Noor Azlinda Ahmad

A Comparative Study on the Positive Lightning Return Stroke Electric Fields in Different Meteorological Conditions

Positive cloud-ground lightning is considerably more complex and less studied compared to the negative lightning. This paper aims to measure and characterize the significant parameters of positive return strokes electric field, namely, the zero-to-peak rise time, 10–90% rise time, slow front duration, fast transition rise time (10–90%), zero-crossing time, and opposite polarity overshoot relative to peak. To the best of the authors’ knowledge, this is the first time such detailed characteristics of positive lightning in Malaysia are thoroughly analyzed. A total of 41 positive lightning flashes containing 48 return strokes were analyzed. The average multiplicity is 1.2 strokes per flash. The majority of positive lightning was initiated from the primary positive charge rather than as a byproduct of in-cloud discharges. The cumulative probability distribution of rise time parameters, opposite polarity overshoot relative to peak, and slow front amplitude relative to peak are presented. A comparison between studies in four countries representing tropic, subtropic, and temperate regions was also carried out. Measured parameters in Florida, Sweden, and Japan are generally lower than those in Malaysia. Positive lightning occurrences in tropical regions should be further studied and analyzed to improve our current understanding on positive return strokes.

Comparative study on preliminary breakdown pulse trains observed in Malaysia and Florida

In this paper, the preliminary breakdown pulse (PBP) trains preceding the negative first return strokes recorded using a broad band antenna system in Johor Bahru, Malaysia and Florida, United States were analyzed. In lightning flashes observed in Malaysia, the ratio between the amplitude of the largest preliminary breakdown pulse (PBP) and the peak return stroke electric field (RS) was 27.8% and the corresponding value in Florida was 29.4%. The time interval between the beginning of the preliminary breakdown sequence and the initiation of the return stroke was 57.6 ms in Malaysia and 22 ms in Florida. The results of the study support the hypothesis that the PBP/RS ratio increases with increasing latitude.

Characteristics of Electric and Magnetic Fields in the Vicinity of a Quadruple Electric Power Line

The relationship between the electric and magnetic fields along with soil resistivity is very important for direct lightning stroke. In this paper, the electric and magnetic fields produced by a parallel quadruple high voltage power lines (PQHVPL) have been measured. The measured fields are substantially high compared to the fields coming from conventional 132 kV and 275 kV power lines. The correlation between electric and magnetic fields emitted from PQHVPL and soil resistivity in the ground below the lines has also been investigated. The electric and magnetic field digital exposure system (EMDEX) hardware and software are used to measure and analyze the results. It is found that the electric field is higher at high soil resistivity and is lower at low soil resistivity.

Measurement of Dielectric Properties of Low-Density Polyethylene Nanocomposites Using “Sub-Hertz” Dielectric Spectroscopy

Recently, many studies have been conducted on the dielectric properties of Low-Density Polyethylene (LDPE) nanocomposites and produced different results. However, the composition of LDPE polymer and boron nitride (BN) as nanofiller has neither been well understood nor producing a convenient result. Similarly, the dielectric spectroscopy measured at “sub–hertz” frequency has been of little interest among researchers since it is often influenced by “conduction-like” effect. This research identified the dielectric properties of LDPE nanocomposites filled with hexagonal boron nitride (h-BN) nanofillers by using dielectric spectroscopy technique. The dielectric loss and relative permittivity for three different filler concentrations were investigated under “sub-hertz” frequency ranges at room temperature. The cylindrical electrode with guard ring configuration was used to conduct the experiment, in accordance to the ASTM D150 standard. The results revealed that 5 wt% filled polymer has lower loss tangent and permittivity compared to the unfilled polymer, due to the strong interaction between nano-particle and the polymer. This strong interaction is believed to limit the movement of the polymer chain. The decrease in loss tangent also indicates lower quasi-DC at low frequency. However, further increase in the filler loading has recorded an increment in the value of permittivity and loss tangent. This higher effective permittivity is mainly due to the influence of the filler permittivity

A Review of Recent Studies on Positive Lightning

Lightning is a natural phenomenon that has much impact on man and man-made systems. Lightning can be generally characterized as either negative return stroke (NRS) or positive return stroke (PRS). PRS have high peak currents and long continuing current that are responsible for more intense damage than negative return strokes. However, PRS are considerably less studied compared to NRS due the complexity and paucity of PRS. This study attempts to provide an overview of the positive lightning characteristic research in recent years. The review is classified into four groups, which are: preliminary breakdown pulse of positive lightning, compact intracloud discharge, positive leader and positive lightning return stroke. In spite of recent progress made in this area, our knowledge on the physics of positive lightning remains considerably poorer than negative lightning. Many questions regarding the characteristic of positive lightning and their properties cannot be answered without further research. It would be of great interest to examine the positive lightning parameters under different meteorological conditions as well.

