The Global System's Effect on Climates
The global pattern of climate is affected by:
* land and sea
* ocean currents
The Equator receives greater amounts of solar heating than latitudes
further north or south. Places therefore nearer the Equator are much
warmer than those closer to the Poles. Nearer the Poles precipitation
will be more variable with lower temperatures. More will fall as snow,
covering the ground for long periods in winter.
The amount of solar energy received by each hemisphere varies because
of the tilt of the Earth and its orbit around the sun. This gives
summer and winter seasons. Places nearer the Poles have greater
differences between summer and winter in temperature and
At the Equator air, warmed from below, becomes less dense and is
forced to rise as strong convection currents, creating low pressure at
the surface (ITCZ). Convectional currents of warm, moist air cool to
give heavy, daily thunderstorms
Strong, steady winds converge to fill the low pressure from the north
and south, but the spinning of the Earth diverts the winds slightly to
the right in the northern hemisphere and they become the north-east
Trade Winds. In the southern hemisphere winds are diverted to the
left, producing the south-west Trade Winds.
Air in the upper atmosphere flows away from the Equator and cools.
Cooling air becomes denser, heavier and descends back to the surface
on the polar sides of the 'Cell', causing zones of high pressure at
about 30° north and south of the Equator (sub-tropical high pressure
zone). Descending air warms and becomes drier, skies are cloudless and
hot desert areas are found in these latitudes.
The ITCZ or low pressure zone moves north and south with the overhead
sun. In June there will be low pressure (ITCZ) over the Tropic of
Cancer (23.5°N). Warm, moist Trade Winds from over the Atlantic Ocean
bring heavy summer rains. In December when the overhead sun is south
of the Equator the sub-tropical high pressure zone moves south over
the Tropic of Cancer. The hot descending air gives a winter dry
Around 60° north and south of the Equator the global circulation of
air produces another zone of low pressure, where warm tropical air
from the south west converges with cold polar air. Depressions form
and at the fronts warm air is forced to rise over the cold...