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

w The lightning frequency model developed by Baker et al. Baker, M.B., Christian, H.J., Latham, J., 1995. A computational study of the relationships linking lightning frequency and other x thundercloud parameters, Q. J. R. Meteorol. Soc., 121, 1525–1548 has been refined and extended, in an effort to provide a more realistic framework from which to examine computationŽ ally the relationships that might exist between lightning frequency f which is now being routinely Ž .. measured from a satellite, using the NASArMSFC Optical Transient Detector OTD and a variety of cloud physical parameters. Specifically, superior or more comprehensive representations Ž . Ž . Ž . were utilised of: 1 glaciation via the Hallett–Mossop H–M process; 2 the updraught structure Ž . Ž . of the model cloud; 3 the liquid-water-content structure of the model cloud; 4 the role of the Ž . reversal temperature T in influencing lightning characteristics; 5 the critical breakdown field rev Ž . for lightning initiation; and 6 the electrical characteristics of the ice crystal anvil of the model cloud. Although our extended studies yielded some new insights into the problem, the basic pattern of relationships between f and the other parameters was very close to that reported by Ž . Baker et al. 1995 . The more elaborate treatment of T restricted somewhat the range of rev 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 might be used to determine values of the ice-content of cumulonimbus ) Corresponding author. MMM Division, NCAR, Department of Physics, P.O. Box 3000, Boulder, CO 80307-3000, USA. Tel.: q1-303-497-8892; e-mail: [email protected] 0169-8095r99r$ see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-8095 99 00009-5 ( ) M.B. Baker et al.rAtmospheric Research 51 1999 221–236 222 anvils: a parameter of climatological importance. The successful launch and continuing satisfacw tory functioning of the OTD Christian, H.J., Goodman, S., 1992. Global observations of lightning from space, Proc. 9th Int. Conf. on Atmospheric Electricity, St. Petersburg, pp. 316–321; Ž . Christian, H.J., Blakesee, R.J., Goodman, S.J., 1992. Lightning imaging sensor LIS for the earth x observing system. NASA Tech. Memorandum, 4350 make it possible—with a high degree of precision—to measure lightning location, occurrence time and frequency f over extensive areas of the Earth’s surface. Measured global distributions of lightning and associated lightning stroke radiance demonstrate that: lightning activity is particularly pronounced over the tropics, much greater over land than over the oceans, and exhibits great seasonal variability; lightning radiance tends to be greater over the oceans, less when lightning activity is high, and greater in the Northern Hemisphere winter than summer. q 1999 Elsevier Science B.V. All rights reserved.