Description

Typically, more than 2,000 thunderstorms are active throughout the world at a given moment, producing on the order of 100 flashes per second. NASA has two different sensors on satellites that measuring flash frequency, the Optical Transient Detector, OTD, and the Lightning Imaging Sensor, LIS. Data from the OTD from 1995 - 2000 and the LIS from 1998 - 2005 has been combined and averaged to create an average annual lightning flash rate map. 11 year of data is included to remove any anomalies that might be present in just one year. The color variations in the map display the average annual number of lightning flashes per square kilometer.

It is clear from this map that the distribution of lightning flashes around the world is uneven. About 70% of all lightning activity occurs in the tropics. The location that receives the greatest number of flashes per year is near the small village of Kifuka in the Democratic Republic of the Congo. The average annual flash rate for this location is about 158 lightning bolts. In the United States, Florida has the highest annual flash rate with an average of 59 lightning bolts per year. Thunderstorms occur most often during the summer, which means that there are only thunderstorms for part of the year. In Central Africa, the climate varies only slightly, allowing for thunderstorms to occur year round. The three key "ingredients" that are needed for a thunderstorm to develop are moisture, instability, and uplift. The moisture is needed for the clouds to develop. Instability in the atmosphere is caused by air that rises because it is warmer than its surroundings. Uplift is what forces the air to initially start rising. Rising air cools and condenses, forming clouds when there is enough moisture. Some examples of uplift mechanisms are mountains that block the path of the airflow, sunlight which warms the air causing it to rise, and front boundaries between weather systems. The land-sea temperature contrast around Florida makes it susceptible to thunderstorms.

Notable Features