By the end of 2007, the Tropical Rainfall Measuring Mission (TRMM) satellite will have collected ten years of measurements for the global tropics and subtropics (35 S - 35 N). Precipitation Features have been defined as contiguous areas with rain indicated by the TRMM Precipitation Radar (PR) and / or TRMM Microwave Imager (TMI). For these Precipitation Features (nearly two million per year, so nearly twenty million total), the Lightning Imaging Sensor (LIS) measures a flash rate.

For this study, Precipitation Features are grouped into various low flash rate and high flash rate categories. Annual cycles of high flash rate and low flash rate storms will be presented for regions throughout the TRMM domain.

To first order, the patterns follow simple expectations - summer has the most thunderstorms; winter has the fewest thunderstorms; spring has the most of the very high flash rate thunderstorms. Further examination shows some interesting traits in particular regions. For example, Mediterranean thunderstorms are seen mostly in the autumn and winter. Subtropical South America sees many more of the very high flash rate storms in the autumn than other regions do. The oceanic ITCZs generally have more thunderstorms during winter than during summer. It must be noted that LIS only observes a particular storm for around 80-90 seconds, so many of the truly low flash rate storms are misidentified as having zero flash rate.

This is part of a broader study aimed at distinguishing those environments that support extreme thunderstorms (very high lightning flash rates, or radar or radiometric signatures suggestive of large hail) in locations around the world. As a result, emphasis in this study is placed on the highest flash rate storms.