85th AMS Annual Meeting

Tuesday, 11 January 2005: 1:30 PM
Hugh J. Christian Jr., NASA/MSFC, Huntsville, AL; and W. Petersen
Our knowledge of the global distribution of lightning has improved dramatically since the advent of space-based lightning observations. Of major importance was the 1995 launch of the Optical Transient Detector (OTD), followed in 1997 by the launch of the Lightning Imaging Sensor (LIS). Together, these instruments have generated a continuous nine-year record of global lightning activity. These lightning observations have provided a new global perspective on total lightning activity. For the first time, total lightning activity (cloud-to-ground and intra-cloud) has been observed over large regions with high detection efficiency and accurate geographic location. This has produced new insights into lightning distributions, times of occurrence and variability. It has produced a revised global flash rate estimate (45 flashes per second) and has lead to a new realization of the significance of total lightning activity in severe weather.

Accurate flash rate estimates are now available over large areas of the earth (+/- 72o latitude). Ocean-land contrasts as a function of season are clearly reveled, as are orographic effects and seasonal and interannual variability. The space-based observations indicate that air mass thunderstorms, not large storm system dominate global activity.

The ability of LIS and OTD to detect total lightning has lead to improved insight into the correlation between lightning and storm development. The relationship between updraft development and lightning activity is now well established and presents an opportunity for providing a new mechanism for remotely monitoring storm development. In this concept, lightning would serve as a surrogate for updraft velocity. It is anticipated that this capability could lead to significantly improved severe weather warning times and reduced false warning rates.

The dominant mechanism that leads to electrical energy generation within a thunderstorm is becoming better understood. It is now well accepted that charge separation occurs during the physical collision of ice crystals with growing graupel pellets. These charged hydrometeors then tend to gravitationally separate in the updraft region of the storm with positively charged ice crystals rising higher in the cloud as the negatively charged graupel settle to lower altitudes. This physical separation produces the well-known dominant charge regions, electrically stresses the cloud and culminates in lightning. The fact that lightning dissipates most of the electrical energy that is generated by the storm enables one to infer the quantity of electrical energy that is being generated from measurements of lightning rates alone. Further, since the electrical generation is controlled by the flux of ice being process in the updraft, we hypothesis that there is a quantitative relationship between ice production and lightning flash rate. Specifically, we propose that the product of downward precipitation flux and upward non-precipitating ice flux is proportional to the total lightning frequency. The tropical Rainfall Measurement Mission (TRMM) Precipitation radar (PR) and LIS data are used to test this ice precipitation - lightning flash rate hypothesis on a global basis.

This talk will summarize our space-based lightning measurements, will discuss how lightning observations can be used to infer ice-based precipitation rates and monitor severe weather, and present a concept for continuous geostationary-based lightning observations.

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