Global electric circuit implications of combined aircraft storm electric current measurements and satellite-based diurnal lightning statistics

摘要

We have combined analyses of high-altitude aircraft observations of electrified clouds with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) that are carried aboard low-Earth-orbiting satellites to reproduce the diurnal variation in the global electric circuit. Using basic assumptions about the mean storm currents as a function of flash rate and location (i.e., land or ocean) and the global electric circuit, our estimate of the current in the global electric circuit matches the Carnegie curve diurnal variation to within 4% for all but two short periods of time, in which the difference was 11% in one time period (0430 UTC) and 6% in the second period (1830 UTC). This excellent agreement with the Carnegie curve was obtained without any tuning or adjustment of the satellite or aircraft data. We assume that (1) the mean values for current and flash rates in the aircraft storm overflight data set (1.7 A and 0.8 flashes min~(-1) for oceanic thunderstorms, 1.0 A and 2.2 flashes min~(-1) for land thunderstorms, 0.41 A for oceanic electrified shower clouds (i.e., electrified but no lightning detected), and 0.13 A for land electrified shower clouds) and (2) the diurnal variations in lightning rates over land and ocean found in the satellite data set are universally applicable. Mean contributions to the global electric circuit from land and ocean thunderstorms are 1.1 kA (land) and 0.7 kA (ocean). Contributions to the global electric circuit from electrified shower clouds are 0.22 kA for ocean storms and 0.04 kA for land storms. The mean total conduction current for the global electric circuit is 2.0 kA. The means that for the number of storms contributing to the global electric circuit, 1100 are land storms with lightning, 530 are ocean storms without lightning, 390 are ocean storms with lightning, and 330 are land storms without lightning. A closer fit to the Carnegie curve is possible if the contributions from electrified shower clouds are increased by a factor of 3 or 4.