Analysis of Cloud-to-Ground Lightning Within 16 Landfalling Hurricanes Danielle 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 ▫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 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  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 Total YearStormCat% Pos% R1% R2% R3% Q1% Q2% Q3% Q4 2007Humberto Katrina Rita Dennis Wilma Ivan Jeanne Charley Frances Claudette Lili Bret Irene Georges Georges Danny 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

YearStormCat6 Hr Before6 Hr After% Increase 2007Humberto Katrina Rita Dennis Wilma Ivan Jeanne Charley Frances Claudette Lili Bret Irene Georges Georges Danny 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): Molinari, et al. “Convective Structure of Hurricanes as Revealed by Lightning Locations.” Monthly Weather Review 127 (1999): 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 – 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): Squires, K., and S. Businger. “The Morphology of Eyewall Lightning Outbreaks in Two Cat. 5 Hurricanes.” Monthly Weather Review 135 (2008):