Investigation of the Main Stage of a Discharge between an Artificially Charged Water Aerosol Cloud and a Grounded Electrode

Paper presents results of experimental investigation of the main stage of the discharge between an artificially charged water aerosol cloud and a rod on the grounded plate beneath it. Three forms of the main stage of the spark discharge between the charged cloud and grounded electrode have been found. Form I has the weak brightness, the maximal current amplitude not more than 8 A, and the sharp tortuosity of their channels. The charge neutralizing in aerosol cloud is ~ 2,0 μC. Form II is more brighter, has the maximal current amplitude up to 20 A, and consists of one or sometimes two parts. The charge neutralizing in aerosol cloud is ~ 1,0 μC. Form III presents very bright sparks, has the maximal current amplitude more than 20 A, and consists of only one part with length up to 1,0-1,3 meters. The charge neutralizing in aerosol cloud is ~ 2,5-3,0 μC. It was found that the main stage parameters and the charge value neutralizing in aerosol cloud significantly depend on the discharge trajectory. The results obtained can help to understand the possible physical mechanisms of the cloud volume charge neutralization in a thunderstorm cloud during the discharge initiation, propagation of intra-cloud discharges, the return stroke, and continuous current stage. INTRODUCTION Investigation of problem of the thunderstorm cloud charge neutralization during the lightning discharge is important as for more deeply understanding of the thunderstorm physics as the forecasting of lightning affection of the different objects. We would like to know the answers on following questions: what part and in what degree of the thundercloud will be neutralized, possibility and direction of the secondary strikes [Bazelyan and Raizer, 2000]. Today there is still no common agreement about what discharge processes occur within the different regions of a thunderstorm, or how lightning flashes are initiated and propagate inside the cloud. There are only basic propositions about how the presence of cloud drops modifies or otherwise affects the initiation and subsequent development of a discharge inside the cloud, and just how extended volumes of cloud charge are effectively neutralized by lightning [Williams et al., 1985]. That is connected with the fact that the mechanisms of a discharge development in the strongly charged aerosol formations (thunderstorm cells) and thunderstorm charge neutralization are less investigated (especially experimentally). Experimental possibilities [Barreto, 1969; Sugimoto et al., 1999] did not allow to receive and to investigate the discharges with the length more than ten centimeters. Paper presents some preliminary results of experimental investigation of the discharge processes between an artificially charged water aerosol cloud and a rod on the grounded plate beneath it. The emphasis is done on the high-current main stage of the discharge that can provide a significant neutralization of the aerosol cloud charge. EXPERIMENTAL SET-UP Scheme of experimental set-up is shown in fig. 1. Charged aerosol generator 1 of a condensate type is used for creation of cloud the strongly charged water aerosol above the grounded plate 2. Artificially charged aerosol cloud has a volume of some cubic meters. Volume density of the aerosol charge on a cloud axis is in the range 1,5⋅10 – 1,0⋅10 C/m, and the cloud potential could achieve 1,5 MV [Temnikov and Orlov, 1996]. As a result, strong electric field is formed between the grounded plate and the charged aerosol cloud 3. Electric field strength can be up to 12 kV/cm near the grounded plate, and 22 kV/cm on the charged aerosol cloud boundary.