Download The Atmosphere and Winds

Oceanography 10, T. James Noyes, El Camino College
8A-1
The Atmosphere and Winds
We need to learn about the atmosphere, because the ocean and atmosphere are tightly
interconnected with one another: you cannot understand what is happening in one without
understanding what is happening in the other. For example, the atmosphere’s winds push water
around, causing ocean currents and waves. Ocean currents shift around the warm and cold water
that produces winds, and ocean water evaporates, giving the atmosphere the moisture needed to
produce “weather” like storms and rain.
In this section, you will learn about one cause
Convection Cells
of winds. The key concept in this section is
A convection oven is an oven in which the hot
the concept of a “convection cell.”
air circulates instead of just rising to the top, so
it cooks food more evenly than a normal oven. Typically a fan is used to keep the air in motion.
A convection cell is also air (or another fluid like water) circulating, but its motion is caused by
changes in its density 1. Sunlight travels through the atmosphere, warming the surface of the
Earth (both the land and the ocean). Some places, though, become warmer than others.
The air above warmer places is warmed by the
Earth, while the air above cooler places is cooled
(tricky, huh? try to keep up ☺), and this imbalance
in temperature is what sets the air in motion. The
warmer, lower-density air rises over the “warm
spot,” and the cooler, higher-density air sinks over
the “cold spot.”
Remember: warming air makes its molecules
move faster. This helps the warm air
molecules push outwards (push aside the
neighboring air molecules), allowing them to
spread and thus lowers their density. The
opposite happens to cold air molecules.
High Altitude Winds
The cold air slides away from the cold
place, replacing and lifting up the warm air.
The warm air pushes aside the air that was
above it, moving it towards the cold place
to replace the air that is sinking there.
Basically the air ends up moving in one big
“circle” or loop.
This, though, is not the end of the story:
The cold air will be warmed by the warm
place on the surface of the Earth, and the
process will repeat again. And again. And again.
Surface Winds
Warm
Cold
Ocean
The air moving horizontally is what we call “wind.”
This is how the major winds of the world are created!
You might be wondering why some places on the Earth become warmer than others. A classic
example, a “sea breeze,” results from our old friend “heat capacity” (see your 4A notes). Both
the land and ocean are warmed by the Sun, but the land becomes warmer than the water owing to
its lower heat capacity. (When water is heated, its temperature only goes up a little bit.) As a
result, the air over the land rises, and cool air from ocean comes in to replace it, a “sea breeze.”
1
It is a “cell,” because the air is trapped in one place, like a criminal walking around their cell, unable to actually go
anywhere.
Oceanography 10, T. James Noyes, El Camino College
8A-2
The opposite happens at night. Both the land and ocean radiate heat into space, but when the
land gives up heat, its temperature drops a lot more than water, so the land becomes colder than
the ocean. The air over the ocean is not warm, but it does have a lower density than the cold air
over the land, so the air over the ocean rises, and cold air from the land moves out to the ocean to
replace it, a “land breeze.”
Sea Breeze
Land Breeze
Wind
Wind
Warm
HOT
Cool
COLD
Notice that the ocean warms up too during the day in the picture above. The land is
warmer, so the air over the land has a lower density than the air over the ocean. Similarly,
both the land and ocean cool down at night, but the land gets colder. Technically speaking,
it is not warm air that rises, but the lowest density air in the environment.
The goal of this entire section is for you to understand the overall motion of the atmosphere: the
pattern and its causes. Here’s your first step: Where is air warmer, at the Equator or the Poles?
Clearly, air is warmer at the Equator. Therefore, air rises at the Equator and sinks at the Poles,
and the cool air from the Poles will slide to the Equator to replace the air rising at the Equator.
In other words, surface winds tend to blow away from the Poles and towards the Equator.
The picture on the right is two pictures in one
(in a way).
The view is from outer space above the Equator. The
green arrows within the globe are giving you a bird’seye-view of the winds that are blowing over the surface
of the Earth.
The red, green, and blue arrows on the side of the globe
are showing you what the air is doing vertically as well
as horizontally (i.e., the convection cells).
Note that the red arrow at the Equator represents air
moving “up,” and the blue arrows at the Poles
represent air moving “down.” “Up” means away from
the surface of the Earth, and “Down” means towards
the surface of the Earth. (Do not describe them from
your own perspective. The world does not revolve
around you! ☺) Similarly, “North” means towards the
North Pole (the high altitude green arrows), and
“South” means towards the South Pole (the low
altitude green arrows).
