ERTH 535: Planetary Climate Change (Spring 2018) Lab Activity #7 (For classes starting Monday, April 2) Dr. Dave Dempsey Dept. of Earth & Climate Sci., SFSU

(For access to color version of the maps in this activity, go to:
http://funnel.sfsu.edu/courses/erth535/S18/labs/act.07.SST_SSS.html)

## Global Patterns of Sea Surface Temperature and Salinity

Objectives:
• Become acquainted with global patterns of sea surface temperature (SST) and sea surface salinity (SSS) and how they vary seasonally.
• Pose hypotheses that might explain some features of these patterns.
• Become acquainted with global ocean surface circulation patterns, and use them to try to explain some features of SST and SSS patterns.
• Based on features of the ocean surface circulation and SST patterns, try to account for at least some of the imbalances in the long-term, zonal average radiative energy budget discovered earlier in the semester.
(1) Imagine dividing global sea-surface temperature (SST) patterns into warm, cool, and cold regions. Using the blank map attatched to the end of this document, lightly draw where you think the boundaries may lie between the warm, cool, and cold areas. Why did you choose to draw the boundaries as you did?

(2) The first two maps below (Figures 1(a) and 1(b)) show SST patterns during the months of February and August 2011, respectively. The next map (Figure 2) shows temperature differences between the two months (August minus February, 2011).

Figure 1(a): Monthly mean sea surface temperatures (°C) for February, 2011

Figure 1(b): Monthly mean sea surface temperatures (°C) for August, 2011

Figure 2: Difference between August and February 2011 sea surface temperatures (°C)

For the purposes of this activity, on Figures 1(a) and 1(b) (the February and August 2011 SST maps), define the boundary between warm and cool SST regions as the 24°C contour line, and between cool and cold SST regions as the 10°C contour line. Draw these boundaries on the February and August SST maps.

• How would you characterize the shapes of these boundaries?

• In what ways are the SST patterns similar among the three oceans and how are they different?

• In what ways are the SST patterns in the Northern and Southern Hemispheres similar, and how are they different?

• How do the boundaries vary seasonally?

• How do your predictions made in (1) compare with the patterns that you observe on these maps? What are the main differences, if any?

(3) Although for the most part SST isotherms are oriented east/west, as you might expect given the decrease in absorbed solar radiation with increasing latitude, you generally should note deviations or bending of the contour lines near the edges of oceans. Can you think of a hypothesis that can account for these equatorward and poleward bends in the isotherms? What kind of data would you need to test your hypothesis?

(4) Examine the following map of surface currents in the ocean :

(5) Based on the patterns of SST in Figures 1(a) and (b) and the ocean surface currents shown on the map above:

• What would you expect the net transport of heat to be in the North Pacific Ocean—poleward, equatorward, or too small to tell one way or the other? What about the South Pacific Ocean? What about the other oceans (North and South Atlantic Oceans and the Indian Ocean)?

• Do these net horizontal heat transfers help balance the imbalances in long-term, zonally averaged radiative energy budgets that we observe at most latitudes (as we discovered in Lab Activity #4: Introduction to the Earth's Energy Budget)? If so, for which imbalances do they compensate and are places where imbalances remain?

(6) Figure 3 below shows the net energy flux (in Watts/m2) into (orange colors) and out of (blue colors) the ocean surface.

• Where is the ocean gaining heat? Where is that heat coming from?

• Where is the ocean losing heat? Where is that heat going?

• Is this pattern consistent with the ideas of heat transfer you developed by looking at SST and currents above?

• Do these net vertical heat transfers help balance the imbalances in long-term, zonally averaged radiative energy budgets that we observe at most latitudes? If so, how? If not, why not?

Figure 3: Energy flux into (oranges) and out of (blues) the sea surface

(7) Figure 4 below is a salinity map for August 2011. Except in isolated spots (notably in the Arctic Ocean), the oceans exhibit very little seasonal variation in salinity, so the map for February would look largely simila (again, except in the Arctic Ocean).

Figure 4: Sea surface salinity (‰) for August 2011

• Describe the main features that you see in the patterns of salinity contours in the Pacific, Atlantic, and Indian oceans.

• What factors might affect surface salinity of the ocean?

• Do the patterns that you observe resemble any of the patterns we found earlier using My World?

• If so, what might be the physical connection(s)?

### Credit:

Images in this activity were downloaded from the National Virtual Oceanographic Data System (NVODS) at http://ferret.pmel.noaa.gov/NVODS/. Be aware that not all Web browsers can successfully access the images at this site; see http://ferret.pmel.noaa.gov/LAS/downloads/os-and-browser-list to see if your's can.

### Map of the Contintents and Oceans

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