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The first electric field pulse of cloud and cloud-to-ground lightning discharges
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. (Åskforskning)
(Åskforskning)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. (Åskforskning)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. (Åskforskning)
Vise andre og tillknytning
2010 (engelsk)Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, nr 2-3, s. 143-150Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as [`]small', [`]medium' and [`]large', depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.

sted, utgiver, år, opplag, sider
2010. Vol. 72, nr 2-3, s. 143-150
Emneord [en]
Cloud discharges, Electromagnetic field, Lightning, Electric field pulses
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot atmosfäriska urladdningar
Identifikatorer
URN: urn:nbn:se:uu:diva-140337DOI: 10.1016/j.jastp.2009.11.001OAI: oai:DiVA.org:uu-140337DiVA, id: diva2:383446
Tilgjengelig fra: 2011-01-05 Laget: 2011-01-05 Sist oppdatert: 2017-12-11
Inngår i avhandling
1. Broadband and HF Radiation from Cloud Flashes and Narrow Bipolar Pulses
Åpne denne publikasjonen i ny fane eller vindu >>Broadband and HF Radiation from Cloud Flashes and Narrow Bipolar Pulses
2011 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Remote measurement of electric field generated by lightning has played a major role in understanding the lightning phenomenon. Even though other measurements such as photographic and channel base current have contributed to this research field, due to practical reasons remote measurements of electric field is considered as the most useful tool in lightning research.

This thesis discusses the remotely measured radiation field component of electric field generated by cloud flashes (ICs) and narrow bipolar pulses (NBPs). The associated HF radiation of these events at 3 MHz and 30 MHz are also discussed. To understand the initiation process of these discharges, a comparative study of the initial pulse of cloud flashes against the initial pulse of cloud to ground flashes was conducted. The result suggests that both discharges might have been initiated by similar physical processes inside the thunderclouds. Comparing the features of initial pulse of cloud and ground flashes with that of pulses that appeared in the later stages of cloud flashes suggests that the initiation process involved in both flashes are not very much different from the initiation of cloud flashes at the later stage. The average spectral amplitudes of electric field of full duration cloud flashes (180 ms) showed -1 frequency dependence within the interval of 10 kHz to approximately 10 MHz. This is in contrast to the standard -2 decrement (or even steeper ) at high frequency region for other lightning processes such as return strokes. It was suggested that small pulses which repeatedly appeared at the later stage of cloud flashes might have contributed to enhance the spectral amplitude at higher frequencies.

Electric fields generated by Narrow Bipolar Pulses (NBPs), which are considered as one of the strongest sources of HF radiation, were measured in the tropics of Malaysia and Sri Lanka.  Their features were also studied and show a good agreement with previously published observations of NBPs from other geographical regions. Thorough analyses and observations of these pulses found previously unreported sharp, fine peaks embedded in the rising and decaying edge of the electric field change of NBPs. Therefore it was suggested that these fine peaks are mostly responsible for the intense HF radiation at 30 MHz.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2011. s. 64
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 822
Emneord
Lightning, Cloud Flashes, Narrow Bipolar Pulses, HF radiation
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot atmosfäriska urladdningar
Identifikatorer
urn:nbn:se:uu:diva-150956 (URN)978-91-554-8067-7 (ISBN)
Disputas
2011-05-25, Å2001, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 14:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2011-05-03 Laget: 2011-04-08 Sist oppdatert: 2011-07-01bibliografisk kontrollert
2. 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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