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					INTRODUCTION:

  As the sun shines on the earth different parts of the land and sea heat
  at different speeds. This results in high and low pressure areas and
  leads to the lift and fall of air masses across the entire globe. Due to
  the angle of the earth while rotating the majority of the heat falls upon
  the middle of the world (equator) and much less towards the ice caps
  of the northern and southern hemisphere this means that as the warm
  air rises on the equator the cold air is pulled in from the ice caps. This
  spreads the warmth across the globe and results in moving air
  patterns.
  To describe air movement across the globe the earth should be viewed
  as six areas. Two polar areas that are covered by Polar Easterlies, two
  Horse latitudes that produce the Westerlies and two Trade wind areas
  that produce the North East and the South East Trade winds. Various
  names have been given to these winds over the years but names like
  The Roaring Forties and the Prevailing Westerlies are still common
  today.

  Wind blows because of these air masses becoming warmer than
  others. In warm air the tiny particles are spread out. So a mass of
  warm air in the same space is lighter than cold air. As warm air rises
  cold air moves in to take its place this movement is the wind blowing.
are the general trends in wind movement around the world. They are
the result of the difference in heat across land masses and bodies of
water.

 3-Cell Model
1) TRADE WINDS

 are huge global patterns of wind trend that over the
 years have been harnessed for use as trade routes.
 These winds are a result of the cold polar regions, the
 suns heating and the spin of the earth all combined. To
 be more specific, the trade winds are those that blow
 towards the equator from the subtropics or Horse
 latitudes. In the Northern Hemisphere they are the
 North East Trade winds and in the Southern Hemisphere
 they are the South East Trade winds. The reason for this
 change of direction around the equator is the spin of the
 earth and the resulting Coriolis effect. Where the two
 winds meet is generally very still and calm air and this
 we call the Doldrums.

 In both hemispheres, it’s also the winds that blow from
 30 degrees latitude from the equator.
CORIOLIS
As the world turns, it has an effect on every thing upon it and
the air masses are not safe from this influence. If we attempted
to draw a top to bottom line on a spinning ball we would see the
effect that the spinning has on the movement of the pencil. The
line would be curved.

The Coriolis effect is very similar, only instead of a pencil line we
have twisting and cyclonic weather fronts and prevailing winds
and trade routes. The French physicist Gasper de Coriolis was
the first person to mathematically prove this theory.

2) Doldrums and Horse Latitudes

 Trade winds of Northern and Southern Hemispheres meet in an
 area of low pressure around      the equator is called the
 DOLDRUMS. Sinking air creates an area of high area is called
 HORSE LATITUDES. Here the winds are weak.
 3) WESTERLIES

Wind belts found in both the Northern and Southern Hemispheres
between 30 degrees and 60 degrees latitude. They flow toward
the poles in opposite direction of the trade winds.
Both sets of Westerlies are the result of being trapped between
the increasing pressure of the Horse latitudes and the falling
pressure at the edge of the polar caps.
It blows mainly from the southwest in the northern hemisphere and
the northwest in the southern hemisphere, bringing moist weather to
the west coast of the landmasses in these latitudes.
Fig. 1. Primary circulation cells and prevailing wind belts of Earth.
4) Polar Easterlies

Wind belts that extend from the poles to 60 degrees latitude in
both hemispheres. They are formed from sinking, cold air
moving from the poles toward 60 degrees north and 60
degrees south latitude.

Each polar cap has its own set of Easterlies. In many respects
they are a replica of the Northeast and Southeast trade winds as
they take their directional flow from the resulting actions of
Coriolis.
Poor 3-cell model
 5) Jet Streams
 are bands of very strong winds which occur at limited altitudes
(generally in the 30-40000 feet area). They can be over 150
miles wide and 1000 miles long and can travel at over 250 mph.
Like most winds they occur when there is a contrast between hot
and cold, and in the jet streams case this means around the
joins of tropical and polar air.
Narrow belts of high speed winds that blow in the upper
troposphere and lower stratosphere. Local Winds: An area's
geography for example a mountain or a shoreline sometimes
produces temperature differences that cause local winds like
land and sea breezes.
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, just under the tropopause. 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 major jet streams are westerly winds (flowing west to east) in
both the Northern Hemisphere and the Southern Hemisphere. 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 Ross by waves provides the
accepted explanation for propagation of the meanders; Ross by waves
propagate westward with respect to the flow in which they are
imbedded.
Global Energy Balance

The surface energy balance is the resultant of radioactive components
such as incoming and outgoing short-wave and long-wave radiation,
and also non-radioactive components such as sensible heating, latent
heating, and the change in energy storage in water or substrate on
land. The following animations show radioactive and non-radioactive
components which emphasize the latitudinal and seasonal variations of
solar input and surface-atmosphere energy exchange.

•Radioactive Components

Net short-wave radiation = short-wave down - short-wave up.
Net long-wave radiation = long-wave down - long-wave up.
Net radiation = net short-wave radiation + net long-wave radiation.
Positive values represent energy moving towards the surface,
negative values represent energy moving away from the surface.
Net Short-Wave Radiation




                           Net Long-Wave Radiation
Net Radiation




                Short-Wave, Long-Wave and
                Net Radiation
•Non-Radiative Components

Sensible heat flux = direct heating, a function of surface and air
temperature.
Latent heat flux = energy that is stored in water vapor as it
evaporates, a function of surface wetness and relative humidity.
Change in heat storage = net radiation - latent heat flux - sensible
heat flux.
Positive values for sensible and latent heat flux represent energy
moving towards the atmosphere, negative values represent

 Sensible Heat Flux
Latent Heat Flux                  Change in Heat Storage




 Sensible Heat, Latent Heat, Change in Storage and Net Radiation
Temperature
Seasonal temperature variations can be explained in terms of the
latitudinal and seasonal variations in the surface energy
balance. The pattern of temperatures are a function of net short-
wave radiation, net long-wave radiation, sensible heat flux, latent
heat flux and change in heat storage.

Seasonal variations in surface temperature

                      Air Temperature
Global Water Balance
The water balance is the inflow, outflow, and storage
of moisture on the earth's surface. The source of
inflow is precipitation, outflow is evaporation and
runoff, and an example of storage is soil
moisture. The following animations are examples of
the seasonal cycle for inflow, outflow and storage of
moisture as part of the global water balance.

 Precipitable water vapor is a measure of available
 moisture in the atmosphere.
 Precipitation rate is the actual measurement of
 precipitation at the surface.
 Precipitation-Evaporation (P-E) represents the
 difference between precipitation and evaporation.
 Runoff/Water surplus are measurements of
 outflow of moisture.
 Soil moisture represents the pattern of storage of
 moisture at the surface.
Perceptible Water Vapor              Precipitation Rate




                    Precipitation - Evaporation
Runoff/Water Surplus
                       Soil Moisture
Hadley cell and ITCZ
N2
     Submitted to: Ms. Tess Consulta

				
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posted:1/10/2011
language:English
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