Part 2—Investigate Sea Surface Temperature (SST) in the Pacific Ocean
Step 1 – Set up a Base Map
- Start My World GIS by double-clicking its program icon or by going to the Start Menu (PC) and navigating to the application.
- From the Welcome screen, click the link titled "Get Started" at the bottom of the screen.
- Switch to the World data library. Then drag the Lines of Latitude & Longitude and the Continents layers to the layer list.
- Click the Visualize tab below the menu items to switch from Construct Mode to Visualize mode. To find the modes, look at the tabs along the top of the map. Their names will show as your cursor hovers over them.
- Once in Visualize, click the Zoom to All
button to re-size the map to fill the window.
Step 2 – Import Sea Surface Temperature (SST) data from the Pacific Marine Environmental Laboratory (PMEL)
- Import SST data for all weekly data for the month of December from 1982 to 1998. You'll import this layer from the Internet using My World and the THREDDS catalog at http://ferret.pmel.noaa.gov/thredds/dodsC/data/PMEL/catalog.xml Be patient while your computer retrieves the list of data available from this server. It can take a minute or so to appear.
The PMEL server offers a range of Earth system data. Whenever you click the name of a data file (files are inside the folders), a brief description of the data appear on the right.
- Use the THREDDS Catalog Chooser to import the "reynolds_sst_wk" for every week in December from 1982 to 1998.In the PMEL online catalog, scroll down to the reynolds_sst_wk folder, select it and import the reynolds_sst_wk as a collection, by clicking the Import as Collection button at the bottom of the screen.
In My World a new window will open with all the reynolds_sst_wk files in the collection listed.
Using the Control(PC) or Command (Mac) key, select all the Weekly Means of SST for the month of December for each year from 1982-1989.
Click the Open Layer button, when finished making your selections.Hint: each year from 1982 to 1998 will have from four to five weeks. Select each years worth of weeks by clicking the first week and then Command(Mac) or Control-click the subsequent 3-4 weeks of December. To select the next year, hold the Control(PC) or Command (Mac) key and click the first one in the group. This can take several tries, so be patient and methodical. When you've made all of your selections, you will have a total of 76 fields. It will take some time for My World to retrieve and import all the grids of data you've just ordered. Wait times of three to five minutes are not uncommon. When the import is complete, you'll see the Weekly Means of SST layer at the bottom of the Layer List.
- My World will add the layer to the bottom of the Layer List.The datasets from the THREDDS server are from the Pacific Marine Environmental Laboratories (PMEL). They are datasets from derived from satellite remote sensing. If your computer had difficulty with downloading the data, then download the following My World project file. PMEL_case_study.m3vz ( 9.1MB Jun5 07) This project file contains all the layers needed for this chapter. To download the file, right-click and save the file to your desktop or documents folder. Do not unzip the file.
- Click the Zoom to All button to re-center the entire map. You should now have a map view that contains three layers.
- Lines of Latitude & Longitude
- Weekly Means of SST (currently colored gray)
Step 3 –Investigate Sea Surface Temperature (SST) in the Pacific Ocean
Answer: Around 30 degrees Celsius.Answer: Around -1.8 degrees Celsius
- Begin your exploration of the weekly SST data by changing the color scheme for this layer from gray to the SST for the week of December 7, 1982.
- This layer represents the weekly SST data for December 07, 1982. The legend along the bottom of the map will help you to interpret what the colors of the map are showing. Just by looking at the colors of the map and the legend, what is the sea surface temperature along the equator?
- Using visual inspection again, what is the SST surrounding the continent of Antarctica?
- Select the pointer tool and place your cursor in the Pacific Ocean on your map. Click your mouse button at several locations and read the information My World reports for each click. This will allow you to select specific locations and read the SST data at that location.
- Change to the SST grid for the week of December 14, 1982.
Hold your mouse button down as you move the pointer tool north or south on the map.
How do the temps change as you move away from the equator toward either pole?
Move the pointer tool east or west. How do the temperatures change as you move along a single line of latitude?Answer: Temperatures decrease moving towards the poles.
Answer: Temperatures stay relatively constant along lines of latitude.Notice that the color scheme changed but the range of temperatures is still about the same. My World doesn't know what kind of data these are, so it assigns color tables randomly. It takes a few steps, but you can select a color scheme for temperature and copy it to all grids so they are consistent.
Step 4 –Edit Appearance of the SST LayerIn order to have the map look more typical you will need to edit the layer 's appearance. First double-click to select the layer "data_ferret.pmel.noaa.gov_thredds_dodsC_data_PMEL_reynolds_sst_wk.nc.jnl". In the Edit Appearance menu, change the name of the layer to "Weekly Means of SST." (Note: if you are using the downloaded version of the project file, this step has already been completed for you.) Next, change the temperature range minimum to -2 and the maximum to 32. Then copy your new color scheme to all the SST grids.
To be sure that you include any outlying data values on other SST grids in the color table, adjust the minimum and maximum values to the next lowest and next highest integers. Be consistent on all the weeks, i.e., pick the same number range.
- Double-click the data_ferret.pmel.noaa.gov_thredds_dodsC_data_PMEL_reynolds_sst_wk.nc.jnl layer.
- Replace data_ferret.pmel.noaa.gov_thredds_dodsC_data_PMEL_reynolds_sst_wk.nc.jnl with "Weekly Means of SST."
- Next to Color Scheme, use the drop-down menu to select 'Temperature'
- As the temperature range appears to be from -1.8 to 30.5, change the minimum value to -2 and the maximum value to 32.
- Click Apply to change the color table of the current grid.
- To copy your new color scheme to all the SST grids, click the Copy button near the top center of the Edit Layer Appearance dialog box.
- In the Copy Color Settings dialog, click the Select All button near the bottom.
- Click the Copy button and that dialog box will disappear.
- Click the Apply button of the Edit Layer Appearance dialog, then click Close.
Step 5 –Investigate SST in a "Normal" Year
In order to establish the "normal" SST pattern for all Decembers, create a new field that is the average (mean) of all the weekly averages from 1982 through 1998. Enter Overall Average SST for December, 1982-98 as the name for the result.
If you were unable to perform all the steps listed above, or would like a completed copy of the project file to this point download this completed PMEL case study part 2.m3vz ( 9.2MB Jul20 11) file. To download the file, right-click and save the file to your desktop or documents folder. Do not unzip the file.
- Click the Analyze tab.
- Under Add Field(s) to Layer, choose By Math Operation.
- In the 'Add Field to the Table of' dialog box, use the drop-down menus to Add a Field to Weekly Means of SST by computing a Mean (average).
- Click the radio button to compute the value from more than two fields, and check all the grids that represent weekly SSTs from 1982 through 1998. Alternately, click the Select All button, then deselect the non-SST layers at the bottom of the checklist.
- Enter Overall Average SST for December, 1982-98 as the name for the result. We'll refer to this field as the Overall Average.
- Select OK which will perform the calculation and return you to Visualize mode. The "Overall Average..." will be displayed.
- While looking at the map, consider the following questions: How realistic do you think it is to refer to the average of all available December SST grids as the "normal" December SST pattern? Do you have other ideas?
- My World will add the layer to the bottom of the Layer List.