Lightning and Tropical TornadogenesisA Case Study of Tropical Storm Lee (2011)Zachary HargroveThe University of North Carolina at Asheville

Purpose

• To determine the relationship between lightning activity and tornadogenesis (tornado formation) in landfalling tropical cyclones

Why is this research important?

• Landfalling tropical cyclones often produce tornadoes

• 59% of landfalling hurricanes from 1948-1986 produced tornadoes (McCaul 1991)

• Tropical tornado signatures are often hard to identify on radar

• Lightning and tornadoes are both usually associated with intense convection

• Past studies have found relationships between lightning and classic supercell tornadogenesis

Why is this research important?

• Lightning is not typically as prevalent in tropical cyclones when compared with classic continental thunderstorms (higher freezing levels in a tropical environment = less ice = less frequent charge separation)

• A relationship between the two processes could give forecasters a real time tool to locate possible “trouble” areas in a large storm. If there is a cluster of increased activity, then maybe something is going on.

Tropical Storm Lee (2011)• Became a tropical depression on September 1st

• Made landfall on the Louisiana coast as a Tropical Storm with sustained winds of 45 mph on September 4th

• Produced 30 confirmed tornadoes. Previous work defined a “severe” tropical tornado outbreak as at least 24 (McCaul 2004)

• Transitioned from tropical to extra-tropical during the morning of September 5th

Tropical Storm Lee (2011)

Image credit: NASA, MODIS Rapid Response System. Taken on September 2, 2011.

Methodology

• 7 embedded tropical supercell case studies were selected – 5 that produced tornadoes and 2 that did not.

• Lightning data obtained from the Earth Networks Total Lightning Network (ENTLN)

• Radar data obtained from the National Climatic Data Center (NCDC) archives.

• Tornadic cases – Strategy

• Non-tornadic cases - Strategy

Radar Image - Case 1 - Baldwin County, AL Tornado

Lightning vs. Time – Case 1

6:537:06

7:147:22

7:307:42

7:507:58

8:078:19

8:278:35

8:438:55

9:049:12

9:209:32

9:409:48

10:0010:09

10:1710:25

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Lightning Strikes vs. Time (UTC) - Baldwin County Tornado - 9/4/2011

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Radar Image - Case 2 - Gulfport, MS Airport Tornado

Lightning vs. Time – Case 2

3:433:51

4:034:11

4:204:28

4:404:48

4:565:13

5:215:29

5:415:47

5:596:08

6:166:24

6:366:44

6:527:01

7:137:21

7:297:37

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Lightning Strikes vs. Time (UTC) - Gulfport Airport and Saucier, MS Tornadoes - 9/4/2011

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Lightning vs. Time – Case 3

4:034:11

4:234:31

4:394:51

4:595:07

5:155:27

5:355:47

5:556:03

6:136:21

6:336:41

6:496:57

7:097:17

7:257:37

7:457:53

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Lightning Strikes vs. Time (UTC) - Mobile County Tornado - 9/4/2011

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Lightning vs. Time – Case 4

8:158:24

8:328:44

8:539:05

9:139:22

9:309:42

9:519:59

10:0710:16

10:2510:34

10:4610:54

11:0311:15

11:2311:32

11:4811:57

12:050

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Lightning Strikes vs. Time (UTC) - Okaloosa County Tornado - 9/4/2011

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Lightning vs. Time – Case 5

1:471:56

2:082:16

2:252:34

2:432:52

3:033:12

3:213:30

3:413:53

4:014:09

4:214:30

4:384:46

4:585:06

5:145:31

5:395:47

5:590

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Lightning vs. Time (UTC) - Hancock County Tornado - 9/4/2011

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Lightning vs. Time – Cases 6 and 7 Non-tornadic

Baldwin (1) Gulfport (2) Mobile (3) Okaloosa (4) Hancock (5) Non-Tornadic #1 (6)

Non-Tornadic #2 (7)

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800 Hourly Lightning Rates For Each Case

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Conclusions• Cases 1 and 2 exhibit some relationship between increased

lightning activity and tropical tornadogenesis.

• Cases 3,4, and 5 are lacking any discernable relationship.

• There are no distinguishable differences between tornadic and non-tornadic cases. Hourly lightning rates also do not help to separate the two.

• The only conclusion we can draw from this small sample size is that there is no relationship between lightning activity and tropical tornadogenesis.

Why do we not see a definitive relationship?• Because tropical cyclones form in tropical environments, the

freezing level is higher in the atmosphere than with mid-latitude cyclones. Because there is less ice, there may be less charge separation.

• Past research has found relationships between lightning and tornado formation in classic Great Plains supercells8. This relationship may be related to updraft strength as classic supercells have much stronger updrafts than tropical storm supercells.

• Future research possibilities.

Acknowledgements • Dr. Christopher Hennon, faculty advisor, The University of

North Carolina at Asheville

• Dr. Christopher Godfrey, Fortran support, The University of North Carolina at Asheville

• Steve Prinzivalli, Earth Networks

• National Weather Service offices in Mobile, AL and Slidell, LA

• Storm Prediction Center (SPC), National Hurricane Center (NHC), National Climatic Data Center (NCDC), and Hydrological Prediction Center (HPC)

References• 1. Gentry, R. C., 1983: Genesis of tornadoes associated with hurricanes. Mon. Wea. Rev., 111,

1793-1805.• 2. McCaul, E. W., Jr., 1991: Buoyancy and shear characteristics of hurricane-tornado

environments. Mon. Wea. Rev., 119, 1954-1978.• 3. McCaul, E. W., Jr., D. E. Buechler, S. J. Goodman, and M. Cammarata, 2004: Doppler radar

and lightning network observations of a severe outbreak of tropical cyclone tornadoes. Mon. Wea. Rev., 132, 1747–1763.

• 4. Novlan, D. J., and W. M. Gray, 1974: Hurricane-spawned tornadoes. Mon. Wea. Rev., 102, 476-488.

• 5. Schneider, D., and S. Sharp, 2007: Radar Signatures of Tropical Cyclone Tornadoes in Central North Carolina. Wea. Forecasting, 22, 278-286.

• 6. Doswell, C. A. III, S. J. Weiss, and R. H. Johns, 1993: Tornado forecasting—a review. Proc., Tornado Symp. III. C. Church, Ed., Amer. Geophys. Union, (in press).

• 7. Zipser, Edward J., Kurt R. Lutz, 1994: The Vertical Profile of Radar Reflectivity of Convective Cells: A Strong Indicator of Storm Intensity and Lightning Probability?. Mon. Wea. Rev., 122, 1751–1759.

• 8. Perez, Antony H., Louis J. Wicker, Richard E. Orville, 1997: Characteristics of Cloud-to-Ground Lightning Associated with Violent Tornadoes. Wea. Forecasting, 12, 428–437.

• 9. Samsury, Christopher E., Richard E. Orville, 1994: Cloud-to-Ground Lightning in Tropical Cyclones: A Study of Hurricanes Hugo (1989) and Jerry (1989). Mon. Wea. Rev., 122, 1887–1896.