**1. Introduction**

Investigation of atmospheric electricity and lightning has started several hundred years ago and intense attention to processes of cloud electrification has been examined over the last several decades. However, our knowledge is still not complete because of our limited abilities to measure and observe processes, which occur in the atmosphere. It is supposed that the existence and development of electric field in the atmosphere is related to cosmic rays [1,2] and synergy of hydrometeors in clouds [3]. Currently, it is widely accepted that the main process leading to cloud electrification and lightning discharges is the process of riming electrification, often called the non-inductive charging [3–6]. In the non-inductive charging, it is assumed that the charging occurs mainly due to collisions of hydrometeors; between ice and graupel hydrometeors in particular [3,5].

Except for mathematical models, research data on electrification processes are available from laboratory experiments [7,8] and field campaigns carried out in thunderclouds (e.g., balloon experiments, aircraft data) [9–13] or they can be derived from satellite or radar observations [14–19]. Cloud radars represent an important data source for estimation of distribution of hydrometeors and for derivation of vertical air velocity. Thereby in thunderclouds, the cloud radars may provide necessary information for the charging mechanism by collisions of hydrometeors. In addition, measurements from polarimetric cloud radars can be used to indicate the electric field in cloud. Vonnegut [20] was the first, who described that ice crystals align within the electrostatic field in thunderstorms. Since that time, there were other

studies suggesting it as well [21–24]. This alignment of highly asymmetric ice particles is assumed to be indicated by clearly higher values of depolarization [25–28].

In this paper, we study differences in distribution of hydrometeors and in values of Linear Depolarization Ratio (LDR) in thunderclouds in dependence on whether a lightning discharge was recorded in the vicinity of the radar site or not. Based on data from a vertically-oriented polarimetric cloud radar, we estimate 5 hydrometeor species and we compare the identified hydrometeor species together with LDR values with lightning observations recorded by EUCLID (European Cooperation for Lightning Detection) network.

The paper is organized as follows. After this introductory section, Section 2 provides the reader with description of the cloud radar and of algorithms, which we apply to derive vertical air velocity (AV) and to classify hydrometeor species (Hclass). This section also provides an overview of analyzed thunderstorms and describes methods of comparison between obtained or derived data from the cloud radar and recorded lightning discharges near the radar site. Section 3 displays results; it details a thunderstorm that occurred on 10 June 2019 from diverse perspectives and then it shows common characteristics and average vertical profiles of LDR of (all) analyzed thunderstorms. Section 4 discusses the obtained results, while Section 5 draws conclusions of this study.
