Storm & Lightning Ground Strike Numbers & Locations · Lightning formation requires large energy...
Transcript of Storm & Lightning Ground Strike Numbers & Locations · Lightning formation requires large energy...
Lightning formation requires large energy transformations. These lightning generators are thunderstorms.Thunderstorms can be found across the continent. Thunderstorms generate updrafts in the atmosphere, largecolumns of falling rain and air, and ground level winds. Straight line winds in a thunderstorm can be caused bydownbursts of various sizes: microbursts (<1 mile diameter & 160 mph winds); macrobursts (>2.5 milesdiameter & 130 mph winds); and, derechos (bands of downburst clusters >240 miles long & >100 mphwinds). Hot, humid air running into colder air masses tend to generate storms with massive, energetic air flows.
Figure 1 shows a historic map of annual thunderstorm days recorded in the United States over a30 year period. Figure 2 shows a current map of thunderstorm day averages per year. Figure 3 provides amap of thunderstorm days per year averaged over the 1990's. Note the general trend for increased thun-derstorms days as you travel South and East in the United States. The Tampa Bay area of Western Floridais the storm (and lightning) capital of the United States.
Storming OnWithin thunderstorms, intense updrafts can occur spinning up into tornadoes. Tornado events are on the
rise in the United States. Since 1950, tornado events have increased roughly seven-hundred percent (7X).Figure 4 shows tornado numbers over the last 55 years. Tornadoes generate intense lightning discharges.Figure 5 provides a map of average number of tornadoes per year expected. The map categories are broad butdemonstrate a concentration of storms in the legendary “tornado alley” of the Great Plains. Separating tornadoinitiated and general thunderstorm lightning events is not possible. Faster updrafts have the potential for greatercharge separation and generation.
Storm Intensity ZonesIn trying to summarize storms and lightning associated damage to trees, the Coder Storm Intensity
Map was developed for the continental United States. This map was created using averages of historicdata for thunderstorms, hurricanes, tornadoes, lightning ground strike frequency, ice glazing events, snowfall accumulation values, and general wind speed values. The result is shown in Figure 6, a map of stormintensity as it relates to potential tree damage.
The range of storm intensity impacting trees are categorized into zones from 0 to 10. The most intensearea of potential tree damage from storms is in zone 10, the southern tip of Florida. Thunderstorms (hurricanesare series of thunderstorms), tornadoes, and lightning events were part of this composite cluster analysis. Notesome areas are dissimilar in climate and weather events, but share similar total composite tree damaging envi-ronments.
Lightning LocationTo arrive at actual lightning ground strikes per year, there are a number of equations using thunder-
storm days per year. One general estimate of lightning ground strikes per year is multiplying thunderstormdays for an area times 0.2. (Uman 2008) A research formula is given in Figure 7. In this figure thenumber of lightning ground strikes per square mile per year is determined by using the number of thunder-storm days per year. This formula is modified using average values from multiple papers. Figure 8provides another way to compare lightning ground strikes per square mile per year with annual thunder-storm days. These thunderstorm days formula are only for rough estimation of lightning strikes.
Dr. Kim D. Coder, Professor of Tree Biology & Health Care, Warnell School, UGA
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2Dr. Kim D. Coder Warnell School University of Georgia
With improving technology, cloud to ground lightning strikes can be directly measured and mapped.Figure 9 is a simplified map of lightning ground strikes per square mile per year over a decade. Figure 10provides ground strikes per square mile per year for the last 15 years. For example, using 40 lightning groundstrikes per square mile per year means there is a 90% chance of a strike within 725 feet, 50% chance of a strikewithin 395 feet, and 10% chance of a strike within 165 feet for any point on the ground per square mile peryear. (Uman 2008).
Comparing ground strike maps from many years suggest complex changes are occurring in numberand location of lightning ground strikes. As global climatic changes increase average temperatures, a 2oFincrease in average temperature increases by 11% atmospheric energy and increases by 10% the number oflightning strikes. (Bouquegneau & Rakov 2010).
3Dr. Kim D. Coder Warnell School University of Georgia
Figure 1: Average thunderstorm days per year.(30 year national summary -- NOAA)
THUNDERSTTHUNDERSTTHUNDERSTTHUNDERSTTHUNDERSTORMORMORMORMORMDDDDDAAAAAYYYYYSSSSS
4Dr. Kim D. Coder Warnell School University of Georgia
Figure 2: Average thunderstorm days per year.
