# Upward Lightning Triggering Study (UPLIGHTS): Project Summary and Initial Findings

### Tom A. Warner, Alana Ballweber, Ryan Lueck, and John H. Helsdon, Jr.

Julia Tilles and Ron Thomas Department of Physics New Mexico Institute of Mining and Technology Socorro, New Mexico, USA

Department of Physics South Dakota School of Mines and Technology Rapid City, South Dakota, USA tom.warner@ztresearch.com

Richard E. Orville Department of Atmospheric Sciences Texas A&M University College Station, Texas, USA

Carina Schumann and Marcelo M. F. Saba National Institute for Space Research INPE San Jose dos Campos, Brazil

triggered upward lightning (LTUL) tends to occur more often during summer months with active storms that contain higher cloud bases and warmer temperatures. [Wang and Takagi, 2012; Zhou et al., 2012]. 3) A large majority of upward lightning involves the development of an upward propagating positive leader which is classified as upward negative lightning in the literature since negative charge is effectively lowered to ground [Miki et al., 2010; Zhou et al., 2012; Warner et al., 2012a; Smorgonskiy et al., 2015; Saba et al., 2016]. 4) The dominate storm type for LTUL is a Mesoscale Convective System (MCS) with an associated stratiform precipitation area over the tall objects that experience upward lightning [Warner et al., 2012b; Saba et al., 2012; Jiang et al., 2014; Yuan et al., 2017]. 5) A majority of LTUL is triggered by preceding horizontally extensive positive cloud-to-ground flashes [Zhou et al., 2012, Warner et al., 2012a; Schumann et al., 2014a, 2014b, 2015; Saba et al., 2012, 2016]. 6) Horizontally extensive flashes that trigger transient luminous events (TLEs) in the upper atmosphere can also trigger upward lightning during the same flash [Lyons et al., 2011; Lyons et al., 2012; Warner et al., 2012c; Lyons et al., 2014; Rison et al., 2014]. 7) Horizontal propagating negative leaders and/or positive cloud-to-ground return strokes that pass near or over tall objects are the primary triggering flash components responsible for initiating upward positive leaders (UPLs) [Mazur and Ruhnke, 2011; Warner, 2012; 2012a; 2012b; Saba et al., 2012, 2016; Schumann et al., 2014a, 2014b, 2014c]. 8) The development of an UPL can lead to the initiation of an upward negative leader (UNL) from a nearby object [Lu et al., 2009]. 9) Lightning-triggered UPLs frequently transition to

Abstract— The Upward Lightning Triggering Study (UPLIGHTS) took place in Rapid City, South Dakota, USA from 2012 through 2014. 38 upward flashes were observed during the summer thunderstorm months (Apr – Sep) with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast antenna systems, and for the 2014 season, a Lightning Mapping Array. All upward flashes were triggered by preceding lightning activity with the +CG flash the dominate triggering type. Intracloud and post +CG return stroke negative leaders passing near the towers were the primary triggering flash component, 2.4 times more frequent than the +CG return stroke triggering component. The one observed upward negative leader was triggered by a preceding -CG return stroke.

Keywords—upward lightning, triggering, initiation

## I. INTRODUCTION

Understanding of upward lightning has evolved significantly over the last ten years due to research efforts around the world. Some of the research locations include Japan, Austria, Germany, Switzerland, Canada, USA, Brazil, China and South Africa. Notable findings include the following: 1) upward lightning can initiate without preceding nearby lightning activity or can be triggered by preceding flashes [Wang et al., 2008; Wang and Takagi, 2012]. 2) Self-initiated upward lightning (SIUL) tends to occur more often in winter months with lower cloud bases, colder temperatures and with stronger winds, whereas lightning-