LAB:Atmospheric and Ocean Circulation

Lab Objectives

• 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 temperature change?

August Air Temperature

January Air Temperature

Questions Continued

• See current Sea Surface Temperatures (SST’s) at: http://www.ssec.wisc.edu/data/sst/latest_sst.gif

• An animation of recent SST anomalies is at: http://www.cdc.noaa.gov/map/clim/sst_olr/sst_anim.shtml

• The diagram at right is data from the NOAA satellite TIROS, which measures long-wave radiation emitted from the Earth’s surface and atmosphere.

• 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 -30ºC.

• 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 the oceans?

6. Is it greater or smaller?7. How does the low heat capacity

of rock influence the seasonal temperature variation of the continents?

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 atmospheric circulation?

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 and winter.

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 pressure systems.

• 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 picture.

Check #14 & Answer 15-1914. 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 CoastJuly: 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 America? 

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 Asia?

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

season?

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.

Ocean Circulation • 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 circulation.

• 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).

Gyres

• So, given a westward displaced gyre, which currents flow fastest and strongest, the eastern boundary currents or the western boundary currents?

• Click the image to the right to help answer the question.

Salinity Variations • The difference between annual

precipitation and evaporation can explain the longitudinal (N_-S) variation in salinity, but explains less of the latitudinal (E-W) variations.

• How might surface water circulation patterns influence surface salinity values as shown to the right?

• 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 your worksheet.

Click on Image to Answer #31

• The diagram to the right shows SSTs for the Monterey Bay Region.

• Note that upwelling, as denoted by the cold regions, occurs at specific areas along the coast.

• Note, the upwelling does not coincide with the location of canyons.

• Based on the shape of the coast line, why does upwelling principally occur along these certain stretches of coastline?

Ocean Circulation and Biologic Productivity.

• 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 productivity.

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 productivity).

• 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

El Niño• Recall: El Niño is defined as the warming of the eastern equatorial Pacific. • 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

SST Anomalies• 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 temperature-depth profiles in the equatorial Pacific.

• These two figures show the development of the 1997-98 El Niño event.

• Click on the figures to the right to answer questions 41-44.

Normal Year in 1999

• Click on the pictures to the right and answer questions 45-46.

Historical Records of El Niño Events

• This diagram shows a historical record of ocean temperatures from Peru, where El Niño was first named.

• Remember that upwelling refers to deep, cold water rising closer to the surface.

• 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 saltywater 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.

References

• http://www.mpcfaculty.net/alfred_hochstaedter/Earth%20Science/circlab.htm