Lesson6b Atmosphere
Weather patterns on the Planets
Figuring out weather patterns.
• Here in Kentucky we are moving about 700
MPH, due to the Earth’s rotation on its axis.
• Which direction is the Earth turning?
• Here in Kentucky we are moving about 700
MPH, due to the Earth’s rotation on its axis.
• Which direction is the Earth turning?
• It turns from west to east. That is why the
sun comes up in the east.
Image a trip from Lexington to Rome, Italy and
back. Assume no wind on the trip.
Direction of
Earth’s
Rotation
• How does the Earth’s rotation affect this trip?
• (Remember we are not considering wind
effects here. Just imagine a windless day)
.
1. The trip to Rome will take
less time than the trip back
to Lexington.
2. The trip back from Rome
takes less time than the
trip to Rome.
3. No effect
• It has no effect.
• The plane flight is the same both ways.
• The plane before take-off is already moving
700 MPH, due to the Earth’s rotation. When it
is flying it is traveling around 500 MPH relative
to the ground plus the 700 MPH it had at take
off.
• Same thing for the return trip. When the
plane is flying back to Lexington, from outer
space the plane will appear to be moving 200
MPH to the East. Lexington is approaching at
500 MPH
• Ancient Greeks used this kind of idea to say
that the Earth was NOT rotating.
• What happens when you jump in the air?
• If you are in the air for one second, here in
Kentucky, the Earth would rotate underneath
you at 700 MPH.
• For one second you would land 300 meters to
the west. That’s 3 football fields.
You land in the same spot.
700 MPH
700 MPH
700 MPH
You land in the same spot.
700 MPH
700 MPH
700 MPH
You land in the same spot.
700 MPH
700 MPH
700 MPH
You land in the same spot.
700 MPH
700 MPH
700 MPH
700 MPH
You land in the same spot.
700 MPH
700 MPH
700 MPH
700 MPH
You land in the same spot.
700 MPH
700 MPH
700 MPH
700 MPH
Canada launches an attack on the Panama Canal
by firing a cannon ball. They aim directly at
Panama.
• Where will the cannonball land?
.
1. It should hit the target.
2. It will hit West of the target
3. It will hit East of the target.
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• The first thing we need to consider is the
rotation speed of the launch site in Canada.
• Let’s assume the launch site is at a latitude of
55o North.
• We know that everyone on Earth has the
same length day, 24 hours. But not everyone
is moving at the same speed.
• At the equator the rotational speed is
v = Circumference/time
v = 24,901 miles/24 hours = 1037 MPH.
• What about the Canadian launch site?
Distance to
rotation axis
35o
55o
Radius of Earth
• The radius of the circle that Canada is making is
given by:
Sin(θ) = (opposite side)/(hypotenuse)
Sin(35o) = (opposite side)/(Radius of the Earth)
Opposite side = (3959 miles)*sin(35o)
radius of circle for Canada = 2,270 miles.
• What about the Canadian launch site?
2270 miles
35o
55o
Radius of Earth
Speed at Canadian launch site
v = (circumference of circle)/length of day
v = (2π(2270 miles))/24 hours
v = 14,268 miles/ 24 hours
v = 594 MPH or about 600 MPH.
Panama is moving at about 1,000 MPH.
Now let’s see what this means.
From outer space.
• Let’s assume the cannon ball travels 500 MPH
and it was pointed due south.
600 MPH East
500 MPH South
Real
Velocity
• So, from outer space the cannon ball has a
sideways component.
• This wouldn’t matter if Panama was traveling
at 600 MPH also. By the time the cannon ball
arrives, Panama would have moved right into
the path. BUT Panama is moving at 1,000
MPH.
Missed to the
West.
What do we see on Earth?
• We know that Canada isn’t falling behind
Panama on the surface of the Earth.
Missed to the
West.
Panama returns fire.
• Panama laughs and thinks Canadians are a
bad shot. So they aim directly at the launch
site and fire due North.
• What will happen?
.
1. Panama will miss the
target and hit East of it.
2. Panama will miss the
target and hit West of it.
3. Panama will hit the
target.
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What do we see on Earth?
• Panama is traveling 1000 MPH and Canada
only 600 MPH.
Missed to the
East.
• The curved path that is witnessed on the
surface of the Earth makes it look like there is
a force pushing the cannon ball off course.