This is how the winds would blow if it were not
for one teeny tiny little fact: the Earth rotates!
(90o N)
North
Pole
60o N
30o N
Surface
Winds
Equator (0o )
30o S
60o S
South
Pole
(90o S)
Oceanography 10, T. James Noyes, El Camino College
8A-3
The Coriolis Effect
As you probably know, the Earth is not stationary: it is rotating/spinning/turning around its axis 2
once per day3. This leads to a phenomena known as the “Coriolis effect:” objects traveling over
the Earth bend off course. This happens because moving objects go straight forward while the
Earth is turning beneath them. As the Earth turns, the directions north, east, south, and west
change (see the figure below), but moving objects continue going in their original direction 4; in
other words, an object moving north continues to move towards the “old” north, not the “new”
north that results from the Earth’s rotation. To you and me and other stationary objects on the
Earth, it looks like nothing has changed except the direction of moving objects, because
everything travels with us 5. Moving objects do not bend off course because they are changing
direction, but because we and our point of view (the north-east-south-west arrows) are moving
with the rotating Earth.
E
North
Pole
North
Pole
N
N
E
W
S
Earth
turns
towards
the East
W
S
I will not ask you to explain how the Coriolis effect
works in detail, but I do expect you to be able
understand a few things about how it works:
• Objects bend off course to their right in the northern hemisphere
• Objects bend off course to their left 6 in the southern hemisphere
• The Coriolis effect is stronger near
the Poles (weaker near the Equator) 7.
The bird’s-eye-view maps on the right show
the directions that the winds bend under the
influence of the Coriolis effect. (Hint: If
this confuses you, turn the paper so that the
wind – the arrow – is pointing away from
you, then your “right” and the wind’s “right”
will be the same!)
2
North
South
East
East
West South
The green arrows show the directions that
the winds "want" to go, and the black arrows
show how they are bent off course by the
Coriolis effect.
An imaginary line drawn from the North Pole to the South Pole.
The Earth turns towards the east. This is why the Sun comes up in the east.
4
Think of your own experience: If you throw something like a ball, it keeps going in the direction you threw it.
5
We don’t realize how fast we are moving, because the motion is so smooth; we don’t feel speed – does traveling in
an aircraft at 400 mph feel any different from traveling in a car at 50 mph? – we feel acceleration or “bumpiness.”
6
As you can see from the picture, the wind really bends in the “same” direction. They only appear to be different in
each hemisphere because one person’s right is the other person’s left.
7
Here is a way to think about it: the Equator is not in the northern hemisphere or the southern hemisphere, so
objects don’t bend left or right. In other words, there is no Coriolis effect on the Equator.
3
Oceanography 10, T. James Noyes, El Camino College
8A-4
There are a few more things that you should know about the Coriolis effect.
The Coriolis effect is only significant for objects that travel a large distance (or a long time)
over the surface of the Earth. Therefore the Coriolis effect is not an important factor in everyday
situations; it does not cause “curve balls” in baseball or the direction that water goes down your
sink or toilet 8. To achieve pin-point accuracy, our military needs to take the Coriolis effect into
account when they fire shells or missiles more than a mile. Airplane pilots who fail to adjust for
the Coriolis effect end up in the wrong city!
Important: The Coriolis effect does not cause winds, just like it does not cause a missile or
airplane to move. All the Coriolis effect only changes the direction of whatever is moving.
What does causes winds? If you are not sure, review the section on “Convection Cells” starting
on page 1.
Coriolis Effect: A More Advanced Explanation
(You do not need to read and understand this section.
It is for students who want to understand the Coriolis effect in more detail.)
The Coriolis effect arises because objects become too fast or too slow for their new latitude. The Earth and
every object on it are constantly moving, because the Earth rotates (spins) all the way around each day. The
closer you are to the Equator, the faster you are moving, because you are farther from the center of the “circle”
(the Earth’s axis, which hits the surface at the North Pole). If an object begins traveling north, its momentum
to the east (from its old latitude) will be too fast, carrying it a bit too far to the east. If an object begins
traveling east, it has become too fast for its current latitude and so spirals outward, away from the North Pole,
as the Earth turns but the object moves “too straight.”
