Download Weather is what is happening in the atmosphere at any time or short

Weather is what is happening in the atmosphere at any time or short period of time. Weather conditions can change suddenly.
Today may be warm and sunny, tomorrow may be cool and cloudy. Weather conditions include clouds, rain, snow, sleet, hail, fog,
mist, sunshine, wind, temperature and thunderstorms.
Weather is driven by the heat stored in the Earth's atmosphere, which comes from energy from the Sun. When heat is moved
around the Earth's surface and in the atmosphere because of differences in temperature between places, this makes winds. Winds
form part of larger weather systems, the most powerful of which is the hurricane. Other weather features like the thunderstorm also
develop because of the movement of heat in the atmosphere. Some thunderstorms in the United States give birth to tornadoes.
Like energy, water is moved between the Earth and the atmosphere. The Earth's water cycle plays an important role in the
development of many weather features like dew, fog, clouds and rain.
Scientists measure the weather so they can forecast it. This involves plotting weather information on special charts. Weather radar
and satellites are now also used to help predict the weather.
The elements of the weather
To describe the weather we must describe the state of the air. We can do this under 5 main headings. These are called the elements
of the weather:
1. air temperature - How hot or cold is it?
2. precipitation (rain, snow, hail, sleet, frost, fog, dew) - Is it wet or dry?
3. cloud cover and sunshine - Is it sunny or cloudy?
4. wind speed and direction -The movement of the air.
5. air pressure
The climate of a place is its average weather. To calculate this we must know what types of weather occur there at different times
of the year.
Weather Words
* The atmosphere is the layer of gases, called air, which surrounds the planet earth.
* The air in the atmosphere is a mixture of gases. These are mainly nitrogen (about
4/5) and oxygen (about 1/5). There are also amounts of water vapor, carbon dioxide
and some rare gases. The amount of water vapor is very important as this gives us
our cloud and rain.
On a weather map we join places of equal pressure with lines called isobars
A High Pressure Area
Pressure Area
A Low
The weather we get from high air pressure is very different from that we get with low air pressure ie :-
We measure wind direction with a wind vane (see
diagram). Wind direction is the compass point from
which the wind is coming eg south, south west, west etc.
The unit of measurement for wind direction is therefore
compass direction.
The jet stream, which blows between 8 to 12 kilometers
above the surface, was discovered during World War. Crews of high-flying B-29 bombers heading west across the Pacific Ocean
ran into ferocious headwinds that prevented them from reaching their bombing targets on schedule.
Jet streams are fast flowing, relatively narrow air currents found in the atmosphere at around 11 kilometers (36,000 ft) above the
surface of the Earth. They form at the boundaries of adjacent air masses with significant differences in temperature, such as of the
polar region and the warmer air to the south. The jet stream is mainly found in the tropopause, at the transition between the
troposphere (where temperature decreases with height) and the stratosphere (where temperature increases with height)[1].
The major jet streams are westerly winds (flowing west to east) in both the Northern Hemisphere and the Southern Hemisphere,
although in the summer, easterly jets can form in tropical regions. The path of the jet typically has a meandering shape, and these
meanders themselves propagate east, at lower speeds than that of the actual wind within the flow. The theory of Rossby waves
provides the accepted explanation for propagation of the meanders; Rossby waves propagate westward with respect to the flow in
which they are embedded, but relative to the ground, they migrate eastward across the globe.
The Gulf Stream, together with its northern extension towards Europe, the North
Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates in
the Gulf of Mexico, exits through the Strait of Florida,and follows the eastern
coastlines of the United States and Newfoundland before crossing the Atlantic
Ocean. At about 30°W, 40°N, it splits in two, with the northern stream crossing to
northern Europe and the southern stream recirculating off West Africa. The Gulf
Stream influences the climate of the east coast of North America from Florida to
Newfoundland, and the west coast of Europe.
Weather Phenomena
Thunderstorms and Lightning - occur when large air masses rise quickly into the atmosphere,
forming
huge cumulonimbus clouds. Severe air currents inside the clouds cause water droplets and ice crystals to crash into one another
continually, and the friction between these particles creates static electricity in the cloud. Over time, opposite charges build
between the top and bottom of the cloud, and the bottom of the cloud and the earth. When these opposing charges become intense,
a gigantic spark occurs (lightning) which jumps the gap between the cloud and the earth. The thunder accompanying lightning is
the noise produced by the discharge.
Hurricanes - are high speed windstorms accompanied by torrential rains. They begin over the ocean where air rising from warm
seas creates a severe low pressure zone. This zone draws air to it with such force the winds rotate around the core (the eye) at up
to 185 mph. The 'eye' averages about 20 miles in diameter while the hurricane may be up to a few hundred miles in diameter.
After the onset of a hurricane at sea, the storm moves slowly toward one of the poles and loses force as it moves into cooler areas
or over land. Hurricanes are usually predicted by meteorologists well in advance of their occurrence.
Tornadoes - One of the most destructive natural phenomena, tornadoes are swirling winds that spin at phenomenal speeds of up to
400 mph. Like hurricanes, they are caused by severe low pressure zones that attract winds with force. They have relatively small
bases, a fact which greatly magnifies their destructive power. Tornadoes are difficult to predict and often strike without warning.
Meteorologists expect to be able to predict a tornado in the near future.
Waterspout - are tornadoes over water which draw up large columns of water. If a waterspout moves from sea to shore, expect
fish and other sea creatures to rain down!
Dust Devil -' are small tornadoes over land that draw up dust and light debris. They are most common in desert areas.
Sundog - are mock suns that appear to the left or right of the sun when it is low on the horizon. They are caused by light refracted
through ice crystals present in cirrus or cirrostratus clouds.
Rainbows - are caused when sunlight penetrates raindrops and is broken into bands of red, orange, yellow, green, blue, indigo and
violet. You can simulate a rainbow easily by placing your back to the sun and looking through the mist of a lawn sprinkler.
Aurora Borealis - is caused when atomic particles from space react with atoms high in the atmosphere. Visible from Canada and
the northern United States, auroras illuminate the night sky with pulsing curtains of colored light.
Do any of these sound familiar to you? Here are their meanings...




"Red sky at night, sailor's delight. Red sky in morning, sailor take warning." (Red sunsets are usually followed by dry
nights. A red morning sky means rain is on the way.)
"A sun-shiny shower, won't last half an hour." (Showers that happen while the sun shines are brief.)
"Mackerel sky and mare's tails make tall ships carry low sails." (Certain clouds are often followed by high winds.)
"Coming storms cause shooting corns." (Aches and pains are aggravated when a storm approaches.)