• This is often called the Coriolis “Force”. But
there is no force acting on the cannon ball.
The path is the result of us on the surface
thinking that we are not rotating. It is a
perspective issue. From outer space the path
makes perfect sense.
• Therefore, the correct name is the Coriolis
Effect.
• Note, the faster a planet rotates, the more
extreme the Coriolis Effect.
• Coriolis Effect video
Hadley
Cell
Motion
Hot air
on the
equator,
rises and
moves
North or
South.
Hadley
Cell
Motion
When it
cools it
sinks
down
and
heads
back to
the
equator
If we add a
little
rotation
the wind
motion
looks like
this.
Venus is rotating very slowly.
Venus is rotating very slowly.
• We would expect that the clouds moving
northward from the equator should bend to
the East. Instead they are bending to the
West.
• What’s up with Venus?
.
1. It is too hot for a Hadley cell to form
2. There is no Coriolis Effect on Venus
3. Venus is rotating the opposite
direction
4. Venus doesn’t have water clouds so
the effect is different
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• Venus has just two Hadley cells, one moving
North and one moving South.
• But Venus rotates slowly in the opposite
direction of the Earth. It actually spins
clockwise when viewed from the North Pole.
• This makes the Coriolis Effect reversed on
Venus.
On Earth the
rotation is
so rapid that
the Hadley
cell turns
east before
it reaches
the North
pole.
There are three major cells
• The Hadley Cell, that moves from the Equator
• The Polar Cell, that moves from the poles
• And the Ferrell Cell, (or mid-latitude cell) that
isn’t really a cell at all. It is the boundary
region between the Hadley and Polar cells.
This transition region is dominated by either
the Hadley or the Polar cells. It is turbulent
and has many different weather patterns.
The Ferrel cell
• Many things can happen between the
latitudes of 30o and 60o.
• For example, warm air from the south can
collide with cold air from the north. The warm
air can ride up on top of the cold air. And the
two streams will mix and produce turbulence.
• Or one cell can over power the other cell and
cause a front to move up into the Ferrel
region.
Downward flow of the Hadley cell
• In the region where the Hadley cell sinks, the
air pressure is normally high.
• High pressure in a region means that the air
tends to flow outward from the region to
places where the pressure is lower.
As air sinks into the more dense air near the
surface, it takes on the speed of the air in that
region
Northward
Hadley Cell
Ferrel Cell
HIGH
PRESSURE
Earth surface
Equator
Northward
Equator
High Pressure region in the Northern
Hemisphere.
What will happen as the air leaves this region?
North
H
Equator
.
1. The northern air flow will
bend east, and the southern
flow will bend west.
2. The Northern air flow will
bend west and the southern
air flow will bend east
3. The air will move straight
out of the region.
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High Pressure region in the Northern
Hemisphere.
Coriolis Effect bends the air flow.
North
H
Equator
High Pressure region in the Northern
Hemisphere.
Air circulation is clockwise around a high
pressure region.
North
H
Equator
High Pressure region in the Southern
Hemisphere.
What will happen as the air leaves this region?
Equator
H
South
High Pressure region in the Southern
Hemisphere.
Rotation is counter-clockwise for high pressure.
Equator
H
South
High Pressure regions
• High pressure regions on Earth are fair
weather regions.
• In order to form clouds, air currents must raise
up to altitudes where water vapor turns into
water droplets and forms clouds.
• High pressure stops the ability for these type
of air currents to form.
• The result is sunny weather.
Regions of low pressure in the Northern
Hemisphere.
• When a region develops where the air
pressure is lower than in surrounding regions
the air flow is into the low pressure region.
North
L
Equator
• What about low pressure in the Northern
Hemisphere?
.
1. The southern air flow will bend
west and the northern flow east.
2. The southern air flow will bend
east and the northern flow west.
3. The air will flow directly in, collide
and make a storm.
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In Northern Hemisphere, low pressure systems
rotate counter-clockwise.
North
L
Equator
Low Pressure Systems
• In the Southern Hemisphere, lows rotate
clockwise.
• Low pressure means that air is flowing into
the region and can develop air currents that
move upwards, where the air is cooler.
• When this happens, water vapor condenses to
from droplets and clouds form
Hurricane
Jupiter
Jupiter