If you are "above" the North Pole looking
down, an object going north towards the
North Poles is going from a latitude where
the ground is moving faster to a latitude
where the ground is moving slower (the
Pole itself rotates, but the ground doesn't
move anywhere, so it has a speed of 0). The
object keeps the momentum to the east that
it has from the "faster" latitude where it
began, so it is going faster to the east than
its new latitude, causing it to bend off
course to the east (to its right).
If an object is in the Southern Hemisphere
and going north, it is heading to the Equator,
where the ground is moving the fastest. The
object is moving too slowly to east, so the
ground gets ahead of it, and the object bends
off course to the west (to its left).
Notice that I apply the same reasoning in
both hemispheres.
8
unless you have a VERY large toilet in your house
Oceanography 10, T. James Noyes, El Camino College
8A-5
The Global Wind Pattern 9
(Figure 6.12 on page 174 in your textbook)
Winds and currents are named for the
direction that they come from, not
the direction that they are going to,
so the westerlies come from the west
and blow towards the east.
(90o N)
North
Pole
Polar Easterlies
o
60 N
Westerlies
o
30 N
The Coriolis effect causes the extra
Trade Winds
convections cells and the winds that go
“backwards” between 30oN/S and 60oN/S.
Equator (0o )
As the air tries to move from the Poles to the
Equator, it is bent off course towards the
Trade Winds
west. The problem is that the farther the air
30o S
travels, the more it gets turns off course. At
Westerlies
some point, it is no longer heading north or
south, and therefore it cannot make any more
60o S
progress towards the Equator. Instead it rises
Polar Easterlies
South
up at this new latitude. The air at 60oN/S is
Pole
not warm (it is in Canada), but it is warmer
(90o S)
than that air at the Poles, so its density is low
enough to rise at this latitude. Similarly, after
air rises at the Equator, it moves north towards the Poles, cooling down as it travels. It is bent
towards the east by the Coriolis effect, and at 30oN/S cannot move any farther towards the Poles.
The air at 30oN/S is not cold (it is close to southern California), but it is colder than the air at the
Equator, so its density is high enough for it sink at this latitude.
Air is always pushed away from the place where it sinks and towards the place where it rises.
Between 30oN/S and 60oN/S, the air is forced to move in another convection cell by the sinking
air at 30oN/S and the rising air at 60oN/S, respectively. Notice that these “middle” convection
cells are the reverse of the convection cells by the Equator and the Poles; they move in the
opposite direction.
You need to memorize the global wind pattern shown above. I suggest that you memorize
the directions of the trade winds: they both blow towards the Equator and towards the west.
This should not be too hard to remember, because the Equator is the warmest place in the world:
the air on the Equator rises, so the nearby air moves toward the Equator to replace the rising air.
As the air moves towards the Equator, it is bent off course by the Coriolis effect. In the northern
hemisphere the air moving south goes to its right, and the in the southern hemisphere the air
moving north turns to its left: in both cases, the air turns towards the west. Once you have the
trade winds memorized, the other winds are a “piece of cake:” the westerlies are the opposites of
the trade winds, and the polar easterlies are the opposites of the westerlies (same as the trade
winds).
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Even this picture of the global wind pattern is a gross oversimplification. The winds shift with the seasons as the
warmest spot on the Earth shifts north and south of the Equator and the land becomes warmer or cooler than the
ocean. (For example, see figure 6.13 on page 176 of your textbook.) All this complexity contributes to the weather
patterns that we experience every day, our next subjects.
Oceanography 10, T. James Noyes, El Camino College
8A-6
Clouds, Rain, and Pressure
Air mainly consists of oxygen molecules and nitrogen molecules. Remember that warm
molecules move faster than cold molecules. This allows warm air molecules to push aside
nearby molecules and spread out, which lowers their density and causes them to rise.
As you’ll recall, atmospheric pressure is caused by the weight of the air above. Thus, up in the
mountains, air pressure is lower, because there is less atmosphere above you (less air pressing
down on top of you).
Therefore, as warm air rises higher into the atmosphere, it experiences lower pressure. Since the
group of warm, rising air molecules are no longer being squeezed together as strongly by the air
above, the group of warm, rising air molecules can now push outward (i.e., the warm air expands
as it rises). However, in pushing outward against the neighboring cooler air molecules, they give
their energy to the neighboring air, causing the warm, rising air to cool down.
Experiment: Blow into your hand. First, keep your mouth opening small, then open wide as if yawning. In
which case does the air feel warm? In which case does it feel cool? When the opening is small, the air is
forced together, and quickly expands once outside your mouth.
