Transcript of "Atmospheric and Oceanic Circulation"
Atmospheric and Ocean Circulation
• to learn about atmospheric and oceanic
circulation and how these two processes
are strongly inter-dependent and strongly
influence each other
Mark Answers on Answer Sheet
• The diagrams to the right show
average sea surface temperatures
(SST) for August and January. The
diagrams are also contoured with lines
of equal temperature.
1. At what northern latitude is the 20ºC
contour in the August?
2. At what northern latitude is the 20ºC
contour in the January?
3. Does the ocean temperature change
radically with the seasons?
4. How does the high heat capacity of
water influence this seasonal
August Air Temperature
January Air Temperature
• See current Sea Surface Temperatures
(SST’s) at: http://
• An animation of recent SST anomalies is
• The diagram at right is data
from the NOAA satellite
TIROS, which measures long-
wave radiation emitted from
the Earth’s surface and
• This kind of radiation is
related to the surface
temperatures on Earth.
• Green and blue colors
represent temperatures below
0ºC. The darkest purple
represent temperatures near
• You will use the data to the
right to answer questions 5-8.
Questions (Click on Image for Help)
5. How does the seasonal
temperature variation of the
continents compare with that of
6. Is it greater or smaller?
7. How does the low heat capacity
of rock influence the seasonal
temperature variation of the
8. How will the differences between
the seasonal temperature
variations in the oceans and
continents affect the locations of
high and low pressure systems in
the atmosphere? Another way of
asking this question is: How will
these differences affect
Click on the Image to Answer #9 & #10
• To the right are average atmospheric
pressure maps for summer and winter.
• Contour lines of equal atmospheric
pressure (isobars) are also shown. In a
very broad sense, low pressure systems
are most often located near the equator
and near 60º, whereas high pressure
systems are most often located near 30º.
• Focus on the differences between summer
9. Complete the table on your answer sheet
by showing whether the region has high or
low pressure during the summer or winter.
Follow the North America example.
10.Why do you think the southern hemisphere
oceans show less seasonal variation in
terms of atmospheric pressure than do the
northern hemisphere oceans?
Which way do the winds blow? Use
for Questions 11-13.
• To answer this question we need to
understand how the Pressure
Gradient Force (PGF) and the
coriolis effect interact to create
circular wind patterns around high
and low pressure systems.
• The PGF is the force that pushes
air away from high pressure
systems and pulls it towards low
• The coriolis effect (caused by the
earth’s rotation) deflects this
moving air, to the right in the
northern hemisphere and to the left
in the southern hemisphere.
• The result is that winds blow
counterclockwise around low
pressure systems and clockwise
around high pressure systems in
the northern hemisphere.
• Click on the images to see a larger
Check #14 & Answer 15-19
14. Draw on the big map (last page of handout) the wind directions that you would predict
from the location of high and low pressure systems.
• You can check your answers by clicking to see the August wind stress and
January wind stress maps, or the North America maps.
15. Based on your predictions, complete the table for North America for wind directions
that you would feel if you were standing on the west or east coast…
East Coast West Coast
July: Winds from (N or S)
Air temp (warm/cool)
January: Winds from (N or S)
Air temp (warm/cool)
16. Now, which has a more moderate climate, the east coast or west coast of North
17. Do you think this is true for other continents?
18. Air masses attain their characteristics from the ground over which they flow. When
would you predict the rainy season is in India and the rest of continental Southeast
19. When is the dry season in India and the rest of continental Southeast Asia?
The Aleutian Low – Pacific High
Today. Questions 20-23
• Look at today's satellite images here. Click on the Pacific region to see a
more close-up image of that area. Press “back” to get back here.
20. Which is more predominate today, the Aleutian Low or the Pacific High?
21. What is it that you see on the satellite image that makes you say this?
22. Does your assessment agree with what you would predict for the current
23. Draw a generalized picture of today's high and low pressure systems in the
Pacific. On your picture draw in and label all the examples of the Coriolis
effect that you can see. This current atmospheric pressure map may help
you identify the location of the high and low pressure systems.
• On your map handout, draw the major surface currents of
the worlds oceans, which should include:
– The California Current, North Pacific,The Kuroshio Current, South
Pacific,The Gulf Stream, North Atlantic, The Canary Current, South
Atlantic, West Wind Drift, Indian, The Peru Current (Note: All of these
are also called subtropical gyres) The North Equatorial Current,The
South Equatorial Current
– Use the next two slides to help you label.
