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Parameters for Engineering Applications. The Term of Reference (TOR) for this Working Group is found in Appendix 1. The document can be viewed as an update on previous CIGRE documents on the subject published in 1975 and 1980: Berger, K., Anderson, R.B., and Kroninger, H. 1975. Parameters of lightning flashes. Electra, No. 41, pp. 23-37. Anderson, R.B., and Eriksson, A.J. 1980. Lightning parameters for engineering application. Electra, No. 69, pp. 65-102. Anderson, R.B., and Eriksson, A.J. 1980. A summary of lightning parameters for engineering application, CIGRE 1980 Session, paper 33-06, 12 p. It is also related to the following CIGRE reports: CIGRE WG 33.01, Report 63. Guide to Procedures for Estimating the Lightning Performance of Transmission Lines, October 1991, 61 p. CIGRE TF 33.01.02, Report 94, Lightning characteristics relevant for electrical engineering: Assesment of sensing, recording and mapping requirements in the light of present technological advancements, 1995, 37 p. CIGRE TF 33.01.03, Report 118, Lightning exposure of structures and interception efficiency of air terminals, October 1997, 86 p. CIGRE TF 33.01.02, Report 172, Characterization of lightning for applications in electric power systems, December 2000, 35 p. CIGRE TF C4.404, Report 376, Cloud-to-ground lightning parameters derived from lightning location systems: The effects of system performance, April 2009, 117 p. Traditional lightning parameters needed in engineering applications include lightning peak current, maximum current derivative, average current rate of rise, current risetime, current duration, charge transfer, and specific energy (action integral), all derivable from direct current measurements. Distributions of these parameters presently adopted by CIGRE are based on direct measurements by K. Berger and co-workers in Switzerland, supplemented by less accurate magnetic link measurements to increase the sample size. There also exist more recent direct current measurements obtained using instrumented towers in Austria, Brazil, Canada, Germany, Japan, Russia, and Switzerland, as well as those obtained in several countries using rocket-triggered lightning. Further, modern lightning locating systems report peak currents estimated from measured magnetic or electric field peaks. One of the objectives of present document is to evaluate these new experimental data, along with the old data, to determine their applicability to various engineering calculations. Evaluation includes both instrumental and methodological aspects. Possible geographical, seasonal and other variations in lightning parameters are examined. Additional lightning parameters such as the number of strokes per flash (multiplicity), interstroke interval, number of channels per flash, relative intensity of strokes within a flash, return-stroke speed, and equivalent impedance of the lightning channel, as well as characteristics of continuing currents and M-components are included. More detailed information than before is given about less frequent, but potentially more destructive, positive and bipolar lightning flashes.