Lightning

 

 

 

 

 

Author: Rachel Hyma, Roger Li, Amrita Raghuraman

Contact Information: hyma1@illinois.edu; rogerli1@illinois.edu; raghura1@illinois.edu

---

 

Table of Contents

Overview Description Formation Destruction Case Study Vodcast Sources

 

 

---

 

 

Overview

 

 

     Lightning is one of the oldest observed natural phenomena on earth. Early Greeks believed that lightning was a weapon of Zeus and reflected the gods’ displeasure. It is extremely powerful and can do tremendous damage.  The damage done is so widespread that it covers damage to property, environment, and people.  Just U.S. lightning costs and losses may exceed $5 to $6 billion per year [1]. Lightning is a major cause of forest fires and is responsible for about 2.1 million acres of forests being reduced to ash [2].

 

 

 Figure 2 West Richland, Washington. A lightning storm is taking place while also in the background is a brushfire being started from the lightning bolts.

 

Table 1. Annual average severe weather fatalities by decade from 1940-1991     Year     Lightning     Tornado     Flood     Hurricane     1940-1949     337     154     144     22     1950-1959     184     135     79     87     1960-1969     133     94     121     59     1970-1979     98     99     182     21     1980-1989     72     52     110     12     1990-1991     73     46     102     8     Total (51 yrs.)     8316     5731     5828     2031     Source: National Weather Service, 1992. (7)

Table 1 clearly displays lightning having a higher annual fatality rate over other severe weather [3]

 

 

     Human casualties are another aspect which lightning factors into. In the United States, an average of 62 people is killed each year by lightning [4]. In addition, 300 more are injured with many cases going unreported. Injuries may include memory loss, sleep disturbances, photophobia, depression, and coordination problems. Most lightning fatalities and injuries occur when people are caught outdoors in the summer months during the afternoon and evening [3].

 

Table 2. Lightning strike victims: frequency 25% or greater.     Memory Deficits & Loss     52% **     Depression     32% *     Attention Deficits     41% **     Inability to Sit Long     32%     Sleep Disturbance     44% *     External Burns     32%     Numbness/Parathesias     36% **     Severe Headaches     32% **     Dizziness     38% *     Fear of Crowds     29% *     Easily Fatigued     37% *     Storm Phobia     29% *     Stiffness in Joints     35%     Inability to Cope     29% *     Irritability/Temper Loss     34% *     General Weakness     29% **     Photophobia     34%     Unable to Work     29% **     Loss of Strength/Weakness     34% **     Reduced Libido     26% *     Muscle Spasms     34%     Confusion     25% **     Chronic Fatigue     32% *     Coordination Problems     28% **     Hearing Loss     25%         * Denotes Psychological ** Denotes Psychological or Organic No Asterisk Denotes Organic

Table 2 lists more possible injuries suffered by lightning strike victims [3].

 

 

 

Figure 3 illustrates the average amount of lightning recorded from 1996-2000 over the Continental United States [5].

 

 

     The fear of lightning is strong since it is not uncommon for strikes to occur many miles from the base of a thunderstorm, even without rain -- and even with the sun shining. Each year, in the continental United States, over 20,000,000 cloud-to-ground lightning strikes are recorded [1].

Figure 4 Taken in Norman Oklahoma, this photograph captures multiple cloud-to-ground lightning strokes during a night time thunderstorm.

 

     Furthermore, at any given moment, there are 2000 thunderstorms in progress somewhere on the earth. This amounts to 16 million storms each year with about 8 million lightning strikes per day. And unbelievably 100 lightning strikes every second [6].

 

     Aside from the danger of lightning, it is nothing more than an electrical discharge in the atmosphere. Each discharge of lightning can reach over five miles in length, soar to temperatures of approximately 50,000 degrees Fahrenheit, and contain 100 million electrical volts. The energy from 100 million electrical volts could light a 100-watt light bulb for more than 3 months [6].

 

 

Figure 5 In the summer months, overlooking Lake Ontario, several cloud to ground strikes can be seen.

