Transcript The Coriolis effect

Chapter VI: Air-Sea Interaction
Essentials of Oceanography, Thurman and Trujillo
Earth’s seasons
Earth’s axis is tilted 23½º
from vertical (tropic of
Capricorn/Cancer)
Northern and Southern
Hemispheres are alternately
tilted toward and away from
the Sun (6 months apart)
Earth is tilted the same
direction during entire sun
orbit (precession is the slow
turning of the direction)
Causes longer days and
more intense solar radiation
during summer
Earth Sun Animation
Figure 6-1
Uneven solar heating on Earth
Solar energy in high
latitudes:
Has a larger “footprint”
Is reflected to a greater
extent (albedo)
Passes through more
atmosphere
Is less than that received
in low latitudes
Temperature is
constant over longer
periods of time. Heat
must be transferred
from low latitudes to
high.
All weather is the
result of this transfer of
heat
Figure 6-1
Oceanic and Atmospheric heat flow
A net heat gain is
experienced in low latitudes
A net heat loss is
experienced in high
latitudes
Heat gain and loss are
balanced by oceanic and
atmospheric circulation
Net heat is the difference
between incoming
shortwave radiation (sun)
and outgoing longwave
(black body) radiation.
Figure 6-3
Table 6.2
Physical properties of the atmosphere: Temperature
Troposphere is:
Lowermost part of the
atmosphere
Where most weather occurs
Contains all earth’s surface
Temperature of troposphere
cools with increasing
altitude
Troposphere is ripe for
convection!
Stratosphere is:
contains ozone layer
Temperature of stratosphere
warms with increasing
altitude
Tropopause is the boundary
between the two
Figure 6-4
Physical properties of the atmosphere:
Density
Warm, low density air rises
(why heaters are near the floor)
Warm air holds moisture, as
it rises it cools, can’t hold
the same moisture, rains
Cool, high density air sinks
(why air conditioner outlets
should be near the ceiling)
Cold air can’t hold the
moisture. Descending air
warms, can hold more
moisture, doesn’t rain.
Creates circular- moving
loop of air (convection cell)
Figure 6-5
Physical properties of the atmosphere: Pressure
A column of warm, less dense air causes low pressure at the surface,
which will lead to rising air (High pressure above)
As air rises, air is replaced with air along the earths surface
A column of cool, dense air causes high pressure at the surface, which
will lead to sinking air (low pressure above)
Air moves horizontally from H go L pressure
Figure 6-6
Physical properties of the atmosphere: Water vapor
Cool air cannot hold much water vapor, so
is typically dry (Cool air is a HIGH pressure)
Descending air is cool (does not hold vapor)
Warm air can hold more water vapor, so is
typically moist (Warmer air is a LOW pressure)
Ascending air is warm (does hold vapor)
Water vapor decreases the density of air
(this is sort of strange, but water vapor is
light! H2O vs N2 vs O2)
So even if same temperature, wet air will rise
Physical properties of the atmosphere: Movement
Summer/day
Air INITIALLY flows
horizontally from highpressure regions toward
low-pressure regions
Moving air is called wind
Sea Breeze in San Diego
Winter/night
Figure 6.13
San Diego’s air
conditioner
Sea Breeze is quickly
reduced as you move
inland (and with it the
cooler temps)
So where is the High
Pressure ?
A hypothetical non-spinning earth
Figure 6.7
The Coriolis effect (force)
Newton’s second law: a body in motion
will continue in motion (unchanged)
unless acted upon
liquid (water) and gas (air) is not attached to
the ground so obeys this law.
We are ‘attached’ to the ground thus rotate
away from bodies that are unattached.
Causes moving objects to APPEAR to follow
curved paths:
In Northern Hemisphere, curvature is to right
In Southern Hemisphere, curvature is to left
A merry-go-round as an example of the
Coriolis effect

A merry-go-round is rotating at angular
velocity Omega (like Earth)
Throw a ball (it follows Newton’s law
and does not change direction or speed
once it leaves your hand)
To an observer above the merry-goround (not on earth), objects travel
straight (Path B or C)
To an observer on the merry-go-round,
objects follow curved paths. You rotate
away, but your sight is still into the
center of the merry go round)
The ball does not curve…you curve!
Internet video of balls being rolled
across a moving merry-go-round
If you have a some vorticity (spin) in the
direction of , coriolis will occur.
Figure 6-8
Planetary Vorticity (Component in the z (along axis) direction)
Standing at the pole, the earth
spins you around like an ice
skater. You have a large
vorticity given to you by the
earth [f= f0• sin(90)=f0]

