What Causes Lightning Without Thunder
Heat lightning, also known as silent lightning, summer lightning, or dry lightning (not to be confused with dry thunderstorms, which are also often called dry lightning), is a misnomer used for the faint flashes of lightning on the horizon or other clouds from distant thunderstorms that do not appear to have accompanying sounds of thunder.
What Causes Lightning Without Thunder
The actual phenomenon that is sometimes called heat lightning is simply cloud-to-ground lightning that occurs very far away, with thunder that dissipates before it reaches the observer. At night, it is possible to see the flashes of lightning from very far distances, up to 100 miles (160 km), but the sound does not carry that far. In the United States, lightning is especially common in Florida, which is considered the deadliest state for lightning strikes in the country. This is due to high moisture content in the lower atmosphere and high surface temperature, which produces strong sea breezes along the Florida coast. As a result, heat lightning is often seen over the water at night, the remnants of storms that formed during the day along a sea breeze front coming in from the opposite coast.
Heat lightning is not to be confused with electrically induced luminosity actually generated at mesospheric altitudes above thunderstorm systems (and likewise visible at exceedingly great ranges), a phenomenon known as "sprites".
Thunder is a direct result of lightning. If you see lightning but don't hear thunder, it is because the thunder is too far away. Sometimes, people refer to this as heat lightning because it most often occurs in the summer , but it is no different from regular lighting.
Lightning comes in the form of a giant electric spark in the atmosphere, or between the atmosphere and the ground. In its early development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. However, when the differences in charges become too much, the capacity of the air breaks down and a rapid release of electricity is discharged, forming what you know as lightning.
It is likely you were further than 12 miles (20km) from the lightning strike, as atmospheric conditions also affect whether thunder can be heard or not, as the sound can be pushed up and away from the surface.
From the clouds to a nearby tree or roof, a lightning bolt takes only a few thousandths of a second to split through the air. The loud thunder that follows the lightning bolt is commonly said to come from the bolt itself. However, the grumbles and growls we hear in thunderstorms actually come from the rapid expansion of the air surrounding the lightning bolt.
Because electricity follows the shortest route, most lightning bolts are close to vertical. The shock waves nearer to the ground reach your ear first, followed by the crashing of the shock waves from higher up. Vertical lightning is often heard in one long rumble. However, if a lightning bolt is forked, the sounds change. The shock waves from the different forks of lightning bounce off each other, the low hanging clouds, and nearby hills to create a series of lower, continuous grumbles of thunder.
If we are watching the sky, we see the lightning before we hear the thunder. That is because light travels much faster than sound waves. We can estimate the distance of the lightning by counting how many seconds it takes until we hear the thunder. It takes approximately 5 seconds for the sound to travel 1 mile. If the thunder follows the lightning almost instantly, you know the lightning is too close for comfort!
Scientists use data from GOES-R series satellites, along with data from the Lightning Imaging Sensor on NASA's Tropical Rainfall Measuring Mission satellite, to study lightning. This complete picture of lightning at any given time will improve "now-casting" of dangerous thunderstorms, tornadoes, hail, and flash floods.
If thunder clouds are anywhere near, you should not be outside. Lightning can travel long distances. It doesn't have to be raining overhead for lightning to strike. Don't wait until the "last minute" to seek shelter. You don't want to be a victim of a "bolt from the blue."
What causes lightning to be colored rather than the usual white or blue?Lightning can appear to be many different colors depending on what the light travels through to get to your eyes. In snowstorms, where it is somewhat rare, pink and green are often described as colors of lightning. Haze, dust, moisture, raindrops and any other particles in the atmosphere will affect the color by absorbing or diffracting a portion of the white light of lightning.What are cloud flashes?A cloud flash is lightning that occurs inside the cloud, travels from one part of a cloud to another, or from the cloud to the air.
Can you tell how far away a storm is?Yes, you can use thunder to tell how far away a storm is. Next time you see a storm, count the number of seconds between when you see the lightning and hear the thunder. Take the number of seconds and divide by 5 and that will tell you how far away the storm is in miles. For example: If you counted 10 seconds between the lightning and the thunder, the lightning is 2 miles away!
