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 MPH700 MPH

You land in the same spot.

700 MPH

700 MPH

700 MPH

700 MPH700 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 2 3

0% 0%0%

1. It should hit the target.2. It will hit West of the target3. It will hit East of the target.

• 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?

55o

35o

Radius of Earth

Rad

ius

of E

arth

Distance to rotation axis

• 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?

55o

35o

Radius of Earth

Rad

ius

of E

arth

2270 miles

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.

• So, from outer space the cannon ball has a sideways component.

600 MPH East500 MP

H S

ou

th

Real Velocity

• 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 2 3

0% 0%0%

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.

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 2 3 4

0% 0%0%0%

1. It is too hot for a Hadley cell to form2. There is no Coriolis Effect on Venus3. Venus is rotating the opposite

direction4. Venus doesn’t have water clouds so

the effect is different

• 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

Earth surface

Equator Northward

Hadley Cell Ferrel CellNorthward

Equator

HIGH PRESSURE

High Pressure region in the Northern Hemisphere.

What will happen as the air leaves this region?

North

Equator

H

.

1 2 3

0% 0%0%

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.

High Pressure region in the Northern Hemisphere.

Coriolis Effect bends the air flow.

North

Equator

H

High Pressure region in the Northern Hemisphere.

Air circulation is clockwise around a high pressure region.

North

Equator

H

High Pressure region in the Southern Hemisphere.

What will happen as the air leaves this region?

South

Equator

H

High Pressure region in the Southern Hemisphere.

Rotation is counter-clockwise for high pressure.

South

Equator

H

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.

Equator

L

North

• What about low pressure in the Northern Hemisphere?

.

1 2 3

0% 0%0%

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.

In Northern Hemisphere, low pressure systems rotate counter-clockwise.

L

Equator

North

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