The Sub-Tropical Gyres
• The Coriolis effect causes water to pile up in the
middle of gyres.
• The “hills of water” are small, only 2-3 meters
high, so you’d never see or feel them.
• Nevertheless, they do influence oceanic
• The center of the gyres are also not in the center
of the ocean basins.
• Because of the eastward rotation of the Earth,
they are displaced westwards (the earth rotates
out from under them, so to speak).
• So, given a westward
displaced gyre, which
currents flow fastest
and strongest, the
currents or the
• Click the image to the
right to help answer
• The difference between annual
precipitation and evaporation can
explain the longitudinal (N_-S)
variation in salinity, but explains
less of the latitudinal (E-W)
• How might surface water
circulation patterns influence
surface salinity values as shown to
• Specifically, why isn’t the surface
water off the coast of California as
salty as in the middle of the north
Pacific at 30ºN?
• Click on the image to the right to
help answer the above question.
Upwelling and Downwelling
• These diagrams show the various ways that upwelling and
downwelling can be created.
• Note that the situation in “A” could also be produced by winds
moving towards you out of the paper. These images will form
the basis for the answers to the following questions.
• Click on each image to help answer question #29 and #30 on
Click on Image to Answer #31
• The diagram to the right shows
SSTs for the Monterey Bay
• Note that upwelling, as
denoted by the cold regions,
occurs at specific areas along
• Note, the upwelling does not
coincide with the location of
• Based on the shape of the
coast line, why does upwelling
principally occur along these
certain stretches of coastline?
Ocean Circulation and Biologic
• Organisms need nutrients to live.
• Thus the availability of nutrients determines the location
and abundance of organisms, especially those at the
base of the food web such as plankton.
• The location of plankton blooms in the oceans can be
identified by satellite because the plankton contains
chlorophyll and appear as different colors to sensitive
satellite instruments such as the Sea-viewing Wide Field-
of-View Sensor (SeaWiFS).
• In general, high concentrations of nutrients, and thus
plankton, correspond to areas of upwelling and high
Ocean Circulation and Biologic
Productivity ?’s 35-37
• Examine the map of global
chlorophyll concentrations (which
corresponds to plankton
concentrations and thus nutrient
concentrations and biologic
• As usual, reds and yellows are high
values, whereas blues and purples
are low values.
• The polar regions generally have
high plankton concentrations
because of the 24-hour light during
summer months in high latitudes.
• Click the image to the right to
answer questions 35-37.
Click on Image to See Animation of
Changing Chlorophyll Values
• Recall: El Niño is defined as the warming of the eastern equatorial
• Under typical conditions, the waters off the west coast of equatorial
South America is relatively cool (left figure), high pressure dominates in
the eastern equatorial Pacific, low pressure dominates in the western
equatorial Pacific, and the trade winds blow strongly to the west.
• During El Niño conditions (fig to right) the eastern equatorial Pacific is
abnormally warm, the low pressure system moves eastward, and the
trade winds weaken.
Normal Conditions El Niño Conditions
• These figures show sea-level height anomalies, from which SST
anomalies may be inferred.
• Anomalies are the difference between the observed sea-level height or
temperature and the normal (average) sea-level height or temperature.
• The white areas indicate sea level 13-30 cm (5-10 inches) above
normal. These figures show the development of the 1997-98 El Niño,
which is one of the strongest on record.
• Use the images below to help you answer questions 38-40. Click on
each image to make them larger.
25 March 1997 25 May 1997 23 October 1997
El Niño Continued
• To investigate some of
the causes and effects of
El Niño, it is useful to get
a 2-dimensional view of
the oceans by looking at
profiles in the equatorial
• These two figures show
the development of the
1997-98 El Niño event.
• Click on the figures to the
right to answer questions
Normal Year in 1999
• Click on the pictures
to the right and
answer questions 45-
Historical Records of El Niño Events
• This diagram shows a
historical record of ocean
temperatures from Peru,
where El Niño was first
• Remember that upwelling
refers to deep, cold water
rising closer to the
• Click on the picture and
answer questions 47-49.
Question 50 Answer on Sheet
• Why is deep Monterey Bay water saltier than surface
Monterey Bay water? There are at lest two possibilities:
1) Evaporation during the summer creates salty
water at the surface that then sinks.
2) The southerly flowing California Current
introduces low salinity over the higher salinity water.
Question 50 Which one of these possibilities is more
likely to be correct? Please explain why.