Unit One: Investigating Motions of the Sky
Doing Science

3. Motions of the Sun in the Sky and Sea Surface Temperatures

Introduction:
In this Investigating Astronomy module, you have observed and modeled the annual motions of the sun across the sky. Are there any important consequences to this motion other than the sun rising and setting at different locations throughout the year? One way to find out is to look at different data sets that are taken throughout the year and look at correlations. One interesting data set is the sea surface temperature. Maps of sea surface temperature around the entire Earth are archived at a number of locations. Use these data to make a movie of global sea surface temperature throughout a whole year to look for changes that may be related to the position of the Sun.

Directions:
The National Oceanic and Atmospheric Administration maintains a site with Sea Surface Temperatures (SST) made at monthly intervals since the year 2000. Go to the site at: http://www.emc.ncep.noaa.gov/research/cmb/sst_analysis/

Scroll down the page and click on Monthly Global SST Plot Archive. Click on one of the files in the archive to bring up a map of the global sea surface temperatures averaged over one month. The month and year are given at the top of the image (the six digits after the underscore in the file name give the month and year as well: 200103 equals the third month in the year 2001). The temperature scale is given at the bottom of the image. Select and download 12 successive images to your computer and open all twelve in order in an image processing program like ImageJ.

Create a movie using your downloaded images. In ImageJ, select Image, Stacks, and Convert Images to Stack. The individual frames will disappear and reappear as a single stack (it may take a few seconds). Select Image, Stacks, and Start Animation to start the movie. Click on the movie to make it stop. Describe the sea surface temperatures throughout the year. Do they change? Is there a pattern?

To connect the sea surface temperature changes to the movement of the sun, go to the NASA Solar System Simulator at: http://space.jpl.nasa.gov/.

Select "Show Me Earth as seen from The Sun," select the date in the middle of the first month and year of your SST data set, and select 18:00 UTC (universal time). Then select "50 percent of the image width" and click Run Simulator. This will produce an image of Earth as seen from the sun at the designated date and time. The point at the middle of the image is the sub-solar point—the sun is directly overhead at that point. (How does this view of Earth fit into your model of the solstices and equinoxes of Activity 1 in Exploration 2?) Create and download a similar image for each month in your SST data set, and compare the two: either frame by frame, or as two movies. Do you see any correlation between the sub-solar point on Earth with sea surface temperatures?

Your Report:
Make a power point to show each of your data set either frame by frame or as synchronized movies. (ImageJ can be used to cut-and-paste corresponding frames of the SSTs and the Earth into a single image for each month that can be collected into a movie.) Provide a written description of any variations of sea surface temperature with the motions of the sun and how they might be connected. This can also be done frame-by-frame in a poster, but it is not as effective as a power point animated version.