Exercise 1: Sea surface temperature
As seen previously, the temperature of the ocean is closely linked to many global processes. Water temperature not only affects global oceanic water transport, but also influences global climate. The sea surface is in direct contact with the atmosphere above it, and so it is important to monitor its temperature for weather and climate prediction, among many other applications.
|  | The Gulf Stream from space - Sea Surface Temperature (SST) | |
There are many ways of measuring Sea Surface Temperature (SST), and there is enough data available to suit different target analyses. In our case, we are interested in tracing a major current system, and for this purpose, the measurement of SST from space, with thermal infrared radiometry or passive microwave radiometry, can give us valuable information.
Both methods have strengths and weaknesses, so the best images are obtained by combining data received by the two types of sensors.
All surfaces emit radiation. The higher the temperature of the surface, the greater the radiant energy it emits. This is referred to as ‘thermal emission’. Infrared radiometry sensors capture the thermal emission of the first 0.01mm of the sea, known as the skin SST. However, particles in the atmosphere (particularly clouds), absorb some of the energy, and so not all of the radiation emitted reaches the sensors. For this reason, thermal infrared measurements are often compiled into weekly or monthly composites, putting together all the information needed to create cloud-free images.
The advantage of passive microwave is that long wave radiation is barely affected by clouds. However, the strength of the radiation in this electromagnetic region is lower, and so accuracy and resolution is poorer compared to SST derived from thermal infrared measurements.
The monthly composite images provided for the following exercise are multi-sensor images collected by both the Advanced Very High Resolution Radiometer (AVHRR) sensor carried on NOAA's Polar-orbiting Operational Environmental Satellite (POES), and the Advanced Microwave Scanning Radiometer - EOS (AMSR-E), which is one of the six sensors aboard the Aqua (EOS PM) satellite.
LEOWorks exercise
Open one of the SST images provided through the link in the right menu.
1. Compare the SST image with a map in your school atlas. Can you identify the Gulf Stream?
2. Carefully examine the SST image. Take a look at the temperature scale - it is measured in Kelvin. What is the average temperature of the Gulf Stream’s surface? You may convert it to degrees Celsius.
Now make an animation with the series of SST data provided from July 2011 to July 2012. Identify the Gulf Stream and observe how its temperature varies throughout the year.
Open Tools/Animation. Add the images and choose a suitable animation speed. You can preview the animation before saving it.
3. Examine the changes and give two reasons why the Gulf Stream can be described as a dynamic current.
4. Identify which month the Gulf Stream is at its lowest temperature, and which month at its highest. What can be concluded about the seasons of the Gulf Stream?
5. Choose a month when the Gulf Stream is most visible by SST. What is the approximate difference in temperature with its surrounding waters? Taking into account the resistance of large water bodies to temperature changes, and compared to the rest of the North Atlantic, would you say it is a significant difference? Is it a gradual transition?
6. Is the temperature difference greater towards higher or lower latitudes? Try to explain what causes this division.
7. Search for the latest SST image of the Gulf Stream. Compare it with the time series provided and describe any differences and/or similarities you can identify.
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