If the water molecules in the air
cool down enough, they will
begin to bond with one another.
(The water molecules are no
longer moving fast enough to fly
apart when they get to close to
one another and strong hydrogen
bonds form between them 10.)
Thus, rising air produces cloudy
and rainy skies 11. As the rising
air cools down more and more,
it loses its water as rain. By the
time the air reaches the location
where air sinks, it is completely
dry; dry air cannot produce
clouds or rain.
water has
fallen out
as rain
lower
pressure
low
pressure
mountain
high
pressure
If the locations of clouds & rain and clear skies do not make sense to you, then you might skip
ahead to “Weather, Climate, and Fronts” where I try to explain why the explanation above may
seen inconsistent with your own experience – but is not.
10
In most situations water vapor needs additional help from aerosols – tiny solid particles like dust or drops of liquid
in the air – to condense: it is easier for water molecule to bond with big, slower-moving objects. The kind and size
of aerosols available can have a big impact on whether clouds form and rain occurs – and how much rain occurs.
11
Moist, humid air has a lower density than dry air, and rises higher than dry air. When water evaporates from the
ocean and enters the atmosphere, water molecules push aside other, heavier air molecules via collisions, thus
reducing the density of the air it is mixed with (but the neighboring dry air becomes more dense). In addition,
remember that water has to lose a lot of heat before it will cool down or condense into rain (put another way, water
has more heat – a higher heat capacity and latent heat – than other substances), so the water molecules’ heat helps
keep the air warm in spite of the cooling that occurs as air rises, allowing the air to rise higher than it otherwise
would.
Oceanography 10, T. James Noyes, El Camino College
8A-7
Typically this cooling of rising air (called adiabatic cooling) does not cause the group of rising
air molecules to become more dense and sink. Why not? Think about how the air became
cooler: as a side-effect of expanding owing to lower atmospheric pressure. At this point in the
class, most of my students know the following: if it is becomes colder, it becomes more dense,
so it sinks. This is true most of the time in the ocean, but it is only part of the story in the
atmosphere: pressure is also an important factor 12. If the group of rising air molecules cools by
expanding (by spreading out, by becoming larger), then their density is not going up: they are
spreading out! This is why
the air up in the mountains is
High Altitude Winds
Clear
colder and stays colder (think
Skies
of the snow that covers the
peaks of mountains), even
though you might expect it to
sink down to sea level: the
lower pressure on the air
High
Low
Surface Winds
molecules allows them to
Pressure
Pressure
spread out, keeping their
density low. Incidentally, this
Warm
Cold
is why the air at high altitudes
is “thin” (harder to breathe,
Ocean
“thin” = “low density”).
Beneath regions of warm, low-density, rising air, the pressure at the surface of the Earth is lower
(fewer air molecules above), and beneath regions of cold, high-density, sinking air, the pressure
at the surface of the Earth is higher (more air molecules above). (Another way to think about
this: if the air is rising – going up – it is not pressing down very hard, and if the air is sinking –
going down – it is pressing down harder.) Thus, lower air pressure at the surface is associated
with cloudy & rainy skies, and high pressure is
associated with clear skies. (Just listen to
(90o N)
North
weather forecasters on the news!)
Clear
Pole
I expect you to memorize the global rainfall
pattern, shown on the right, as well as the global
wind pattern. If you know where surface winds
come together and the air rises, then you know
where it rains. Similarly, where surface winds
move apart, air sinks, and the skies are clear.
It is worth noting that often winds cannot reach all
the way from the high pressure (“sinking, cold air”)
place to the low pressure (“rising, warm air”) place,
because they are bent off course by the Coriolis
effect. As a result, winds of spiral out of regions
of high pressure and into regions of low pressure.
(See figure 6.14 on page 177 of your textbook.)
12
Pressure is also important in the ocean,
but it is much less important than temperature and salinity.
60o N
Rainy
30o N
Clear
Equator (0o )
Rainy
30o S
Clear
60o S
Rainy
South
Pole
(90o S)
Clear
Oceanography 10, T. James Noyes, El Camino College
8A-8
Mountain Effect
Air can rise for many reasons. For example, when winds hit mountains they are forced upwards to
get up and over them. As the air rises, it cools and water vapor in it condenses into clouds are rain.
