Analysis of Cloud-to-Ground Lightning Within 16 Landfalling HurricanesDanielle Nagele

Previous Literature

•Squires and Businger 2008▫ RI outbreaks – strike density increased (decreased) rapidly

before (after) reaching max. strike density

•Samsury and Orville 1994▫ Hugo had only 33 flashes, Jerry had 691 flashes▫ Majority of flashes on right side

Previous Literature

•Molinari et al. 1999▫ Findings support 3 regions

eyewall inner bands, 20–80 km outside the eyewall outer bands, outside of the 100-km radius

▫ Predictive value of eyewall flashes Lightning outbreak in core of storm can indicate intensity

changes

•Lyons and Keen 1994▫ Lightning within convective elements of outer bands during

most stages of life cycle▫ Lightning bursts within 100-150 km of the center may indicate

intensification

Hypothesis and Goals

•Climatology of CG lightning within hurricanes during landfall period▫ Reveal patterns with regards to the number/location of

flashes

•Hypothesis▫ There will be bursts of CG lightning along the coast as

the right, front quadrant moves across land

• Greater updraft strength▫ Increase in surface convergence due to friction cause by

surface roughness

• Powell 1982, Powell 1991, and Powell 1996 looked at Hurricanes Fredric, Hugo, and Andrew respectively▫ Enhanced convergence to the right of the center, divergence to

the left▫ Powell 1982 – ratio of wind speeds directly inland to

immediately offshore from .74 to .84

• Results in more graupel-sized particles above the freezing level and more vigorous charge seperation▫ Enough to create small bursts in lightning during this

time

Hurricanes

Methodology

• Data▫ NLDN lightning data (Vaisala)

Updated in 1995, increasing detection efficiency to 80-90%, 2002/2003 to 90-95%

Reliable up to 400 km away from sensor▫ NEXRAD WSR-88D Level II radar data (NCDC)▫ HURDAT satellite data (NCDC)▫ Six hourly best track (NHC)▫ H*Wind track files (HRD)

• Lightning, radar, satellite data viewed on ANGEL (IDL GUI created by Dr. Kyle Wiens)

Methodology• Rainbands start interacting with coast - six hours after

landfall Storm center within 300 km of the coast

• Storms from 1997-2007 Landfall as a hurricane along the Gulf or Florida coasts

• Landfall defined as the time center of the eye passes over land

• Overlay range rings centered around the center of the eye

• Overlay approximate storm track

• Break storms into three regions – inner core, inner rainband, outer rainbands

• Break three regions up into four storm relative quadrants

• Record flashes every ten min.

Schematic

R1 - Inner Core

R2 - Inner Rainband

R3 - Outer Rainband

Methodology

•Bursts:▫Increase by 50% from one ten minute

period to the next Avg. flash rate less than five, threshold 15 Avg. flash rate more than five, threshold 20

▫Analyzed each burst that occurred inland, within 20 km of the coast Gridded radar, examined cross sections Height of 35 dBZ line, max. dBZ, lightning

Bursts•Summary:

▫ 252 bursts in all▫ 190 over water▫ 27 inland, beyond 20 km of the coast▫ 37 inland, within 20 km of the coast

3 occurred within an eyewall▫ Q1-100, Q2-95, Q3-32, Q4-25▫ Most bursts - Katrina, Ivan, Bret, Danny

•Height of 35 dBZ line▫ In 8 bursts, greatest height 1 or 2 scans before burst▫ In 12 bursts, greatest height scan during burst▫ In 5 bursts, greatest height 1 or 2 scans after ▫ In 2 bursts, no correlation seen

Example Burst (during)

Burst

Example Burst (before)

Burst

Percentage of TotalYear Storm Cat % Pos % R1 % R2 % R3 % Q1 % Q2 % Q3 % Q42007 Humberto 1 8 14.9 2.2 82.8 66.7 19.3 1.9 12.12005 Katrina 3 13 1.0 0.7 98.3 55.3 27.8 3.1 13.7

Rita 3 14 3.5 2.4 94.1 13.5 80.2 5.0 1.2Dennis 3 21 9.5 0.0 90.4 45.7 48.6 2.4 3.3Wilma 3 32 11.2 1.6 87.2 3.9 0.7 6.2 89.2

