Tropical cyclone lightning distribution and its relationship to convection and intensity change

The long distance National Lightning Detection Network (NLDN) was used to monitor the distribution of lightning strokes in various 1998 and 1999 western North Atlantic tropical cyclones. These ground-based lightning observations together with the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) and the Tropical Rain Mapping Mission (TRMM) Microwave Instrument (TMI)-derived convective rain rates were used to monitor the propagation of electrically charged convective rain bands and to qualitatively estimate intensification.

An example of the lightning analyses was performed on hurricane George between 25-28 September, 1998 when the system left Key West and moved towards the Louisiana coast. During this period of time, George’s maximum winds increased from 38 to 45 ms-1 on 25 September and then remained steady state until it made landfall. Time-radius displays of the lightning strokes indicated that the greatest number of lightning strokes occurred within the outer core region (> 165 km) with little or no lightning strokes at radii less than 165 km. The trend in these lightning strokes decreased as George move into the Gulf of Mexico and showed no inward propagation. The lack of inward propagating lightning strokes with time indicated that there was no evidence that an eye wall replacement was occurring that could alter George’s intensity. Since George was steady state at this time, this result is not surprising.

Time-azimuth displays of lightning strokes in an annulus whose outer and inner radii were respectively, 222 and 333 km from George’s center were also constructed. A result from this analysis indicated that the maximum number of strokes occurred in the forward and rear right quadrant when George was over the Gulf of Mexico. This result is consistent with the aircraft and satellite observations of maximum rainfall.