(part I) Dr. Kim D. Coder Professor of Tree Biology & Health Care Warnell School, University of Georgia
Disclaimer 1.No financial interests or conflicts of interest 2. NOT lightning system installation
TODAY introduce lightning information tree damage process use of tree lightning conduction systems Not installation guide Not international, national, or state tree lightning protection standards & practices
ground somewhere on Earth 9 million per day 6,200 per min 100 per sec
Injuries & Damage ~500 seriously injured ~100 (20%) killed feed lot & pastured animals property ~$175 million utility losses trees in forest & yards severely damaged
Unlucky People tallest object, within tallest object area, boating, open field recreation, driving farm tractor in field, golfing, exploring granite outcrop, taking shelter under or near tall objects (males, 4:30pm, weekends & Weds.) --symptoms for humans-- cardiac arrest, dizziness, temporary paralysis, ruptured eardrums & hearing problems, temporary blindness, physical collapse, thrown by shock wave, crushing, & burns
severely damages & kills thousands of trees each year
Annual T-Storm Days
Annual T-Storm Days
Annual T-Storm Days 1990-1999
Annual T-Storm Days 1990-1999
Annual Strikes per square mile last 15 years
Annual Strikes per square mile -- 1997-2011
Storms & Lightning Generation
generate large updrafts pull moisture to high, cold altitudes
Charge Separation In Cloud Collisions between: falling graupel (wet ice particles 1/12 to 1/6 inch diameter) & rising small ice crystals (ice particles 1/400 inch diameter or smaller)
Charge Size & Location
Types of Lightning internal cloud cloud-ground cloud-cloud cloud-air most (60%) is internal cloud
Lightning & Tree Damage cloud-ground exchanges 90% negative polarity 9% positive polarity 1% other here = negative polarity cloud-ground exchanges
Lightning Strike Development Process
near invisible fingers of negative charge pushing downward from bottom of cloud
Ground Streamers enhanced field along Earth s surface below storm pulled (or stream) upward toward cloud base flow up & off top of tall objects as standing charge wave passes
enhanced charge field under storm clouds fire towers -- strong ground steamer
Normal Electrical Field
Enhanced Electric Field
Connection! cloud leaders push downward from cloud base ground streamers flow upward off tall objects electrical connection ~100 to 400 feet above ground or tip of structure
Charge Exchange Path opens & rapidly exchanges temporarily neutral massive charge exchange generates light
visible stroke moves 1/3 speed of light spews light & heats air several charge exchanges within one strike to neutralize charge
Several trees in row damaged from different strokes in one strike Some trees struck many times!
Lightning Path unpredictable can jump onto adjacent houses or through people strike changes local air & material resistance to electrical charge exchange each millisecond presents new potential pathway
lightning strike = number of strokes (average 3-4) each stroke = 10's of milliseconds strike duration ~1/2 second (human perceived flicker)
Average Strike 100 million volts 35,000 amps strike core 1/5 to 1/2 in. diameter ionized envelope 4-6 in. diameter bright light corona 1-5 ft. diameter
Average Strikes (1 micro-second = 0.000,001 second)
Core Shockwave
9% strikes positive lightning more powerful, impacts larger ground area, & last longer (fire!)
Annual CG Strikes Per Square Mile
Years Between Strikes
Horizontal Strike Distance
Grounding charge exchange path opens energy races along soil surface dissipates across surface & into soil soil channeling large voltages
Step Voltage
Step Voltage
Step Voltage
Step Voltage Soil Resistance
flash & sound generated thunder 770 mph at 70 o F count seconds times 1/5 mile
heat & shockwave along tree >40 atms for <1/5 in. acoustic wave (thunder) generated in 2 in.
heat generation & steam (S) strong shockwave (10S)