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Weather Systems
Circulation Cells

Insolation is greatest at the equator,
humidity is high, the airmass is unstable.
 The cold air at the poles is more dense, so
there is a pressure gradient of about 1 in
8,000 toward the poles.
 Air rising at the equator moves towards the
poles down the pressure gradient.
CORIOLIS EFFECT.

Earth's rotation produces a force on
winds and currents. The force is
perpendicular to the wind and current. It
acts to the right of the flow looking
downstream in the northern
hemisphere. This effect is referred to as
the CORIOLIS EFFECT.
Hadley Cells

Convection in the tropics is deep and massive.
Large amounts of latent heat are released in the
towering cumulus clouds of the tropical
atmosphere, providing further driving for the
upward motion. At the top of the tropical
troposphere (12-15 km), the atmosphere is stable
and the upward motion is brought to a halt. This
forces the air to diverge poleward on both sides of
the equator.
Hadley Cells

The further the poleward moving air gets
from the equator, the larger the Coriolis
force, and the air begins to deflect to the
right (in the Northern Hemisphere) and left
(in the Southern Hemisphere). The result (in
both hemispheres) is an eastward flow of air
(westerly winds). The further poleward we
go, the stronger the westerlies become, till
we reach the jet stream latitude.
Polar Front

At the polar front the cold dense air
undercuts the warm tropical air pushing it
upwards, setting in motion the process that
causes weather fronts
Formation of fronts

Some air from the mid latitude Hadley cell
runs northwards at the surface and meets
cold polar air flowing South, forming a
polar front which circles the planet
 At this boundary a sharp gradient in
temperature occurs between these two air
masses, each at very different temperatures.
Jet Stream

The jet stream is a narrow snaking tube of
strong winds associated with the polar front.
 It has a significant effect on the formation
of fronts and and the track of depressions
Wind

This all has the effect of creating areas of
high and low pressure and moving the
airmass to create wind.
 Variations in atmospheric pressure channel
the wind like hills and valleys. The air tries
to flow from high to low pressure
 The flow is affected by the Coriolis affect.
Highs and Lows

In the northern hemisphere wind blows anti
clockwise into a low pressure. It rises and
flows outward at altitude.
 The wind blows clockwise at altitude into a
High and the descends and flows out at the
surface.
Fronts

A weather front is a boundary separating
two masses of air of different densities, and
is the principal cause of meteorlogical
phenomena
Cold Fronts

Cold fronts may feature narrow bands of
thunderstorms and severe weather, and may
on occasion be preceded by squall lines or
dry lines.
 Cold fronts and occluded fronts generally
move from west to east,

Warm Fronts

Warm fronts are usually preceded by
stratiform precipitation and fog. The
weather usually clears quickly after a front's
passage. Some fronts produce no
precipitation and little cloudiness, although
there is invariably a wind shift.
 warm fronts move poleward

Speed

Because of the greater density of air in their
wake, cold fronts and cold occlusions move
faster than warm fronts and warm
occlusions. Mountains and warm bodies of
water can slow the movement of fronts.
Occluded front 1
Occluded Front
Occluded Front
Warm Sector

This is the area between a leading warm
front and a trailing cold one.
 The cold front moves faster than the warm
front, and catches it up
 Away from the low pressure there is a
chance of good weather
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