|
|
| |
|
|
| |
|
|
|
|
| |
 |
| A shelf cloud,
associated with a heavy or severe thunderstorm,
over Swedish island of Öland in the Baltic Sea
in July 2005. |
Storms
A storm is any disturbed state of an environment or in
an astronomical body's atmosphere especially affecting
its surface, and strongly implying severe weather. It
may be marked by significant disruptions to normal
conditions such as strong wind, tornadoes, hail, thunder
and lightning (a thunderstorm), heavy precipitation
(snowstorm, rainstorm), heavy freezing rain (ice storm),
strong winds (tropical cyclone, windstorm), or wind
transporting some substance through the atmosphere as in
a dust storm, blizzard, sandstorm, etc.
Storms have the potential to harm lives and property via
storm surge, heavy rain or snow causing flooding or road
impassibility, lightning, wildfires, and vertical wind
shear. Systems with significant rainfall and duration
help alleviate drought in places they move through.
Heavy snowfall can allow special recreational activities
to take place which would not be possible otherwise,
such as skiing and snowmobiling.
The English word comes from Proto-Germanic *sturmaz
meaning "noise, tumult".
Storms are created when a center of low pressure
develops with the system of high pressure surrounding
it. This combination of opposing forces can create winds
and result in the formation of storm clouds such as
cumulonimbus. Small localized areas of low pressure can
form from hot air rising off hot ground, resulting in
smaller disturbances such as dust devils and whirlwinds. |
|
 |
| Desert storms are
often accompanied by violent winds, and pass
rapidly. |
Classification
A strict meteorological definition of a terrestrial
storm is a wind measuring 10 or higher on the Beaufort
scale, meaning a wind speed of 24.5 m/s (89 km/h, 55
mph) or more; however, popular usage is not so
restrictive. Storms can last anywhere from 12 to 200
hours, depending on season and geography. In North
America, the east and northeast storms are noted for the
most frequent repeatability and duration, especially
during the cold period. Big terrestrial storms alter the
oceanographic conditions that in turn may affect food
abundance and distribution: strong currents, strong
tides, increased siltation, change in water
temperatures, overturn in the water column, etc.
Types
There are many varieties and names for storms: |
- Blizzard – There are varying
definitions for blizzards, both over time and by
location. In general, a blizzard is accompanied by
gale-force winds, heavy snow (accumulating at a rate of
at least 5 centimeters (2 in) per hour), and very cold
conditions (below approximately −10 degrees Celsius or
14 F). Lately, the temperature criterion has fallen out
of the definition across the United States
- Bomb cyclone – A rapid deepening of
a mid-latitude cyclonic low-pressure area, typically
occurring over the ocean, but can occur over land. The
winds experienced during these storms can be as powerful
as that of a typhoon or hurricane.
- Coastal Storm – Large wind waves
and/or storm surge that strike the coastal zone. Their
impacts include coastal erosion and coastal flooding
- Derecho – A derecho is a widespread,
long-lived, straight-line wind storm that is associated
with a land-based, fast-moving group of severe
thunderstorms.
- Dust devil – A small, localized
updraft of rising air.
- Dust storm – A situation in which
winds pick up large quantities of sand or soil, greatly
reducing the visibility
- Firestorm – Firestorms are
conflagrations which attain such intensity that they
create and sustain their own wind systems. It is most
commonly a natural phenomenon, created during some of
the largest bushfires, forest fires, and wildfires. The
Peshtigo Fire is one example of a firestorm. Firestorms
can also be deliberate effects of targeted explosives
such as occurred as a result of the aerial bombings of
Dresden. Nuclear detonations generate firestorms if high
winds are not present.
- Gale – An extratropical storm with
sustained winds between 34–48 knots (39–55 mph or 63–90
km/h).
- Hailstorm – A type of storm that
precipitates round chunks of ice. Hailstorms usually
occur during regular thunderstorms. While most of the
hail that precipitates from the clouds is fairly small
and virtually harmless, there are occasional occurrences
of hail greater than 2 inches (5 cm) in diameter that
can cause much damage and injuries.
- Hypercane – A hypothetical tropical
cyclone that could potentially form over 50 °C (122 °F)
water. Such a storm would produce winds of over 800 km/h
(500 mph). A series of hypercanes may have formed during
the asteroid or comet impact that killed the non-avian
dinosaurs 66 million years ago. Such a phenomenon could
also occur during a supervolcanic eruption, or extreme
global warming.
