Schumann, C.Saba, MWarner, T.Ferro, M.Helsdon Jr, J.H.Thomas, R.Orville, R.E.2020-01-222020-01-222019-12Schumann, C. et al. 2019. On the Triggering Mechanisms of Upward Lightning. Scientific Reports 9 (1), Article number 9576. DOI: 10.1038/s41598-019-46122-x2045-2322https://hdl.handle.net/10539/28750The authors would like to acknowledge and thank Lie Bie (Benny), Amanda Paiva, Guilherme Aminger, Kleber Naccarato, Hugh Hunt, Alana Ballweber, Chip Redmond, John Hamilton and Ryan Lueck, for their assistance in obtaining some of these observations. The authors would like to thank Claude Leon Foundation and University of the Witwatersrand. The authors would also like to thank Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for supporting the research through the projects 2012/15375-7 and 2013/05784-0. This research was made possible through National Science Foundation (NSF) grant AGS-1048103. Additional funding came from NSF grant ATM – 0813672, which provided funding for concurrent high-speed optical spectra observations during UPLIGHTS. Data for this study is available on request. Please contact the corresponding author for details.Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the continuing current that follows a positive return stroke.en© The Author(s) 2019. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Cre-ative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not per-mitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.Upward lightningLightning protectionCloud chargeFlash activityArticle