Link to the UNESCO-IOC website
Link to the Bilko website
Earth from space
Annual sea surface temperature

4.2 Inter-annual variability of Sea Surface Temperature Patterns.

Seasonal and inter-annual variability     Transects    



back to bottom of page next

List of journal references


Images and tools

(HTML pages)

Useful information:

Surface currents

Surface wind

Global currents


East Greenland Current

North Atlantic Drift

Canary Current

South Equatorial Current

Seasonal and inter-annual variability

You are now going to investigate the magnitude of seasonal and inter-annual variability at various locations using the ATSR ASST data cube. To do this you are going to use the Transect function of Bilko to `drill down` through the stacked data sets that you are using. As the image data sets you are working with are stacked one on top of each other and each image is sequenced by time, the resulting transect will produce a time series of SST at a given location.

Activity/Question 1

  1. From the toolbar select the point tool (button with a cross).

  2. Right-click the mouse and select New... select Transect document, make sure Apply Stretches is unchecked. Bilko will bring up a new transect document showing the SST at the location of the cursor for all images in the vertical stack of images. As you can see, there is a break in the plot where data is missing due to the ATSR-2 scan mirror problems early on in the time series.

  3. Arrange the stack and the transect window so you can see both at the same time; a good way to do this is to select Tile Vertical from the Windows menu. Move your cursor around to observe how the time series in the plot changes. The plot is a dynamic plot so that when you move the cursor to a new location in the stacked image, the SST transect will automatically redisplay the time series at this new location.

  4. Spend a little time moving the cursor around the image stack noting the character of the SST time series for different regions. In addition to the gap caused by the mirror problem, there are breaks in the SST time series due to clouds or ice preventing the retrieval of SST.

Look at the magnitude and phase shape of temperature variations.


What are the general characteristics of the seasonal SST variability in Tropical latitudes, mid-latitudes and higher latitudes?


Is there any evidence for more variability on the western side of ocean basins?

to bottom of page    

Another way to look at SST variability is to take a transect along a line in each image data set and plot the data from each image data set this on the same axis. We will consider a north-south transect in the Western Atlantic basin following a brief introduction to some of the main ocean currents in this region.

A complete description of currents can be found at

(Resizable pop-ups)

Answer 1

Answer 2

Back up to:
Q1   Q2  


Activity/Question 2:

  1. Select the line tool from the Bilko toolbar, hold down the left mouse button, and draw a transect line in a north-south direction in the central Atlantic Ocean.

  2. Right click and select New » transect and make sure Apply Stretches is unchecked. Bilko will produce a plot with all of the data along the transect line from each image plotted on the same axis. (like this)

  3. You can also draw transects using the arrow keys on the keyboard to move the cursor to the starting position and then hold down the shift key to draw the transect, again using the arrows. Finally you can use the Edit -> Go To to locate the first point and set the increments (DX and DY). Try this method for a new transect plot starting at [017° 15`W,83°45`N] ending at [017°15`W, 76°15`S].

Hint: you can view the current coordinates in the bottom right of the bilko window, if they are not ther switch them on with View » Coords.

The finished plot should look like this.


Using Figure 3 and the information above, describe the main features of the resulting x-y plot you have produced. Can you suggest reasons for these features?

Note: it will be helpful if you return to the stacked image and press the animate tool button - don`t click into the image as you will loose the location of your transect line!

to bottom of page    
back to top of page next

Next: Hovmöller Diagrams.

  Link to ESA's Envisat website Link to NOC's website