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5Dr. Kim D. Coder Warnell School University of Georgia
Figure 3: Average thunderstorm days per year.(national 1990-1999 data)
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THUNDERSTTHUNDERSTTHUNDERSTTHUNDERSTTHUNDERSTORMORMORMORMORMDDDDDAAAAAYYYYYSSSSS
6Dr. Kim D. Coder Warnell School University of Georgia
Figure 4: General trend line for tornado numbersin the United States over 55 years. (NOAA data)
1950 1960 1970 1980 1990 2000 year
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7Dr. Kim D. Coder Warnell School University of Georgia
Figure 5: Average tornadoes per year. (45 year data -- NOAA)
TTTTTORNORNORNORNORNADOESADOESADOESADOESADOES
8Dr. Kim D. Coder Warnell School University of Georgia
Figure 6: Coder composite storm damage intensity mapfor potential tree injury / damage, with lightning as one of the
damaging components. (highest risk = 10; lowest risk = 0)
TREE DTREE DTREE DTREE DTREE DAMAAMAAMAAMAAMAGEGEGEGEGE
9Dr. Kim D. Coder Warnell School University of Georgia
Number of LightningNumber of LightningNumber of LightningNumber of LightningNumber of LightningGrGrGrGrGround Strikound Strikound Strikound Strikound Strikeseseseses
per squarper squarper squarper squarper square mile per ye mile per ye mile per ye mile per ye mile per yearearearearear= N= N= N= N= N
Number ofNumber ofNumber ofNumber ofNumber ofTTTTThunderhunderhunderhunderhunderstorstorstorstorstorm Dam Dam Dam Dam Daysysysysys
per yper yper yper yper yearearearearear= T= T= T= T= T
N =N =N =N =N =(0.015 X ((0.015 X ((0.015 X ((0.015 X ((0.015 X (TTTTT)))))1.341.341.341.341.34 ) X 2.59 ) X 2.59 ) X 2.59 ) X 2.59 ) X 2.59
Figure 7: Estimating cloud to ground lightning strikes persquare mile per year using thunderstorm days per year.
(after Cooray & Fernando 2010)
10Dr. Kim D. Coder Warnell School University of Georgia
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2.62.62.62.62.6
0.260.260.260.260.26
lightninglightninglightninglightninglightninggggggrrrrroundoundoundoundoundstrikstrikstrikstrikstrikeseseseses
(per square mile(per square mile(per square mile(per square mile(per square mileper yper yper yper yper year)ear)ear)ear)ear)
0 0 0 0 0 2020202020 4040404040 6060606060 8080808080thunderthunderthunderthunderthunderstorstorstorstorstorm dam dam dam dam daysysysysys
(per y(per y(per y(per y(per year)ear)ear)ear)ear)
Figure 8: Annual lightning ground strikes compared withannual thunderstorm days. (Rakov & Uman 2013)
11Dr. Kim D. Coder Warnell School University of Georgia
Figure 9: Cloud to ground lightning stikes per square mileper year. (1997-2007 national data)
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LIGHTNINGLIGHTNINGLIGHTNINGLIGHTNINGLIGHTNINGGRGRGRGRGROUND STRIKESOUND STRIKESOUND STRIKESOUND STRIKESOUND STRIKES
12Dr. Kim D. Coder Warnell School University of Georgia
Figure 10: General cloud to ground lightning strikes persquare mile per year (national data of past 15 years)
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LIGHTNINGLIGHTNINGLIGHTNINGLIGHTNINGLIGHTNINGGRGRGRGRGROUND STRIKESOUND STRIKESOUND STRIKESOUND STRIKESOUND STRIKES
Citation:Coder, Kim D. 2018. Storm & lightning ground strike
numbers & locations. Warnell School of Forestry& Natural Resources, University of Georgia,Outreach Publication WSFNR-18-21. Pp.13.
The University of Georgia Warnell School of Forestry and Natural Resources offers educational programs, assistance andmaterials to all people without regard to race, color, national origin, age, gender or disability.
The University of Georgia is committed to principles of equal opportunity and affirmative action.
Publication WSFNR-18-21 February 2018