mesoscale phenomena (supercellular thunderstorms) have certain features during their dynamic evolution. Of great importance in understanding the evolution of supercells is the splitting process (separation of the convective cells in two other ones rotating opposite to one another, namely, cyclonic and anticyclonic), a process that takes place during the evolution of convective developments and is closely linked to the state of mesoscale dynamic configuration, especially vertical wind shear [6, 7]. This process has been studied both qualitatively [8–18] and by numeric analysis [19–21], highlighting the interaction between horizontal vorticity from the vertical profile of horizontal wind and the updraft. Depending on the curvature of the hodograph, the
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