=90o
 =30o
=0o
Step off the pole, you have
just reduced the component of
spin PARALLEL to the earth’s
axis…but not by much.
By 30o latitude you have
reduced your vorticity by 1/2.
[f =f0 • sin(30)=f0/2]
By the equator you have no
vorticity given to you by the
earth [f0•sin(0)=0]
The Coriolis effect
Changes with latitude:
No Coriolis effect at Equator (Recall
Vorticity is ZERO)
Maximum Coriolis effect at poles (Recall
Vorticity is MAXIMUM)
f is positive (curvature to right) in the
Northern Hemisphere (Recall Vorticity is
positive)
f is negative (curvature to left) in the
Southern Hemisphere (Recall Vorticity is
negative)
Missile paths demonstrate the Coriolis effect

The missiles do not change
path, you rotate (over your left
shoulder in the Northern
Hemisphere)
This occurs in all compass
directions (east and west as well)
As long as your vorticity
(spin) has a component
along the earth’s axis,
coriolis will occur.
Would you see this if the earth
was a cylinder?
Animation
Figure 6-9b
An ADDITIVE effect complementary to Coriolis

ONLY in N-S direction
As Earth rotates, different
latitudes travel at different
speeds
[Speed is v =  • r where
v: speed in the east
direction, r: distance from
the earth’s axis]
Missile will keep eastward
speed from the latitude it was
launched from as it moved to
other latitudes
What about a cylinder? A
cone?
Figure 6-9a
Table 6.3
Why don’t we see…….
….. coriolis when rolling a ball across a table?
The time is not enough for the rotation of the
earth to be important. Friction, inertia is more
important over short times.
Coriolis is a ‘weak’ force, it only becomes apparent
over a large amount of TIME!!!! A super-fast
missile will not see coriolis.
...coriolis in a toilet? No. It is too small and the
time of the flush is too fast.
How much time is necessary? 1/2 day to be
apparent
A hypothetical non-spinning earth
Figure 6.7
Wind belts of the world
Coriolis turns winds to
the right
Weird/Silly Historical
Legacy: In describing
winds the direction is
where the winds are
coming FROM
(atmospheric convention)
In describing ocean
currents the direction
is where the currents
are going TO
(oceanographic convention)
Figure 6-10
Global Wind
Animation
Table 6.4: Characteristics of the
Wind Belts and Boundaries
Evaporation/Precipitation Latitudes:
Comparison with winds
Figure 6.10
Figure 5.8
Surface Salinity
Figure 5.20
Surface salinity variation
Pattern of surface
salinity:
Lowest in high
latitudes
Highest in the
tropics
Dips at the Equator
Surface processes
help explain pattern
Figure 5-19
Coriolis effect influences air movement
right hand rule (northern hemisphere)
What about southern?
Southern Hemisphere questions are always good questions on exams,
if you understand the process involved you should be able to keep the
hemispheres straight.
Figure 6-12
Cyclonic
Animation
Weather Maps
Pressure Map
Wind Map
Weather Map
Pressure Map
H: Sinking air
L: Rising air
Precipitation Map
Air masses that affect U.S. weather
Figure 6-14
Sea-Level Mean Atmospheric Pressures in January
Figure 6.11 High pressure over continents/oceans in
winter/summer hemisphere; Low pressure over
continents/oceans in summer/winter hemisphere. WHY?
Weather Pattern Animation
Fronts:
Contact between cold and warm air masses
Regardless if the cold front is moving into warm air or if warm air
is moving towards cold; the warm air rises.
Cold air moving: produces a sharp front and REAL thunderstorms
L
Fonts animation
L
Weather maps
The cold front is the
dividing line
between warmer and
colder air masses.
In this case we have
cold air moving into
warm air. The warm
air is due to the high
pressure winds
coming from the SW
bringing warm
temps.
A very weak front.
Jet Stream
Area of fastest winds which travel around the north (and south)
poles.
The Jet Stream is high in the atmosphere
It ‘steers’ air masses about.
If you know where the Jet Stream is you can basically tell what
our weather will be.
http://squall.sfsu.edu/crws/jetstream.html
Origin and paths of tropical cyclones
Tropical cyclones
are intense low
pressure storms
created by:
Warm water
Moist air
Coriolis effect
Includes:
Hurricanes (western
hemisphere)
Cyclones (indian)
Typhoons (eastern
pacific)
Figure 6-16
Hurricane occurrence
Hurricanes have wind speeds of at least 120
kilometers (74 miles) per hour (tropical
storms below)
Worldwide, about 100 storms grow to
hurricane status each year
In the Northern Hemisphere, hurricane
