During this study, the Vaisala Long Range Lightning Detection Network (LLDN) included National Lightning Detection Network (NLDN) sensors and Canadian Lightning Detection Network (CLDN) sensors to detect cloud-to-ground lightning flashes up to three thousand kilometers from the coasts of North America. In addition, Vaisala's LLDN included several long range sensors located in the North Pacific Ocean. During 2008, Vaisala has continued to expand the LLDN by installing several sensors in the Caribbean and Mexico.

LLDN detection efficiency decreases with increasing distance from the LLDN sensors. Detection efficiency also varies as a function of time of day due to the interaction of lightning signal propagation with the ionosphere. Detection efficiency is higher at night than it is during the day. Approximate daytime and nighttime detection efficiency corrections have now been applied to all 2004-2007 tropical cyclones within range of the LLDN in the Atlantic.

Vaisala has expanded prior studies of inner core lightning rates, so that the dataset now includes all tropical cyclones from 2004 to 2007. Lightning flashes were compiled within 100 km of the centers of tropical depressions, storms and hurricanes as reported by the National Hurricane Center (NHC), and within 90 minutes of the NHC reported location. Results from this expanded analysis show that lightning occurs within the inner core of tropical cyclones during more than sixty percent of all time periods. In addition, the new distributions, for a larger dataset and with both day and night corrections, continue to show the same results as before, namely that inner-core lightning rates vary systematically with storm category. The largest numbers of flashes are located in tropical storms, and fewer inner core flashes occur in hurricanes and tropical depressions. These results will be shown by distributions by storm type for a large number of time periods and tropical cyclones. A few time series from individual storms will also be discussed.