GLOBAL LIGHTNING - TOTAL, CLOUD AND GROUND FLASH ESTIMATES

A worldwide survey of the ratio of cloud flashes to ground flashes in thunderstorms using CGR3 (Cloud-Ground Ratio #3) instruments at sites covering a latitude range from 59.9 degrees N to 27.3 degrees S betwee n 1986 and 1991 inclusive has provided information on the latitudinal variation of total flash density and the ratio of cloud flashes to tot al flashes. Two surveys of global lightning occurrence using satellite s, the Defense Meteorological Satellite Program (DMSP) survey using op tical sensors to detect lightning at near local midnight and the Ionos pheric Sounding Satellite-b (ISS-b) survey using radio-frequency light ning detection equipment, were used in conjunction with the CGR3 obser vations to obtain the latitudinal variation of total flash density ove r each major land mass and each major ocean. These three surveys and o ther sources provided data on the annual and diurnal variation in ligh tning occurrence at various latitudes. We have combined the above info rmation in a computational model of global lightning occurrence and ha ve separated total flashes into cloud flash and ground flash component s. Using this model, we estimate the global annual number of total fla shes to be 2.05 x 10(9) yr(-1), corresponding to a mean rate of 65 s(- 1). This estimate is probably low because of inadequate detection of w eak cloud flashes. Depending on the assumption made concerning the lat itudinal variation of the ratio of cloud flashes to total flashes, the mean rates of occurrence are between about 51 s(-1) and 55 s(-1) fur cloud flashes and between about 10 s(-1) and 14 s(-1) for ground flash es. The uncertainty in these estimates is a factor of 2 in either dire ction. The calculated global diurnal variation has a peak rate of occu rrence of about 1.6 rimes the mean rate at about 1400 universal time ( UT) in the northern hemisphere spring and has its lowest rate of about 0.5 times the mean rate at about 0300 UT in the northern hemisphere s ummer. About 54% of all lightning occurs in the northern hemisphere. T he mean global land total flash density is about 8.3 km(-2) yr(-1). Th is is about 3.4 times the mean global total flash density over oceans.