CLOUD-TO-GROUND LIGHTNING AND TROPICAL CYCLONES
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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