Characteristic of preliminary breakdown preceding negative return stroke in Malaysia

This paper describes a study on the characteristics of preliminary breakdown pulses (PBPs) preceding negative return strokes. Such characterization is needed due to the lack of available data, especially for negative lightning, in Malaysia. Measurements were carried out in Johor Bahru, Malaysia in October 2014 using broadband antennas and a high resolution Picoscope. It was found that 84% of the negative return strokes (RS) were preceded by PBPs. 70% of the PBPs fit the BIL model and another 30% the BL model. The arithmetic mean of the PBP-RS interval is 13.2ms, which is about four times smaller compared to a similar measurement made during April to June, 2009. The difference may probably be due to a variation in the thundercloud formation which is dependent on the monsoon period in Malaysia. Further studies are required to characterize the PBPs and their relations with the monsoon period and with geographical region.

Removal of Bisphenol A (BPA) in Surface Water by Ozone Oxidation Process

The removal of Bisphenol A in river water can be accomplished with the application of ozone. Ozone is widely used to disinfect drinking water due to its strong oxidizing properties. This study was conducted to investigate the removal of Bisphenol A in different areas of Skudai River. Batch experiments were conducted at initial Bisphenol A concentration of 0.5 mg L-1. The concentrations of Bisphenol A and dissolved ozone were measured using Ultra High Performance Liquid Chromatography (UHPLC) and UV-Visible spectrophotometer respectively. Based on the results obtained the stability of ozone in the water were very fast. Ozonewas quickly decomposed in water samples. The results indicated that the depletion of ozone varied from different dissolved organic carbon (DOC) value of water samples. Concentration of dissolved ozone was reducing rapidly after spiked into high DOC value (9.17 mg L-1) of river water. The results of the study have shown that ozonation could be used to effectively remove the Bisphenol A from water. The ozone depletions in river water at 120 seconds were about 87%-99%.

Wavelet analysis of narrow bipolar pulses in tropical region

In this paper, we reported the wavelet analysis of lightning electric field of Narrow Bipolar Pulses (NBP) measured during two different monsoon season in Johor, Malaysia. The lightning electric field of NBP were divided into Narrow positive Bipolar Pulses (NPBP) and Narrow Negative Bipolar Pulses (NNBP). Analysis on the wavelet and frequency spectrum reveals that the energy spectrum for both NBPs concentrates at higher frequency (200 kHz to 600 kHz) in comparison to return strokes. Further, NBPs radiated higher energy power spectrum during northeast monsoon with average peak power spectrum of the initial stage NNBP and NPBP are 76,650 (V/m)2 and 76309 (V/m)2, respectively.

Wavelet analysis of chaotic pulse trains prior to subsequent return strokes in Malaysia

This paper presents a wavelet transformation of chaotic pulse trains (CPTs) prior to negative subsequent return strokes in Malaysia. A total of 593 recorded waveforms were examined. Even though several hundred waveforms were identified as containing CPTs, only 47 waveforms with CPTs preceding subsequent return stroke were selected for analysis. 19 samples are classified as CPTs associated with dart or dart-stepped leader (Type 1 CPTs) with spectral and spread regions average frequency range of 34.8-154.3 kHz and 56.2-81.4 kHz respectively. 28 samples are classified as chaotic pulse trains alone (Type 2 CPTs) with spectral and spread regions average frequency range of 24.6-121 kHz and 40.3-62 kHz, respectively. The Type 1 CPTs tends to radiate at a higher frequency range compared to Type 2 CPTs. The maximum power radiated by the largest pulse in Type 1 CPTs is more than six times larger than that for the Type 2 CPTs. In addition, the Type 1 CPTs have larger electric field variations, higher frequency, and higher power radiated spectrum compared to Type 2 CPTs. The reported radiated energy can be further compared with other lightning activities to give a better insight on the in-cloud breakdown processes prior to subsequent return strokes.

Wavelet analysis for negative return stroke and narrow bipolar pulses

Lightning generates electric fields are known to have negative consequences. In this study, two types of lightning electric fields which are Negative Return Stroke (NRS) and Narrow Bipolar Pulses were thoroughly analyzed using wavelet analysis. Hence, analysis on the wavelet and frequency spectrum reveal that the energy spectrum for NBP concentrates at high frequency (200 kHz to 500 kHz) with average peak power of the initial stage for NNBP and NPBP are 76,650 (V/m)2 and 76309(V/m)2 respectively. However, the initial stage peak power corresponding to NRS is about 118,931(V/m)2 with lower frequency spectrums (60 kHz). The results suggest that NBP radiates energy at high frequency region compared to NRS. Hence it can be concluded that, electric field pulse for NBP experience more extensive and rapid ionization process compared to NRS.