Cyclones are large masses of air that circulate around a region of low pressure in the atmosphere. If cyclones gather enough energy, they become hurricanes, one of the most destructive weather phenomena on earth. In this activity you will investigate cyclone patterns and their causes. 1. Before you begin this , make sure that you have completed the reading for this week, in particular, page 139 (Coriolis force), page 171-3 (humidity) and 211-15 (tropical cyclones -yes, reading ahead, but it will be helpful) of your text. 2. You will need use a program called to view several movies associated with this lab. If you do not have a copy of this freeware program, , and follow the directions to install it. If you do not want to do this, the computers in the Foothill labs have this installed. 3. Read through this assignment once, follow the steps below. Relative humidity is the ratio (expressed as a percentage) of the amount of water vapor that is actually in the air (content) compared to the maximum water vapor that the air could hold at a given temperature (capacity). Relative humidity is calculated as follows: Example: An air mass at 15*C has a water vapor pressure content of 9.8mb. The saturation vapor pressure (maximum capacity) of the air to hold water vapor at that temperature is 17.0. Therefore the relative humidity is: Relative humidity varies due to evaporation, condensation and temperature change. I like to think of the air as a sponge that soaks up water. When the sponge is holding as much water as it possibly can, it is saturated, or at 100%. If the sponge is holding half of the water that it hold, it would be at 50%. The amount of water that the sponge can hold varies depending on the size of the sponge. A large sponge can hold more water at saturation than a small one. The same goes for the air. As the temperature of the air increases, its ability to hold water (the size of sponge) increases. The key is that the size of the airs sponge or its capacity to hold water is not linear. Below is a graph of the saturation vapor pressure versus temperature. Click on
the graph to view a larger version. This will open a new window. Cyclones draw their power from the latent heat energy in water. As you saw above, warm air holds a lot more water and therefore more energy than cold air. Warm water also holds more energy than cold water, so the tropical cyclones that we will be focusing on in this lab require warm water and warm air to sustain their energy. Open the . This will open in a new browser window, you may switch back and forth between the ETUDES window and movie. Close the new window when you are done. Luis swept through the Atlantic 27 to September 11, 1995. Luis was a 4 hurricane (using the -Simpson Hurricane damage potential scale see page 235 of your text), with winds reaching speeds of 225 mph, and a lowest central pressure of 935 . See a of LUIS (click the back button to get back to this window) Before you play the movie, orient yourself: you are looking at the Atlantic , with coastlines and states outlined in yellow. Play the movie several times, observing Luis path and the motion of the hurricane itself. You can step through the movie frame-by-frame using the right and left arrow buttons on the navigation bar. Recall from homework 2 that is not distributed evenly over the surface of the earth. Furthermore, water heats up and cools down more slowly than land due to its greater heat capacity. In the second part of this exercise, you will explore the relationship between the sea surface temperature and the formation of cyclones. Open up your second browser window: the (this will open a new browser window). Recall from week 1 that GIS (Geographic Information Systems) is a suite of software products that allow geographers to view and manipulate spatial data. In this case, we will be using a simulated GIS to look relationship between four datasets: Sea surface temperature in February, sea surface temperature in August, of cyclones in February, and of cyclones in August. You can turn on various map layers by clicking in the boxes next to the layer name. By clicking in multiple boxes, you can view multiple layers at once.