| 1. |
- Ahmad, Mohd Riduan, et al.
(författare)
-
Chaotic Pulse Train in Cloud-to-Ground and Cloud Flashes of Tropical Thunderstorms
- 2014
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we report for the first time the observation of chaotic pulse train (CPT) preceding natural subsequent negative return strokes and also CPT occurrence in IC flashes from tropical thunderstorms in South Malaysia. In CG flashes, all CPTs were occurred in between return strokes with 41.1% have occurred between the first and second return strokes. The maximum number of CPT in one sequence is 3, which can be observed between the first and third return strokes only. In IC flashes, all CPTs were observed to occur in between IC flash pulses.
|
|
| 2. |
|
|
| 3. |
- Ahmad, Mohd Riduan, et al.
(författare)
-
Emission Heights of Narrow Bipolar Events in a Tropical Storm over the Malacca Strait
- 2017
-
Ingår i: 2017 International Conference On Electrical Engineering And Computer Science (Icecos). - : IEEE. - 9781479976751 - 9781479976768 - 9781479976744 ; , s. 305-309
-
Konferensbidrag (refereegranskat)abstract
- Emission heights for narrow bipolar events (NBEs) have been reported mostly from observations at mid latitudes but none have been reported from tropical regions. In this paper, we are reporting for the first time the heights of NBE emissions from a tropical storm over the Malacca Strait, a narrow water passage between the Malay Peninsula and Sumatra Island. A total of 49 positive NBEs (+NBEs) were detected from the storm. The NBE activity can be divided into two stages according to the emission heights and radar reflectivity data. The first stage (or S1) lasted for only 6 minutes, started with the first detected NBE, and produced 20 NBEs (41%). The emission heights ranged between 12.0 and 16.7 km. Radar reflectivity data showed that the storm reached maximum values at 55 dBZ within the period S1. In contrast, the second stage (S2) lasted longer (32 minutes) and produced 29 NBEs (59%). The emission heights were lower and ranged from 8.5 to 13.7 km. Radar reflectivity data showed that the storm reached maximum values at 50 dBZ within the period S2.
|
|
| 4. |
- Ahmad, Mohd Riduan, 1980-
(författare)
-
Interaction of Lightning Flashes with Wireless Communication Networks : Special Attention to Narrow Bipolar Pulses
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 5. |
|
|
| 6. |
- Ahmad, Mohd Riduan, et al.
(författare)
-
Lightning interference in multiple antennas wireless communication systems
- 2012
-
Ingår i: Journal of Lightning Research. - : Bentham open. - 1652-8034. ; 4, s. 155-165
-
Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes the interference of lightning flashes with multiple antennas wireless communicationsystems operating in the microwave band at 2.4 GHz and 5.2 GHz. A bit error rate (BER) measurement method was usedto evaluate BER and packet error rate (PER) during 5 heavy thunderstorms on January 25 and March 17 to 20, 2011,respectively. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW)conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-ofsight(LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higherrecorded BER. The maximum recorded BER was 9.9·10-1 and the average recorded BER and PER were 2.07·10-2 and2.44·10-2 respectively during the thunderstorms with the average fair weather BER and PER values under the influence ofadjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10-6 respectively. Weconclude that multiple antennas wireless communication systems operating at the microwave frequency can besignificantly interfered by lightning.
|
|
| 7. |
|
|
| 8. |
- Ahmad, Mohd Riduan, et al.
(författare)
-
Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses
- 2014
-
Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 810-813
-
Konferensbidrag (refereegranskat)abstract
- In this paper, temporal characteristics of several initial electric field pulses of preliminary breakdown process (PBP) from very close negative cloud-to-ground (CG) flashes are compared to close narrow bipolar pulses (NBPs) to observe any similarity that may exists. Interestingly, we found that the initial PBP pulses are similar to close NBP with zero crossing time less than 5 mu s, do not preceded by any slow field change and followed by pronounce static component. As NBPs are believed to be a result of relativistic runaway electron avalanches discharge, this finding is an indication that the initial electric field pulses of PBP are perhaps the result of the same discharge mechanism.
|
|
| 9. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
-
Microwave and Very High Frequency Radiations of The First Narrow Initial Breakdown
- 2021
-
Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- This paper reports the observation of microwave and very high frequency (VHF) radiation pulses associated with the first narrow (<10us) initial breakdown (IB) pulses of ten negative cloud-to-ground (-CG) flashes. The centre frequency of microwave and VHF sensors was 0.97 GHz and 60 MHz, respectively. We found that all microwave pulses were the initiation event led the first VHF pulses ranging between 0.03187 and 2.57968 mu s and led the first narrow IB pulses ranging between 0.02382 and 2.70202 mu s. Half of the VHF pulses were observed to lead the first narrow IB pulses ranging between 0.03453 and 0.128 mu s. Moreover, polarity of microwave radiation pulses was always positive while the polarity of the first narrow IB pulses always negative. On the other hand, half of VHF radiation pulses had the same polarity as microwave radiation pulses.
|
|
| 10. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
-
Microwave radiation associated with positive narrow bipolar events
- 2023
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 242
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examined seven isolated positive Narrow Bipolar Events (NBEs), one positive NBE that initiated an IC flash progressed to a single-stroke Cloud-to-Ground (CG) flash, and one positive NBE that initiated an IC flash. Seven NBEs have been accompanied by significant Very-High Frequency (VHF) and microwave radiation pulses. We recorded all NBEs from two measurement stations (ST1 and ST2) separated at 13.3 km apart which consisted of fast antenna (FA) and slow antenna (SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (0.97 GHz). The waveforms were sampled at 2.5 GHz (400 ps). The key finding is that all microwave radiation pulses have been found to precede both the VHF radiation pulses and NBEs with average lead time of 63 +/- 39 ns and 122 +/- 143 ns, respectively. In comparison to stepped leader pulses or SLPs (conventional breakdown), the average lead time of microwave to VHF for NBEs (fast breakdown) was 88% faster compared to the average lead time of microwave to VHF for SLPs. Moreover, the average lead time of VHF to NBEs was 56% faster when compared to the average lead time of VHF to SLPs. The VHF interferometer map for an isolated NBE (NBE6) showed upward propagation of VHF radiation sources (fast negative breakdown) with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 10.2 +/- 0.3 km, 2.9 +/- 0.6 km, and 1.8 x 108 and 2.8 x 108 ms-1, respectively. On the other hand, interferometer map for an NBE that initiated a single-stroke CG (NBE3) showed bidirectional fast streamers propagation with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 14.0 +/- 0.4 km, 2.9 +/- 0.82 km, and 1.6 x 108 and 2.8 x 108 ms-1, respectively. Clearly, the microwave and VHF radiation pulses associated with positive NBEs have been emitted by different processes of fast breakdown mechanism. Therefore, it can be suggested that the microwave radiation is emitted by electron avalanches/corona while the VHF ra-diation is emitted by fast propagating streamers.
|
|