 

 

---

Description

---

Formation

 

 

 

 

Without clouds, the electric field of the atmosphere during a “fair weather” day is very small at roughly 100 volts per meter. However, the electric field within a cloud that is producing lightning can be as high as 3,000,000 volts per meter. To build this immense electric field in a thunderstorm, charge separation must occur. Atmospheric scientists have discovered that these charges are divided at two main levels within the cloud where the negative charges accumulate at the bottom and positive charges accumulate at the top. To achieve this incredible build up of charge, the thunderstorm requires one main ingredient: ice. Without ice, the charge separation on these scales is not achievable. [3]

 

 

Charge separation within the updraft of a thunderstorm, occurs due to the countless collisions between ice particles. Within a thunderstorm, ice takes on many different shapes. Some ice forms as crystals, aggregates of these crystals become snowflakes, soft small spongy balls of ice are called graupel and larger more solid balls of ice are called hail (all shown in Figure 6).[3]

 

 

 

 

Figure 6

These three panels illustrate the difference between snowflakes, graupel, and hail.

 

 

When these ice crystals collide they act like conductors and exchange electrons – similar to the way electrons are transferred into your feet when you drag them across a shaggy carpet. It has been discovered that this exchange happens very efficiently when the smaller ice crystals and snowflakes collide with  hail and graupel. When they collide, the snowflakes and ice crystals often transfer an electron  to the hail or graupel. This interaction leaves the snowflakes and ice crystals positively charged while the graupel and hail now have a net negative charge. Being heavier, the hail and graupel fall to the base of the cloud taking their negative charge while the snowflakes and ice crystals are carried upward into the tops of the cloud with their net positive charge. These interactions occur countless numbers of times within the storm and as a result the charge build up is immense with positive charges accumulating at the top of the cloud and negative charges accumulating at the bottom. (See Figure 7 and Figure 8 Panel 1) The ground under the cloud tends to have a net positive charge as the negative base of the cloud repels negative charges beneath it. Lightning is simply the result of these charges trying to equalize themselves. When this stroke occurs, a huge amount of energy is discharged but quickly built back up again by the countless collisions of ice particles within the storm. [3]

 

 

 

 Figure 7. This picture illustrates charge separation for various types of lightning. 

Source: http://media-2.web.britannica.com/eb-media/78/7578-004-7C794BAD.gif 

 

 

 

There are many different types of lightning as seen in Figure 7. These include cloud to ground strokes, cloud to air, in-cloud and cloud to cloud [2]. Cloud to ground strokes occur when electrons move towards the ground through a cloud base while searching for a path of least resistance to positive charges on the ground in small steps. This initial surge of electrons is called the “Stepped Leader” and is very faint and typically unperceivable to the naked eye. See Figure 8 Panel 2.(The stepped leader can be seen in the video below as the branching charges leaving cloud base searching for positive charges).

 

 

 

Source: http://www.todaysbigthing.com/2008/08/07 

 

When the last step comes very close to making contact with positive charges on the surface of the earth, the positive charge jumps towards the negative charge and creates a “traveling spark”. This traveling can be seen on tall objects like tree tops, antennas and power lines as a faint glowing spark that reaches upward. See Figure 8 Panel 2. Once the stepped leader and traveling spark meet, a return stroke occurs from that connection and the electrons from cloud base rush downward as the current flows upwards heating the air along its way to about 30,000 ^oC. This bright flash, called the return stroke, is the most visible part of the lightning strike and in roughly 95% of cloud-to-ground lightning strikes, the return stroke travels from the ground to the cloud. See Figure 8 Panel 3. After the first return stroke occurs, the path that the stroke took is still ionized. As a result, any leftover electrons can follow that same path to the positive charges on the ground, rather than forging a new path. This second stepped leader is called a “dart leader” as it “darts" down the opened ionized path. When this dart leader meets the positive charges on the ground, a second return stroke occurs. This process may continue several times leading to multiple return strokes. To the human eye this appears as one lightning bolt that flashes multiple times [3].

 

 

Figure 8

Source: http://www.srh.noaa.gov/srh/jetstream/lightning/lightning.htm 

 

Panel 1 illustrates the main charge separation within a thunderstorm and ground prior to a cloud-to-ground lightning strike. [1]

Panel 2 illustrates the stepped leader that follows a pathway towards the positive charge on the ground [1]

Panel 3 illustrates the return stroke once the negative and positive charges meet [1]

 

 

Other types of lightning

 

 

Cloud to air lightning strokes do not touch the ground and instead discharge in the open air. In-cloud lightning, as seen in Figure 9 panel 1 will often light up entire sections of cloud, which is why it is commonly referred to as “sheet lightning”. Cloud to cloud lightning strokes travels between clouds and often makes an intricate web of discharge paths as seen in Figure 9 Panel 2. This type of lightning is commonly called spider lightning [2].

