Download Unit 9 Atmospheric Circulation and Hurricanes

Unit 9 Atmospheric Circulation and Hurricanes
9.1 Air Circulation

We can’t understand the oceans without understanding the atmosphere.

Both the oceans and atmosphere are _________ that constantly interact

Currents, wind, and waves all result from the interaction of ocean and atmosphere.
What do you remember from Physics about convection?

______________ is the movement of __________ through fluid movement (gases and liquids)

Convection currents move in air and water because of differences in _____________

Warm fluids ___________ because they are less dense

Cool fluids ___________ because they are more dense
Convection is what causes wind

_________ are currents of air

Wind develops whenever two adjacent bodies of air have different
___________ (measured in air pressure)

Wind always blows from areas of _________ pressure to areas of
________ pressure
Convection is how the earth moves heat from the equator to the poles

Why is the equator hotter than the poles?

Not because it’s closer to the sun, but because of its ___________ to the
sun.

Each ray of sun is more __________________ at the equator because it
heats a __________ area of land and because it has less atmosphere to
travel through
All that heat at the equator must go somewhere or the oceans would boil!

In a simplistic model of the earth’s circulation…

hot air _______ at the equator and drifts towards the poles

__________ from the poles drifts towards the equator to replace the hot rising
air

Two simple convection cells are, formed, one for each hemisphere
But we also have to account for the spinning earth!

The speed at which the earth is spinning depends on where you are between the
equator and poles

Here in Waco we are moving at 1400 km/hr
Imagine a missile shot from the pole or equator

Objects moving towards the equator deflect left

Objects moving towards the poles deflect right
Why does the missile curve?

From your perspective the missile shot from the pole appears to curve to the ______

In reality the missile traveled in a _____________ and the earth moved while it was in flight

The missile shot from the equator was already moving to the right at 1700 km/hr

As it travels north it continues to move to the right at 1700 km/hr while the earth under it is moving _________
as it moves toward the pole so it appears to curve to the _________.
How does the earth’s rotation affect the winds?

Just like the missile…

Air moving towards the poles deflects to the _________

And air moving towards the equator deflects to the __________
Three convection cells form in each hemisphere – The Hadley Cell

At the equator (also called the intertropical convergence zone) hot humid air rises, drops its moisture as rain,
and drifts towards the poles at high altitude.

It gradually becomes cooler and more dense and finally sinks at about 30° latitude (called the _______ latitudes)

The cool air then moves back down along the surface towards the equator.

The air moving towards the equator deflects west creating the _________ winds

Sailors call the equator “the __________” because the rising air produces weak, light, shifting winds
The Polar Cell

The Polar Cells are located between 60° and 90° N and S latitudes.

At 60° the air is still warm and moist enough to ________ and drift towards the pole

Like the Hadley Cell, the dense polar air drifts down along the surface and deflects west

This forms the winds called Polar ___________ (moving from east to west)

Winds are named for the direction they are coming ____________
The Ferrel Cell

Between the Hadley and Polar Cells the cycle ________.

Some descending air at 30 ° from the Hadley Cell shifts
to the poles, and some of the rising air at 60 ° from the
Polar Cell shifts to the equator forming the Ferrel Cell

Because the surface air is moving in the ___________
direction as the Hadley and Polar Cells, it deflects
towards the ___________

This pattern results in the winds called “Prevailing
____________” (moving from west to east )
9.2 Hurricanes – Nature’s Fury
What exactly is a hurricane?

A hurricane can best be described as a huge tropical storm (up to ______ miles in diameter)

Winds can be up to _______ mph!

Storm usually doesn’t last for more than 7-10 days

It moves across the ocean at around ________ mph….not too fast reallyl.

The winds are strongest around the _________. The eye of the storm is usually about 20 miles in diameter.

Within the eye, winds are calm and the weather is great.

Strongest winds are on the ________ side, heaviest rain is usually on the ________ side.

FACT: The energy contained in a single large hurricane is greater than that generated by all energy sources in
the United States over the past 20 years.
Scary….So when do I need to watch out for these things?

The “hurricane season is just a name for the time period when we expect to see tropical systems develop. The
hurricane season in the Atlantic Basin runs from ____________ to ____________________.

Peak season is the middle part of September. Why do you think that is?
So where do hurricanes form?

All hurricanes form in the _______________________________________ (ITCZ)

The ITCZ is an area of low pressure located roughly _____degrees North and South of the Equator. It is a place
where air converges, rises, and condenses (forming clouds). It is the ______________ place on Earth!

Storms of the Atlantic Basin will begin forming in one of three places
o
Off the coast of ____________ (around the Cape Verde Islands)
o
In the ____________________
o
In the __________________
So what does a hurricane need in order to develop?

Warm ocean water (more than _____ F) provides energy fro the hurricane and causes more evaporation making
humid air and clouds

Winds coming together forcing air upward

Winds flow outward above the storm allowing the air below to _________

Humid air rising makes the ___________ of the storm

Light winds outside the hurricane steer it and let it _________

So a hurricane needs warm water, time to grow, and favorable upper level winds in the troposphere. If the
winds are too strong, they will blow the hurricane apart—we call that _____________.
Evolution of a hurricane --Stages
Stage 1 – Tropical Depression: Usually has begun its life off the west coast of Africa in the ITCZ. Tropical
depressions have winds of less than 39 mph and are not given a name.
o
Tropical depressions lack structure. No well-developed feeder bands or __________.
Stage 2 – Tropical Storm: At this point the tropical storm is beginning to develop some serious structure.
Winds range from 40-73 mph. In the Atlantic, storms are given a name when they reach this stage.
o
________________ are beginning to develop. You can see the center of the low pressure system more
easily. the Eye and eye wall are still not well formed.
Stage 3—Category 1 Hurricane: Winds range from 74-94 mph
o
Well developed feeder bands. An eye begins to form (although it is covered in clouds). Storm is
___________ around it center.
Stage 4—Category 2 Hurricane: Winds range from 95-110 mph.
o
Well developed feeder bands. An eye and eye wall are usually very well formed. Storm continues to
tighten around its center.
Stage 5—Category 3 Hurricane: Winds range from 111-130 mph.
o
Now considered a “_________ Storm” Intense flooding and building damage will occur to most areas
on the coast. Further inland, the damage will still be substantial.
Stage 6—Category 4 Hurricane: Winds range from 131-155 mph.
o
All shrubs, signs, and trees blown down. Complete destruction of _______________ homes. Extensive
damage to doors and windows. Major damage to lower floors of structures near the coast.
Stage 7—Category 5 Hurricane: Winds greater than 156 mph!

o
Complete roof failure on many residential and industrial buildings. Some complete building failures with
small utility buildings
o
Massive evacuations of residential areas within ____________ miles of the coastline may be required.
Saffir-Simpson Scale of Hurricane Intensity (Ranks Hurricanes from Category 1 through 5 depending on wind
speed)
Storm Surge

The sea level rises in front of a hurricane because of the wind and low atmospheric pressure system

Storm surge is greatest on the ___________ side of a hurricane (in the Northern Hemisphere)

Most hurricane damage is due to storm surge not winds.
Hurricane Naming System –Why do they have names anyway?

In 1953 the National Weather Service began naming storms after ___________.

In 1979, _________ names were added to the list of hurricane names.

In the Atlantic, there are ________ lists of names that are recycled.
 In the case of storms so devastating that reusing the name is inappropriate, the name is taken off the list and
another name is used to replace it. The name “_____________” is one that will be removed from the list.