2012 International Conference on Lightning Protection (ICLP), Vienna, Austria Thunderstorm warning alarms methodology using electric field mills and lightning location networks in mountainous regions López, J., Pérez E., Herrera, J., Aranguren, D. National University of Colombia Bogotá, Colombia jalopezt@unal.edu.co Porras, L. Interconexión Eléctrica S.A E.S.P Medellín, Colombia lfporras@isa.com.co Abstract— This paper presents a methodology for thunderstorm warning alarming using electric field measurements and lightning location data under mountainous conditions in Medellín – Colombia. The methodology is used to set warning criteria for preventing human and sensitive systems risks and damages. Keywords- Electric field mill, lightning location system, two area method, forecast verification, non flat terrain. I. INTRODUCTION Colombia, due to its inter-tropical location, has a high cloud to ground lightning activity [1]. Several authors have found a ground flash density higher than 40 flash/km 2 into the territory. The high lightning activity represents a countless Compatibility Electromagnetic problems, as well as lot of human injuries and fatalities. For example, the last year more than 50 injuries and fatalities were reported by Colombian news networks. Daily, the aviation systems, oil transporting and storage systems, electrical systems, outdoors sports activities and others have to hol on this inclement natural phenomenon. Despite a lightning strike is impossible to be avoided, several strategies could be designed to deal with it and to generate warning alarms to prevent fatalities and human injuries, failures, material damages, economic losses and others problems related with the lightning activity. Nowadays, lightning data are becoming more available and cheaper; however this information requires processing efforts to be useful.Tthe lightning warning systems are between the main applications of this data..Several studies worldwide have been developed about this subject; some authors use the cloud to ground information [2]-[4], others the total lightning activity from lightning location networks [5], and recently electric field measurement have been included into warning methodologies [6], weather information such as radar reflectivity and satellite images [7]-[8] have been used jointly implemented or separated. This work presents a preliminary methodology for triggering thunderstorm warning alarms in mountainous regions based on the measurement of the environmental electric field variations obtained from an electric field mill, and cloud to ground lightning information obtained from the Colombian Lightning Location Network (SID). The spatial and temporal characterization of thunderstorm’s activity over Medellín, with previous measurement systems, summarized in [9]-[10], allowed designing several criteria for triggering lightning alarms. The obtained results from this previous methodology showed that the traditional method, used in generating this kind of alarms known as the “two area method” [2]-[11], is not completely optimal when it is applied to regions with high altitude variations, as it is presented in the Colombian territory. Nevertheless, the criteria developed in this study improve the the efficiency and effectiveness indicators in order to obtain a more optimal TWS over non flat terrain.. II. THUNDERSTORM WARNING AND PREDICTION METHODOLOGY A. Owerview about international standars over TWS Nowadays, few international standards have been developed around the thunderstorm warning systems. For example, the European Committee for Electrotechnical Standardization – CENELEC published the standard EN50536 [12] – Protection Against Lightning - Thunderstorm Warning Systems. The goal of this standard is to provide information on the characteristics of thunderstorm warning systems and information for the evaluation of the usefulness of lightning real time data and/or storm electrification data in order to implement lightning hazard preventive measures.. Similarly, the Federal Aviation Administration – FAA, in the ACRP report 8 [13] – Lightning Warning System for Use by Airports, summarized the impact of the total cessation of activities in airports, the safety and operational ramp, when outdoors activities should be halted, the cost of suspending ramp operation, the aircraft delay, labor delay, passenger time delay, and in the worst case the remuneration cost by human fatalities. B. Prediction methodology – “ Two area method” The Two area method was introduced by Muypy et al [3]- [4]. This method defines two concentric areas at a geographical