- Ice storm – Ice storms are one of
the most dangerous forms of winter storms. When surface
temperatures are below freezing, but a thick layer of
above-freezing air remains aloft, rain can fall into the
freezing layer and freeze upon impact into a glaze of
ice. In general, 8 millimetres (0.31 in) of accumulation
is all that is required, especially in combination with
breezy conditions, to start downing power lines as well
as tree limbs. Ice storms also make unheated road
surfaces too slick to drive upon. Ice storms can vary in
time range from hours to days and can cripple small
towns and large metropolitan cities alike.
- Microburst – A very powerful
windstorm produced during a thunderstorm that only lasts
a few minutes.
- Ocean Storm or sea storm – Storm
conditions out at sea are defined as having sustained
winds of 48 knots (55 mph or 90 km/h) or greater.
Usually just referred to as a storm, these systems can
sink vessels of all types and sizes.
- Snowstorm – A heavy fall of snow
accumulating at a rate of more than 5 centimeters (2 in)
per hour that lasts several hours. Snow storms,
especially ones with a high liquid equivalent and breezy
conditions, can down tree limbs, cut off power
connections and paralyze travel over large regions.
- Squall – Sudden onset of wind
increase of at least 16 knots (30 km/h) or greater
sustained for at least one minute.
- Thunderstorm – A thunderstorm is a
type of storm that generates both lightning and thunder.
It is normally accompanied by heavy precipitation.
Thunderstorms occur throughout the world, with the
highest frequency in tropical rainforest regions where
there are conditions of high humidity and temperature
along with atmospheric instability. These storms occur
when high levels of condensation form in a volume of
unstable air that generates deep, rapid, upward motion
in the atmosphere. The heat energy creates powerful
rising air currents that swirl upwards to the tropopause.
Cool descending air currents produce strong downdraughts
below the storm. After the storm has spent its energy,
the rising currents die away and downdraughts break up
the cloud. Individual storm clouds can measure 2–10 km
across.
- Tornado – A tornado is a violent,
destructive whirlwind storm occurring on land. Usually
its appearance is that of a dark, funnel-shaped cloud.
Often tornadoes are preceded by or associated with
thunderstorms and a wall cloud. They are often called
the most destructive of storms, and while they form all
over the planet, the interior of the United States is
the most prone area, especially throughout Tornado
Alley.
- Tropical cyclone – A tropical
cyclone is a storm system with a closed circulation
around a centre of low pressure, fueled by the heat
released when moist air rises and condenses. The name
underscores its origin in the tropics and their cyclonic
nature. Tropical cyclones are distinguished from other
cyclonic storms such as nor'easters and polar lows by
the heat mechanism that fuels them, which makes them
"warm core" storm systems. Tropical cyclones form in the
oceans if the conditions in the area are favorable, and
depending on their strength and location, there are
various terms by which they are called, such as tropical
depression, tropical storm, hurricane and typhoon.
- Wind storm – A storm marked by high
wind with little or no precipitation. Windstorm damage
often opens the door for massive amounts of water and
debris to cause further damage to a structure. European
windstorms and derechos are two type of windstorms. High
wind is also the cause of sandstorms in dry climates.
|
|
 |
| A tornado in Binger,
Oklahoma during the 1981 outbreak. |
Effects on human society
Shipwrecks are common with the passage of strong
tropical cyclones. Such shipwrecks can change the course
of history, as well as influence art and literature. A
hurricane led to a victory of the Spanish over the
French for control of Fort Caroline, and ultimately the
Atlantic coast of North America, in 1565.
Strong winds from any storm type can damage or destroy
vehicles, buildings, bridges, and other outside objects,
turning loose debris into deadly flying projectiles. In
the United States, major hurricanes comprise just 21% of
all landfalling tropical cyclones, but account for 83%
of all damage. Tropical cyclones often knock out power
to tens or hundreds of thousands of people, preventing
vital communication and hampering rescue efforts.
Tropical cyclones often destroy key bridges, overpasses,
and roads, complicating efforts to transport food, clean
water, and medicine to the areas that need it.
Furthermore, the damage caused by tropical cyclones to
buildings and dwellings can result in economic damage to
a region, and to a diaspora of the population of the
region.