If winds tend to come from one direction, the side of the mountain facing the winds gets lots of rain,
so it tends to have lots of vegetation. This is why Palos Verdes (a hill by the coast) can often be
quite foggy. The side facing away from the wind is gets very little rain (the moisture fell on the
other side), so it tends to be dryer and more desert-like.
About 70% of our water in California comes from snow that falls in our mountains. If we did not
have mountains stretching from north to south, we would have a lot less water in California.
Weather, Climate, & Fronts
Up till now, we have been discussing climate, not weather. Climate is the long-term average of
weather conditions (what the weather is usually like). For example, Southern California has a
warm, dry climate. This does not mean that it is always warm (we have our cooler days) or that
it does not rain in Southern California; it means that our weather is warm most of the time and
that rain is less common here than elsewhere. Another way to think about it: weather is what
conditions are like a particular day, climate is what conditions are like over a season or a year.
Your own experience of actual storms and rain may contradict something that I said before:
warm, rising air leads to clouds and rain. Many of you will say: wait a minute, the weather is
cold when it rains!
Before:
After:
Storms often form along what meteor-ologists
Warm Air
call “fronts,” a place where 2 “air masses” meet.
An air mass is a collection of air with similar
Cold Air
Warm Air
Cold Air
properties (e.g., temperature, moisture), often
determined by where it comes from. For
example, warm, moist air moves up into the
United States from the Gulf of Mexico, while
cool, dry air comes down from Canada. We also use the word “front” to describe the location
where two opposing armies meet and are shooting at one another. As in the military, the
frontlines typically are where the action is (clouds, rain, hail, snow, etc.) in the atmosphere. At
the locations where air masses meet (the “front”), the cooler air pushes the warmer air up, sliding
in underneath to replace it, or the warmer air can move up and over the cooler air.
As the warmer air rises, it becomes cooler, and if the change in temperature is strong enough and
the rising air contains enough moisture, the water vapor in the rising air will condense into rain.
If the warmer, rising air does not contain water, there cannot be rain along the front.
Thus, the weather is cooler when it rains, because cooler air is coming in and lifting up the
“warmer” air. (Remember, the “warmer” air might not be very warm, it is just “warmer” than
the cooler air on the other side of the front.)
Oceanography 10, T. James Noyes, El Camino College
8A-9
The Heat Balance of the Earth and the Seasons
In this section, you will learn why temperature changes with the seasons, why some parts of the
world are warmer than others, and how the motion of the ocean and atmosphere keep the warm
places from getting too hot and the cool places from getting too cold.
The Equator is warmer than the Poles, because it receives more heat from the Sun. Sunlight
shines directly down upon the Equator, but approaches the Poles at an angle. As a result,
sunlight is spread out over a wider area at the Poles (It is less “concentrated,” so these places are
colder.) In addition, sunlight that
Spread Out
comes in at an angle is more
likely to get reflected back into
space (the white snow and ice at
North
the Poles help a lot too) rather
Pole
than absorbed, and passes
through more of the atmosphere
Sun
(which absorbs a little bit more
Equator
light than normal).
Concentrated
Experiment: Get a flashlight. Hold your hand flat with your fingers pointing towards
the ceiling. Hold the flashlight horizontal and shine it on your hand. Now, tilt you palm
upwards towards the ceiling. What happens to the circle of light on your hand? You can
see how sunlight is spread out at the Poles because it strikes the surface at an angle.
These factors also help explain
why some parts of the year are
warmer than other parts of the
year (in other words, why we
have seasons). Notice how the
Earth is “tilted” relative to the
Sun; the Earth’s North Pole
always points towards a star
we call Polaris (creative,
huh?), also known as the
“North Star.” So, as the Earth
orbits (travels around) the Sun,
its tilt never changes 13.
Location of the Warm Spot?
Earth
N. Pole
Equ
ato
r
Actually, the Earth’s tilt wobbles
very slowly in a small circle over
thousands of years.
Equ
ato
r
Sun
S. Pole
S. Pole
Northern
Hemisphere
Winter
Northern
Hemisphere
Summer
Earth
13
N. Pole
Sun
Earth
Oceanography 10, T. James Noyes, El Camino College
8A-10
During our summer, the northern hemisphere is tilted towards the Sun, so we get more sunlight
and become warmer. The southern hemisphere, on the other hand, is tilted away from the Sun,
so it gets less sunlight and becomes cooler. It takes the Earth 1 year to travel all the way around
the Sun, so in 6 months, the Earth will be on the other side of the Sun. The tilt does not change
(it always points towards the north star, Polaris), so now the northern hemisphere is tilted away
from the Sun. We get less sunlight during this part of the year, so it is our winter.
