Analysis of cloud-to-ground lightning in Hurricane Andrew

Abstract

In August of 1992, Andrew joined a long list of tropical storms that have caused considerable damage and loss of life as they made landfall near a populated area. However, Andrew was unique in the sense that no previous landfalling tropical storm in the United States has provided such an excellent opportunity to study the cloud-to-ground (CG) lightning associated with this type of storm. While numerous thunderstorm systems, particularly the severe storms of the Great Plains, have been studied for lightning characteristics, the ability to conduct similar studies on hurricanes has been limited due to the small number which have occurred since the relatively new National Lightning Detection Network has been operational. 17,036 CG strikes over a 77 hour period were attributed to either the eyewall region or the primary spiral rainbands of Andrew. The overall distribution by polarity of the lightning was found to be 2.1% positive and 97.9% negative. As the storm was dissipating over land in Mississippi all lightning observed near the pressure center was positive. Throughout the lifetime of the storm, the negative first stroke peak current decreased while the positive first stroke peak current increased. The mean multiplicity of the negative flashes was 2.6, while the positive lightning had a mean value of 1.2. High-multiplicity flashes (negative CG flashes with 10 strokes or greater) tended to occur in four distinct groups and in time intervals of 19 to 23 hours apart in an area corresponding to the right-forward quadrant to right flank of the storm structure. Comparison of radar data to the lightning data shows that the deep convective regions of the outer rainbands were the areas with the most lightning. A lack of significant lightning observed in the eyewall region is consistent with previous research suggesting microphysical processes in this part of the storm are not favorable for charge separation.