Heat lightning
Encyclopedia
Heat lightning is a misnomer
for the faint flashes of lightning
on the horizon or other clouds from distant thunderstorms that do not have accompanying sounds of thunder. This occurs because the lightning occurs very far away and the sound waves dissipate before they reach the observer. Heat lightning was named because it often occurs on hot summer nights and to distinguish it from lightning accompanied by audible thunder and cooling rainfall at the point of observation. Lightning results from the discharge of negative ions created from the friction
of ice and water particles bumping into each other at the bottom of a cloud. Heat lightning can be an early warning sign that thunderstorms are approaching. In Florida
, heat lightning is often seen out 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.
through the troposphere
. This refraction results in spaces through which the thunder does not propagate. The sound of thunder often reflects off the Earth's surface. The rumbling sound is partly due to these reflections. This reflection and refraction leaves voids where thunder cannot be heard.
also contributes to distant observers not hearing the thunderclap. Thunder is more likely to be bounced off the Earth's surface before it reaches an observer far from the strike, and only the right refraction and reflection of the sound off of the atmosphere will give it range it needs to be heard far away. The reflection and refraction in the troposphere determines who hears the strike and who doesn't. More often than not, the troposphere will reflect the light, and leave out the sound - in these cases some fraction of the light emanating from distant thunderstorms (whose distant clouds may be so low to the horizon as to be essentially invisible) is scattered by the upper atmosphere and thus visible to remote observers.
. This 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."
) and dust and sand storm
s. In some instances, heavy falling snow has silenced thunder from cloud to ground lightning strikes as close as one to two miles (1.6 to 3.2 km) from the observer and severe dust storms are even more effective in many cases.
Misnomer
A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...
for the faint flashes of lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
on the horizon or other clouds from distant thunderstorms that do not have accompanying sounds of thunder. This occurs because the lightning occurs very far away and the sound waves dissipate before they reach the observer. Heat lightning was named because it often occurs on hot summer nights and to distinguish it from lightning accompanied by audible thunder and cooling rainfall at the point of observation. Lightning results from the discharge of negative ions created from the friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
of ice and water particles bumping into each other at the bottom of a cloud. Heat lightning can be an early warning sign that thunderstorms are approaching. In Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
, heat lightning is often seen out over the water at night, the remnants of storms that formed during the day along a sea breeze front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
coming in from the opposite coast.
Atmosphere
The movement of sound in the atmosphere depends on the properties of the air, such as temperature and density. Because temperature and density change with height, the sound of thunder is refractedRefraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
through the troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
. This refraction results in spaces through which the thunder does not propagate. The sound of thunder often reflects off the Earth's surface. The rumbling sound is partly due to these reflections. This reflection and refraction leaves voids where thunder cannot be heard.
Curvature
The Earth's curvatureCurvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...
also contributes to distant observers not hearing the thunderclap. Thunder is more likely to be bounced off the Earth's surface before it reaches an observer far from the strike, and only the right refraction and reflection of the sound off of the atmosphere will give it range it needs to be heard far away. The reflection and refraction in the troposphere determines who hears the strike and who doesn't. More often than not, the troposphere will reflect the light, and leave out the sound - in these cases some fraction of the light emanating from distant thunderstorms (whose distant clouds may be so low to the horizon as to be essentially invisible) is scattered by the upper atmosphere and thus visible to remote observers.
Under optimum conditions
Under optimum conditions, the most intense thunderstorms can be seen at up to 100 miles (161 km) over flat terrain or water when the clouds are illuminated by large lightning discharges. However, an upper limit of 30-50 (48–80 km) miles is more common due to topography, trees on the horizon, low to mid level clouds, and the fact that local visibilities are generally no more than 25 miles (40 km). Variability of anvil height (an anvil is the large, plume-like top of a thunderhead) also contributes—45,000 feet (13,715 m) is very common in the mid latitudes for warm season thunderstorms, but the anvil height can range from 35,000 (10,665 m) to a current record of 78,000 feet (23,770 m). There is evidence that suggests some cases of heat lightning are, in fact, slow, diffuse discharges of electricityElectricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
. This is not to be confused with electrically-induced luminosity actually generated at mesospheric
Mesosphere
The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere temperature decreases with increasing height. The upper boundary of the mesosphere is the mesopause, which can be the coldest naturally occurring...
altitudes above thunderstorm systems (and likewise visible at exceedingly great ranges), a phenomenon known as "sprites."
Silent lightning
Silent lightning also occurs where airborne matter muffles the thunder, such as heavy snow in winter storms (thundersnowThundersnow
Thundersnow, also known as a winter thunderstorm or a thunder snowstorm, is a relatively rare kind of thunderstorm with snow falling as the primary precipitation instead of rain. It typically falls in regions of strong upward motion within the cold sector of an extratropical cyclone...
) and dust and sand storm
Sand Storm
Sand Storm is a 1992 action game in which you are shooting an anti-air ballistic weapon. The premise of the game is similar to that of Sabotage. You must defend your home base from planes , Patriot Missiles, and Scuds. If a missile or bomb touches the ground, some of the buildings in the base are...
s. In some instances, heavy falling snow has silenced thunder from cloud to ground lightning strikes as close as one to two miles (1.6 to 3.2 km) from the observer and severe dust storms are even more effective in many cases.
External links
- http://www.islandnet.com/~see/weather/whys/heatlightning.htm
- http://whyfiles.org/137lightning/applet/index.html
- http://www.theweatherprediction.com/habyhints/274/
- http://www.weather.com
- http://www.buzzle.com/articles/heat-lightning-facts.html