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Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
2007 (Engelska)Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, nr D12, s. D12205-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Electric field measurements above ground have shown that the space charge layer created by corona at ground level shields the background electric field produced by the thundercloud. Therefore it is expected that this space charge layer can also influence the conditions required to initiate upward lightning from tall objects. For this reason, a numerical model that describes the evolution of the main electrical parameters below a thunderstorm is used to compute the space charge layer development. The time variation of the electric field measured at 600 m above ground during the 1989 rocket triggered lightning experiment at the Kennedy Space Center (Florida) is used to drive the model. The obtained space charge density profiles are used to compute the conditions required to initiate stable upward lightning positive leaders from tall towers. Corona at the tip of the tower is neglected. It is found that the space charge layer significantly affects the critical thundercloud electric fields required to initiate upward lightning leaders from tall objects. The neutral aerosol particle concentration is observed to have a significant influence on the space charge density profiles and the critical thundercloud electric fields, whereas the corona current density does not considerably affect the results for the cases considered in the analysis. It is found that a lower thundercloud electric field is required to trigger a lightning flash from a tall tower or other tall slender grounded structure in the case of sites with a high neutral aerosol particle concentration, like polluted areas or coastal regions.

Ort, förlag, år, upplaga, sidor
2007. Vol. 112, nr D12, s. D12205-
Nyckelord [en]
North America, United States, Florida, density currents, Current density, concentration, particles, aerosols, Charge density, experimental studies, time variations, Thunderstorm, digital simulation, numerical models, Thundercloud, shields, electrical field, lightning, Space charge
Nationell ämneskategori
Teknik och teknologier Geovetenskap och miljövetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-97284DOI: 10.1029/2006JD008308ISI: 000247534000003OAI: oai:DiVA.org:uu-97284DiVA, id: diva2:172150
Tillgänglig från: 2008-05-14 Skapad: 2008-05-14 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
Ingår i avhandling
1. On the Attachment of Lightning Flashes to Grounded Structures
Öppna denna publikation i ny flik eller fönster >>On the Attachment of Lightning Flashes to Grounded Structures
2008 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis deals with the physical modeling of the initiation and propagation of upward positive leader discharges from grounded structures during lightning strikes. It includes the analysis of upward leaders initiated under the influence of the electric field produced by a dominant negative cloud charge and due to the combined action of a negative thundercloud and a descending downward stepped negative leader. Thus, a self-consistent model based on the physics of leader discharges is developed for the evaluation of the attachment of lightning flashes to any kind of grounded structure. The predictions of the model have been found to be in good agreement with the results of laboratory long air gap experiments and with classical and altitude rocket triggered lightning experiments.

Due to the high application level and predictive power of the developed model, several contributions to the physical understanding of factors influencing the initiation and propagation of upward positive leaders during thunderstorms have been made. For instance, it has been found that the initiation of upward connecting leaders is strongly affected by the average velocity of the downward stepped leader. Similarly, it is shown that the switching voltage impulses used in the laboratory do not “fairly approximate” the electric fields produced by a descending downward leader, as claimed by supporters of Early Streamer Emission (ESE) devices. Furthermore, it is found that the space charge layer created by corona at ground level significantly increases the thundercloud electric fields required to initiate upward lightning leaders from tall objects. On the other hand, it is also shown that the upward leader velocity depends on the downward leader average velocity, the prospective return stroke current, the lateral distance of the downward leader channel and the ambient electric field.

By implementing the model to the analysis of complex structures, it has been observed that the corners of actual buildings struck by lightning coincide rather well with the places characterized by low leader inception electric fields. Besides, it has been found that the leader inception zones of the corners of complex structures do not define symmetrical and circular regions as it is generally assumed.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2008. s. 85
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 438
Nyckelord
Engineering physics, Lightning, Lightning attachment, Positive leader discharges, Lightning protection, Thunderstorms, Numerical modeling, Teknisk fysik
Identifikatorer
urn:nbn:se:uu:diva-8871 (URN)978-91-554-7216-0 (ISBN)
Disputation
2008-06-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2008-05-14 Skapad: 2008-05-14 Senast uppdaterad: 2010-04-23Bibliografiskt granskad

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