 

                                                              

 

 

Figure 9

Source: http://www.nssl.noaa.gov/primer/lightning/ltg_basics.html 

 

Panel 1 shows an example of an in-cloud stroke which lights up the cloud itself rather than reach the ground [2].

Panel 2 shows an example of a cloud to cloud stroke ( also called spider lightning) [2].

 

 

Roughly 95% percent of cloud-to-ground lightning strikes occur as described above, where negative charges on the bottom of the cloud meets with the positive charges from the earth. Positive polarity lightning strikes however, occur when positive charges from the cloud meet with the negative ions on the ground..Although this type of lightning strike is much less frequent, it is a much stronger stroke because the charge must travel along a longer path as it comes from the top of the cloud to the ground. The bright, well-defined bolt seen on the left side of Figure 10 is an example this type of lightning strike . [4]

 

 

Figure 10

Source: http://www.srh.noaa.gov/jetstream//lightning/positive.htm

 

This picture is an example of a positive-polarity lightning stroke. [4]

  

 

---

Destruction

 

 

     Second only to floods, fatalities from lightning each year in the United States kills more people each year than hurricanes and tornadoes combined [1].  According to the National Weather Service (NWS) statistics over the last thirty years, lightning on average kills 62 people yearly.  Over the last ten years, lightning on average has claimed 44 lives yearly [3]. Despite these large numbers, lightning is one of the only severe weather phenomenon that has shown a marked decrease in deaths since the NWS has been keeping records.  Shown in Figure 1 are the lightning fatalities since 1940. Notice the dramatic the drop in this statistic over time. The decrease in deaths over these years owes to better physical understanding of lightning, improved safety and awareness, and advances in medical treatment.

 

             Figure 1

 

     Even with improved physical understanding of lightning, damages and costs caused by it are phenomenal.  Lighting has the ability to severely damage buildings and homes, produce enormous forest fires, and instantly kill exposed animals.  As shown in Image 1, concrete exploded from the foundation of a home due to a lighting strike, Image 2 shows cattle struck dead by lighting, and Image 3 demonstrates the damage inflicted upon a tree from a bolt of lightning. 

 

  Image 1- Damaged foundation from lightning strike      Image 2-Cattle struck dead by lightning                  Image 3- Damaged tree from lightning strike

 

      According to the National Lightning Safety Institute, “research suggests realistic U.S. lightning costs and losses may exceed $5 to $6 billion per year. [5] ” The NLSI also reported that annually 5.2 million acres of land are set on fire due to lightning [5].  

 

     The risks to human life, health and property are often underestimated by average civilians.  History has shown that better understanding, awareness and education have dramatically reduced the impacts of lightning. For example, one may think they are safe before a thunderstorm arrives or after a storm passes but according to the NWS, “…studies have shown most people struck by lightning are not struck at the height of a thunderstorm, but before and after the storm has peaked. [1]” People may not also be aware of how lightning can branch off of a tree, fence, pole, or any other tall object to a person.  Lightning also have the ability to travel through power or telephone lines, plumbing pipes, and water putting people at risk who are in contact with electronics, corded telephones, electric appliances, a plumbing fixture, in the bathtub, pool, or under running water from a shower during a storm [2]. An interesting list of “It Can’t Happen To Me”  lightning stories have been catalogued by the National Lightning Safety Institute [7]. Furthermore, In Table X, the NSLI lists several specifics about lightning fatalities in the U.S. over the last 35 years [8].

