Determination of ice precipitation rates and thunderstorm anvil ice contents from satellite observations of lightning

Abstract

The continuous satisfactory functioning of satellite-borne devices for the detection of global lightning offers the opportunity to explore relationships between lightning frequency f and other thundercloud parameters, notably, in this paper, the precipitating and non-precipitating contents and fluxes of ice. Simple calculations predict that the lightning frequency f is proportional to the product of the downward flux of solid precipitation through the body of the thundercloud and the upward flux of ice crystals into its anvil. This prediction is reinforced by computations performed using the multiple lightning model of Baker et al. [Q. J. R. Meteorol. Soc. 121 (1995) 1525; Atmos. Res. 51 (1999) 221]. Calculations indicate that the separation of charge and associated field development in thunderclouds are not significantly limited by charge saturation of the interacting hydrometeors: and that the mutual interactions of graupel pellets in the charging zones of thunderstorms can significantly enhance electric field development, culminating in lightning. An examination of data from the satellite-borne Lightning Imaging Sensor (LIS) and TRMM Microwave Imager (TMI) suggests that thunderstorms with the highest frequency of total lightning also possess the most pronounced microwave scattering signatures at 37 and 85 GHz. A total of 292 individual thunderstorms were examined, and a log-linear relationship was shown to exist (one for each frequency) between the number of optical lightning pulses produced by each storm and the corresponding microwave brightness temperatures. These relationships are consistent throughout the seasons in a variety of regimes (12 sites encompassing five continents, as well as oceanic measurements), suggesting that global relationships may be found to exist between lightning activity and cloud ice content.