Does lightning happen during the winter?Lightning occurs less frequently in the winter because there is not as much instability and moisture in the atmosphere as there is in the summer. During the winter, the land surface is cooler because there is not as much heating by the sun to warm it up. Warm air holds more water vapor. And, when water vapor condenses into liquid water cloud drops, latent heat is released which fuels the thunderstorm. So, warm, moist air near the surface (and the proper conditions aloft to give you lots of instability) can result in deep convection, which may produce lightning discharges. Clouds become electrified when strong updrafts (fueled by the instability and moisture) bring supercooled liquid water drops and ice crystals at temperatures less than freezing (0 deg C) together. In this environment, interactions between the ice crystals and supercooled water droplets produce electric charges. The exact mechanisms by which this charging happens remain unknown. The electrical charges build up until they are strong enough to overcome the resistance of the surrounding air. The breakdown of the electric fields produced by these charges is the lightning bolt.
What is thundersnow?Although thunderstorms are less common in the winter, sometimes lightning can occur within snowstorms. Called thundersnow, relatively strong instability and abundant moisture may be found above the surface, such as above a warm front, rather than at the surface where it may be below freezing. Thundersnow is sometimes observed downstream of the Great Salt Lake and the Great Lakes during lake-effect snowstorms, too.
What is forked lightning?Forked lighting appears as jagged lines of light. They can have several branches. Forked lightning can be seen shooting from the clouds to the ground, from one cloud to another cloud, or from a cloud out into the air. This lightning can strike up to 10 miles away from a thunderstorm.What is sheet lightning?Sheet lightning appears as flashes of light that seem to light up or illuminate entire clouds.
What is heat lightning?Heat lightning is a term used to describe lightning flashes that are too far away from you to hear the thunder. The reason that it is called heat lightning is that it appears most often on a hot summer day when the sky is clear overhead.
Essentially, thunder is the sound produced by lightning. When lightning strikes, the narrow channel of air through which it travels reaches temperatures of up to 30,000 C almost instantly. This intense heating causes the air to rapidly expand outward into the cooler air surrounding it creating a rippling shockwave which we hear as a rumbling thunder clap.
Depending on its formation and location, this thunder clap can be heard as either a sudden, loud crack or a low, long rumble. Thunder lasts longer than lightning due to the time it takes for the sound to travel from different parts of the lightning channel.
When a lightning strike is close, the thunder is heard as a loud clap or snapping sound. When the sound of thunder has a rumbling quality, it is the sound waves reaching the listener at different times owing to the shape of the lightning strike. In rare cases, the sound of thunder at very close range has been known to cause injury to humans and damage to property.
Thunder will always be heard after the lightning strike is seen owing to the fact that light travels significantly faster than sound. Both the lightning and thunder clap are generated simultaneously but with the speed of light at 299,792,458 m/s and the speed of sound at 340.29 m/s, there will be always be a gap between the two to the observer.
Your distance from a thunderstorm can be estimated by measuring the time between seeing the lightning flash and the hearing the start of thunder. The length of this interval in seconds can be divided by three to give an approximate distance in kilometres.
Sometimes lightning may be seen but there is no thunder heard. This is either because thunder is rarely heard more than 20 km away or because the atmospheric conditions lead to sound bending upwards and away from the surface.
A downward-moving initiates the less common CG flashes, positively-charged stepped leader, followed by an upward travelling return stroke that lowers the positive charge to earth. Such lightning is usually associated with supercell thunderstorms and trailing stratiform precipitation regions behind squall lines. Positive cloud-to-ground lightning strikes are typically very bright (relative to other lightning activity) and can be identified by their distinct lack of branching near the ground. Thunder from such lightning is very loud and may sound like a series of deep, low-frequency sonic booms. Sprites (see side box) are usually associated with more intense positive CGs. 041b061a72