Relationships between lightning activity and various thundercloud parameters: satellite and modelling studies

The lightning frequency model developed by Baker et al. [Baker, M.B., Chris tian, H.J., Latham, J., 1995. A computational study of the relationships li nking lightning frequency and other thundercloud parameters, Q. J. R. Meteo rol. Sec., 121, 1525-1548] has been refined and extended, in an effort to p rovide a more realistic framework from which to examine computationally the relationships that might exist between lightning frequency f (which is now being routinely measured from a satellite, using the NASA/MSFC Optical Tra nsient Detector (OTD)) and a variety of cloud physical parameters. Specific ally, superior or more comprehensive representations were utilised of: (1) glaciation via the Hallett-Mossop (H-M) process; (2) the updraught structur e of the model cloud; (3) the liquid-water-content structure of the model c loud; (4) the role of the reversal temperature T-rev in influencing lightni ng characteristics; (5) the critical breakdown field for lightning initiati on; and (6) the electrical characteristics of the ice crystal anvil of the model cloud. Although our extended studies yielded some new insights into t he problem, the basic pattern of relationships between f and the other para meters was very close to that reported by Baker et al. (1995). The more ela borate treatment of T-rev restricted somewhat the range of conditions under which reverse-polarity lightning could be produced if the cloud glaciated via H-M, but confirmed the earlier conclusion that such lightning would not occur if the glaciation was of the Fletcher type. The computations yielded preliminary support for the hypothesis that satellite measurements of f mi ght be used to determine values of the ice-content of cumulonimbus anvils: a parameter of climatological importance. The successful launch and continu ing satisfactory functioning of the OTD [Christian, H.J., Goodman, S., 1992 . Global observations of lightning from space, Proc. 9th Int. Conf. on Atmo spheric Electricity, St. Petersburg, pp. 316-321; Christian, H.J., Blakesee , R.J., Goodman, S.J., 1992. Lightning imaging sensor (LIS) for the earth o bserving system. NASA Tech. Memorandum, 4350] make it possible-with a high degree of precision-to measure lightning location, occurrence time and freq uency f over extensive areas of the Earth's surface. Measured global distri butions of lightning and associated lightning stroke radiance demonstrate t hat: lightning activity is particularly pronounced over the tropics, much g reater over land than over the oceans, and exhibits great seasonal variabil ity; lightning radiance tends to be greater over the oceans, less when ligh tning activity is high, and greater in the Northern Hemisphere winter than summer. (C) 1999 Elsevier Science B.V. All rights reserved.