The characteristics of multiple stroke negative cloud to ground (CG) lightning flashes in Padang, Indonesia based on electric field recording were investigated. 100 negative CG lightning flashes containing 623 strokes, recorded from August to October 2014, were examined. It was observed that all first return strokes (RS) negative CG lightning flashes were preceded by preliminary breakdown pulses (PBPs). However, only 40% of the detecable PBP trains could be analyzed statistically on PBP train duration, PBP-RS separation, and PBP/RS ratio, while the detectable leader pulses was 69%. In addition, it was also found that the arithmetic mean (AM) and maximum number of strokes were 5.2 and 18, respectively. The AM and geometric mean (GM) interstroke interval were 55.34 and 34.71 ms, respectively. Furthermore, 2% of the subsequent return stroke (SRS) peak electric fields were larger than those of the first return stroke (RS). The AM and GM ratios of SRS/RS were 0.36 and 0.3, respectively.Keywords: negative cloud to ground, preliminary breakdown, leader, return stroke, interstroke interval, peak electric field ratio IntroductionNegative cloud to ground (CG) lightning flashes is the most common type of CG discharges and has thereafter studied by many authors. A CG lightning flash usually contains preliminary breakdown pulses (PBPs) in the cloud and downward stepped leader (SL) propagation followed by the first return stroke (RS). The characteristics of a negative CG could largely be determined by the magnitude of the so called lower positive charge regions (LPCR) [1][2][3][4]. A larger LPCR causes the direction of negative leader propagation to be predominantly horizontal, even though finally the stepped leader propagates toward the ground. Meanwhile, a smaller LPCR causes negative stepped leader propagation to be predominantly vertical [5][6]. The time separation between PBPs and RS is approximately several milliseconds to hundreds of milliseconds. The generated electric field signature differentiates these processes. Nag and Rakov [5] stated that in negative CG lightning flashes, PBPs may not be detected on the first return stroke when the magnitude of the LPCR is very small. They claimed that CG lightning flashes vary in detectable PBP percentage according to latitude. Higher latitudes have a higher percentage of detectable PBPs than lower latitudes. In contrast, many researchers have argued that the first return stroke always involves PBPs in all negative CG flashes [7][8][9]. Their studies revealed that the detectable PBP percentage does not depend on latitude. A PBP can be detected if the amplitude of the PBP is above the noise level of the environment and electric field change sensors. However, Marshall et al. [9] have stated that they "cannot be certain that detection of PBPs always equals 100%" for all latitudes. In a more recent study, Zhu et al. [10] found that PBP detectability is not only affected by the sensor noise level but also by storm type, RS peak current and observation distance. The diffe...

Abstract:The characteristics of 77 electric field changes of positive cloud to ground (CG) flashes in the tropics of Indonesia were investigated. It was found that the arithmetic mean (AM) and geometric mean (GM) values for 0%-100% and 10%-90% rise time were 12.7 µs, 11.9 µs and 6.1 µs, 5.8 µs, respectively. The percentages of single, double, and triple strokes of lightning flashes were 83% (64 cases), 16% (12 cases), and 1% (1 case), respectively. The AM and GM of the interstroke intervals and the return stroke (RS) amplitude ratios were 163.9 ms, 0.29, and 13.3 ms, 0.26, respectively. Furthermore, it was also found that 7 (9%) of 77 positive CG flashes had double peak return stroke waveforms with AM and GM values for 0%-100% and 10%-90% rise time of subsequent return strokes that were 6.7 µs, 6.4 µs and 4.1 µs, 4 µs, respectively. We inferred that these double peaks are produced by two ground terminations with a time interval varying from 7 to 560 µs.

Abstract. In the palm oil industry, open ponding, aerobic and anaerobic digestion, physicochemical treatment and membrane filtration are generally applied as conventional treatments of palm oil mill effluent (POME). In this study, a sand filtration-dielectric barrier discharge (DBD) system was investigated as an alternative process for treating POME. This system can reduce land usage, processing time and costs compared to conventional systems. The removal efficiency of chemical oxygen demand (COD), biological oxygen demand (BOD 5 ), and oil-grease in relation to the applied voltage were studied. Furthermore, the pH and temperature profiles were investigated. The obtained results indicate that the removal efficiency of COD, BOD 5 , and oil-grease increased with an increase of the applied voltage. The electrical energy consumption needed is about 10.56 kWh/L of POME.

A new technology to produce biogas using a dielectric barrier discharge (DBD) plasma system from palm oil mill effluent (POME) was investigated. The batch experiments were examined at applied voltages of 15, 20 and 25 kV. The results showed that the highest yields of hydrogen and methane were achieved at an applied voltage of 25 kV after 1 hour were 2.42 and 1.32 mL/mL of POME, respectively. The biogas was composed of 65% hydrogen and 35% methane. In order to make the results of this study applicable to biogas plants, the effects of flowrate and consumed energy are important parameters that should be further investigated in a future study.

Positive lightning can do more damage than negative lightning. We have observed 77 positive cloud to ground (CG) flashes preceded by preliminary breakdown (PB) in Padang, Indonesia. It was found that there were two types of polarity between the PB pulse train and the following first return stroke (RS) pulses, namely the same polarity (type S) and composite polarity (type C). The occurence percentages of type S and type C were 92.2% and 7.8%, respectively. The aritmathic mean (AM) and geometric mean (GM) PB/RS separations and durations were 97.31 ms, 76.33 ms and 98.15 ms, 77.49 ms, respectively. The AM and GM PB/RS ratios were 12.26% and 10.20%, respectively. In addition, the characteristics of the PB pulse such as individual pulse duration, pulse train duration, and interpulse duration are discussed in this paper.