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YAHOOWEATHER
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WEATHER
The weather is the set of all
extant phenomena in a given atmosphere at a given time. The term usually
refers to the activity of these phenomena over short periods (hours or
days), as opposed to the term climate, which refers to the average
atmospheric conditions over longer periods of time.
When used without qualification, "weather"
is understood to be the weather of Earth. |
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Weather most often results from
temperature differences from one place to another. On large scales,
temperature differences occur because areas closer to the equator
receive more energy per unit area from the Sun than do regions closer to
the poles. On local scales, temperature differences can occur because
different surfaces (such as oceans, forests, ice sheets, or man-made
objects) have differing physical characteristics such as reflectivity,
roughness, or moisture content.
WEATHER NEWS | WEATHER
FORECAST
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Updated :
Gustav remains a tropical storm, churning toward Jamaica this morning. The storm will pass over the island today, accompanied by torrential rain and gusty
Preparations along the Gulf Coast should be beginning, if not underway already, for another strike with a major hurricane. The weather will cooperate,
The risk to lives and property will be high in the Caribbean through Saturday. Gustav has the potential to become a moderate hurricane as it presses
The outflow of any hurricane is an essential part of storm intensity. If more air is leaving from the top of the hurricane than coming in at the
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Surface temperature differences in turn
cause pressure differences. A hot surface heats the air above it and the
air expands, lowering the air pressure. The resulting horizontal
pressure gradient accelerates the air from high to low pressure,
creating wind, and Earth's rotation then causes curvature of the flow
via the Coriolis effect. The simple systems thus formed can then display
emergent behaviour to produce more complex systems and thus other
weather phenomena. Large scale examples include the Hadley cell while a
smaller scale example would be coastal breezes.
The strong temperature contrast between polar and tropical air gives
rise to the jet stream. Most weather systems in the mid-latitudes are
caused by instabilities of the jet stream flow (see baroclinic
instability). Weather systems in the tropics are caused by different
processes, such as monsoons or organized thunderstorm systems.
Because the Earth's axis is tilted relative to its orbital plane,
sunlight is incident at different angles at different times of the year.
In June the Northern Hemisphere is tilted towards the sun, so at any
given Northern Hemisphere latitude sunlight falls more directly on that
spot than in December (see Effect of sun angle on climate). This effect
causes seasons. Over thousands to hundreds of thousands of years,
changes in Earth's orbital parameters affect the amount and distribution
of solar energy received by the Earth and influence long-term climate
(see Milankovitch cycles).
Source: Wikipedia
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YAHOOWEATHER
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