those general trends mentioned above are subject to much
Even a small change to the atmosphere in one place can grow large
affect other areas.
The old saying about the beat of a butterfly’s wing on one side of the
glob affecting the weather on the other side is, to an extent true.
The general pattern of convection, causes lower air to flow towards the
while that in higher layers (jet stream) flows towards the poles is
affected by air pressure, humidity, clouds, and rainfall.
Water vapor makes up a large proportion of the atmosphere.
As a result the water cycle has a significant effect on the weather
Clouds insulate the earth’s surface from the sun, helping to regulate
As we all know, the clouds are formed by water vapor evaporating from
surface of the ocean and the warmer the air the more moisture it can
However, this evaporation also cools the surface water and as the water
condenses into cloud or mist the air is cooled.
Also, as the air rises the atmospheric pressure falls allowing it to
cool as the clouds are formed.
As the temperature and moisture and pressure alters between one place
another winds are generated.
On a weather map the pressures are shown by isobars, the closer they
together the greater the pressure gradient, and the stronger the winds.
And in their turn the winds accelerate the rate at which all these
influences move across the surface.
Tropical storms resulting from rapid changes in the tropics can
cause dramatic weather effects over huge areas of the globe.
Local topography will also have an affect on conditions.
The land heats up and cools down more quickly than the sea, so during
air rises over the warm land and is replaced by cooler air flowing in
And where the coast rises the moist onshore winds are forced upwards,
vapor then condenses to form a line of cloud along the coast.
The global effects we have
looked at so far are north south (longitudinal) effects.
However, these are then affected by the Earth's rotation.
This is known as the Coriolis Effect.
This Coriolis Effect or force is the apparent deflection of the
viewed from the rotating earth's surface.
As the earth spins on its axis, we who are stuck to its surface go with
atmosphere however isn’t so well stuck to the surface so it lags
However the atmosphere isn’t completely independent of the earth, it is
also affected by gravity and friction, more so in the lower layers.
The result is that the latitudinal air movement begins to be rotated as
Coriolis Effect comes into play.
And this is how those typical circulating weather patterns are formed
they appear to be deflected eastwards.
The global circulation is basically the same in both hemispheres,
are differences due to the different distribution of land and sea, the
amount of land mass in the northern hemisphere being yet another
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