Characteristics of upward lightning flashes in Brazil

Abstract

Up to January 2012, no upward flash had ever been registered in Brazil. With the help of some video cameras, we recorded during January, March and April, fifteen upward lightning which started from one or more towers located on Peak Jaraguá in the city of São Paulo. This research project aims to characterize upward lightning hitherto observed and studied in Brazil and aims to answer some questions that the early and recent observations have raised: What is the frequency of such discharges? How do they initiate? What kind of structures is favorable for their initiation? What physical processes rule them? How different they are from the downward lightning flashes extensively observed by the group in recent years? Are they different from upward lightning observed in other countries? How lightning locating systems installed in our country detect and locate them?To answer these and other questions in this document, we will combine observations of high temporal resolution video cameras, electric field measurements and data from lightning detection networks. The data collection will be done through three observation campaigns. Two of them to observe upward lightning from towers in Jaraguá Peak and Paulista Avenue, and from the skyscraper Edifício Itália, a campaign sponsored by the National Science Foundation (NSF) and the University of Arizona (Dept. of Atmospheric Sciences) to observe upward lightning in a wind turbine farm towers in Kansas and from towers in South Dakota, USA.As the current lightning protection standards are based on downward flashes, this research intends to identify risks uniquely associated with upward lightning, which are not currently known and not even included in protection standards. As the ground contact of upward flashes is known this research will also help to improve the lightning locating systems that detect and monitor the incidence of lightning in Brazil.Much of the instrumentation needed for this study is already available in the group, and most of the costs involved for the campaigns are covered by international cooperation. The most relevant acquisition for the accomplishment of this project will be the purchase of a camera that meets the specific needs for this pioneer study in Brazil. The required camera has better temporal and spatial resolution, higher sensitivity and mobility to observe the physical processes of the upward flashes than the current cameras in the group. (AU)