Principal Investigator: Christopher E. Samsury
Collaborating scientist(s):
Robert A. Black
Michael L. Black
Richard E. Orville (Texas A&M)
Objective: To identify the location and characteristics of cloud-to-ground (CG) lightning with respect to a hurricane's center, and to explain why certain regions of the hurricane are more electrically-active than others.
Rationale: Until recently, very little research had been done specifically on the topic of CG lightning in hurricanes. With the aid of the National Lightning Detection Network (NLDN) and/or other detection systems, we now have a unique opportunity to examine whether CG lightning occurs in tropical storms and hurricanes and what regions are most favorable for electrification. As mentioned in "TROPICAL CYCLONE ELECTRIFICATION STUDIES", many aspects of charge separation and cloud microphysical processes are poorly understood. The further analysis and gathering of cloud-to-ground lightning data along with aircraft measurements will aid in our ability to better understand hurricane electrical properties and hurricane structure.
Method: CG lightning data from the NLDN is examined for hurricanes that track near the United States coast and radar data from the NOAA P-3 research aircraft and the National Weather Service land-based system are used. In the future, microphysical and electrical measurements from the P-3 will also be analyzed. To minimize the subjectivity in the determination of which lightning flashes are/are not associated with a storm, a finite area centered on the storm is defined that best approximates the width of the storm's precipitation structure. The CG lightning data associated with 1995 Hurricanes Erin, Felix, and Opal is currently being assembled through the assistance of Dr. Richard E. Orville at Texas A&M University.
Accomplishment: Research into lightning in hurricanes (Samsury and Orville 1994; Molinari et. al 1994; Samsury et al. 1995) has shown that when lightning does occur it most often happens in the convective outer rainbands that are seen in many tropical cyclones (frequently on the eastern side of the storm) (Figure 1). While the eyewall has stronger updrafts than rainbands, CG lightning is relatively scarce in the eyewall region (Figure 1). Although it has been documented by Black and Hallett (1986) that the eyewall lacks the conditions necessary for much electrification (little or no supercooled water in the presence of ice/graupel/etc.), it is thus far unclear why the outer rainbands are so much more likely to have CG lightning. Moreover, the lightning studies noted above have identified a large variability in many of the lightning characteristics between different storms. The Hurricane Electrification experiment has been designed as part of the Hurricane Research Division field program to gather data that will help us to further address some of these issues.
Key reference:
Samsury, C. E., and R. E. Orville, 1994: Cloud-to-ground lightning in tropical cyclones: A study of Hurricanes Hugo (1989) and Jerry (1989). Monthly Weather Review, 122, 1887-1896.

Molinari, J., P. K. Moore, V. P. Idone, R. W. Henderson, and A. B. Saljoughy, 1994: Cloud-to-ground lightning in Hurricane Andrew. Journal of Geophysical Research, 99, D8, 16665-16676.

Samsury, C. E., M. L. Black, and R. E. Orville, 1995: The relationship of cloud-to-ground lightning with radar reflectivity and vertical velocity in Hurricanes Bob (1991) and Emily (1993). 21st Conference on Hurricanes and Tropical Meteorology, Miami, FL, 257-259.

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