 

 

Location of Incident: 40% Unreported 27% Open fields & recreation areas (not golf) 14% Under trees (not golf) 8% Water-related (boating, fishing, swimming…) 5% Golf/golf under trees 3% Heavy equipment and machinery-related 2.4% Telephone-related 0.7% Radio, transmitter & antenna-related Gender of victims = 84% male; 16% female Months of most incidents = June 21%, July 30%, Aug 22% Days of week of most incidents = Sun./Wed./Sat Time of day of most incidents = 2 PM to 6 PM Number of victims = One (91%), two or more (9%) Deaths by State, Top Five = FL, MI, TX, NY, TN Injuries by State, Top Five = FL, MI, PA, NC, NY   Source

Table X-Specifics about lightning fatalities 

 

If a person is struck by lightning and not killed, they will most likely suffer through some sort of long-term, serious injury.  These injuries include nerve damage, memory loss, personality change, and emotional problems.  Burn marks can also occur where metal comes in contact with or is in close proximity to the body, such as jewelry and belt buckles, and also where the body has been sweaty such as the feet, underarms, and chest. Image 4 shows a man who has been struck by lightning and has burn marks on his back.

 

 

Image 4- Man with burn marks

 

 Burns from the lightning itself are typically not permanent or severe [2]. Although the temperature of the bolt can reach 54,000°F, it occurs so quickly that severe lasting tissue burns are rare [4].

 

      Safety measures must be taken seriously during a storm in order to be safe from the effects of lightning.  Avoidance of all objects and situations noted previously is of the greatest importance.  The safest places to be during a storm are large encloses structures such as shopping centers, schools, office buildings, and private residences.  Another safe place to be is in an enclosed metal vehicle such as an automobile, van, or school bus [1].  If all of these precautions are observed, then any fear of being harmed by lightning should be eliminated. 

 

 

---

Case Study

 

 

     On 2 September 2007, Lightning struck in El Paso County, Colorado. The lightning strike lead to the death of a 21 year old male.  He was killed by lightning while inside a tent. The lightning struck 8 miles southwest of Colorado Springs, Colorado.

 

 Figure 1: Satellite view of the location

 

A survey of the lightning strike site revealed that the tent was located at the very top of a hill.

 

 Figure 2: The arrow marks the site of the tent

 

 

Figure 3: Rips along the bottom of the tent.

   

 

     The Lightning damage included rips in the tent. A total of 6 tears were found along the bottom of the tent.  The flash struck the top of the boulder which was immediately behind the tent. The lightning traveled through the boulder into the ground and across the bottom of the tent surface. No other damage could be found in the area around the tent.

  

     Three other people were present, but only received minor injuries. The man who was killed was lying down on the ground inside the tent at the time of the flash.

 

     The lightning strike was documented at 7:52 pm local time. At the time, radar indicated a convective shower producing heavy rain was located just to the northeast of Lookout Point and was moving southwest at 15 mph. The fatal flash occurred just after the heaviest rain had moved over the tent. From 7:25 pm till leading up to the death there were 84 cloud to ground strikes. That is nearly 3.2 strikes per minute.

 

 

Figure 4: Radar image of the region where the lightning took place. The white dot represents the campgrounds location.

 

Table 1: Shows Latitude and Longitude of  cloud to ground lightning flashes between 7:45 pm and the time of the fatal flash 7:52:29. Pm. The letter "kA" represent KiloAmpheres. A negative sign "-" in front of this value represents a negative flash. The last column is the distance between the flash and the location of where the fatality occurred.

Date Time (UTC) Latitude Longitude kA Distance (sm) 3-Sep-07   00:45:07 38.769283 -104.916382 -17 1.93 3-Sep-07   00:45:35 38.771847 -104.930267 -17 2.32 3-Sep-07   00:45:47 38.762875 -104.916382 -11 1.50 3-Sep-07   00:46:04 38.764156 -104.909973 -25 1.56 3-Sep-07   00:46:13 38.768002 -104.932404 -15 2.14 3-Sep-07   00:46:17 38.73724 -104.882202 -17 1.61 3-Sep-07   00:46:33 38.759029 -104.923859 -21 1.38 3-Sep-07   00:46:43 38.74493 -104.904633 -17 0.44 3-Sep-07   00:46:56 38.757748 -104.912109 -7 1.12 3-Sep-07   00:47:20 38.728268 -104.904633 -7 0.99 3-Sep-07   00:47:59 38.706478 -104.890747 -55 2.67 3-Sep-07   00:49:08 38.720577 -104.854431 -17 3.40 3-Sep-07   00:49:22 38.746212 -104.922791 -17 0.68 3-Sep-07   00:49:32 38.755184 -104.920654 -7 1.06 3-Sep-07   00:50:14 38.750057 -104.943085 -49 1.79 3-Sep-07   00:51:10 38.747494 -104.945221 -47 1.85 3-Sep-07   00:51:26 38.720577 -104.868317 -15 2.75 3-Sep-07   00:51:55 38.730831 -104.929199 -23 1.20 3-Sep-07   00:52:29 38.739803 -104.908905 -29 0.19

 

     Several key factors led to the death of the camper. lightning has a preference to strike tall objects. The location of the tent in this case study was was found to be located on the very top of a tall hill. The location had a major factor in the lightning strike.

