atmosphere is circulating around our planet and doesn’t stay still. causes of
circulation due to air pressure difference which is due to energy given by sun to
different latitudes
tri-cell model: equator, sun shines directly and warms earth’s surface, warm air
rises creating area of low pressure. in sub tropics, air sinks as colder and denser
then returns to tropics to replace rising air, circulation called Hadley cell.
polar cell is same, warm air rises at lower latitudes and moves pole ward, when air
reaches polar areas, its cooled and descends as a cold dry high-pressure area.
cell between polar and Hadley is called Ferrell. only exists because of other two
cells and mirrors other cell movements. transfers warm air
to high latitudes and shifts cold air back to subtropics
where it’s warmed.
equator is the start of the circulation and the equator isn’t
actually referring to line of latitude but the true thermal
equator (hottest place on earth) and moves depending on
time of year. January = south Africa and Australia. July =
Sahara, north India and Mexico
does pattern of high and low pressure stay same all year
round? air pressure varies depending which hemisphere.
varies more from season to season in northern hemisphere
compared to southern as more ocean in southern and
oceans don’t vary in pressure or temp as much as land
does. one variation in southern hemisphere is the sub-tropical high over
Australia/south Africa is broken in summer. one variation in northern hemisphere is
that in winter there’s still the sub-tropical high but in summer land breaks this up
and low pressure occurs over continental areas such as south Asia.
theories on air circulation…
wind and air pressure variations: rising air creates low pressure and air descending
creates high pressure. tri-cell model causes there to be bands of high and low
pressure across certain latitudes. global winds blow from high to low pressure,
blow at an angle rather than straight (Coriolis effect). deflection of moving object
caused by rotation of earth, deflects moving objects to the right of their course in
northern hemisphere and left of their path in southern hemisphere.
