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Weather
is an all-encompassing term used to describe all of the many
and varied phenomena that can occur in the
atmosphere of a planet.
The term is normally taken to mean the activity of these phenomena
over short periods of time, usually no more than a few days
in length. Average atmospheric conditions over significantly
longer periods are known as climate.
Usage of the two terms often overlaps and the concepts are
obviously very closely related. |
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Weather
is driven by the different amounts of energy received
from the Sun
on different parts of the planet. Because of a planet's
curvature, sunlight
is incident at different angles at different latitudes
(higher latitude -> lower angle
of incidence -> less heating). Different types
of surface (e.g. ocean,
forest,
ice)
have different properties of reflectivity ( albedo)
and absorb differing amounts of energy. |
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Composite satellite
image showing the progress of a hurricane weather system
approaching the East Coast of the United States |
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It
is mainly due to these two factors that the surface is heated
to different extents.These surface temperature
differences cause vertical wind currents as the hot surface
heats the air directly above it. This hot air expands and
rises lowering the air
pressure and drawing colder air into its place, which
is in turn heated and rises and so on. When the hot air later
cools it shrinks and sinks lower, increasing air pressure
and displacing the air already below it. Horizontal wind currents
are formed at the boundaries between differentially heated
areas and can be exacerbated by the presence of sloped surfaces.
The simple systems thus formed can then display emergent behaviour
to produce more complex
systems and thus all other weather phenomena. A large
scale example of this process can be seen in the Hadley
cell and other forms of atmospheric
circulation, a smaller scale example would be coastal
breezes. The only two fundamental causes of weather
are thus surface temperature, and to a lesser extent,
elevation.
Any precession
in a planet's orbit will affect the amount of energy received
at a particular spot throughout the
year. This effect causes seasons
and may influence long term weather patterns.
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Fair weather
Cumulus clouds |
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The
Earth's
atmosphere is one large chaotic
system so small changes to one part can have large effects
elsewhere. This makes it very difficult to accurately predict
short term weather changes more than a few days in advance,
though weather
forecasters are continually working to extend this limit
through the science of the study of weather, Meteorology. |
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Along
with plate
tectonics and ocean
circulation, weather is one of the fundamental processess
that have shaped the Earth since its creation and will continue
to do so as long as it exists. The process of weathering
breaks down rocks and soils into smaller fragments and
then into their constituent substances. These are then free
to take part in chemical reactions that can affect the surface
further (e.g. acid
rain) or are reformed into other rocks and soils. Weather
also plays a major, if indirect, role in erosion
of the surface, moving surface constituents around. |
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| New Orleans after Hurricane Katrina. |
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One
such event that is celebrated is the saving of Japan
from invasion by the Mongol
fleet of Kublai
Khan by the Kamikaze
winds in 1281.
The Little
Ice Age of the 14th to 18th centuries had wide ranging
affects in the northern hemisphere, including decimating the
fledgling Viking
colonies of Greenland,
catalysing the formation of leagues among the American
Indians and forcing the change of patterns of agriculture
across Europe to accomodate the shortened growing season.
A series of great storms throughout the 13th
century caused the powerful English Cinque
Ports to be silted up and hence lose their influence.
More recently, Hurricane
Katrina forced the temporary abandonment of the entire
city of New Orleans
in 2005. Because of the large affect that weather
has on day-to-day life and due to the impossibility of any
type of forecasting before the advent of modern technology,
a large body of
folklore aimed at trying to explain the weather has grown
up, some of which is fairly accurate, most less so. A well
known example is the Groundhog
Day celebrated near the end of winter in parts of the
United States.
The effect of seasons on the life of primitive
peoples also caused them to observe and celebrate certain
events during the calendar,
some of which, in adulterated form, are still observed today.
Christmas,
for example, is the Yule
of the pagans,
celebrated around the winter
solstice (the shortest day of the year).
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It
is the goal of some scientists to control
the weather. Experiments have been carried out for many
years, but the results are usually ambiguous. On a grander
scale, science
fiction authors have long posited the idea of terraforming
other planets in order to make them habitable by human beings.
While this may be possible in the distant future, this is
far beyond current technology. |
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Weather
phenomena and systems on other planets are thought to
be similar to those on Earth, but often occur on a much
bigger scale or involve different substances to those
familiar to Earth dwellers. The Cassini-Huygens
mission to Titan,
for example, discovered clouds formed from methane
or ethane which deposit rain composed of liquid methane
and other organic compounds. Extra-terrestrial weather
systems can be extremely stable; one of the most famous
landmarks in the solar
system, Jupiter's
Great
Red Spot is an anticyclonic
storm known to have existed for at least 300 years.
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| Jupiter's Great Red Spot |
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On other gas
giants, the lack of a surface allows the wind to reach
enormous speeds: gusts of up to 400 metres per second (900
mph) have been measured on the planet Neptune.
This has created a puzzle for planetary
scientists: The weather is created by the differential
action of the Sun's energy on different places and the amount
of energy received by Neptune is very, very small, relative
to the Earth, yet the strength and magnitude of weather
phenomena on Neptune is far, far greater than on Earth.
This mystery is still to be solved [2].
Earth's weather appears to behave based on about a half-dozen
latitudinal weather zones. Jupiter's banded appearance shows
over a dozen such zones, while Venus
appears to have no zones at all. Studying how the weather
works on other planets has been seen as helpful in understanding
how it works on Earth.
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Weather
is not limited to just planetary bodies however. A star's
corona
is constantly being lost to space, creating what is
essentially a very thin atmosphere throughout the
solar system, known as the solar
wind. Inconsistencies in this wind and larger events
on the surface of the star, such as Coronal
Mass Ejections, form a system that has features
analogous to conventional weather systems (i.e. pressureand
wind), and |
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| Categories: Meteorology | Weathe |
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though
not true weather, is generally known as space weather. The
activity of this system can affect planetary atmospheres and
occasionally surfaces. The interaction of the solar wind with
the terrestrial atmosphere can produce spectacular aurorae,
but can play havoc with electrically sensitive systems such
as electricity
grids and radio
signals. |
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