 

     Another vulnerability in this case study was the fact that the victim was lying down. For example, he was creating more surface area for lightning strikes to enter his body. Thus it is recommended to minimize the amount of area on the ground one covers. The electrical current entered through his elbow and traveled through his torso, and exited his buttocks. The other three occupants in the tent were better off, because they were standing at the time of the flash.

 

     The campers were aware that lightning was occurring. It would have been advisable if they chose to leave and look for shelter, instead they remained in the tent. If there car was anywhere in the vicinity they should have sought refuge there. Simple lightning safety knowledge may have been able to prevent the death of the camper. [1]

 

---

Vodcast

 

Fliqz has shut down their service. To access this video, email support with this video id: 803c600271d14272a37fc85a8df74293

      

---

 

Sources

 

Overview 

[1] http://www.economics.noaa.gov/?goal=weather&file=events/lightning

[2] http://www.lightningsafety.com/nlsi_lls/nlsi_annual_usa_losses.htm

[3] http://www.lightningsafety.com/nlsi_lls/sec.html

[4] http://www.weather.gov/os/hazstats.shtml

[5] http://www.lightningsafety.noaa.gov/lightning_map.htm

[6] http://www.thedenverchannel.com/sh/idi/weather/lightning/stats.html

 

Formation

 [1] “How Lightning is Created.” NWS Jetstream 08 Oct 2008 2 Nov 2008 <http://www.srh.noaa.gov/srh/jetstream/lightning/lightning.htm.>

 [2] "Lightning Basics." NOAA National Weather Storms Laboratory 07 Jul 2008 2 Nov 2008

          <http://www.nssl.noaa.gov/primer/lightning/ltg_basics.html.>

 [3] Rauber, Robert M., John E. Walsh, and Donna J. Charlevoix. Severe and Hazardous Weather. 2nd ed. Dubuque, Iowa: Kendall/Hunt

          Publishing Company, 2005.

 [4] "The Positive and Negative Side of Lightning" NWS Jetstream 08 Oct 2008 2 Nov 2008 <http://www.srh.noaa.gov/jetstream//lightning/positive.htm.>

 

 

Destruction

 

[1]"Lightning." National Weather Service 08 October 2008 2 Nov 2008 http://www.srh.noaa.gov/jetstream//lightning/lightning_intro.htm

[2]"Damage and Impacts." National Severe Storms Laboratory http://www.nssl.noaa.gov/primer/lightning/ltg_damage.html

[3]"Weather Fatalities." NOAA's National Weather Service 28 Oct 2008 http://www.weather.gov/os/hazstats.shtml

[4] “Burn, Lightning Injuries.” eMedicine 29 Nov 2008 http://www.emedicine.com/plastic/topic517.htm

[5] “ Lightning Costs and Losses from Attributed Sources.” National Lightning Safety Institute 29 Nov 2008  http://www.lightningsafety.com/nlsi_lls/nlsi_annual_usa_losses.htm

[6] “Lightning Damage Photos.” National Lighting Safety Institute 29 Nov 2008 http://www.lightningsafety.com/nlsi_info/damage_photos.html

[7] “Selected Incidents From ‘It Can’t Happen to Me’ Library.” National Lightning Safety Institute 29 Nov 2008 http://www.lightningsafety.com/nlsi_lls/incidents.html   

[8] “35 Years of Lightning Deaths and Injuries” National Lightning Safety Institute 29 Nov 2008 http://www.lightningsafety.com/nlsi_lls/35_years_injuries.html

 

 

Case Study

[1] http://www.crh.noaa.gov/pub/?n=/ltg/ltg_070902_goldcamp.php