season is generally between June 1 and
November 30
Current state of the tropical oceans
Is there a strong chance of SD experiencing
a hurricane?
Hurricane structure
Hurricanes have:
Circular cloud bands
that produce torrential
rain
The ability to move
into the mid-latitudes
A central eye
Low pressure
Figure 6-17
Hurricane
Animation
Figure 6-19a
Hurricanes produce storm surge
Storm surge:
Is a rise in sea level
coming ashore
Can be up to 12
meters (40 feet) high
Causes most
destruction and
fatalities associated
with hurricanes
Does it have to be a
hurricane?
Figure 6-18
Storm Surge
Other Storms can push water toward the downwind
side of lakes/bays causing flooding. Bays that are wide
at the entrance and narrow in the direction of the wind
are especially vulnerable. animation
Climate regions of the ocean
Figure 6-20
Why do temperate regions appear to extend further north (Northern hemisphere) on
the east side of the ocean? The Atlantic is the best example.
Short wave vs Longwave Radiation
Visible light is shortwave, Ultraviolet radiation is even shorter.
Infrared is longwave, and this is where the earth loses heat (night
vision goggles) Black Body radiation
How a greenhouse works (the greenhouse effect)
Sunlight passes through
the clear covering of a
greenhouse
It converts to longer
wavelength heat energy
(black body radiation)
Heat cannot pass
through the covering
and is trapped inside
Figure 6-23
Figure 6.24 The Earth’s Heat Budget
Anthropogenic gases that contribute to the
greenhouse effect
Greenhouse Gas
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Tropospheric ozone (O3)
CFC-11
CFC-12
Relative contribution
60%
15%
5%
8%
4%
8%
What was the percentage of CO2 in todays atmosphere?
Anthropogenic
greenhouse gases
What was the percentage of CO2 in
today’s atmosphere? Oxygen = ~21%
etc.
Carbon dioxide is increasing in the atmosphere
As a result of
human activities,
carbon dioxide in
the atmosphere
has increased by
30% since 200
years ago
Wait a
minute…why do
we think it is due
to humans?
Figure 6-26
Longer term CO2 history
Recent measurements are around 360ppmv. Do we now
have higher concentrations or are the methods used to get
the below type of time series flawed?
Earth’s average temperature is rising
Earth’s average surface
temperature has risen at
least 0.6°C (1.1°F) in the
last 130 years
Earth’s average ocean
temperature has
increased in the last 30
years… especially in
higher latitudes.
May be related to
increase in atmospheric
carbon dioxide
Lots of wiggles! Are we
sure!
LIKE Figure 6-27
Feedback:
A secondary change to a primary
change.
Negative- tends to counter the primary cause
Volcanos erupt emitting ash/soot into upper atmosphere, blocks incoming
sunlight
Ash emitted by coal burning (etc) does similar
Increased CO2, makes plants grow, removes CO2. Ash also creates particles
for water to condense around (clouds)
Positive- tends to amplify the primary cause
Ocean warms releasing additional CO2 to atmosphere Tundra melts releasing
additional CO2 to atmosphere.
Glaciers (Antarctica, Arctic?) melt releasing fresh water (light) shutting off
deep water formation which would have sequestered CO2
Medieval warm period and Little Ice Age in England
Variability of 1oC (but over ~300 years)
Predicted changes with increased
greenhouse warming
Higher than normal sea surface AND deep ocean
temperatures that could affect world climate
As oceans warm it releases more CO2 (assign)
More severe droughts or increased precipitation
Water contamination and outbreaks of water-borne
diseases
Longer and more intense heat waves
Shifts in the distribution of plants and animals
Potential melting or enlargement of polar ice caps
Is science sure of these?
Climate Change wrap-up
What we know for sure!
The process (science) of global warming is real. It has
happened throughout time and continues to this day.
We have pumped a great deal of Carbon Dioxide into the atmosphere since
the beginning of the industrial revolution.
The earth (ocean and atmosphere) has warmed since the industrial
revolution.
What we don’t know for sure!
Is the increase of temperatures due to us (we think so, or it is a
mighty big coincidence) or is this just natural variability.
What are the feedbacks (positive and negative) that will occur
as the earth warms
End of Chapter VI
Essentials of Oceanography
8th Edition
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