The temperature of a place is not merely a matter of how much heat it receives, because if an
object only gains heat, then it continues to get hotter and hotter. Objects also lose heat by
conducting it to the neighboring environment (for example, your hand if you touch a cold
surface) or radiating it away as infrared “light” (invisible to us because our eyes cannot capture
it, but we can feel its heat when we get close to a hot object). Irrespective of how the heat is lost,
the basic rule of heat loss is:
The hotter an object is,
the more heat it gives off.
(Rocket science, huh?) As an object gives away heat, it cools down, and therefore it gives away
less and less heat over time. This is kind of like someone who suddenly receives a lot of money:
at first, they spend it freely (after all, they have plenty), but if they keep this up, sooner or later
they are forced to lower their spending if they don’t want to be left with nothing. Even frozen
objects give off heat, and therefore get even colder! (They just get colder slower and slower.)
Fortunately for us, the Earth does not run out of heat, because it gains more heat each day from
the Sun. Every moment of the day and night, the Earth gives away heat to the atmosphere (via
conduction) and radiates the rest towards outer space as infrared “light” (electromagnetic waves).
The heat given to atmosphere is eventually radiated into space too, helped by the fact that warm
air rises upward (transporting the heat
Most of the atmosphere is made of nitrogen and
through the greenhouse gases like carbon
dioxide that absorb infrared “light,” trapping oxygen. Carbon dioxide, water vapor, and all the
other gases in the air combined only make up
its heat in the atmosphere and keeping our
about 1% of the atmosphere!
planet from becoming a giant ball of ice!).
The Poles are colder than the Equator, so they give off less heat than the Equator, but they still
radiate heat into space. Interestingly, observations 14 show that the Poles give off more heat each
day than they receive from the Sun. Similarly, the Equator radiates less heat into space then it
receives from the Sun. If the Poles are sending away more heat than they receive, they should
get colder, and if the Equator sends away less heat than it receives, it should get warmer. But, of
course, they are not getting warmer or colder; their temperatures are stable (global warming
issues aside). An object’s temperature is stable (does not increase or decrease) if the amount of
heat it receives is exactly equal to the amount it gives away (just like how your bank account
won’t go up or down if the deposits are exactly equal to the withdrawals).
14
from satellites looking down, for example.
Oceanography 10, T. James Noyes, El Camino College
8A-11
The temperatures of the Poles and Equator are not increasing or decreasing, because the ocean
and atmosphere are moving (“transporting”) heat from the Equator towards the Poles (so the
Equator has less to “spend” and the Poles more to “spend”). In convection cells, the cool air
moves away from the “cold spot” and towards the “warm spot.” The air then warms up at the
“warm spot,” and rises (absorbs heat from the “warm spot,” cooling it down). Similarly, the
“cold spot” cools the air above it. In other words, heat goes from the air to “cold spot,” warming
the cold spot. Thus, the air moving in the convection cell is cooling down the “warm spot” (the
Equator) and warming up the “cool spot” (the Poles). As we will see in the next lecture, the
ocean does the same thing by moving warm water from the Equator towards the Poles and cool
water from the Poles towards the Equator.
The movement of water between the ocean and atmosphere also plays an important role in
transporting heat from low latitudes (e.g., the Equator) towards high latitudes (e.g., the Poles).
Warm ocean water evaporates under the clear skies of 30oN/S (e.g., southern California), moving
heat from the ocean into the atmosphere. (Remember: the “hot,” fastest-moving water molecules
tend to be the ones that evaporate.) Some of the air moves towards the Poles in the winds called
the “westerlies” (the convection cell between 30oN/S and 60oN/S). The air gives up its heat to
the cooler ground beneath (e.g., Seattle), causing the water to condense into clouds and rain.
Thus, the motion of the atmosphere keeps the Poles from becoming too cold and the Equator
from becoming too hot. As the air moves, it carries the heat away from the hot places and moves
cold air away from the cold places. The motion of the
Who would want to live
ocean – the ocean currents – performs a similar job,
in Canada if it were even colder and
making the Earth a much more pleasant place to live.
in Mexico if it were even warmer?
Oceanography 10, T. James Noyes, El Camino College
8A-12