Physics of Electrical Storms

The physics of lightning and thunder has been determined to be caused by the difference in charge between the thunder cloud and the foreign surface, such as a different layer of the cloud or the ground. Normally the cloud gains a positive or negative charge. When the difference between the two regions reaches a certain point, the air between the charges breaks down, allowing the two surfaces to form a circuit and discharge. The first step in formation of lightning is the gathering of charge in the clouds.


- Physics of Electromagnetism

Lightning is based off the physics of electromagnetism. Electromagnetism is the science of the interactions between charges, electric fields, and electric currents. In order to gain a better understanding of lightning, the basic principles of electromagnetism must be understood.

• Electron
  
  An electron is an elementary particle of charge, which orbits the nucleus of an atom. Electrons have a charge of -1.602 * 10^-19 coulombs.
  
  
• Charge
  
  Charge is caused by having an excess or deficit number of electrons in an isolated system. This is caused by the transfer of electrons between atoms, a process called ionization. Charge can be quantified as a positive net charge or a negative net charge. Since the charge of an electron is negative, an excess of electrons in a system creates a negative net charge and a deficit creates a positive net charge. Charge is dependent only on the number of electrons, due to the structure of atoms and molecules. This charge creates an electric field, based on the location and polarization of the charges.
  
  
• Electric Field
  
  An electric field is created by charges in a system. The electric field can be visualized as the force being exerted on a charged particle. Each charged particle emits its own electric field and the summation of these fields creates a net effect on all charged particles in the environment. The general rule for electric fields is that electric fields from a certain charged system flow toward a system of opposite charge, while the fields of the two systems of opposite charge repel from each other. As a result, opposite charges attract and like charges repel each other.
  
  
• Opposites Attract, Likes Repel
  
  The reason opposites attract and likes repel is because the system of charge wants to be in equilibrium. Positive charges want to be with negative charges. When two objects of opposite charge are placed together, they want to get close enough so that they can discharge (exchange charges/electrons) and become neutral or in equilibrium. The opposite happens when you have two objects with the same charge sign. They want to repel like magnets with the same poles.
  
  
• Breakdown of Air/Ionization
  
  Since opposite charges attract, when two regions of strong, opposite charge are present, they will attract and exchange electrons. When they are separated and cannot exchange electrons through contact, they must exchange charge through a medium. In thunderhead systems, the air serves as the medium between the two regions. Since air is not conductive, electric current cannot pass through it easily, so in order for the regions to exchange electrons, the air molecules must be arranged so electrons can pass through it. The process of ionization performs this procedure, allowing neutrally charged molecules to become electrically charged. This happens when a large amount of charged particles attempts to pass through the neutral medium, causing the electrons and protons of the medium to separate in order to create a path between the two regions on which charge can flow.
  
  

- Charging the Clouds

The generally accepted theory of how clouds gain charge is related to static electricity. As the moisture and water vapor rise and develop into small water droplets or ice fragments they collide, exchanging electrons. This exchange occurs due to the friction between the particles in the collisions, causing different charges to accumulate in the clouds. With the significant number of small particles in a thunderhead system, the charge may grow to extremely high levels. This accretion of strong charge is the beginning of the development of lightning.

- How the Charges are Arranged

The exact arrangement of charge in the clouds has not been determined, but one model hypothesizes that the upper regions of the clouds have a strong positive charge, the center has a strong negative charge, and the lower regions have a weak positive charge. This is based on the idea that heavier and larger particles tend to gain a negative charge while lighter particles tend to gain a positive charge in collisions. The charged particles then separate due to the differences in size and density, moving to certain levels of the cloud system. This model has been demonstrated consistently in laboratory simulations of the inside of a thunderhead. The amount of total charge and polarity is also affected by the temperature in the layer of the cloud, the content of the water particles, and several other conditions. This theory is the most widely accepted, although it is just one of many which attempt to explain the properties of the charge buildup in electrical storms.



- How Lightning Occurs

Lightning occurs due to the extreme difference of charge between two regions. When the difference of the charge reaches a certain point, the air between the two regions becomes ionized (i.e. breaks down) and lightning occurs. When this happens, an extreme amount of energy is used up and is converted into light, heat and sound. That is what is seen as lightning and heard as thunder.

- Types of Lightning

• Ground to Cloud
  
  Ground to cloud lightning is the usual type of lightning that most people see. Lightning discharges from the ground to the cloud or vice versa. The ground acts as a pool of electrical charge, and when the clouds gain charge, the ground attempts to balance out the charge by gathering the opposite charge beneath the cloud system. When the difference between the charges increase to a high enough point, the break down of air occurs and lightning between the cloud and the ground occurs. Normally the lightning starts from the ground and flows upward toward the clouds, but the opposite may also occur.
  
  
  
• Cloud to Cloud/Intra-cloud
  
  This is similar to ground to cloud lightning but it occurs between two clouds or two layers of a cloud. The two clouds or layers must have opposite charges and the difference between the two charges must be great enough for the air to break down.
  
  
  
• Ball Lightning
  
  Ball lightning is a phenomenon where a luminous sphere, only several centimeters in diameter, floats through the air near the ground. It lasts a few seconds, and then dissipates or explodes.