Hot Water and Hurricanes

Part A: Earth's Ocean: A Storage Unit for Heat

Three-quarters of Earth's surface is covered with a substance that is a very effective heat-storage material—water. Liquid H₂O can absorb and store a tremendous amount of heat energy without becoming too hot itself. The effectiveness of a substance at storing heat energy depends on a parameter called specific heat.

Specific heat is a measure of how much energy something absorbs compared to how hot it gets. More precisely, the specific heat of a substance is the amount of energy it takes to raise the temperature of 1 gram of that substance by 1 degree Celsius.

Watch a short video from that demonstrates a "trick" that depends on the high specific heat of water.

Quantifying Specific Heat

Quantitative experiments show that 4.18 Joules of heat energy are required to raise the temperature of 1g of water by 1°C. Thus, a liter (1000g) of water that increased from 24 to 25°C has absorbed 4.18 J/g°C x 1000g x 1°C or 4180 Joules of energy. For comparison, alcohol (ethanol) has a lower specific heat: it takes only 2.2 Joules of energy to increase the temperature of one gram of ethanol by one degree Celsius.

To calculate the amount of heat energy gained or lost by a substance, multiply the mass of the substance by its specific heat constant multiplied by the change in temperature.

Where does all that heat energy go?

The ocean is constantly moving. Currents of water move through the ocean powered by global winds and differences in density. Generally, heat energy gained by water in the the tropical regions moves toward the poles.

 

Though we can't see currents in photographic images, we can detect them in sea surface temperature (SST) images like the one on the right. Instruments on several Earth-orbiting satellites gather data that is processed to show the surface temperature of water.

Watch the beginning of this animation and note the Gulf Stream Current moving north in the Atlantic Ocean and the entire Atlantic Ocean warming up as the seasons change. As you watch the animation, mentally visualize the current as a river of heat energy. Pause at about 24 seconds in and play again from 10 seconds to see the year repeat. Use the key for Sea Surface Temperature at the right.

Watch the remainder of the animation to see a visualization of what is called the Sea Surface Temperature Anomaly in the Gulf Stream. Anomaly indicates how much warmer or colder the ocean surface was compared to normal. At right is a different color key (Ocean Temperature Departure) for reference.

Once you've viewed the video, read this NOAA NESDIS article to learn more about the data in this animation.