Website on severe weather hazards

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  1. What is a lightning actually?
  2. Why do you see a flash during the discharge?
  3. Why do you hear a thunder during the discharge?
  4. Why do you see flash first and hear thunder later?
  5. Does every cloud produce an atmospheric pressure discharge?
  6. How to behave during storm when there is nowhere to hide?
  7. What to do when someone is struck by a lightning?
  8. Is it is safe to stay in your car during storm?
  9. Does the use of mobile phone can "attract" a lightning?
  10. Are lightning rods effective?
  11. Are surge protectors effective?
  12. Where do the atmospheric pressure discharges mostly occur?
  13. What kinds of lightnings exist?
  14. How much can a lightning measure?
  15. What is St. Elmo’s fire?

What is a lightning actually?
Lightning is an electric discharge whose current intensity is very high. A negative charge runs towards the ground creating a highly ionized air. The effect of this process is the emergence of branched paths. Every path is expanding towards the earth’s surface until they reach the ground. This part of the discharge is called a leader. When leader reaches the ground, a highly intense flow of positive charges travels towards the cloud for a split second on a path marked by a leader. This process is repeated few times within a split second until the electrical potential difference is neutralized.

Why do you see a flash during the discharge?
Flash occurs because air is heated to a high temperature which is caused by the flow of highly intense current. Gasses comprising the air such as nitrogen and oxygen begin to glow when exposed to a high temperature (23000°C).

Why do you hear a thunder during the discharge?
Thunder is a result of a rapid heating of air. The difference in air temperature causes rapid increase of air pressure. This disturbance takes the form of a sound wave.

Why do you see a flash first and hear thunder later?
The difference is connected to speed at which sound wave and light wave travel. Light waves travels at approx. 300 000 000 m/s, whereas sound wave travels at 343 m/s. This is the reason why the difference is noticeable during the atmospheric pressure discharge. The further the lightning strikes, the easier it is to notice the difference. This is also the method to approximate the distance between the storm and your location. For every second falls approx. 350 m. By counting seconds between a flash and a thunder, it is possible to approximate the distance between the strike and your position.

Does every cloud produce an atmospheric pressure discharge?
The only type of cloud which can cause atmospheric pressure discharges is Cumulonimbus. The shape of this cloud reminds a gigantic anvil, mushroom or a tower seen from the distance. It has to be noted, however, that Cumulonimbus clouds can be hidden among clouds of a different type, e.g. Nimbostratus. The latter cloud type is classified as a layered cloud and may cover the entire sky. The atmospheric pressure discharge itself can occur also during eruption of a volcano or a sandstorm. Cumulonimbus-type clouds may not appear during such natural events.

How to behave during storm when there is nowhere to hide?
Duck in a lowest place possible, put your legs together and pull them underneath (sitting and lying is forbidden). Avoid hideouts located near masts, trees and other tall structures which may be struck by a lightning. When you find yourself in an open space like water leave water immediately as it is a perfect electricity conductor. In the case of groups disperse to leave backup in case someone gets struck by a lightning.

What to do when someone is struck by a lightning?
Call ambulance at 999 (these number are active in Poland only) or 112 for cell phones. The most important thing to do is to remain calm – make sure you are safe in order to provide the injured with help effectively. Check whether the injured is breathing and whether he or she has pulse. If not, start resuscitation. Lay the injured on his or her back on a hard ground. Kneel beside that person and put your index finger and middle finger on one of his or her lowest ribs. Slide your fingers until you sense that curves of the ribs join and form the lower part of a breastbone. Middle finger should be placed exactly in that spot whereas index finger should be placed on the breastbone. Put your other hand on the breastbone and slide down until you reach the index finger of your first hand. You will press this spot. Put your first hand atop the other hand and lock your fingers. Bend yourself over the injured person, straighten your arms and press the breastbone until it lowers by approx. 4-5 cm (adults). Next, release the pressure but hold your hands in the same position. Repeat this action and maintain the same rhythm – approx. 60-80 compressions of heart per minute. If CPR is needed inhale two times (take a deep breath, cover the mouth of the injured tightly and exhale until you notice his or her chest rising) for every 30 compressions of chest. CPR must not be stopped until breath and pulse are restored or until emergency unit arrives.

Is it is safe to stay in your car during storm?
Car is a safe spot unless it is driven during a violent storm. Furthermore, the place of car’s stopover needs to be carefully selected, i.e. is it under the tree or other construction which can be vulnerable to strong winds. Direct strike of the lightning in the body of the car is not dangerous, however it has to be remembered that metal elements of the car should not be touched. The shape of the car’s body reminds Faraday cage which perfectly protects from being struck by a lightning. After car was struck by a lighting and when the danger passes, it is advised to check whether tires have not been damaged before continuing the ride.

Does the use of mobile phone can "attract" a lightning?
Cell phone works similar to any other radio receiver. The power emitted by the mobile phone is little, so it seems that its power to “attract” lightnings is also limited. Nevertheless, it is advised to avoid exposure in open areas or telephone conversation in the open during the storm.

Are lightning rods effective?
They will not provide 100% security but they serve as an additional protection for home against fire. In the case of devices placed inside of the building it seems a little more problematic. After the lightning strikes the lightning rod, electric charges begin to flow which creates a strong electro-magnetic field particularly harmful for electric devices. Such devices can be damaged in this process.

Are surge protectors effective?
Surge protectors can never be trusted in 100%. When the lightning strikes the power grid directly, surge proctor is unable to block entire power emitted by the lightning. Such solutions are helpful to protect power lines against minor temporary power surges. The option to use during the storm is to unplug electrical devices, unless the device needs to operate non-stop.

Where do the atmospheric pressure discharges mostly occur?
Most of the atmospheric pressure discharges is detected in the equator area – in the tropical climate zone. Particularly great number of storms is recorded in central Africa. Indonesia is the most stormy region – in the vicinity of Java island lightnings strike most often (322 days per annum).

What kinds of lightnings exist?
There are three types of lightnings. lightning is the most often occurring lightning to be observed in nature. It takes shape of a glowing straight line which may branch itself. Second type of lighting is a ball lightning which reminds a small-shaped ball. This phenomenon occurs extremely rarely. The lightning of this kind travels in various directions and emits a hissing or growling sound. This phenomenon lasts from few to couple of seconds. The third and least known type is bead lightning. It reminds a little chain consisting of separate glowing elements.

How much can a lightning measure?
Lightings most often stretch to 1 kilometer. Although lightnings exceeding 10 kilometer length occur from time to time, the lightning which overall measure reached 150 kilometers remains the record-holder!

What is St. Elmo’s fire?
This is the name of minor and silent electric discharges. They appear during atmospheric pressure discharges and can be observed on the sharp edges of objects such as: masts, antennas and rocks. The fire is very picturesque – at night it looks like tiny, hissing, glowing sparks. This phenomenon can be read as a warning against possible lightning strike.