Results from Vaisala’s long range lightning detection network (LLDN) tropical cyclone studies Nicholas W. S. Demetriades Applications Manager, Meteorology Business Area Vaisala, Inc. Monterey, CA 24 March 2009

©Vaisala | date | Ref. code | Page 2 Hurricane Rita (2005)

©Vaisala | date | Ref. code | Page 3 Demetriades and Holle (2008) Introduction - Goal Study inner core lightning rates throughout the full lifecycle of Atlantic tropical cyclones for a large sample size

©Vaisala | date | Ref. code | Page 4 Methodology Full lifecycle of tropical cyclones that occurred in Atlantic basin from 2004 through 2007 Landfall not excluded Subtropical storms not studied Tropical cyclone position and maximum sustained wind speeds obtained from National Hurricane Center best track data Interpolated positions and maximum sustained wind speeds between 6-hour intervals to obtain 3-hour values Tropical cyclone inner core lightning defined as 3-hourly CG lightning flash rates within 100 km of center of storm position Day/Night detection efficiency corrections were applied

©Vaisala | date | Ref. code | Page 5 Methodology Tropical cyclone intensity categories Tropical cyclone intensity categoryMaximum sustained wind speeds Tropical depression (TD)<35 knots Tropical storm – weak (TS-W)35-49 knots Tropical storm – strong (TS-S)50-63 knots Hurricane – weak (H-W)64-95 knots Hurricane – strong (H-S)>95 knots

©Vaisala | date | Ref. code | Page 6 Atlantic basin results Day/Night, DE-corrected cumulative lightning rate distribution table Tropical cyclone intensity category Sample sizePercentile of first non-zero lightning count 50 th percentile75 th percentile90 th percentile Tropical depression (TD) 48042% Tropical storm – weak (TS-W) 65835% Tropical storm – strong (TS-S) 44629% Hurricane – weak (H-W) 51247% Hurricane – strong (H-S) 37329%

©Vaisala | date | Ref. code | Page 7 Atlantic basin results Inner core lightning with respect to landfall

©Vaisala | date | Ref. code | Page 8 Conclusions New finding: Atlantic tropical cyclones produce the highest inner core lightning rates during the tropical storm stage and the lowest inner core lightning rates during the hurricane stage High inner core (eyewall) lightning rates occur infrequently in category 3-5 hurricanes Appear to be related to eyewall replacement cycles (Knabb et al., 2008) Atlantic tropical cyclones produce more inner core lightning during the 24-hour period leading up to, and including landfall, than they do during the 24-hour period after landfall

©Vaisala | date | Ref. code | Page 9 Hurricane Katrina (2005) Eyewall replacement & Continuous eyewall lightning

©Vaisala | date | Ref. code | Page 10 Hurricane Wilma (2005) Eyewall replacement

©Vaisala | date | Ref. code | Page 11 Hurricane Felix (2007) Eyewall replacement