In this thesis, the features of electric field signatures of narrow bipolar pulses (NBPs) generated by cloud flashes are investigated and their effects on wireless communication systems are studied. A handful amount of NBPs (14.5%) have been observed to occur as part of cloud-to-ground flashes in South Malaysia. Occurrence of NBPs in Sweden has been reported for the first time in this thesis. The electric field waveform characteristics of NBPs as part of cloud-to-ground flashes were similar to isolated NBPs found in Sweden and South Malaysia and also to those isolated NBPs reported by previous studies from various geographical areas. This is a strong indication that their breakdown mechanisms are similar at any latitudes regardless of geographical areas. A comparative study on the occurrence of NBPs and other forms of lightning flashes across various geographical areas ranging from northern regions to the tropics is presented. As the latitude decreased from Uppsala, Sweden (59.8°N) to South Malaysia (1.5°N), the percentage of NBP emissions relative to the total number of lightning flashes increased significantly from 0.13% to 12%. Occurrences of positive NBPs were more common than negative NBPs at all observed latitudes. However, as latitudes decreased, the negative NBP emissions increased significantly from 20% (Sweden) to 45% (South Malaysia). Factors involving mixed-phase region elevations and vertical extents of thundercloud tops are invoked to explain the observed results. These factors are fundamentally latitude dependent. In this thesis, the interaction between microwave radiations emitted by cloud-to-ground and cloud flashes events and bits transmission in wireless communication networks are also presented. To the best of our knowledge, this is the first time such effects are investigated in the literature. Narrow bipolar pulses were found to be the strongest source of interference that interfered with the bits transmission.

Temporal and wavelet characteristics of initial breakdown pulses are meticulously studied especially during the earliest moment of lightning events. Any possible features during the earliest moment that may exist which lead to either negative cloud-to-ground (CG), positive cloud-to-ground, cloud or isolated breakdown flashes in Sweden are investigated. Moreover, the occurrence of narrow bipolar pulses (NBPs) as part of a CG event that has been recorded from tropical thunderstorms are also included in the investigation. Electric field signatures selected from a collection of waveforms recorded using fast electric field broadband antenna system installed in Uppsala, Sweden and Skudai, South Malaysia are then carefully analyzed in order to observe any similarities or/and differences of their features. Temporal analysis reveals that there are significant distinctions within the first 1 ms among different types of lightning flashes. It is found that a negative CG flash tends to radiate pulses more frequently than other flashes and a cloud flash tends to radiate shorter pulses than other flashes but less frequently when compared to negative CG and isolated breakdown flashes. Perhaps, the ionization process during the earliest moment of negative CG flashes is more rapid than other discharges. Using a wavelet transformation, it can be suggested that the first electric field pulse of both negative CG and cloud flashes experiences a more rapid and extensive ionization process compared to positive CG and isolated breakdown flashes. Further temporal analysis on NBPs found to occur as part of CG flashes show the disparity of the normalized electric field amplitude between the NBPs prior to and after the first return stroke. This indicates that the NBPs intensities were influenced by the return stroke events and they occurred in the same thundercloud. The similarity between the temporal characteristics of NBPs as part of CG flashes and isolated NBPs suggests that their breakdown mechanisms might be similar.