Estimates of lightning ground flash density in Australia and its relationship to thunder-days

A method of deriving lightning ground flash density from CIGRE lightning flash counter registrations based on the detection efficiency of the instrument, independent of the latitudinal variation of cloud flash-to-ground flash ratio is presented. Using this method, the annual mean ground flash densities, Ng, over a period of up to 22 years were recalculated from the counter registrations for 17 selected Australian sites. The results were compared with the corresponding thunder-day data, Td, to obtain an empirical formula of the form Ng = a Td b. The best estimates of the empirical constants a and b derived using the proposed method were found to be 0.012 and 1.4 respectively. The derived Ng values were compared with the values obtained from three other established formulae developed by earlier workers in different countries. The Ng values were also compared with values derived using present methods of estimating lightning ground flash density which utilises the ratio of cloud flashes to ground flashes. Taking into account the improved method of calculation and the relatively long period of observation, we believe that the new empirical formula presented in this paper gives the best estimates of lightning ground flash density in Australia.