2004 Ivan 3 33 0.0 2.0 97.9 60.6 38.9 0.5 0.0Jeanne 3 30 9.3 0.0 90.7 25.6 9.3 9.3 55.8Charley 4 25 6.2 0.7 93.1 65.4 3.3 2.6 28.7Frances 2 8 0.6 0.4 98.4 15.9 35.5 39.5 9.2

2003 Claudette 1 20 3.6 6.4 90.0 4.3 73.5 20.9 1.32002 Lili 1 17 12.2 1.1 86.7 60.0 36.1 0.3 3.71999 Bret 3 6 0.4 0.2 99.4 33.3 58.7 6.1 2.0

Irene 1 13 11.8 16.8 71.4 63.9 18.4 0.3 17.31998 Georges1 2 16 8.3 3.1 88.5 30.7 46.7 11.3 11.3

Georges2 2 16 0.0 0.0 100.0 35.3 62.8 1.9 0.01997 Danny 1 11 7.5 10.0 82.5 51.2 33.4 11.1 4.3

• Irene, 3 stdev. above mean for R2 • Irene, 2 stdev. below mean for R3• Frances, 3 stdev. above mean for Q3• Wilma, 3 stdev. above mean for Q4

Year Storm Cat 6 Hr Before 6 Hr After % Increase

2007 Humberto 1 621 1090 76

2005 Katrina2 3 574 2656 363

Rita 3 481 1814 277

Dennis 3 699 523 -25

Wilma 3 83 109 31

2004 Ivan 3 793 731 -8

Jeanne 3 18 1 -94

Charley 4 1272 7240 469

Frances 2 321 433 35

2003 Claudette 1 857 1356 58

2002 Lili 1 429 433 1

1999 Bret 3 1887 623 -67

Irene1 1 111 329 196

1998 Georges1 2 783 1945 148

Georges2 2 82 595 626

1997 Danny 1 1112 2622 136

Before and After Landfall

Patterns• Rita, Katrina, Ivan, Georges1, Danny, Bret, Charley showed similar

pattern ▫ Steady decrease in R3 lightning before landfall, slight or large increase after

• Rita, Irene, Humberto, Dennis all had a peak in R1 flashes during landfall▫ Wilma had a peak ~1 hr. before and Charley ~1 hr. after

• Dennis (1200) and Humberto (0600) had peak in R1 flashes at min. press.

Conclusions

• Bursts along coast seen in right, front quadrant▫ Isolated, within outer bands or eyewall▫ Most bursts correspond with an increase in the 35 dBZ line

(scan before or during burst)▫ Multiple bursts from same rainband occurring in regular

intervals

• Bursts along coast predominantly in Q1 ▫ Only 7 of 37 in other quadrants

• Of all types of bursts, largest concentration seen in Q1 and Q2▫ 195 in Q1 and Q2, 57 in Q3 and Q4

Conclusions• Most lightning concentrated in outer band, Q1

• 7/16 storms show similar trend of a gradual decrease in flashes before landfall

• On avg., stronger storms had a higher % of pos. flashes, but lower % of inner core flashes

• The 3 storms that made landfall on west coast of FL, had a higher than avg. % of flashes in Q4

• Weaker storms had a greater increase in flashes after landfall

• Inner core lightning may be correlated with strengthening and/or landfall

References

Lyons, Walter A., and Cecil S. Keen. “Observations of Lightning In Convective Supercells within Tropical Storms and Hurricanes.” Monthly Weather Review 122 (1994): 1897-1916.

Molinari, et al. “Convective Structure of Hurricanes as Revealed by Lightning Locations.” Monthly Weather Review 127 (1999): 520-534.

Powell, Mark D. “The Transition of the Hurricane Fredric Boundary-Layer Wind Field from the Open Gulf of Mexico to Landfall.” Monthly Weather Review 110 (1982): 1912 – 1932.

Samsury, Christopher E., and Richard E. Orville. “Cloud-to-Ground Lightning in Tropical Cyclones: A Study of Hurricanes Hugo (1989) and Jerry (1989).” Monthly Weather Review 122 (1994): 1887-1896.

Squires, K., and S. Businger. “The Morphology of Eyewall Lightning Outbreaks in Two Cat. 5 Hurricanes.” Monthly Weather Review 135 (2008): 1706-1726.