The storm surge, or the increase in sea level due to the
cyclone, is typically the worst effect from landfalling
tropical cyclones, historically resulting in 90% of
tropical cyclone deaths. The relatively quick surge in
sea level can move miles/kilometers inland, flooding
homes and cutting off escape routes. The storm surges
and winds of hurricanes may be destructive to human-made
structures, but they also stir up the waters of coastal
estuaries, which are typically important fish breeding
locales. |
 |
| Lightning storm,
Port-la-Nouvelle. |
Cloud-to-ground lightning frequently occurs within the
phenomena of thunderstorms and have numerous hazards
towards landscapes and populations. One of the more
significant hazards lightning can pose is the wildfires
they are capable of igniting. Under a regime of low
precipitation (LP) thunderstorms, where little
precipitation is present, rainfall cannot prevent fires
from starting when vegetation is dry as lightning
produces a concentrated amount of extreme heat.
Wildfires can devastate vegetation and the biodiversity
of an ecosystem. Wildfires that occur close to urban
environments can inflict damages upon infrastructures,
buildings, crops, and provide risks to explosions,
should the flames be exposed to gas pipes. Direct damage
caused by lightning strikes occurs on occasion. In areas
with a high frequency for cloud-to-ground lightning,
like Florida, lightning causes several fatalities per
year, most commonly to people working outside.
Precipitation with low potential of hydrogen levels
(pH), otherwise known as acid rain, is also a frequent
risk produced by lightning. Distilled water, which
contains no carbon dioxide, has a neutral pH of 7.
Liquids with a pH less than 7 are acidic, and those with
a pH greater than 7 are bases. "Clean" or unpolluted
rain has a slightly acidic pH of about 5.2, because
carbon dioxide and water in the air react together to
form carbonic acid, a weak acid (pH 5.6 in distilled
water), but unpolluted rain also contains other
chemicals. Nitric oxide present during thunderstorm
phenomena, caused by the splitting of nitrogen
molecules, can result in the production of acid rain, if
nitric oxide forms compounds with the water molecules in
precipitation, thus creating acid rain. Acid rain can
damage infrastructures containing calcite or other solid
chemical compounds containing carbon. In ecosystems,
acid rain can dissolve plant tissues of vegetations and
increase acidification process in bodies of water and in
soil, resulting in deaths of marine and terrestrial
organisms.
Hail damage to roofs often goes unnoticed until further
structural damage is seen, such as leaks or cracks. It
is hardest to recognize hail damage on shingled roofs
and flat roofs, but all roofs have their own hail damage
detection problems. Metal roofs are fairly resistant to
hail damage, but may accumulate cosmetic damage in the
form of dents and damaged coatings. Hail is also a
common nuisance to drivers of automobiles, severely
denting the vehicle and cracking or even shattering
windshields and windows. Rarely, massive hailstones have
been known to cause concussions or fatal head trauma.
Hailstorms have been the cause of costly and deadly
events throughout history. One of the earliest recorded
incidents occurred around the 9th century in Roopkund,
Uttarakhand, India. The largest hailstone in terms of
diameter and weight ever recorded in the United States
fell on July 23, 2010 in Vivian, South Dakota in the
United States; it measured 8 inches (20 cm) in diameter
and 18.62 inches (47.3 cm) in circumference, weighing in
at 1.93 pounds (0.88 kg). This broke the previous record
for diameter set by a hailstone 7 inches diameter and
18.75 inches circumference which fell in Aurora,
Nebraska in the United States on June 22, 2003, as well
as the record for weight, set by a hailstone of 1.67
pounds (0.76 kg) that fell in Coffeyville, Kansas in
1970. |
 |
| A snow blockade in
southern Minnesota in 1881. |
Various hazards, ranging from hail to lightning can
affect outside technology facilities, such as antennas,
satellite dishes, and towers. As a result, companies
with outside facilities have begun installing such
facilities underground, in order to reduce the risk of
damage from storms.
Substantial snowfall can disrupt public infrastructure
and services, slowing human activity even in regions
that are accustomed to such weather. Air and ground
transport may be greatly inhibited or shut down
entirely. Populations living in snow-prone areas have
developed various ways to travel across the snow, such
as skis, snowshoes, and sleds pulled by horses, dogs, or
other animals and later, snowmobiles. Basic utilities
such as electricity, telephone lines, and gas supply can
also fail. In addition, snow can make roads much harder
to travel and vehicles attempting to use them can easily
become stuck.
