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Negative cloud-to-ground lightning flashes in Malaysia
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
Vise andre og tillknytning
2014 (engelsk)Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 108, s. 61-67Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The characteristics of the negative cloud-to-ground lightning flashes in Malaysia are studied by analyzing the electric fields generated by the whole flash in nanosecond resolution. A total of 405 strokes obtained from 100 successive negative cloud-to-ground lightning flashes were analyzed, which were recorded from seven convective thunderstorms during the southwest monsoon period, i.e. from April to June 2009. It was found that the total number of interstroke intervals has an arithmetic mean value of 86 ms, a geometric mean value of 67 ms and does not depend on the return stroke order. Of the 100 negative ground flashes, 38 flashes (38%) have at least one subsequent return-stroke (SRS) whose electric field peak was greater than that of the first return-stroke (RS). Furthermore, 58 (19%) out of 305 SRS have electric field peak larger than those of the first RS. The arithmetic and geometric mean ratio between the peak electric field of the SRS and the peak electric field of the first RS are 0.7 and 0.6, respectively. The percentage of single-stroke flashes was 16% while the mean number of strokes per flash and maximum number of stroke per flash were 4 and 14, respectively.

sted, utgiver, år, opplag, sider
2014. Vol. 108, s. 61-67
Emneord [en]
Negative cloud-to-ground lightning flashes, Number of strokes per flash and interstroke interval
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot elektricitetslära
Identifikatorer
URN: urn:nbn:se:uu:diva-221965DOI: 10.1016/j.jastp.2013.12.001ISI: 000331684900007OAI: oai:DiVA.org:uu-221965DiVA, id: diva2:711400
Tilgjengelig fra: 2014-04-10 Laget: 2014-04-07 Sist oppdatert: 2017-12-05bibliografisk kontrollert
Inngår i avhandling
1. Characterizations of ground flashes from tropic to northern region
Åpne denne publikasjonen i ny fane eller vindu >>Characterizations of ground flashes from tropic to northern region
2014 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig) [Kunstnerisk arbeiden]
Abstract [en]

This thesis portrays new information concerning the cloud-to-ground (CG) lightning flashes or ground flashes produced by thunderclouds. It emphasizes the importance of characterizing lightning studies as the relationship between lightning mechanisms, and of incorporating the influence of geographical location, latitude and storm type. Sweden, Malaysia and USA were chosen as the main locations for field experiments in 2009 to 2011 to gather a significant number of negative and positive CG flashes. This work provided data on a total of 1792 CG lightning flashes (1685 negative and 107 positive ones) from a total of 53 thunderstorms by monitoring both the slow and the fast electric field and the narrowband radiation field at 3 and 30 MHz signals simultaneously. This thesis is comprised of: (i) the relationship of the Low Positive Charge Region (LPCR) and Preliminary Breakdown Pulse (PBP) trains to the occurrence of negative CG, (ii) slow field changes generated by preliminary breakdown processes in positive and negative ground flashes, and (iii) the occurrence of positive and negative ground flashes. It was revealed that the PBP train appeared have a higher strength in the in Sweden. The strength of the PBP train was caused by the LPCR; in contrast,  weak PBP trains were characteristic in tropical countries constituting insignificant LPCR and needing little energy to break the “blocking” agent to allow the flash to propagate downward to the ground. The second contribution concerns the characteristics of the PBP train mentioned; this includes novel information for Malaysia. Further, it is stated that there are some different characteristics in the PBP trains in Johor, Malaysia and Florida, USA. The studies of slow field changes generated by preliminary breakdown processes clarifies unclear features concerning the starting position of slow field changes generated by preliminary breakdown processes in positive and negative ground flashes. It was found that the slow field changes did not occur before the initial process of the commencement of preliminary breakdown. Single-station electric field measurements incorporating narrowband radiation field measurement and high resolution transient recording (12 bits) with an accuracy of several nanoseconds, allows one to distinguish between the intracloud activities and the preceding processes of ground flashes. The results for the interstroke intervals, amplitude distribution of subsequent return-stroke (SRS) and the number of strokes per flash in the tropics, subtropics and northern regions were similar. Finally, a significant number of positive return-stroke (RS) electric fields provided statistically significant information on the characteristics of these strokes.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2014. s. 78
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1145
Emneord
Positive/negative cloud-to-ground lightning flashes, Initiation position, slow field changes, close ground flashes, preliminary breakdown process
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot atmosfäriska urladdningar
Identifikatorer
urn:nbn:se:uu:diva-222838 (URN)978-91-554-8946-5 (ISBN)
Disputas
2014-06-03, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:00 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Research Council, 621-2006-4299
Tilgjengelig fra: 2014-05-12 Laget: 2014-04-15 Sist oppdatert: 2018-05-28

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