The ocean is the key element in Earth's hydrologic cycle (water cycle). Students will construct a simple model of the hydrologic cycle to help them visualize and understand the movement of liquid water and heat.
The hydrologic cycle is the continual movement of water from one place to another
and from one state of matter to another.
The hydrologic cycle plays a major role in distributing water and heat around the planet.
This activity can be set up as a demonstration by the teacher or as a small
group activity. Final interpretation should be done by the whole class. The
effects of this demonstration are more dramatic if a larger aquarium is used.
You might wish to set up the aquariums on one day and begin the observations on the next day. If so, you can leave the light shining overnight.
Rain and snow bring water to Earth's surface. Where does the water go from there? How does water move around the planet? Will Earth ever run out of water? Write a hypothesis that explains the movement of water between the ocean and the atmosphere.
What you have observed in your aquarium is a very simple version of Earth's hydrologic cycle. Through the process of evaporation, the liquid water became water vapor. Water vapor is invisible. As the water vapor cooled at the top of the container, it formed tiny water droplets. This process is called condensation, the process of water vapor changing into liquid. The hydrologic cycle is one mechanism for distributing water and heat on Earth. The oceans play an important role in the cycle. Water evaporates from the ocean and, in some instances, the winds carry the water vapor inland. Eventually, the water vapor cools in the atmosphere and forms tiny water droplets that combine into larger raindrops. Note: This is a very simplified explanation for an extremely complex process.
The atmosphere interacts with the ocean, which in turn, interacts with the atmosphere. Winds in the atmosphere create ocean waves, and the heat supplied from the ocean warms the atmosphere. Atmospheric patterns determine the oceanic flows, which influences where - and how much - heat is released to the atmosphere. Moreover, atmospheric cloud cover determines by how much - and where - the ocean will be heated.
Atmospheric water vapor is important because heat released by rain fuels atmospheric circulation. Water vapor is also related to sea surface humidity, which controls the transfer of latent heat (heat required for evaporation) from the oceans to the atmosphere. In addition, water vapor is a greenhouse gas which affects how the earth retains heat. Monitoring the global water vapor content is thus an important task for understanding the role of the oceans in weather and climate change.
The TOPEX/Poseidon satellite measures atmospheric water vapor with an onboard microwave radiometer. Have your students watch a color-coded data animation showing how atmospheric water vapor changes over time. What factors might cause such changes? They can also see updates to these data on the world wide web: http://topex-www.jpl.nasa.gov.