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. You will need use a plugin program called Quicktime to view several movies associated with this lab. If you do not have a copy of this freeware program, download it now, and follow the directions to install it. If you do not want to do this, the computers in the Skyline labs have this sofware installed.
2. Read through this assignment once, then follow the steps below.
Part I, Humidity and latent heat energy: the fuel for the cyclone engine
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:
Reative humidity =
actual water vapor content of the air
maximum water vapor capacity of the air
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:
Reative humidity =
0.57647 X 100
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 could 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 it’s “sponge”) increases. So warm air holds more water than cold air.
The key is that the size of the air’s “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.
Questions Answer the following using the graph and table above:
1. (1 points) What is the difference in saturation vapor pressure between -25*C and -35*C (the actual number, not just a description)?
2. (1 points) What is the difference in saturation vapor pressure between +25*C and +35*C (the actual number, not just a description)?
3. (2 points) Consider your answers to questions 1 & 2. In one paragraph, compare the ability of air to hold water at warmer temperatures with its ability to hold water at cooler temperatures. Is this an arithmetic or a geometric relationship? If you are not sure what these terms mean, please see this link.
Round the following answers to the nearst tenth. If you are not sure how to round decimals, see this link. Note in that as in the example above, you should round at the last step in your calculation. If you are not sure what a ‘tenth’ in decimals is, see this link. Please note that this is approximately 5th grade math… so it is okay if you are a little rusty, but you should be able to do this in a college course. Points will be deducted for incorrect rounding or inaccurate decimals.
Basic math refresher:
tenths = 1 number after the decimal point: 1.2
hundredths = 2 numbers after the decimal point: 1.22
thousandths = 3 numbers after the decimal point: 1.222
Note that zeros are places too. So if you were to round 1.20459 to the nearest hundredth it would be 1.20
4. (2 points) Consider the saturation vapor pressures listed in the table above. An air mass at 25*C actually contains water vapor exerting 16.2mb of pressure. What is the relative humidity of this air mass (expressed as a percentage)? Round your answer to the nearest tenth of a percent (eg. XX.X%). Show your work.
5. (2 points) Consider the saturation vapor pressures listed in the table above. An air mass at 15*C actually contains water vapor exerting 5.2mb of pressure. What is the relative humidity of this air mass (expressed as a percentage)? Round your answer to the nearest tenth of a percent (eg. XX.X%). Show your work.
Part II, Hurricane Luis
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 Quicktime movie of hurricane Luis. This will open in a new browser window, you may switch back and forth between this window and quicktime movie. Close the new window when you are done.
Luis swept through the Atlantic ocean August 27 to September 11, 1995. Luis was a catagory 4 hurricane (using the Saffir-Simpson Hurricane damage potential scale), with winds reaching speeds of 225 mph, and a lowest central pressure of 935 mb. See a color satellite picture 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 ocean, 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 quicktime navigation bar.
Questions Answer the following in complete sentences.
6. (1 points) Did the winds in Luis spin clockwise or counter clockwise? What phenomena accounts for this? If you are having trouble observing this in the movie, consider what you know about cyclones (are they low pressure or high pressure zones?).
7. (2 points) The north coast of Australia is very prone to cyclones. Do the winds in cyclones that occur along the north coast of Australia blow clockwise or counter clockwise? What phenomena accounts for this?
8. (3 points) Why is it that the west coast of the United States never has problems with tropical cyclones, while tropical cyclones annually cause significant destruction along the east coast of the United States?
Part III, Cyclone Cycles
Recall that insolation 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.
In America we accustomed to talking about temperatures in Farenheit rather than Celsius. You probably have a pretty good feel about how ‘warm’ 80° F is, or how ‘cold’ 50° F. In science we use Celsius to talk about temperatures, so before we go any further, let’s get a feeling for what ‘hot’ and ‘cold’ really mean in the Celsius scale. Remember to do a reality check with your calculations: based on the temperature map in the GIS (see below), is your result physically reasonable?
°F = (°C*1.8)+(32)
Use the conversion formulas to the left to calculate the following:
2°C = _____
12°C = _____
22°C = _____
32°C = _____
Questions (you do not have to answer these in complete sentences)
9. (2 points) List the following temperatures in the Farenheit scale: 2°C, 12°C, 22°C, 32°C Round your answer to the nearest tenth. Show your work!
Open up your second browser window: the HTML GIS viewer (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 a the relationship between four datasets: Sea surface temperature in February, sea surface temperature in August, occurence of cyclones in February, and occurence 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.
Use your HTML GIS viewer to answer the following questions:
Questions (Answer in complete sentences)
10. (2 points) How is the tilt of the earth related to the pattern of ocean heating? Give specific examples.
11. (2 points) What is the optimal temperature for cyclone formation in Celsius? Why do you think that this is the case?