Proceedings of Technical Sessions, 29 (2013) 15-22 15 Institute of Physics – Sri Lanka Luminosity Variation during Propagation of Lightning Channels Luminosity Variation during Propagation of Lightning Channels S.P. Amila Vayanganie, Mahendra Fernando and Upul Sonnadara Department of Physics, University of Colombo, Colombo 3 email: upul@phys.cmb.ac.lk ABSTRACT Luminosity variations of natural cloud-to-ground lightning flashes were studied by analyzing a set of high speed video recordings. The frame rate and resolution of the camera was 5000 fps at 512×512 pixel resolution. The frames were stored as black and white sequence (SEQ) files which were converted to sequence of image files using the software provided by the camera. Algorithms were developed to scan the image files and extract maximum brightness of channels as well as maximum brightness at selected locations along the channels. The variation of current along the channel was analyzed by assuming that the brightness of the channel is directly proportional to the current that flows through it. The study shows that there is a loss of current in lightning channels when current flowing through the channel. The amount of current reduction increases with the propagating distance. Preliminary estimates show that there is approximately 3% reduction in current when propagation from cloud-to-ground. 1. INTRODUCTION Lightning is a one of the impressive and frequently observed natural phenomena. Although there are number of microphysical and numerical models available to model the lightning discharges, the process of lightning discharge is not yet fully understood. In general lightning is an electrical discharge exchanging between cloud-to-cloud or cloud-to-ground. Ice crystals inside a cloud is thought to be the key element in lightning development which is responsible for the separation of positive and negative charges within the cloud. When positive and negative charges accumulate in separate regions, large electrical field can be developed between the charged regions as well as between a charged region and the ground. When this voltage developed 50 to 500 million volts, the air in-between may become significantly ionized and form a plasma column which is the electrically conducting channel we see as lightning [1]. Normally, each cloud to ground lightning flash involves roughly 10 9 to 10 10 J amount of energy [2]. However, all this energy is not delivered to the strike point of the ground. Bulk of the energy is lost as heat, light and sound. The estimated range of energy delivered to the strike point of the ground due to lightning is from 10 6 to 10 7 J, which is only 10 -2 to 10 -4 of the available total energy [2]. Also due to the horizontal electric field gradient, part of energy along the lightning channel dissipated as the corona discharges. Thus, it is very conceivable that there is a loss of current in each cloud to ground lightning flash. In this work we tried to estimate qualitatively, the loss of current in cloud to ground lightning flashes along the channel using optical measurements.