The combined effects can lead to a "snow day" on which
gatherings such as school, work, or church are
officially canceled. In areas that normally have very
little or no snow, a snow day may occur when there is
only light accumulation or even the threat of snowfall,
since those areas are unprepared to handle any amount of
snow. In some areas, such as some states in the United
States, schools are given a yearly quota of snow days
(or "calamity days"). Once the quota is exceeded, the
snow days must be made up. In other states, all snow
days must be made up. For example, schools may extend
the remaining school days later into the afternoon,
shorten spring break, or delay the start of summer
vacation.
Accumulated snow is removed to make travel easier and
safer, and to decrease the long-term effect of a heavy
snowfall. This process utilizes shovels and snowplows,
and is often assisted by sprinkling salt or other
chloride-based chemicals, which reduce the melting
temperature of snow. In some areas with abundant
snowfall, such as Yamagata Prefecture, Japan, people
harvest snow and store it surrounded by insulation in
ice houses. This allows the snow to be used through the
summer for refrigeration and air conditioning, which
requires far less electricity than traditional cooling
methods. |
|
 |
| A sunshower storm in
the Mojave desert at sunset. |
Agriculture
Hail can cause serious damage, notably to automobiles,
aircraft, skylights, glass-roofed structures, livestock,
and most commonly, farmers' crops. Wheat, corn,
soybeans, and tobacco are the most sensitive crops to
hail damage. Hail is one of Canada's most expensive
hazards. Snowfall can be beneficial to agriculture by
serving as a thermal insulator, conserving the heat of
the Earth and protecting crops from subfreezing weather.
Some agricultural areas depend on an accumulation of
snow during winter that will melt gradually in spring,
providing water for crop growth. If it melts into water
and refreezes upon sensitive crops, such as oranges, the
resulting ice will protect the fruit from exposure to
lower temperatures. Although tropical cyclones take an
enormous toll in lives and personal property, they may
be important factors in the precipitation regimes of
places they affect and bring much-needed precipitation
to otherwise dry regions. Hurricanes in the eastern
north Pacific often supply moisture to the Southwestern
United States and parts of Mexico. Japan receives over
half of its rainfall from typhoons. Hurricane Camille
averted drought conditions and ended water deficits
along much of its path, though it also killed 259 people
and caused $9.14 billion (2005 USD) in damage.
Aviation
Hail is one of the most significant thunderstorm hazards
to aircraft. When hail stones exceed 0.5 inches (13 mm)
in diameter, planes can be seriously damaged within
seconds. The hailstones accumulating on the ground can
also be hazardous to landing aircraft. Strong wind
outflow from thunderstorms causes rapid changes in the
three-dimensional wind velocity just above ground level.
Initially, this outflow causes a headwind that increases
airspeed, which normally causes a pilot to reduce engine
power if they are unaware of the wind shear. As the
aircraft passes into the region of the downdraft, the
localized headwind diminishes, reducing the aircraft's
airspeed and increasing its sink rate. Then, when the
aircraft passes through the other side of the downdraft,
the headwind becomes a tailwind, reducing lift generated
by the wings, and leaving the aircraft in a low-power,
low-speed descent. This can lead to an accident if the
aircraft is too low to effect a recovery before ground
contact. As the result of the accidents in the 1970s and
1980s, in 1988 the U.S. Federal Aviation Administration
mandated that all commercial aircraft have on-board wind
shear detection systems by 1993. Between 1964 and 1985,
wind shear directly caused or contributed to 26 major
civil transport aircraft accidents in the U.S. that led
to 620 deaths and 200 injuries. Since 1995, the number
of major civil aircraft accidents caused by wind shear
has dropped to approximately one every ten years, due to
the mandated on-board detection as well as the addition
of Doppler weather radar units on the ground. (NEXRAD)
Recreation
Many winter sports, such as skiing, snowboarding,
snowmobiling, and snowshoeing depend upon snow. Where
snow is scarce but the temperature is low enough, snow
cannons may be used to produce an adequate amount for
such sports. Children and adults can play on a sled or
ride in a sleigh. Although a person's footsteps remain a
visible lifeline within a snow-covered landscape, snow
cover is considered a general danger to hiking since the
snow obscures landmarks and makes the landscape itself
appear uniform. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Search Fun Easy English |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
About
Contact
Copyright
Resources
Site Map |
