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Lightning
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This
glossary can help you learn some of the words you may need as you
find out more about lightning and thunderstorms..
BLUE
JETS
Blue jets are fountains coming from the top of thunderstorms at speeds
of 60 miles per second. Research into these phenomena has expanded
as NASA has included observations and experiments from the space shuttle.
CUMULONIMBUS
Cumulonimbus clouds are also called thunderstorm clouds. They are
frequently accompanied by heavy showers, lightning, thunder, and sometimes
hail, tornadoes or strong, gusty winds. This cumulus cloud is vertical
and often appears with an anvil-shaped cloud on top. A thunderstorm
occurs from a cumulonimbus cloud. They produce deadly lightning and
can be dangerous to people, animals, crops, and property.
DOPPLER
RADAR
Weather radar that measures direction and speed of a moving object,
such as drops of precipitation moving toward or away from the radar.
Using the Doppler effect, it measures the speed of particles. It was
named for J. Christian Doppler, an Austrian physicist, who in 1842
explained why the whistle of an approaching train had a higher pitch
than the same whistle when the train was going away.
DOWNDRAFT
A sudden descent of cool or cold air to the ground, usually with precipitation,
and associated with a thunderstorm or shower.
FLASH-BANG RULE
How close is the lightning? You can do a rough calculation this way:
When you see the flash, begin to count the seconds until you hear
the thunder. Divide this number by 5. The number you get is the approximate
distance of the lightning in miles.
For example, if you count nine seconds between the flash and the thunder,
the lightning struck just under two miles away.
HEAT LIGHTNING
Heat lightning appears as a glowing flash on the horizon. It is actually
lightning occurring in distant thunderstorms, just over the horizon
and too far away for thunder to be heard.
LIGHTNING
Lightning is a sudden and visible discharge of electricity produced
in response to the build up of electrical potential between cloud
and ground, between clouds, within a single cloud, or between a cloud
and surrounding air. The lightning present in all thunderstorms is
an electrical discharge that balances the difference between positive
and negative charges within a cloud, between two clouds, or between
a cloud and the ground.
MICROBURSTS
Microbursts are also called downbursts. Severe thunderstorms can create
incredible violence as they pass over an area. Among their most devastating
aspects are down bursts. A downburst is a severe localized wind blasting
down from a thunderstorm. These strong downward currents are classified
by meteorologists as microbursts if the downburst covers an area less
than 2.5 miles in diameter and as macrobursts if the down burst covers
an area of at least 2.5 miles in diameter.
RED
SPRITES
Red sprites have been observed during thunderstorms, primarily by
high-altitude aircraft. Sprites are very short duration optical flashes
that extend into the ionosphere ( an atmospheric zone that extends
between 50 and 400 miles above the earth's surface. ) during storms.
SEVERE
THUNDERSTORMS
Thunderstorm that contains any one or more of the following three
weather conditions are called severe:
Hail that is 3/4 of an inch or greater in diameter
Winds 58 miles per hour or greater
Tornadoes
Severe thunderstorms may also produce torrential rain and frequent
lightning. Severe thunderstorms are most prevalent during the spring
and fall, The risk of lightning is perhaps the most common and deadly
event that can occur during a thunderstorm.
SEVERE THUNDERSTORM WARNING
A severe thunderstorm warning means a severe thunderstorm has actually
been observed by spotters or indicated on radar, and is occurring
or imminent in the warning area.
SEVERE THUNDERSTORM WATCH
A Severe thunderstorm watch means conditions are right for the development
of severe thunderstorms in and close to the watch area.
SUPERCELL
A supercell is a severe thunderstorm characterized by a rotating,
long-lived, intense updraft. Although not very common, they produce
a relatively large amount of severe weather, in particular, extremely
large hail, damaging winds, much lightning, and practically all violent
tornadoes. They are the most violent and dangerous thunderstorms.
THUNDER
The sound emitted by rapidly expanding gases along the channel of
a lightning discharge. Over three-quarters of lightning's electrical
discharge is used in heating the gases in the atmosphere in and immediately
around the visible channel. Temperatures can rise to over 10,000 °C
in microseconds, resulting in a violent pressure wave, composed of
compression and rarefaction. The rumble of thunder is created as one's
ear catches other parts of the discharge, the part of the lightning
flash nearest registering first, then the parts further away.
THUNDERSTORM
Thunderstorms are produced by a cumulonimbus cloud. It is characterized
by thunder, lightning, gusty surface winds, turbulence, hail, icing,
precipitation, moderate to extreme up and downdrafts and possibly
tornadoes.
TORNADO
A tornando is a violently rotating column of air. They can occur anywhere
in the world given the right conditions, but are most frequent in
the United States in an area bounded by the Rockies on the west and
the Appalachians in the east. Tornados frequently develop during severe
thunderstorms.
TURBULENCE
Turbulence is the irregular and sudden motions of air. It can be caused
by thermal or convective currents, differences in terrain and wind
speed, along a frontal zone, or variation in temperature and pressure.
Turbulence during severe thunderstorms causes problems for aircrafts.
UPDRAFT
An updraft is a small scale current of air with vertical motion. If
there is enough moisture, then it may condense, forming a cumulus
cloud which is the first step towards thunderstorm development.
WIND SHEAR
Wind shear is any sudden change of speed or direction in wind flow.
A microburst is a sudden vertical drop of air which produces considerable
wind shear.
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