EAR 203
Name: ______
Date: ______
Block: _____
EAR 203 EARTH SYSTEM SCIENCE
SYRACUSE UNIVERSITY
LAB 5D- ATMOSPHERIC AND OCEANIC CIRCULATION
OBJECTIVE
The main goal of this lab is to reinforce the concepts learned about atmospheric and oceanic circulation, and to explain how these two processes are strongly inter-dependent and strongly influence each other.
PROCEDURE
You will use the website to access the color images for this lab, since color makes the information much easier to see. All images on the websites are thumbnails, so that clicking on them will bring you to larger versions. The diagrams are reproduced here on these pages so that you can use them to write notes and remember the pertinent points of this lab.
Atmospheric Circulation
The diagrams to the left shows 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 20C contour in August?
2. At what northern latitude is the 20C contour in January?
3. Describe howocean temperature changes with the seasons?
4. How does the high heat capacity of water influence this seasonal temperature change?
See current SSTs at:
Animations of recent SST anomalies are at:
The diagramsto the left are 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 0C. The darkest purple represents temperatures near -30C. The top diagram is for August and the bottom diagram is for January.
5. How does the seasonal temperature variation of the continents compare with that of the oceans? Is it greater or smaller?
6. How does the low heat capacity of rock influence the seasonal temperature variation of the continents?
7. 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 the differences in seasonal temperatures affect atmospheric circulation?
Below 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 60 (N or S), whereas high pressure systems are most often located near 30 (N or S).
Focus on the differences between summer and winter. Complete the following table by showing whether the region has high or low pressure during the summer or winter. Follow the North America example.
Location / July / JanuaryNorth America / LOW / HIGH
South America
Asia
Africa
North Pacific
South Pacific
North Atlantic
South Atlantic
Indian
W Equatorial Pacific
E Equatorial Pacific
8. 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? To answer this question we need to understand how thePressure 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 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.
Draw on the mapsbelow the wind directions you would predict from the location of high and low pressure systems:
Check your answers by clicking o the August wind stress and January wind stress maps, or the North America maps.
Based on your predictions, complete the tablefor wind directions that you would feel if you were standing on the west coast or the east coast of North America:
Location / East Coast / West CoastJuly: Winds from (N or S)
Air temp (warm/cool)
January: Winds from (N or S)
Air temp (warm/cool)
9. Which has a more moderate climate, the east coast or the west coast of North America?
10. Is this true for other continents? Why or why not?
11. Air masses attain their characteristics from the surface over which they flow. Which month would you predict the rainy season occurs in India and the rest of continental Southeast Asia?
12. When is the dry season in India and the rest of continental Southeast Asia?
TRY THIS: The Aleutian Low-Pacific High Today
Look at today's satellite images here. Click on the Pacific region to see a more close-up image of that area.
13. Which is more predominate today, the Aleutian Low or the Pacific High?
14. What is it that you see on the satellite image that makes you say this?
15.Does your assessment agree with what you would predict for the current season?
Draw a generalized picture of today's high and low pressure systems in the Pacific in the space below. 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 the map below, draw the major surface currents of the world’s oceans.
Label the following currents and gyres on your map:
Currents / GyresThe 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
The Sub-Tropical Gyres
The Coriolis effect causes water to pile up in the middle of these 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 not in the center of the ocean basins; instead, because of the eastward rotation of the Earth, they are displaced westwards (the earth rotates out from under them, so to speak).
16. Given a westward displaced gyre, which currents flow fastest and strongest - the eastern boundary currents or the western boundary currents?
17. Explain your answer. You can use the image to the left to help.
Salinity Variations
18. 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 below? Specifically, why isn’t the surface water off the coast of California as salty as in the middle of the north Pacific at 30N?
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.
The diagram below shows a map on the left and a cross section on the right. Assuming a north wind as shown on the map, draw in the direction of surface currents and deeper water currents on the cross section.
19. How does your diagram show evidence for upwelling? Would you expect the upwelled water to be warm or cold?
The diagrams to the left shows SSTs and bathymetry for the Monterey Bay region. Note that upwelling, as denoted by the cold regions, occurs at specific areas along the coast, and that it does not coincide with the location of canyons.
20. 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.
21. Why do high concentrations of nutrients and plankton at the surface correspond to zones of upwelling?
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.
22. Examine the coasts of the continents. In general, which coasts of continents have higher biologic productivity: the east coast or west coast? Why?
23. The centers of the subtropical gyres have the lowest biologic productivity values. Why?
24. Why do the equatorial regions have productivity values that are higher than the centers of the gyres?
The data in this section comes from SeaWiFS, a satellite project that records the color of the ocean from space. Their home page is at
Check out this animation of changing chlorophyll values:
El Niño, La Niña, or La Nada
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 (fig to left), high pressure dominates in the eastern equatorial Pacific, low pressure dominates in the western equatorial Pacific (see figs at beginning of exercise), 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.
Current Equatorial Pacific SST and SST anomalies are at
An animation of recent SST anomalies is at:
A cool El Nino animation is here:
Everything you could ever want to know about El Nino/La Nina is here:
25. Are we currently in an El Niño, La Niña, or La Nada? How do you know?
Whereas the previous figures showed actual sea surface temperatures (SST), 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.
26. Why would warmer water produce a sea-level height anomaly?
27. Considering the above figures, are there any signs of an El Niño event in the inferred SSTs in March of 1997?
28. As the El Niño event developed in October of 1997, what happened to the SSTs in the western Equatorial Pacific?
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 diagrams show the development of the 1997-98 El Niño event.
29. What are the axes on the upper diagrams?
30. What are the axes on the lower diagrams?
31. What is the difference between the upper and lower diagrams?
32. Where within the oceans are the largest temperature anomalies during October of this particular El Niño event? Is it on the surface or lower?
These set of diagrams show the situation in 1999, a more “normal” year.
33. Are there any major anomalies anywhere? If so, where?
34. What do these results imply about upwelling during El Niño events?
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.
35. During what time of year does upwelling occur in Peru?
36. During what years in the past have there been other El Niño events?
37. Why would it be useful to plot the ocean water temperature at 60 meters depth, as has been done in the lowermost plot?
The diagram to the right is for Monterey Bay. It shows temperature and salinity profiles contoured against time from a mid-Monterey Bay location. The lowermost diagram is a measure of density, which is calculated from temperature and salinity.
38. Draw arrows that show upwelling events on these diagrams.
39. During what time of year does upwelling occur in Monterey Bay? Why is it not the same time as in Peru?
40. Does upwelling bring higher salinity or lower salinity water to the surface?
41. Can you find the 1997-98 El Niño event on the Monterey Bay record? Label it.
42. Can you find the 1991-92 El Niño event on the Monterey Bay record? Label it.
43. During which time of year is biologic productivity likely to be highest in the Monterey Bay area?
One question that remains is why deep Monterey Bay water is saltier than surface Monterey Bay water. There are at least 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.
44. Which one of these possibilities is more likely to be correct? Please explain why.
All the Monterey Bay data comes from Francisco Chavez’ Biological Ocean Group at MBARI:
He has compiled lots of time series data of Monterey Bay chemistry:
A location map of his permanently moored CTD stations is at:
Lab 5D – Atmospheric and Oceanic Circulation Page 1