## 2 Experimental Schemes
To analyze the influence this factor had on the experimental results, all model elements were divided into three groups according to the electric field amplification coefficient: group I had an amplification coefficient < 10; group II had an amplification coefficient < 25; group III had an amplification coefficient > 25. Examples of the formation of upward streamer discharges from the grounded rods and elongated model elements under the negative polarity artificial thunderstorm cell are shown in Figures 3 and 4, respectively. Figure 2: Second scheme of experimental and measurement setup: 1—grounded electrostatic screens; 2—artificial thunderstorm cell; 3.4—cylinder electrodes; 5—isolated elongated elements; 6—shunts: 7—insulators. The characteristic oscillograms of the current impulse of powerful streamer corona flash and the corresponding induced electromagnetic effects (induced current) on the close rod or elongated model element are shown in Figure 5. The discharge current was registered using low-inductance shunts (6, Figures 1 and 2). The current induced by the discharge was registered using flat antennas (A1 and A2, Figure 1). Both signals were recorded in the same way as  
recorded by digital oscilloscopes Tektronix DPO7254 and Tektronix TDS3054C (Tektronix, Inc., Beaverton, OR, USA). For the impulse streamer corona flash of the upward discharge current amplitude, maximal current rise velocity, flowing charge, and impulse duration were determined. For induced electromagnetic effects on the signal amplitude of the nearby model elements, the  
Figure 5: **(a)** Oscillograms of the upward streamer discharge current (upper) and induced electromagnetic effects (bottom). **(b)** Focused oscillograms of the formation of the upward streamer discharge current (upper) and induced electromagnetic effects (bottom). duration of the induced signal was determined. The maximum value of the current pulse was described as the current amplitude (Imax). The time between the start and end of the impulse was described as the impulse duration. The start time of the pulse was decided based on the first time it crossed the zero value; similarly, the end time was decided based on the time of the first signal zero value following Imax. The maximal current rise velocity was specified as the ratio of the difference between 0.9 and 0.3 Imax of the signal duration between the points corresponding to 0.9 and 0.3 Imax (Figure 5b). The flowing charge was estimated by the integration of the current pulse from the pulse start time to the end time. The spectral characteristics of the discharge current and the induced signals were determined based on a wavelet analysis, using the specially created program and the \"Mexican Hat\" wavelet [23,24]. In mathematics, a wavelet series is a representation of a square-integrable (real- or complex-valued) function by a certain orthonormal series generated by a wavelet. The fundamental idea behind wavelet transforms is that the transformation should only allow changes in the time extension, but not the shape. While the Fourier transform creates a representation of the signal in the frequency domain, the wavelet transform creates a representation of the signal in both the time and the frequency domain, thereby allowing efficient access to localized information about the signal. The upper level of the characteristic frequency, maximal intensity, and frequency of the maximal intensity in the wavelet spectrum was found. The characteristic wavelet spectrum for the currents and induced signal presented in Figure 5 are shown in Figures 6 and 7, respectively. Figure 6: Wavelet spectrum of upward streamer corona current impulse.