Global lightning variations caused by changes in thunderstorm flash rate and by changes in the number of thunderstorms

Global lightning activity is highly variable on many timescales. This varia bility is attributable to changes in the flash rate per thunderstorm, the n umber of thunderstorms, or a combination. The Tropical Rainfall Measuring M ission provides lightning observations from the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS) in space. Both are used to exa mine the response of these parameters to thermodynamic forcing of deep conv ection on the diurnal and annual timescales. On both timescales, the change s in the number of storms dominate the variations in total lightning activi ty. On the diurnal timescale, there is evidence that the mean flash rate ma y vary with cloud buoyancy, peaking in early afternoon and declining in lat e afternoon, but the contribution of number of thunderstorms is 2-3 times g reater than the mean storm flash rate. On the annual timescale, almost all of the total lightning response is due to changes in the number of storms, with a negligible contribution from flash rate. Evidence is presented that the LIS/OTD "area'' is a meaningful objective identifier for a thunderstorm , despite known limitations in this data product.