107 Australian Meteorological and Oceanographic Journal 61 (2011) 107-112 Occurrence of positive and negative polarity cloud-to-ground lightning fashes: Case study of CGR4 and GPATS data for Brisbane, Australia (Manuscript received October 2010; revised March 2011) Y. Kuleshov 1,2 , P. Hettrick 3 , D. Mackerras 4 , M. Darveniza 4 and E. R. Jayaratne 5 1 National Climate Centre, Australian Bureau of Meteorology, Melbourne, Australia 2 School of Mathematical and Geospatial Sciences, Royal Melbourne Institute of Technology (RMIT) University, Melbourne, Australia 3 Observations and Engineering Branch, Australian Bureau of Meteorology, Melbourne, Australia 4 The University of Queensland, and Lightning and Transient Protection Pty Ltd, Brisbane, Australia 5 Queensland University of Technology, Brisbane, Australia The occurrences of positive and negative polarity cloud-to-ground lightning fashes were detected by ground-based lightning fash counters CGR4 in Bris- bane, Australia. Positive (negative) fashes constituted 2–5 per cent (95–98 per cent) of total cloud-to-ground fashes. These results were compared with data obtained by a GPATS lightning location system over the period 2005–2008. It was found that prior to January 2007 the GPATS lightning location system was reporting an excessive proportion of ground fashes as being positive, with a correspondingly low proportion as negative. Over the same period, the CGR4 lightning fash counter reported positive to negative ground fash ratios consis- tent with those obtained by other researchers both in Australia and elsewhere using a range of instrumentation. The high proportion of positive ground fashes (up to 50 per cent) recorded by the GPATS lightning location system in Australia prior to 2007 may be attributed to one or more possible factors, including (i) changes in the processing of raw GPATS sensor data implemented in January 2007, (ii) upgrades to sensor frmware, and (iii) the installation of more GPATS sensors. Introduction The hazards associated with lightning are common in Australia. In some instances, the effects of lightning-initiated bushfres are so extreme that they are classifed as natural disasters. Knowledge about geographical distribution and seasonal variability of lightning activity for the Australian continent are vital for developing adequate lightning protection measures. In this paper, we present an overview of instrumental methods used for recording lightning activity in Australia, and compare the occurrence of positive and negative polarity cloud-to-ground lighting fashes (ground fashes or GF) obtained from stand-alone ground-based lightning fash counters (LFCs) and a network-based lightning location system (LLS). To describe lightning activity, we use the number of negative GF (NGF), positive GF (PGF), intra- cloud fashes (cloud fashes or CF) and total fashes (TF = NGF + PGF + CF) within a specifed radius at a particular locality. Accurate knowledge about occurrences of PGF and NGF are of high importance for lightning protection. PGF are typically more intense than NGF and consequently potentially more damaging. Corresponding author address: Y. Kuleshov, National Climate Centre, Bu- reau of Meteorology, GPO Box 1289, Melbourne Vic. 3001, Australia Email: y.kuleshov@bom.gov.au