General Circulation

Outside Links: Lab Guide
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Experimental Setup

The goal of this experiment is to show how Hadley cell circulation works in real time. First, we filled the tank and set the rotational speed to approximately 1 revolution per minute (this is very important if the rotation speed is too great eddies will form and you will not achieve the desired results). We then let it spin for about a half an hour to allow the water to reach a steady state. Confetti pieces were added to the surface of the water so we could tell when this state was achieved. Once all the confetti pieces were moving together around the tank steady state had been achieved. Once at steady state we added a half gallon jar of ice to create the temperature differential (we found it easier to freeze a cylindrical half gallon jar of water in the freezer over night instead of trying to hunt down ice, make sure to freeze it with the top off or it will shatter your jar. This didn't happen to us just making sure people remember that water expands as it freezes). Once the heat differential was set up the steady state dissipates and the water flows down along the side of the jar to the bottom of the tank, out to the outside wall of the tank, back up and in towards the jar again.
In addition to this flow, the water on the inside of the tank closest to the jar revolved at a faster rate than the water on the outside. This phenomenon was made apparent by the confetti pieces on the surface of the water. We allowed the system to run for approximately 1 half hour to allow the flow regimes to reach there maximums. Again this was made apparentby the movement of the confetti on the surface of the water (the confetti on the inside moved faster than the confetti on the out side). Once the appropriate flows were set up in the tank, dye was added to the the water close to the side of the jar. Due to the thermal winds created by the temperature differential and the rotation of the tank, the dye closest to the surface was pulled quickly around the jar in the direction of rotation while the dye that went lower in the water column was pulled in the direction opposite the rotation. This stretched the the die in both directions creating a streak of dye situated diagonally down through the water column as in photos 1 and 2.
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Photo 1
Photo 2
An optional thing one can do if there is time is take a long eyedropper and put a dot of dye directly on the bottom of the tank. This allows you to see the slow flow at the bottom of the tank. The dye will fan out along the bottom of the tank and curl back and to the right, as circled in red in photo 3.
Photo 3

1.) Two different colors of liquid food coloring dye
2.) Colored confetti pieces
3.) A non-insulated container (straight glass jar is ideal)
4.) Ice
5.) Long Eye dropper (optional)

Real world Applications of Hadley cell circulation

Hadley cells occur from 0 to 30 degrees north and south of the equator and are the major cause of the aridity around 30 degrees north and south. The sun heats the water and land around the equator and this warms the air about which then moves up into the atmosphere as this moist warm air rises it cools and falls out as rain, but the air that contained it keeps moving. It heads away from the equator and then the now cool dry air falls back to the Earth around 30 degrees north and south. As you can see from figure 1, this cool dry air descends around 30 degrees north and south and creates droughts and the formation of deserts. An example of this is Earth's largest desert the Sahara desert in Northern Africa.
Desert Formation.jpg
Figure 1

The Trade Winds
The trade winds are the winds that occur by the influence of Hadley cell and Earth’s rotation which cause the trade winds to move from the East to the West (also called Easterlies). The Trade winds have been used for commerce since early 14th century and because humans use it for commerce we have named them the trade wind which mean “the wind for commerce”. These wind have a number of pros as well as cons. As we know, winds always carry some dust or particles. In 1970s, the trade winds caused a lot of damage in marine ecosystem particularly to the coral reefs around Florida and Caribbean Sea. This is because they brought a lot of dust from the North African Sahara desert. Dust is not the only problem associated with the winds. They also bring bacteria, heavy metals and pathogens as well. The animation form NASA’s Total Ozone Mapping Spectrometer (TOMS) reveals the dispersion of dust storm from Sahara desert that passed through the Atlantic Ocean and Caribbean Sea. This potentially resulted in the death of many corals because the dust covers the Atlantic Ocean and Caribbean Sea and reflects solar radiation which reduces the sea surface temperature and photosynthetic production (animation 1).
Animation 1